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 approx 75KHz. The reason for this filter is because I use the Buffalo II DAC in voltage-out mode connecting straight to the Amp. The values are R=220 ohm, C=10 nF

I may adjust the filter to the values used by the Legato I/V which I believe has a cut off frequency of 400KHz.

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]