Modding Antique Sound Labs Wave-8 Tube Amp

Yeap, it is a tube amp. The Amps are push-pull mono design and are approx 11 years old. They were introduced as “best bang for the buck” for $99. They became an instant hit especially with the diy/modder crowd. Unfortunately, many off the documented mods have disappeared from the web. That was before the time of free blogging . The last known troubleshoot/mod report is from 2009 [link]

They also got great reviews such as this:

At an entry-level price of only $99 per side, few power amps compare to the amazing rendition of high-end audio that these charmers give. If there is an entry level tube amp out there for neophyte audiophiles, or simply some one who wants the most “tube bang for their audio buck” with their above average efficiency speakers, these have got to be the ticket. They certainly punched mine. [link]

And this:

Let me begin by talking about the amp these replaced. I previously had a stock Phase Linear 400 II. 200watts/ch. I kept the Phase Linear in my rack to compare but I liked the Waves so much I didn’t even bother to check the Phase Linear for a month. For me, audiophile nervosa is a powerful force and the fact that I didn’t do a “reality check” back with my old amp for a month speaks volumes about the difference. [link]

And this:

Straight from the box these amplifiers (given of course proper burn in) will impress you. They will never impress those with thousands of dollars invested because hey how could something that cheap be any good? Just keep it your little secrete so all the other folks who love sound but not high prices can enjoy them. We don’t want Antique Sound Lab to start selling them for what they are really worth now do we? [link]

At  this price the company was probably just breaking-even. And anything that had little to do with the sound was spared. For example, the power and output transformers covers are just raw steel without any kind of finish. But even so, if you were to buy these transformers in the retail market, they would probably set you back $40 a piece, so likely they manufactured their own transformers and probably everything else for the absolutely minimum cost.

I have been using them in their original factory-stock configuration for my bedroom system connected to a Sony SACD player through a passive volume control and powering KEF bookshelf speakers. No complains so far but having been presented with the opportunity to get expert advise in modding this amp, I couldn’t pass the chance. That expert advice came from Scott [Scott17 at diyaudio].

After a few conversations with Scott, I realized that he was selling tube kits. So I asked him for a few modding tips for my amp. Scott was extremely generous with his time and knowledge and after a few exchanges where I described the innards and measurements of the amps, he developed a complete plan for me.  In a way he was even more excited about this project than I was, often expressing his excitement and anticipation for the results. I can only imagine the level of support and care he gives to the people who buy his kits.

CIRCUIT DIAGRAM

I have also scanned the full factory documentation and posted it here: [Wave8 Manual]

INSIDE DETAILS

Here are the innards of the Wave-8 fully stock from the factory:

Fairly good components: film resistors, name brand capacitors, spacious PCB, ready for modding. The tall blue power supply capacitors are high voltage Nichicon VX electrolytic capacitors. I think those models have been discontinued as the current configuration for VX capacitors are axial rather than radial. According to this document [link], the VX have been replaced by the VR capacitors. The ones used are Nichicon 450V 47 uF and are good standard capacitors at $2.58 each [link] (the equivalent from the new series).

POWER SUPPLY

The high voltage DC is provided by the 4 diodes and a CRC filter of C9, R17 and C8. C9=C8=47 uF, R17=100 ohm

MODDING THE POWER SUPPLY

Scott suggested that the most noticeable improvements would come from modifying the power supply section. The following mods were recommended (in order of importance):

• Replace R17 with 4-Henry DC choke: [link], making a CLC filter which provides better filtering than a CRC filter
• Replace C9 with 630V 47 uF film capacitor (used 400V 40uF instead): [link]
• Replace C8 with 450V 220 uF Nichicon KX electrolytic capacitor (used 400V 180 uF KX instead): [link]
• Replace the diodes with ultrafast recovery types (UF4007) [link], further reducing noise

Why use a choke? Why not just a big series resistor?

A choke is used in place of a series resistor because the choke allows better filtering (less residual AC ripple on the supply, which means less hum in the output of the amp) and less voltage drop. An “ideal” inductor would have zero DC resistance. If you just used a larger resistor, you would quickly come to a point where the voltage drop would be too large, and, in addition, the supply “sag” would be too great, because the current difference between full power output and idle can be large, especially in a class AB amplifier [link].

Sizing

The first thing you realize, is that film capacitors are “gigantic” in size. DC chockes are also large in size and even the higher value electrolytic capacitors would be difficult to fit. So before you embark in buying the components, it would be wise to figure out where to put the components and whether they will fit inside the case. After doing some mockups and measurement, and based on stock availability from the different supplies, I ended up with the components specified above. The clearance from the bottom of the PC board to the edge of the chassis is 40 mm. So most components would have to be 40 mm or less in one of their dimensions.

I did several mockups to see if the components would fit. here is an earlier mockup. Eventually ended with a single 40 uF film capacitor instead of two 20-uF capacitors by doing some “clean-up” on the PC board.

“CLEARING THE PCB”

I notice that there is a lot of space in the PCB board and that the layout can be made more efficient. The 40 uF film cap I selected would fit well in the back of the board by moving some components. The first thing I did was to move the fuse, switch and associated wiring to a small board and the resistors I re-installed in the backside of the board.

Actually, it is way better to have the input AC wiring off to another board. You move a lot of wires out of the way.

Although not recommended in the mods, I replaced the IEC socket with one with built-in EMI filter.

C8 and C9 would also be replaced, so we can remove those too. Now we have a nice empty space where we can install the large film capacitor.

The diameter of the film cap is 40 mm. Any larger would not fit in this location.

Replacing the diodes with ultra fast recovery diodes and installing C8. C8 is installed in position C9 (to free up space for the large film cap, which is C9). This requires that we cut the + trace and find a place to connect the + terminal of C8.

The KX series are designed for audio use.

C8 is in position C9. We need to cut the trace as shown and connect to the + connection of C8 (short orange jumper – you can see the trace goes around and connects to + of C8 position)). The long orange jumper connects the + connection of C9 to the large film capacitor which replaces C9 (not in the picture).

