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33.8688 MHz Oscillator: Discrete Choice

MOTIVATION

If your are looking for a 33.8688 MHz oscillator, you are pretty much out of luck. I looked at the usual shops and they are not in stock. Such frequencies were used for CD players and they are  not widely manufactured anymore. Modern disc players derive all the necessary frequencies (including the 33.8633 MHz frequency) out of a 27 MHz oscillator or crystal and an integrated multi-frequency clock generator.

I have a couple of Denon SACD/DVD players and wanted to see if the clock can be improved. On the DVD2910, The audio section of the player derives the 33.8688 MHz frequency from a 27 MHz crystal, generated by a SM8701 clock generator. The specification of the clock generator indicates that the output jitter for the 33.8688 MHz frequency clock is 150 psec. On the DVD1920, the audio section of the players uses a 33.8688 MHz clock derived from the SM8707H clock generator. To my surprise, this lower end model jitter specification is better than the higher end model DVD2910 (and also the DVD3910 and top of the line at that time DVD5910). The DVD1920 is a newer generation device and thus uses newer parts. The SM8707H part has a jitter specification of 70 psec (2X better).

The published jitter figure is “period jitter” and in order to compare it with a standalone oscillator one needs to compare the phase-noise plots. For example, the popular Crystek C33xx oscillators are specified at around 1 psec Jitter RMS if measured at the 12kHz~80MHz phase noise band (this is the accepted norm for telecom applications). However, if one uses the “audio band” which starts at 10 Hz, the jitter measurement results in around 30 psec. Under similar measurements the top-of-the-line CCHD-950 measures 0.5 psec. I can’t find any reference as to how the jitter numbers were measured for the clock generators, but if one assumes that they have been measured within the “audio band”, then these numbers are not too bad.

Note: to add to the confusion of jitter numbers, some of the datasheets publish jitter values in “phase jitter” numbers. Period jitter is a “frequency weighted” function of phase jitter an as a value, it is typically smaller but close to the period jitter number [In short, period jitter is integrated similarly to phase jitter but with a frequency weighting factor of 4sin2(πfτ) -link]. The only consistent way to measure jitter is to look at their phase-noise plots, but seldom do you see phase noise plots in datasheets.

THE “TRADITIONAL” MOD

The traditional mod recommends replacing the crystal that feeds the clock generator. This is typically 27 MHz crystal connected to the clock generator. As can be seen from the above analysis, replacing this crystal with a low jitter oscillator will do nothing to lower the jitter of the generated clocks because of their inherent jitter. Thus if reducing jitter is the goal, the clocks to replace are the generated ones out of the clock generator chip.

I wanted to explore the option of discarding the derived clock and using a separately generated 33.8688 MHz frequency. Note: the derived 33.8688 MHz clock is synchronous with the 27 Mhz master clock which is used elsewhere. At this point, it is not proven (or dis-proven) that a asynchronous 33.8688 MHz clock would work in the device. I cannot find any report on the success or failure of this proposed mod.

CHOICES

There are only a few possible (reasonably priced) candidates for a 33.8688 MHz oscillator:

1- The eBay solution (around $30). There is a review in diyaudio on these oscillators:

 

2- The famous Tent Labs oscillator (available in many frequencies including 33.8688 Mhz), >$30:

The Tent is the only one that is backed by a phase noise plot (just happen it is the phase noise plot of the 33.8688 frequency):

If we calculate the RMS jitter from the plot at 10 Hz forward (which is what Crystek uses for their measurements), we get: ~0.32 psec RMS (see sidebar for link to jitter calculator). This is an impressive number! Equivalent to the Jitter figure for the Crystek  CCHD-957 oscillators. Note the figure from the chart gives 0.9589 psec jitter RMS because it is measured from 1 Hz.

3- The next option is the Silicon Labs programmable oscillator Si570. These are also non-existent in the usual parts distributors, but you can find them from Ham Radio web sites, in particular KM5H.com (~$20) and SDR-Kits (~$23).

Si570 photo from here: [link]

The Si570 is a favorite of Ham Radio aficionados because it allows you to “dial-in” any frequency. There is a ($40) diy kit that lets you do just that:

And it is amateur radio people like it because of its low phase noise. Clifton Labs has done an extensive study on phase noise for the Si570 and other oscillators. These guys are even more serious about jitter than audio people

The only potential “disadvantage” of this oscillator is that it requires a local uP to program the oscillator every time it is powered on.

4- DIY discrete oscillator from the diyaudio group buy (~$25). This is a differential Colpitts design with dual shunt regulators.

