It’s all here. Before I ended up doing the work myself, I started to gather notes, from this very thread, to answer questions my previous mod-tech might have. His eyes are getting worse, so he didn’t want to do SMD stuff required for VOCM (it’s not VCOM or VOCOM). Seek and ye shall find.
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Start here
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so, are you saying that each added cap is put in exactly the same configuration from left to right on the board? all 8 caps go in the same way…???
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Thanks. 
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Welcome to the craziness. It’s worth it.
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Finally got my DAC back from the technician with XS4400 transformers upgraded to APS, all R5 and R6 replaced with thin film equivalents and R6 paralleled with an extra 47uF to stabilise Vocm. While I’m sure there’s going to be some burn-in time before it settles in there are some immediately discernible improvements.
The DAC volume control remains fixed at 92 like it was before. With the transformer change the output level is higher so I have to use different positions on the pre-amp’s potentiometer volume control to get the same volume. I don’t think that impacts these observations though.
First, the noise floor is obviously lower. In the opening verse of Dire Straits’ song Brothers in Arms, there is an almost-muted high hat gently marking selected off-beats. I think I discovered this via headphone listening some years prior to getting this DAC and the DS has always struggled to extract that detail through my speakers. Not any more, it’s plain as day once you turn the volume up high enough.
There’s a similar story in the bass but it comes across as grip and control rather than “detail” or a lower noise floor. In the silent bar right before the 2 minute mark in Angus and Julia Stone’s Yellow Brick Road, there’s a very low level kick drum pacing out beats 2, 3, 4. This is another detail I haven’t heard from my system in years but here it is just like I recall having discovered on some other setup I can’t recall.
But the bass overall is just so much better. It isn’t louder but it’s stronger and deeper and better timed. The pulsing bass in Jewel’s What’s Simple Is True is finally rhythmic. Groove Armada’s Suntoucher drops into the abyss but no longer disappears. Piano Black on the first disc of the Cowboy Beebop OST now has clear bass notes on every beat of every bar instead of just most of them.
Along with the extension and timing comes more harmonic structure down low, like in dense piano chords. And plucked double-basses have never had so much presence in the room – feel the air compress around you when the bassist aggressively mutes their instrument on the 2nd count of every 4 in Umi Yushida’s version of This Masquerade.
Thanks yet again to Ted, and JKRichards and son for the chance to enjoy continued improvement on this DAC over such a long period. This should keep me satisfied for a few years until a MkII with APS transformers eventually seduces me.
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Sorry to bring back the discussion. Is the VOCM mod just for these components? I remember seeing some implementations where larger capacitors were installed, maybe it wasn’t the VOCM mod.
The definition of the Vocm mod is to add capacitance across R6. jk has offered one particular version of doing that, while some of the earlier experiments people did used electrolytic capacitors which are much larger, physically speaking.
People have also added or changed capacitors in various other locations which are unrelated to Vocm.
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Perfect, and from the experience of most users who made this mod, the best alternative in sound results is the one proposed by Jk? The higher the capacitance the better? Or is it more related to the quality of the capacitor?
Ted has pointed out more than once that using through-hole components (ie large capacitors with legs) has some significant downsides because of their ability to act as antennas for noise, so for that reason if no other we are encouraged to use surface-mount devices. Since R6 is in an 0805 package it makes sense to choose a capacitor of the same physical size to piggy-back on top of it.
I imagine there’s a point at which increasing capacitance has some negative impact also. I mean in the extreme hypothetical case your inter-galactic capacitor would just keep soaking up current without the voltage ever rising to the level needed to function as Vocm reference. But I’ve no idea how much starts to be too much – I just went with what most others have done and have a notion that it was also Ted’s recommendation, ie 47µF. JK suggested 220µF based on his experience, and I have no reason to doubt that it would also deliver a good result.
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As far as the type of capacitors used, turbotk started using the electrolytic caps because that’s what he had on hand and they work well. This was the very first experiment with improving Vocm. Later we started using the 0805 tantalum capacitors as they are faster to install and a better fit. I can install a set of 8 in about 15 minutes. I use the 220uf as that’s the largest available in 0805 at 4v and have had very good success with them. Anything over 47uf will do fine. Remember 4 of these are in parallel so the total would be 880uf if we use 220uf each.
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A post was split to a new topic: JK’s trafos and adapters available
Locked?
Nope
You just posted in the thread. It therefore is not locked. 
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…and more.
No reason to get into why he may have moved on, and wishing JK and APS well with their services going forward.
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And:
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I would prefer the discussion continue here.
I won’t be participating in the Wild, Wild West that is Audiogon forum threads.
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