Installing C9. The 47 uF electrolytic capacitor is replaced with a film capacitor. Because of the size, I used a smaller-sized 40 uF 400V film capacitor. The + connection of C9 connects the + connection of the 4-diode bridge rectifier.

According to this article [link]:

One of the best amplifier power supply grounding schemes is a “star” ground system, where all the local grounds for each stage are connected together, and a wire is run from that point to a single ground point on the chassis, back at the power supply ground. Even better is a two-point star, where the power supply grounds (PT center tap, first filter cap ground) and output stage grounds (output tube cathodes for fixed bias, or cathode resistors for cathode biased, and output transformer secondary ground) are connected together and to the chassis at a single point, right at the ground of the first filter capacitor. The ground of the second filter capacitor, after the choke or filter resistor, is the star ground point for the preamp stage grounds. Use a local common point for each preamp stage ground, and run a wire from this common point back to the second star point. If two stages are out of phase with each other, the can share a common local ground, but don’t use more than two stages per local common ground.  This concept can even be taken further, with multiple star points for various amplifier stages.

I used a single star ground approach (since the ground of the second filter capacitor is right next to ground of the first filter capacitor) with the negative lead of the film capacitor as the star ground. To this ground connects the negative output of the 4-diode bridge rectifier, the speaker GND connection and the GND from the “front-end” where the input signal ground is connected. From here, there is a single cable that connects to the chassis.

It is important that you pay close attention to grounding. This means good solder contacts, good contact to chassis (scrape the paint off) and good wiring. Make sure you measure continuity and resistance from all the ground points.

The choke is installed to the side of the chassis. The choke replaces the 100 ohm power resistor.

“This is the most common 90mA DC rated Fender* type choke used in many of their amplifier applications. Provided with shields for extra protection. Paper layer wound choke like vintage era originals!”

A bit of “Made in USA” in a Chinese Amp

The choke, the film cap and the electrolytic capacitors are near flush with the edge of the chassis.

REPLACING THE COUPLING CAPACITORS

After the PS mod, the coupling capacitors will also make a big difference.

Scott recommended the use of ERSE caps as an economical upgrade of the coupling capacitors.

The ERSE replaces the BENNIC capacitors.

OTHER MODS

Change R14 and R15 with lower noise versions. The cathode bypass caps C6 & C7 should be changed to 220uF. The stock configuration of 390R/100uF yields a -3dB corner frequency of 4Hz. As a general rule, the -3dB corner frequency should be 1/10th of the desired low-end response of 20Hz, which is 2Hz. This mod will achieve just that.

I used components that I already have. The resistor is a thin film type and the capacitors is a bipolar MUSE. There is no need to use such large-size capacitor.

THE COMPLETED BOARD

Before and After

FURTHER MODS:

More bypass capacitor options:

There are so many choices and reviews. According to reviewers, their performance also depends on their application.

Capacitor review links

• http://singaporehifi.blogspot.com/2010/09/capacitor-shoot-out.html
• http://www.enjoythemusic.com/diy/0708/capacitor1.htm
• http://www.humblehomemadehifi.com/Cap.html
• http://www.laventure.net/tourist/caps.htm

According to Joseph Lau, the designer of the amp, the calculated value of the bypass capacitor is 0.1 uF. 0.22 uF is already overdesiged. [link]

0.22uF Cap	Photo	LxD mm	Price
Bennic XPP 400V		~18×10	<$1
Erse MPX 630V		20×11	$1.37
Auricap 600V		20×14	$11.45
AmpOhm tin foil 630V		54×25	$20.55
AudioCap Tin Foil PPT Theta		30×17	$8.06
ClarityCap SA 630V		21x1928x20(.47 uf)	$3.70
ClarityCap ESA 630V		20×24	$7.90
Multicap PPFX 400V		28×15	$6.45
Russian Teflon FT-3 600V		72×31	$5.50
Jantzen Z-Superior 1200V		43×22	$8.64
Audyn Plus 1200V		43×25	$6.50

Even more mods [link]

Don’t use the cage as it makes things sound worse however the IEC allows you to use a quality after market power core and that is well worth the few extra dollars.

The parts count inside is very good and I did not feel that replacing caps and resistors would yield a big enough difference to justified the expense. The amp can and does respond to bypass caps and these are most cost effective and easy to install. Bypass the power supply caps with 1000 Volt ceramic disk caps.

All large value caps were bypassed with 0.1 uf plastic caps (despite what people say Mylar sound fantastic). All the small value caps were bypassed with 0.01 uf plastic caps.

I removed the “bell” or “end” caps from the output and power transformers. I then installed an electrostatic copper wrap shield around both of the transformers and in my case turned the output transformer 90 degrees to the power transformer and re mounted both transformers on rubber grommets to reduce vibration to the chassis. Removal of the “Bell” caps really opened up the sound and gave a sense of life and new dynamics. I have found this to be true on other amplifiers also. I did not do a direct before and after comparison with the physical orientation of the two transformers however with two chokes you want them aligned this way to place one in the exact electrical/magnetic “null” of the other an so minimize coupling between the two. This makes sense so I decided to do it with the two transformers even though it did involved making some of the lead wires longer.

The second last change that I made was to replace the input interconnect and to shield the power on/off wires which run to and from the front of the chassis to the back to the chassis. This one is up to you to do as you see fit.

Last but by no means least I froze the tubes down to liquid nitrogen temperature. If you haven’t tried this do so as it is a great upgrade all on it’s own. Sound is smoother and there is more detail with greater resolution and an apparent increase in dynamics. I can assure you that once bit (frozen) you will never go back to non frozen tubes or other parts for that matter.

Next go to Elliott Sound Products and read his article on a passive volume control “project 01″ build one to use with your “Wave” amplifiers and then you will enjoy a level of performance you probably have never dreamed you even reach. The price of entry is a laugh. You will now be able to make your “Audiophile” friends so sick with what they own and with what they paid for it that they will in the words of J C Morrison “want to go and find a high place from which to throw off their gear”.