In terms of performance (noise), the diy discrete oscillator is probably  not the best, but also not the worse. Although the designer of the oscillator has not measured its phase noise performance, there is some measurement on phase noise for a the discrete Colpitts oscillator from Clifton Labs:

My home brew Colpitts oscillator, designed without paying particular attention to low phase noise, has slightly lower phase noise than the Raco oscillator module, most noticeable when viewed with 1 and 10 KHz spans.

The designer further says:

Unfortunately I don’t have the equipment necessary to produce a quotable figure for jitter. I have taken both objective and subjective measurements (comparisons of the jitter at a CD player’s output and listening tests) that indicate that it has significantly lower jitter compared to a stock CD player master clock.

Further, there is also the fun factor in building your own oscillator.

DECISIONS, DECISIONS

Seems the best choice for this mod, based on jitter specification is the Tent clock. However, I have already bought the diyaudio discrete clock kit and whether it is better or not than the published 70 or 150 psec jitter of the 33.8688 MHz clock remains to be seen. I would guess it is probably better than a derived clock, so worthwhile to implement.

INSIDE A CAN OSCILLATOR, CAN CRYSTAL

Inside a can crystal

FURTHER READING

• HP oven controlled oscillator: http://www.realhamradio.com/GPS-oven-journey.htm.
• HP 10811A/B Quartz Crystal Oscillator Manual: http://www.hparchive.com/Manuals/HP-10811AB-Manual.pdf
• Discussion on clock selection: http://www.diyaudio.com/forums/digital-source/194965-clock-selection-experts.html
• This is how Ham Radio people build their oscillators [link]

Apple Remote Codes

A reader alerted me that all Apple Remotes have the same code (I’d mistakenly assumed there were two sets of codes)

There is currently only ONE model of Apple remote. You should look at those codes again.

The codes from all Apple remotes ever made are identical. The small exception is that the silver remote sends TWO codes for the Select and Play/Pause button.

The big “aha” missing from this discussion comes from the assumption that Apple codes are NEC format. They’re not. The next assumption is that the button codes are 8 bits. They’re not.

Apple’s IR format is custom and only “based” on NEC. They have taken the premise and re-used all the command bits in a custom fashion.

7 bits for the button code
1 PARITY bit
8 bits for ID

The parity is a XOR sum of the button and ID bits, and since it flips around between 1 and 0 depending on the other bits, of course you’ll think the codes are different between two remotes with two different IDs.

I’ve corrected the information here: [link]. When I get a chance, I’ll update the code so that it will work with any Apple remote.

 

Texas Instrument Audio Guide

Download here: [link]

Notable is the direction the company is taking with respect to new DACs:

• No more investment in “ultra high end” DACs
• Development is concentrated in the new 32-bit Vout DACs and USB DACs
• Adding “miniDSP” into the DAC

As the product map indicates, the latest generation are the PCM51xx family of DACs. The first one, the PCM5102 was released last year and has been implemented in devices such as the Musiland 02 Dragon, the Jundac XI, and diy projects.

According the the TI product manager,

… it uses a next generation architecture based on the PCM1792 (The flagship 132dB DAC that TI has)

So the “flagship architecture” is now in the PCM51xx family. The new devices are incorporating good features such as I2C control and integrated DSP functions. Prime candidates for Arduino interfacing, and possible digital crossover filters.

miniDSP

Musiland 03US Dragon

Update (5/11/12): Released. Performance-wise, a small improvement over the regular 03US. However, the new version completely overhauls the power section

Summary of improvements:

• Limited edition (9500 units) to commemorate the Year of the Dragon
• Price is 999 RMBs (compared to 868 RMBs for the current 03US model). At the current exchange it is US $160
• External looks identical to the regular 03US model except for a silk-screened “dragon” icon
• I/V op-amp upgraded from MC33079 to LME49740 
• All new digital power section similar to 03 USD
• All new analog power section boosting the headphone amp section to 18V
• “Greener”: 95% efficient at low volume, 90% efficient at max volume (for headphone)

The digital power section is the same as in the 03USD

The PHKI is an adjustable switching regulator from TI: TSP62200 (or one of its variants) switching regulator. Thus the use of large inductors. This is certainly an innovation. Switching regulator technology has developed tremendously especially driven by by mobile device industry segment. If indeed this configuration is more effective and lower noise to what they were using before, then the jitter performance can be somewhat improved by providing cleaner power to the FPGA.

Does “Mastered for iTunes” matter to music?

A nice, detailed article on the subject [link]

We enlisted Chicago Mastering Service engineers Jason Ward and Bob Weston to help us out, both of whom were somewhat skeptical that any knob tweaking could result in a better iTunes experience. We came away from the process learning that it absolutely is possible to improve the quality of compressed iTunes Plus tracks with a little bit of work, that Apple’s improved compression process does result in a better sound, and that 24/96 files aren’t a good format for consumers.