And more mods [link]

(These recommended by Joseph Lau, the designer of the amp)

…

I then started thinking about resistors. Joseph Lau recommended replacing 4 resistors in the signal path per unit. R4, R7, R10 and R11. Those are a 33k, 390k, and 2 1ks. I thought, what the hell and I ordered full compliments of Rikens, AN Tants, Holcos and Roederstein Resistas from Angela.com, Michael Percy, and Audio Note North America.

I began by replacing one amp with all Rikens. The bass response increased dramatically and I liked that (Tom Waits never sounded more gravel-ly and unshaven), but after closer examination I felt the highs were rolled off and there was way too much of a “tubey” or “hollow” sonic characteristic. Also some low end distortion.

I switched out the Rikens for all Holcos, but that didn’t seem exactly right either. It swung the other direction and I found it was too lean for my taste and lacked deep dynamic punch. Tom Petty whined too much.

I then put in all AN Tants which were very musically satisfying in the bass but the top end was restrained, or oddly veiled, but better overall than the other pure attempts. Ry Cooder had post nasal drip. hahaha

I then started thinking that I should try combinations, looking for the optimal blend. I put in the 33k and 390k Rikens for bass, with 1k Holcos in R10 and R11 and wow. Very nice highs, not too bright, but “there” with deep bass. I decided to try a variation on the other amp which was AN Tants in the 33k/390k positions and Holcos in the 1k positions and then duel the two off, A-B.

Upon extended HEAVY DUTY listening, there was more bass with the Rikens, but the Rikens were muddying or smearing the bass somehow, while the Tants were producing very slightly less bass, but it was a VERY well defined and musical bass. There was no comparision. The more I listened, the more I got goosebumps, and the more I loved this combination. AN Tants in the 33/390 positions and Holcos in the 1k positions created tonal characteristics nothing short of spectacular IMHO.

All the music I tried sounded “just right” in tight bass and extended yet not overly bright highs. Sampled music included Tom Petty Wildflowers, Ry Cooder Bop ‘Till You Drop, Les Nubians Princesses Nubiennes, Sheila Chandra Roots and Wings, Tom Waits’ Foreign Affairs, Eric Truffaz The Mask.

I did pop in 1k Roederstein Resistas in the 1k positions in one amp to test that possibility that they would increase dynamics, but they were a bit dry and substantially less dynamic than with the Holcos in the 1k slots.

There certainly are other combinations I didn’t try, but I think I’ve found a real winning combination that bring these little Wave-citos up a few big notches that have them competing sonically with my Zen Select amp for tonal character, but they’ve got muscle behind them.

I did find that when I put in Caddock TF020Rs in my volume shunt on my Foreplay Preamp, it made a huge difference and was the best I had tried (over Rikens, AN Tants, Holcos and Resistas). I may go ahead and get some Caddocks for the 1k slots, but I’m pretty certain that the AN Tants are the bomb in the 33/390k positions as they seem to tame the other stock metal film resistors which tend to be so bright, while the 1k slots keep the sound open and let in the high dynamics.

I’m no expert and I’m using “down home” language to try to explain my experiments and what I’m hearing. My Waves are singing beautifully.

I’d love to hear what anyone else has done to these fun little amps.

Overall, a very fun project. At about $50 per amp (and free guidance from Scott), it is a heck of a good deal…

Part II of the mods here: [link]

Hypex UCD-180HG and Connex SMPS300RE

(See update to listening impression)

Finally finished updating the power supply for my Hypex UCD amps. Each amp module was upgraded from a linear, unregulated power supply to a switched, regulated power supply from Connexelectronic. Even with all the debate between linear vs switching supplies, I think the power switching technology (and affordability of that technology) has finally caught up to the advantages of linear supplies (low noise) and surpasses them by providing regulation. Not to mention weight, size and efficiency. There is also no excuse not to try because Connex sells these modules under $60. Just the transformer for a linear supply of equivalent power would cost you more than that.

ORIGINAL CONFIGURATION

This is the original configuration for the UCD 180HG amp modules: ~40V unregulated linear supply, using a 150VA toroid transformer from Apex Jr, and a snubberized PS module from Chipamp. At that time, these cost me about $60 for each which coincidentally is the same price as the connex unit.

This configuration has served me well for more than 5 years. It is a bullet-proof design, and have no complains about it.

THE NEW POWER SUPPLY MODULE

The new configuration uses a +/- 45v Resonant SMPS with regulated outputs, the 300RE. This is based on the latest resonant SMPS designs resulting in lower noise and higher efficiencies. I’ve described this PS in more detail in this post [link].

THE COMPLETED AMP

The Hypex modules are “far away” from the power supplies to avoid any interference. I’ve also installed a metal plate in between for further isolation.

Since the recycled case had too many holes in its face, I installed individual power switches for each of the power supply modules and also enable switches for each of the amp modules. These switches were already present in the old configuration so I just imported them here. In addition to allowing individual control of the amp modules and PS modules, these switches were useful while I was building up the amp for testing and safety.

The PS modules have been set for exactly +/- 45V operation which is the specified recommended “typical” operating voltage for the amp modules. The output voltage can be adjusted approx +/- 10%.

I followed the hookup configuration of the data sheet, which includes fuses for the positive and negative DC power lines for protection of the amps and the speakers.

Chinese binding pots from eBay… Pretty good looking and they are “fat” making them very easy to use.

The PS modules each incorporate input (and output) EMI filters, thus no additional filtering is necessary. However, I added a cable ferrite which seems to be “standard practice” for switching supplies.

I use the AUX supply just to power an LED .

The Hypex UCD180HG modules.

These were the original version of the “HG” models. I believe the current version has a revised PCB and the maximum voltage also increased. According to the datasheet of this original model [UcD180HG_datasheet2] the operating voltage range is as follows:

45V is likely the optimum PS supply voltage as the performance data is based on this value.

Input signals are carried by trusted Cat5E patch cables. I also have a passive RC filter currently configured with a -3db cutoff at 75KHz. I may adjusted to the values used by the Legato I/V which I believe has a cut off frequency of 400KHz. The reason for this filter is because I use the Buffalo II DAC in voltage-out mode which connects straight to the Amp.

Doesn’t look too bad even…

Got to find something to put in those 3 empty holes

HOW DOES IT SOUND?

It was imperative that I finish the amps for proper listening with the Amanero USB interface (which quickly made playing DSD files from a computer an affordable reality). My queue of projects (Ian’s FIFO bard, the new AVCC supply for the Buffalo DAC) also requires a proper working listening environment. Previously I had disassembled one amp in preparation of the power supply update and for a while had been “listening” to different experiments with just one channel.

Anticipating the sound of the “new amp”, my own experience tells me that changes in the audio path are often subtle and big differences are far in between  and in general, I also think not having inflated expectations and not rushing in trying the latest and greatest allow me to be more objective in perceiving any changes. Thus for this power supply upgrade, I did not expect any big changes in the sound.

After only one listening session, I was pleasantly surprised!

Upon powering the amp and playing the first track, I immediately noticed the huge “surrounding” soundstage. Hmmm, this is weird. OK, fixed that. I had switched the channels . Play again…

This time I noticed the soundstage again. From memory, I did not recall ever experiencing the soundstage this way (maybe this is somewhat related to having listening to one channel for a while but…). Certainly it was not this expansive, not this large, not this 3D. Yes the speakers disappeared, but now the speakers disappeared even more:-). Pinpointing my attention to the speakers, no sound was coming out at that location at all. This sounds really, really good. Play more tracks…

The bass was also different. Now it was more controlled. I played and compared tracks where from memory I thought the bass was a bit booming. Now they sounded more controlled, more defined. The “boominess” was gone.

The rest of the audio spectrum seemed the same as before, perhaps a tad more “crispiness” in the higher frequencies, but can’t tell for sure.

Overall, music appeared more dynamic. Perhaps the additional headroom (45V supply vs the old 40V supply) combined with a better bass definition creates that perception. The new PS can also deliver more power.

In summary, this has been one of the best upgrades I’ve had in my system. This is another indication that the quality the power you use is perhaps the most important ingredient for a good sounding system. Certainly it makes the obsession of tweaking of the power supply almost justifiable:-). It is the first time I have use a regulated power supply for an amplifier and it is certainly consistent with the trend in the audiophile community of migrating from linear-unregulated supplies to switching-regulated supplies. Hypex has purposely designed a switching supply for their latest NCore modules.

The Connexelectronic PS modules are not only very affordable, but incorporate the latest low noise SMPS soft-switched resonant technologies. In addition, the 300RE incorporates more filtering in the form of an output CLC network. If you have UCD180 amp modules or equivalent, this upgrade is highly recommended.

Update (12/15/12): False alarm!

The larger soundstage was caused by inverting the balanced connection for one of the channels. After listening for a while, I noticed that the soundstage was somewhat artificial. So I traced the speaker cables, the connections from the amp module to the speaker and finally the input to the amp modules. One of the input wires was reversed.

After fixing this error, the soundstage “collapsed”, but now more realistic. Now the soundstage is more or less the same as before. At the least this showed me how phase issues would sound like.

The bass did remain more controlled, but not as pronounced (not as tight?)  as before. Overall, still an improvement to the old PS and still highly recommended.

I did play a “silent” track to see if there is any noise coming from the amp: total silence. Increasing the volume to zero dB did show a faint hiss if one would press the ear to the speaker. But the hiss was coming from the DAC! The amp is totally silent.

FURTHER READING

Here is a similar project using the SMPS500 with the UCD400: http://diyclassd.blogspot.fr/

Impressions shared in diyaudio:

[link] I exchanged in my power amp with two Hypex UCD400HG modules the two 1KW toroid transformers and the New Class D PSU with split foil caps to two SMPS500R.

What is the difference, in my opinion not so much. Maybe the bass has a little bit more pressure but it is only a feeling. For the rest everything is the same like before.

For that reason the SMPS500R stays in. These things are absolute quiet and the best of all they save energy without any compromise in sound quality.

A SMPS300 + UCD180 Kit (illustrated build guide) [link]

Got my AVCC 2.1 Shunt Supply from TPA

THE SRA2.1 (“SHUNT REGULATOR AVCC 2.1″?)

(Update 12/2/12): Russ White commented on the design rationale behind the SRA 2.1. Check the comments section.

Superb workmanship and finish.

PREVIOUS VERSIONS

Here is the “SRA1″ version that was bundled with the Buffalo II DAC (the one I have)

Here is the “SRA2″ version that was available prior to the introduction of the AVCC 2.1. This “SRA2″ version has been available for quite a while, at least since the the BII switched from an 80 MHz clock to a 100 MHz clock. Notice the thicker traces and different circuit topology (gone are the n-channel transistors QN1 and QN2)

Here is on a BIII

Here is the “SRA2″ on a BII-100 [link]

Boy, my AVCC is two generations old!, and I didn’t even know it. Maybe because it has been hiding on the bottom of the DAC board

NEW OPAMP

According to TPA, the new opamp (OPA2209)  is a better choice than the original opamp (LMP 7732)

Lets start with the “ideal opamp” characteristics:

1. Infinite voltage gain
2. Infinite input impedance
3. Zero output impedance
4. Infinite bandwidth
5. Zero input offset voltage (i.e., exactly zero out if zero in).

Parameter	LMP7732 (Old)	OPA2209 (New)	COMMENTS
Voltage Gain	130 db	132 db
Input Impedance	38 Kohm	200 Kohm
Output Impedance	“Low”	“Low”	Data sheet has graphs but they use widely different units, so it is hard to compare.
Bandwidth (GBW)	22 MHz	18 MHz
Input offset (max)	0.006 mV	0.035 mV	Seems the old one has an edge for these first 5 parameters
CMRR (typical)	130 dB	120 dB
Input Voltage Noise Density	2.9 nV/sqrHz	2.2 nV/sqrHz
Slew Rate	2.4 V/usec	6.4 V/usec	Here the new opamp has an edge. This seems a critical component for good performance [link]
Phase Margin	60 degrees	80 degrees	Here the new opamp has a slight margin for stability
Price	~$3.53	~$4.29

The comparison above does not give a clear indication as to why the new opamp is superior to the old one. I am sure the enhanced performance is in the circuit design and choice of component values. Without doing a circuit simulation, and testing/measuring, is is not possible to say which one is better. We trust, however, that TPA has made the right selection for opamp.