To test this, Ward downloaded a track from a recently mastered album available on iTunes. He then loaded the original 24/96 master file and used Apple’s supplied iTunes mastering tools to compress the file to iTunes Plus format. He then played both tracks back in iTunes, using the studio’s equipment to switch back and forth between the two versions. The version created directly from the 24/96 master did indeed have a slightly brighter, crisper sound, according to our observations.

Readers would probably know that I use iTunes as my music player. And now with the iCloud shackle, I can’t move to any other player

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 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]

ODAC Revealed…

Mr. NWAVGuy has published one of his most interesting and technically revealing posts: The ODAC

LESSONS LEARNED: If this project has taught me anything, it’s that getting much better than 16 bit (96 dB) performance can be challenging. The first version of the ODAC, despite following the reference design, only had about 98 dB DNR. That’s about the same as the FiiO E10. The photo to the right shows a few dozen assorted surface mount parts that were laboriously swapped out one at a time and measurements repeated dozens of times using the dScope. Some improvements were far from intuitive. Audiophile preferred polyphenylene capacitors performed worse than less expensive types. Additional filtering on the digital power supply dramatically increased jitter. Chasing down the last few dB of dynamic range the chip is capable of proved to be especially challenging. When it was said and done, the DNR went from 98 dB to over 111 dB. That’s a huge difference and something the design-by-ear crowd would have never achieved.

The ODAC is based on very familiar components (Tenor 7022l and ESS 9023 DAC -both not having a freely available datasheet), but according to NWAVGuy, only after extensive component experimentation and measurement, was he able to achieve the numbers published in the DAC’s datasheet. This indeed is a very remarkable achievement given the fact that the entire board is USB powered, including the ESS DAC.

The final product is a collaborative effort with Yoyodyne Consulting and very affordable priced: $99 starting price.

(Another photo of a prototype board from diyaudio)

(Update 5/10/12): Production (with minor tweaks to the layout, resulting in improved jitter (-106 db)

I’m pleased to report the production version has even lower jitter. In the last ODAC article I reported the jitter components adding up to –103.3 dB. In the production version, as you can see below, it’s over 3 dB better at –106.5 dB with far fewer components.

I believe it’s related to some minor changes in the USB ground scheme. When you’re dealing with jitter components below -110 dB, even small changes in the digital grounds can impact jitter. You’re correct such changes carry a risk of making things worse instead of better. So, especially where the PC board layout is involved, we tried to play it safe with the final revisions based on everything I had learned along the way.

(Rev 4)

(Rev 2 (left) and Rev 1)

Notice the following:

• Replaced can-type of bypass capacitors with SMT types
• Replaced radial through-hole bypass caps with SMT types
• Use of large inductor in front of DAC supply regulator

Perhaps these larger-feature capacitors act like antennas and pick up more air-born EMI causing jitter problems? I notice a similar “trend” on the Musiland USB devices: newer models have done away with through-hole components (maybe it is just cost-savings). Compare the new 01 USD with the old 01 USD:

The ODAC is similar in design to the Calyx Coffee

Some wisdom from the comments section

(Whether you agree or disagree with NWAVGuy’s approach, there is always something to learn in his posts and comments)

Cable ferrite for noise suppression

Use of ferrite bead on USB cable and choosing a “free” USB port [link]. I have been doing this for a while in my own setup

The ferrites do suppress common mode noise and also radiated noise. That lowers noise on the ODAC’s power supplies, which in turn, slightly improves the overall performance. The ferrites are also a good idea for RFI suppression from cell phones, etc. The ODAC has ferrite filtering on board, but it helps to keep as much noise as possible from even reaching the ODAC.

Audibility of jitter [link]

The ODAC and DAC1 both measure sufficiently well to be transparent. But they do measure differently and the DAC1 has a performance advantage in several areas, especially jitter. Yet they sound the same. This is further evidence you’re not going to get better sound by trying to further improve the ODAC, use the XMOS interface, etc.

Put another way, I doubt the XMOS interface beats the DAC1 for jitter. Yet the ODAC and DAC1 sound the same. And it’s not surprising. All the audible ODAC jitter components, using a worst case signal designed to expose the maximum amount of jitter, are below -110 dB and the total is below -103 dB. Consider Ethan Winer’s distortion audibility test. The distortion is entirely masked by the music around -75 dB. A level of -103 dB is massively lower. Ethan very conservatively sets the bar at -100 dB for assured total transparency.

Stay tuned to the next article which will be more technical in nature. Mr. NWAVGuy will go into more detail how he went about the improvements. This is a very valuable source for us diy types with no measuring equipment (and with bad ears ).