Indeed, as Russ has commented,

Bottom line is that the old op-amp was excellent on paper (and probably for other applications), but was not so good for AVCC in practice. It was also strangely finicky, meaning it could work perfectly usually – but occasionally be upset just by changing rail voltage or applying the right kind of external stimuli or load.

OPERATION

Output voltage

The output voltage of the AVCC starts at 3.6V. After the LEDs warm up, the output voltage settles at around 3.56V. This is typical of regulators that use LEDs as references. Input voltage is 6.2 V.  The load resistors for the test are 72 ohm. The output current is therefore 3.56/72= 50 mA.

Maximum Current

At first I had use a 33 ohm resistor. This load was pulling 108 mA and the voltage dropped down to about 2.5V. The regulator cannot source more than 100 mA (as specified).

Compared with the V1 (shown below), the LEDs are evenly lit.

HURRY AND UPGRADE

Original Buffalo IIs (the ones which came with the SRA1 AVCC supply) should benefit the most from the new AVCC 2.1 because both the circuit configuration, layout and opamp has been updated/upgraded. NICE!

If upgrading from the later 2.0 version, the layout, opamp has been updated/upgraded and the circuit has been tweaked with the compensation capacitors. Nice upgraded but not as nice as upgrading from the original BII

Fiio D3: Power Supply Tweaks

Now, turning our attention to the other end of the spectrum: the Fiio D3. This little DAC seems pretty popular according to the number of customer feedback at Amazon:

I had purchased and reported about the Fiio D3 a long while back. The D3 was interesting because it was selling for under thirty bucks and yet it implemented a Wolfson WM8805 SPDIF receiver which is typically found in much higher-end devices. (Note: the original version implemented the Wolfson chip. The latest version has switched to the Cirrus CS8416 SPDIF receiver)

I hadn’t even listened to it until now.

The first thing I did was to do some measurement on the power section. The motivation to do this came from the datasheet: The Cirrus 4344 DAC can operate at 3.3V and at 5V. At 5V operation, you get 2 dB better performance pretty much across the board.

By measuring the voltage on the power pin of the DAC (VA, Pin 9), the DAC is actually operating at 4.8V which is pretty much the specification for best performance.

At first I thought the operating voltage was 3.3v  because there is a zener diode regulating to 3.3V for the Wolfson part and thought that voltage was used throughout the device. Not true. Every chip has its own dedicated “supply line”.

In addition, the output stage OpAmp is also operating at the same 4.8V. Therefore, there is no need to do any modding here to get the better performance.

This 4.8V  is directly coming from the external supply.  So any improvements to the external supply and/or any improvement in the filtering should directly benefit the analog components of the DAC.

Actually this 4.8V may be regulated/filtered by the “power circuitry” you see in the upper right corner of the photo below. I’ve not traced this circuit, so I don’t know what it does, but it is related to the +V supply that powers the DAC and OpAmp.

I  proceeded to mod the input capacitor. Space is very tight, so must use similar sized capacitor. I used a standard class ELNA 1000 uF capacitor, bypassed with a 22nF film cap. The original was 470 uF, 16V. Detail after removing existing capacitor:

After the large capacitor, the power line is filtered through a ferrite, and then bypassed by two ceramic capacitors. It then connects to V+ in the opamp

Detail after replacing capacitor and bypassed with film cap

LISTENING TEST (for the power supply)

I connected the D3 to the optical spdif output of a Denon DVD player. And listening with a NAD receiver and small monitor speakers. At the same time I also connected the analog outputs of the Denon DVD player to the receiver for easy comparison.

The FiiO D3 is powered by an included wall DC 5V DC adapter. There has been reports that this is a noisy adapter. However at normal listening volume, with the player in PAUSE, there is absolute no noise that can be heard from the speakers even with the ear next to the speaker. If the volume is cranked up all the way, then there is some faint hissing when listening next to the speaker, whereas with the analog output of the DVD player it is completely silent.

FURTHER EXPERIMENTS

I used a ferrite with a few turns turns at the plug end of the power cable and combined that with a 1000uF capacitor across the + and – terminals forming an LC filter.

Result: no difference. Still hear a faint hiss when cranking the power all the way up. I’ll leave the capacitor in place, since it probably helps.

Next, I used a linear 5V supply, and spliced a mini USB plug with a built in ferrite.

Result: no difference. Still hear the faint hiss when I crank up the volume all the way. At normal listening levels, there is absolutely no noise.

Conclusion: the included switching power supply seems plenty good with respect to low noise. A linear supply may be an improvement in other areas…

Buffalo II, Musiland 03US Cap Mods Results

INTRO

The normal operation of the Buffalo DAC is to have the DPLL set at “BEST” and with this setting, there are no unlocks whether you are using I2S input or SPDIF input. Even during warm up, with the DPLL set at “BEST”, there are no unlocks.

The DPLL has several settings, and in theory, when set at “LOWEST”, the built-in ASRC rejects the most jitter. It has been widely reported that when the “LOWEST” setting is used with I2S input, the DAC will experience unlocks: a lot during warm-up and then occasionally afterwards. Unlocks will also happen with higher sample rate material if using the lower settings of the DPLL.

The mods I’ve been experimenting with and the resulting measurements have been aimed at understanding and correcting what causes these unlocks. Essentially, the DPLL in the DAC cannot lock into the incoming signal because of jitter. In this post, I report my latest results.

LATEST MODS

I have added input and output capacitors to the Musiland 03US [link] local regulators and also added output capacitors to the Bufflao II DAC local regulators [link]. These were fairly easy and straightforward mods.

RESULTS

As I said in the previous post, my experience (and my ears) tells me that the current state of the art has long passed my level of audible discernment. All of these devices sound really great with or without the modifications. So I have to use my “poor man’s jitter measurement tool” to see the effects of the mod.

DPLL set at lowest, 44.1KHz material.

This is a remarkable result: never in the past was I able to get unlock-free playing until after the 50 minute mark. In this test, note that there are no more unlocks after the 30 minute mark. Granted this is just a single test,

Second test:

We are back to having unlocks until the 50 minute mark. So the first test was probably an exception. In fact, the behavior is mirrors the behavior of the average of 5 tests performed before the cap mod. Nevertheless, I was never before able to get zero unlocks after 30 minutes.

Now the full 24 hour test (click for larger image):

Zero unlocks at last!

Wow! This result is even more remarkable: FIRST TIME I GET ZERO UNLOCKS IN A 24 HOUR PERIOD. And this when during the afternoon and night hours I was using the computer that was playing music (browsing the web, writing this blog entry, etc) and the family was at home turning lights on/off, using appliances, computers, TV, etc.

Compare with my last long term test where I thought I had reached the best possible results. Those result were quite good but not unlock-free [link],

I think the biggest effect of the cap mods is to add further filtering of the power supply and thus reducing the effect of external disturbances that can cause unlocks after the initial warmup.

SECOND TEST

I modded the Musiland further by adding a ceramic capacitor to the LC filter of the first regulator. Now both regulators have increased input capacitance and also increased output capacitance in the output LC filter. The capacitance on both LC filters have been increased from 10 uF to 30 uF.

I ran the long term test again:

Again, solid performance after the warm-up. Note the lack of unlocks after the 30 minute mark.

MORE TESTS

Decided to re-install the capacitors in a different configuration and use larger values. Also while trying to tidy up the ceramic capacitor, the “end cap” detached from the capacitor body. The end cap of these ceramic capacitors seems pretty fragile. I decided to use a horizontal SMT electrolytic capacitor without the plastic encasing while I purchase new capacitors. Ceramic caps have lower ESR.

Here are a 4-hour test starting at around 6:30 PM which seems the electrically noisiest time at home

Again, this is what we would expect, clean (no unlocks) after warm up. I think the Musiland device can provide solid (unlock-free) performance when matched with the Buffalo DAC

Was able to salvage more Kemet Tantalum capacitors. These are 22 uF, 25v and they are not cheap, at about $1 each [Digikey]. According to spec, the ESR is not too bad, 0.8 ohm. Probably not as important here in the LC filter since it is not used as a bypass cap. Besides, it is already an improvement to the existing tantalum capacitor.

Here is the latest iteration of the mod:

After this last mod, I did another long term test for 20.5 hours. This time I got two unlocks (in the same 10 minute interval). I guess there is still room for improvements. For now, I think this is as good as it can get. I think further improvements will come from additional power and EMI isolation.

SUMMARY

In summary, the cap mods were easy, economical and resulted in achieving zero unlocks after the warm-up period. It was very satisfying to see this particular mod cap (no pun intended) the long quest for zero-unlocks while having the DPLL set at “LOWEST”.

This is how it was before all the mods. The graph shows the number of unlocks per 10 minute interval just like the current charts, so about 5 hours worth of measurements.

These were the things I tried. I also implemented all of them except where noted:

Mods that definitely worked

• Cap mods on the local supplies for the Buffalo DAC and Musiland interface
• Shielding of the Sabre 32 DAC chip
• Shielding of the DAC board

Mods with potential value (there seem to be some improvements)

• IL715 Isolator (not used because in theory it adds jitter to the signals)
• Mechanical damping of the clocks
• Mechanical isolation of the case, etc
• Ferrite on the USB cable

Mods that very likely did not improve things

• Really short I2S wires (like cutting to 3″ from 12″ -after you cut the wires, no use lengthening them again )
• Ferrite bead on the I2S bit clock wire (not used, seemed to be worse)
• Night time use vs day time use (well, not a mod, but testing noise in the power grid)

In my setup I already had a power filter/conditioner, so it was already used for all the tests.

Buffalo II DAC PS Output Cap Mod

The Buffalo II DAC still is one of the best engineered and the best “bang-for-buck” ESS DAC out there. The power section was designed with solid engineering practice (4-layer PCB, close-to-the-chip bypass capacitors, etc), using low noise series LDOs in the digital section and shunt regulation in the analog section. I think the robustness and reliability of the IC regulators in the digital section is actually an advantage over using shunt type regulators such as the Trident regulators. The Digital section of the DAC does not require quick response and close tracking to changing current demand as in the analog section, but rather just provide a solid, steady and noise-free power delivery. This is perfectly accomplished by series LDO regulators.

One possible place to mod is the output capacitor for the on-board power supplies for digital section of the chip. The regulators are based on the LT1763 low noise LDOs with a specified noise figure of 20 uV RMS.  According to some reported measurements the noise figure can be further reduced by increasing the output capacitor. The results have been reported in diyaudio:

[link] Connecting a TL1763 LDO, however, I managed to get noise down to 8-10 uV, with reduced HF components… Throw away your 7805 and LT1086s, and try something better. The LT1763 has 20 uV specified noise, but a 150 uf OSCON at the output did the business.

[link] I have now finally had the patience to rig up the 100 mA LT1761-5. Powering a 45.1584MHz XO, I am in the 10nV/sqrtHz noise again, with a 150 uF OSCon at the output . Like the LT1763, the 1761 needs a 3×2 cm ground plane connected to -ve but under the module to reject a slight hum pickup.

EXISTING CONFIGURATION

The current configuration of the on-board LT1763 consist of an input capacitor of 100 uF (an OSCON SVP type), a bypass capacitor of 10 nF and a ceramic output capacitor of 10 uF. If you look at the photo above for the bottom supply, C18 is the input capacitor, c21 is the bypass capacitor and c22 is the output capacitor [link]. It is configured as per spec except for the input capacitor which is 100 uF. In addition, there is further filtering provided by a series ferrite bead which, together with the bypass capacitor near the ESS chip, forms an LC/RC filter. This is not just a solid implementation of the LT1763 regulator, but goes further in the noise department. Adding the output capacitors will further improve this already excellent implementation.

The bypass capacitor is already at the maximum required (10 nF or 10000 pF)  to reduce the output noise to its minimum specified. Thus no need to mod this part.

We have to make sure that the added capacitor, especially because it is a low ESR type will not cause stability issues in the regulator. The stability graph tells us we are safe even with ESR=0.

INSTALLING THE CAPACITORS

The specification does not measure noise with varying output capacitor size, so we are basing this mod on experiments by other audiophiles as reported above. This mod is very easy. Just piggy back the capacitors on the existing ceramic output caps as shown in the following photos:

Installed the capacitors horizontally for two reasons:

1. Keep the same size profile as the original board
2. It was very hard to get the solder tip to the soldering position with the capacitors in upright position, so there was no easy way to install them upright

I decided to use 100 uF for the digital supplies and a larger 820 uF 4V capacitor for the clock power supply. The clock supply is more critical and needs to be more stable in order to keep the clock stable.

The capacitors already had the leads cut for board stuffing, making them very short. I had to extend the leads with cat5 wire.

Soldering onto the ceramic output capacitors was very easy. These ceramic capacitors are fairly big in comparison to what is used in the Musiland boards.

Even reworking was easy. Here I first installed a 100 uF capacitor, but later decided to install a 820 uF capacitor. Removing the first cap and installing the new one was a breeze. Use leaded solder and high flux content…

A NOTE ON CAPACITOR RATED VOLTAGE

The capacitor I used for the clock supply is rated at 4V (5.2V surge). Is this safe enough? The output voltage of the regulator is 3.3v, thus the margin is about 20%. I think this is safe enough.

In case of failure, we can expect the following:

According to the OSCON-GENERAL CATALOG the failure mode of an OSCON capacitor is a short circuit:

The main causes of failure are thermal stresses cause by the soldering or thermal use environment, along with heat stresses, electrical stresses or mechanical stresses. The most common failure mode is a short circuit

Fortunately, the LT1763 has current limit protection. In the event of a short circuit in the capacitor, the LT1763 will protect itself by limiting the current. The output voltage will be zero and the clock will just stop operating. The Placid supply which is feeding the BII DAC is also limited to about 300-400 mA and when it cannot supply the current shunt by the short circuit, the entire DAC will just gracefully shutdown. I think the only damage will be the capacitor itself.

Thus there are already several safety measures built-in in the event of the OSCON capacitor failing in a short.

RESULTS

At this level of noise and resolution, I can’t tell by listening whether there has been a positive change or not. My experience (and my ears) tells me that the current state of the art has long passed my level of audible discernment. All of these devices sound great with or without the modifications. And in many cases, the gratification comes in being able to add the mods and tweaks, sort of like saying “the journey is the destination” .

I am also doing some unlock measurements, will report later…

 

A NOTE ON OSCON CAPACITORS

The capacitors used in the mod are the older series, now discontinued, which uses organic semiconductor dielectric. The new series (lke the OSCON-SVP types used in the BII DAC), uses conductive polymer as dielectric. They are identical in all respects except the new series exhibits very minor variations in temperature characteristics vs minor variation in temperature characteristics in the older series. You can read all about it in the OSCON-CONSTRUCTION specification.

The OSCON SH and OSCON-SP capacitors I used are an upgrade from the standard SC types:

In fact the SP series are specifically “Optimum for audio”:

Additional info here: [link]

The TPS7A47 Eval Board

Just got in the evaluation board for the new TI ultra low noise regulator, the TI TPS7A4700

I would consider this a real bargain for audio diy at $20 including shipping. In came in a huge box and it was shipped Federal Express in an even bigger box. I think TI should cut the shipping cost and pass the savings to the customers. But I suppose it is more important for business customers to get it on time and without damage than saving a few bucks.

Here are some photos

Here are the packaging and shipping boxes. I did a quick check on on the FedEx site for shipping cost for a FedEx box: $17.67. You are basically getting the board for free!

Data sheet of device: [link]

Data sheet of Eval Board: [link]

OUTPUT VOLTAGE SELECTION

Output voltage selection is done by shorting jumpers. The resultant output corresponds to the addition of the internal voltage reference (1.4 v) and the voltages indicated by the jumpers.

The board clearly labels how to select the output voltage:

Internally, the jumpers just change the value of the voltage divider resistor as shown by the diagram below. Certainly much cheaper than implementing a potentiometer.

NOISE

The TI “7A47″ has half the RMS noise as the ADP-150 at 4.17 uV RMS. (The dotted blue line is the noise plot for a 5V LT1763. Compare that to the noise plot for Vout=5v -blue solid line)

Compare the above noise plot with that of the ADP-150 shown below

New TI TPS7A4700

Just got in the mail information on the new TI ultra low noise regulator, the TI TPS7A4700

• Can source 1 A of current
• Noise figure of 4.5 uV, puts it at the top of the regulator list
• Voltage configurable evaluation board can be purchased for $20.

Is there a reason to use anything else?

The TPS7A47 is designed with bipolar technology primarily for high-accuracy, high-precision instrumentation implications where clean voltage rails are critical to maximize system performance. This feature makes the device ideal for powering operational amplifiers, analog-to-digital converters (ADCs), digital-to-analog converters (DACs), and other high performance applications…

Seems they designed this part for us diy audio nuts!

I’ve been thinking about what to use to power Ian’s FIFO reclocker board. This is its perfect match.

Load Step Transient Response

The load step transient response is the output voltage response by the LDO to a step change in load current whereby output voltage regulation is maintained. The worst-case response is characterized for a load step of 10 mA to 1 A (at 1 A per microsecond) and shows a classic critically-damped response of a very stable system. The voltage response shows a small dip in the output voltage when charge is initially depleted from the output capacitor and then the output recovers as the control loop adjusts itself. The depth of the charge depletion immediately after the load step is directly proportional to the amount of output capacitance. However, to some extent, the speed of recovery is inversely proportional to that same output capacitance. In other words, larger output capacitance act to decrease any voltage dip or peak occurring during a load step but also decrease the control-loop bandwidth, thereby slowing response.

The worst-case off-loading step characterization occurs when the current step transitions from 1 A to 0 mA. Initially, the LDO loop cannot respond fast enough to prevent a small increase in output voltage charge on the output capacitor. Because the LDO cannot sink charge current, the control loop must turn off the main pass-FET to wait for the charge to deplete, thus giving the off-load step its typical monotonic decay (which appears triangular in shape)

Connex SMPS300RE

Purchased pair of power supplies from Connex. This is their their mid-power, heatsink-less power supply. When I ordered, Cristi of Connexelectronic was kind enough to inform me that a new version was in the works and asked me if I wanted to wait for the new model instead of getting the current model at that time. Obviously, I waited for the new model

The latest edition of this supply, the “RE” model, incorporates a CLC output filter to further clean up the output waveform. Factory measurements show 7-11 mV peak-to-peak @ +/-45V at 2A [link]. In addition, I like the following features:

• ‘Perfect” companion to the Hypex UCD-180 amplifier module in terms of size and power for a dual-mono configuration
• The input high-voltage capacitors have been increased in size (as compared with the photo of the older model)
• Based on the latest ST L6599A resonant controller
• $uper deal!

Here is a closer look at the output CLC filter. I we use the reported ripple value of 7-11 mV peak-to-peak for an output voltage of +/-45V, we get .011V/90V=0.012% or .009% RMS for the high value and .005 % RMS for the low value. These values are in the same  ballpark as the (0.003%) number for a LM7805 regulator.

The input capacitors have been increased in size as compared with the photo in the Connex website (or this is the size for the 120V model. The 400V input caps are probably for the 200V world)

The auxiliary supply filter caps.

Here is the previous model without the CLC output configuration

The ST L6599A [link] is the resonant controller. This “resonant LLC” topology is widely used for the 80-Plus Gold and Platinum PS’s for PCs because it allows for highest efficiency( [example 1], [example 2]). There are also indications that Hypex is also using this topology for their SMPS: [link]

The use of resonant LLC also results in lower EMI emissions due to the soft switcingh of the FETs and sinusoidal current [link]. In hard-switching topologies, fast changes in voltage and current generally results in higher amounts of EMI.

TECHNOLOGY: CONVENTIONAL VS RESONANT

According to a Fairchild design document:

“The Conventional PWM technique processes power by controlling the duty cycle and interrupting the power flow.  All  the  switching  devices  are  hard-switched  with  abrupt changes  of  currents  and voltages, which  results  in  severe switching  losses  and  noises.”

“Meanwhile,  the  resonant technique  process  power  in  a  sinusoidal  form  and  the switching  devices  are  softly  commutated. Therefore,  the switching  losses  and  noises  can  be  dramatically  reduced.”

“Among   many resonant  converters,  the  half-bridge  LLC-type  resonant converter  has  been  the  most  popular  topology  for  many applications since this topology has many advantages over other topologies; it can regulate the output over wide line and  load  variations  with  a  relatively  small  variation  of switching frequency, it can achieve zero voltage switching (ZVS)  over  the  entire  operating  range,  and  all  essential parasitic  elements,  including  junction  capacitances  of  all semi-conductor devices and the leakage inductance of the transformer, are utilized to achieve soft-switching.”

Soft switching is the main reason for much reduced EMI

The transformer has a new look -a cap- (don’t know if it is functional or just esthetics)

The output FETs are ST W20NM50. Specified at 500V / .22ohm /20amp. It is also rated at 14 amp continuous at 100 degrees C. Ample current carrying headroom mitigates the need for heat-sinks. These two parts alone are worth near 25% of the entire cost of the supply

OPERATION

Selecting mains voltage: 230V or 120V.

At first I was getting 0V. at the outputs. It turned out that the supplies are shipped for 230V operation. For 120V operation, the “120V jumper” must be installed (right photo).

Output voltage adjustment.

The nominal voltage of the supply is +/- 45V. There is a pot for voltage adjustment as shown in the photo below. I also replaced the output metal tabs for screw connectors for easier hookup.

These are the high and low values for the output voltage (previously measured with 330 ohm 10W power resistors loading the outputs)

INSTALLATION

I gutted an old discarded MUZAK PA amplifier and salvaged the case.

Reused the power cord and the lighted power switch. I added a ferrite bead to the power cord to further filter any potential EMI coming in our out through the power cable. The power supplies already have built-in EMI filters (as most SMTPs do).

The two green LEDs are connected to the auxiliary supplies and indicate that the power supplies are ON. I will later expose the LEDs from the UCD amplifier modules. Thus there will be light indicators for the AC in, the power supplies and the amplifier modules.

For testing and voltage adjustment, I use 1.5 Kohm 5W power resistors connected at the outputs.

The output voltage is very stable. The starting voltage is shown (44.96v). Eventually, it stabilizes at 45.00V.

In addition, with or without loading the outputs with the resistors, the power supplies are dead quiet (at least with my ears a few inches away from the supplies avoiding being zapped with high voltage ).

ADDITIONAL READING

What is PFC? [link], [link]

Some thoughts on PFC in Audio: [link], [link]

Musiland MINI Power Mod: Less Jitter?

Most people’s idea to improve the power of a USB device is to replace the USB power with an external linear supply. Although this kind of mod would improve the incoming power to the device, the ultimate noise performance is determined by the local regulators that directly feed the chips.

Additionally, because I value the convenience of using USB power, I took a different route: I decided to replace the local regulators with low noise types. The factory regulators are  AMS1117. The ones I am upgrading are LT1963. Noise density figures for the AMS1117 is approx 990 nV (3.3v regulator) and for the LT1963 is approx. 125 nV (3.3v regulator).

The AMS 1117 regulators are similar in noise performance as the very popular LM317 types. The LT 1963 are cousins of the LT 1763 used in Buffalo II. They have higher noise (but are still low noise) due to their higher current carrying capability.