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Post by skunkworks on Apr 9, 2009 11:33:03 GMT
Hi all, I've pulled my V-dac apart again to make a list of the caps. This was what I found: jamicon 2x -47uF 16v NP 13x -10uF 63v 3x -1uF 63v 10x -100uF 25v 1x -1000uF 16v Now a question for the cap masters at Rock Grotto: What cap's should I replace the jamicons with to get the biggest bang for the buck? Crap did I ask something stupid again?  |
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Post by traf on Apr 9, 2009 13:38:36 GMT
I don't think so  I was just having a think about this myself this morning. I'm pretty content with the noises coming from my V-Dac with just an opamp change, but there is obviously more to be wrung out of the thing. Most of the electrolytic caps fitted are actually pretty small in value so its not clear to me if fiddling with most of them would make that big an improvement. The exception of course is the output cap which can be shorted if the dc component across it is only a few mV. Best cap = no cap. One thing about this unit is the use of 2x DC-DC converters (the two 7660S chips near the power input socket) to construct a -12V supply to the opamps. Noting that these things use 1kHz switching internally, and must add some noise to the supply, I do wonder if its best to concentrate on the power supply side. I've just lashed up a -15Vdc-0-+15Vdc supply to the V-Dac by running a few wires from my SCHA setup (which uses the Jaycar PSU board and a JLH) with a 30VA transformer:  This has made a big difference, even though the supply is now feeding both the DAC and headamp at the same time - tigher bass, much bigger soundstage, increased instrument separation and better dynamics - I can't identify anything that isn't better - its like some fog has cleared, although I wasn't aware of too much fog being there in the first place. To be honest, the change in PSU and opamps is bringing this little thing very close to the DAC stage in my KW250S, which uses broadly the same digital and analogue topology. We might be able to get a bit more by changing some caps, but I think I would suggest a decent psu and a change in opamps for starters, even though its not the cheapest way to start modding it. cheers simon |
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Post by Deleted on Apr 9, 2009 21:43:36 GMT
Simon
This is what I have done with my X-DAC V3 . It uses an outboard dual regulated +-15.5V supply with a JLH incorporated.
Obviously, the V-DAC should sound a little better again, if it wasn't sharing power with the SC HA.
Alex
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Post by traf on Apr 9, 2009 22:04:56 GMT
Well I've just bought a 100VA tranny (overkill possibly?) off ebay for £5 so a mk2 psu is in prep. Here's a question though (not really being the electrical kind): I can see that feeding the same regulated output to different components is not ideal but is it ok to feed separate regulators from the same transformer winding? eg. feed two separate Jaycar PSU boards from the same windings, with separate JLH boards, one feeding the SCHA, the other the VDAC? I hope to put everything in one box (maybe not the same Galaxy case as I'm using for my SCHA  ) and don't really want to use two transformers. cheers s |
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Post by Deleted on Apr 9, 2009 22:36:18 GMT
Well I've just bought a 100VA tranny (overkill possibly?) off ebay for £5 so a mk2 psu is in prep. Here's a question though (not really being the electrical kind): I can see that feeding the same regulated output to different components is not ideal but is it ok to feed separate regulators from the same transformer winding? eg. feed two separate Jaycar PSU boards from the same windings, with separate JLH boards, one feeding the SCHA, the other the VDAC? I hope to put everything in one box (maybe not the same Galaxy case as I'm using for my SCHA ) and don't really want to use two transformers. cheers s Simon Sounds like a good ,space saving solution. Alex |
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Post by traf on Apr 17, 2009 11:35:55 GMT
My modded V-DAC now has its own 100VA transformer feeding a Jaycar +-15V regulated PSU. This is getting better and better - tighter and more dynamic that it was when fed from the same supply as the SCHA, with lovely clean shimmering treble  I now need to knock up another JLH board to see if that makes a further improvement. So I think I'll conclude that in stock form (as with most MF stuff) the V-DAC is a very good piece of kit - better in my opinion than the stock CA Dacmagic which I have just sold, even if the casework is basic. BUT it can be significantly improved at modest cost by dropping in some decent opamps and lashing up a decent regulated +-15V psu arrangement. simon |
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Post by Deleted on Apr 17, 2009 12:05:15 GMT
Simon
Keep us all posted how you find it after the other JLH is made. I have always been tempted to make another one to fit in my Class A amp, so there would be one for each channel, but I always seem to find another use for any spare JLH.
Alex
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robertkd
Been here a while! 
Electronics Engineer from sunny Queensland
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Post by robertkd on Apr 17, 2009 12:23:38 GMT
My modded V-DAC now has its own 100VA transformer feeding a Jaycar +-15V regulated PSU. This is getting better and better - tighter and more dynamic that it was when fed from the same supply as the SCHA, with lovely clean shimmering treble I now need to knock up another JLH board to see if that makes a further improvement. So I think I'll conclude that in stock form (as with most MF stuff) the V-DAC is a very good piece of kit - better in my opinion than the stock CA Dacmagic which I have just sold, even if the casework is basic. BUT it can be significantly improved at modest cost by dropping in some decent opamps and lashing up a decent regulated +-15V psu arrangement. simon Simon, I'm not surprised given that this will effectively provide each stage with it's own isolated low impedance supply. Of course your going for the jugular with the LME49720HA's (LM4562HA's)  I would however also consider some local supply decoupling to further improve the sonic qualities. Unfortunately I haven't had that much time to seriously compare the LME49720HA <==> LM4562HA I have a few other projects on the go ATM not the least the 8 * TDA1543 DAC for one  Robert |
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Post by traf on Apr 17, 2009 12:35:37 GMT
Hi Robert
"I have a few other projects on the go ATM not the least the 8 * TDA1543 DAC for one"
Oh God...thats the thing that got me started on the slippery DAC slope a few years ago - I bought an DAC-AH unit which I thought was pretty good (well compared to my c**p CD player it was). I started with the usual bypassing of the output stage and ended up piggy-backing another 8xTDA1543 on top of the existing 8 (I should have put sockets in....). It did get a bit hot but sounded rather nice - very different in sound to the MF DACs I moved on to.
cheers
simon
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Post by PinkFloyd on Apr 17, 2009 12:35:53 GMT
Hi all, I've pulled my V-dac apart again to make a list of the caps. This was what I found: jamicon 2x -47uF 16v NP 13x -10uF 63v 3x -1uF 63v 10x -100uF 25v 1x -1000uF 16v Now a question for the cap masters at Rock Grotto: What cap's should I replace the jamicons with to get the biggest bang for the buck? Well..... it depends on what any particular cap is doing... you don't just go in with one type holus bolus you, let's say, remove the 10 x 100uF first and fit in some replacements you then listen and see if that change has made an improvement to the sound quality... if so, take a note of what the improvements were...... you can experiment with a few varieties of 100uF and decided what type of cap is the best. Once you are content there is an improvement you can now move on to the 47uF and repeat the above process.... it's imperative that you take notes at every stage and if something sounds worse then remove it and retrofit the stock cap..... The blunderbuss technique sometimes works (ie: throw a large bunch of high quality caps in and keep your fingers crossed) but 8 times out of ten it's essential to do any cap swaps in stages taking notes at each stage. If I were to shoot this DAC with my blunderbuss I'd probably go with Panasonic FM and a sprinkling of ELNA cerafine for colour ;D |
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Post by traf on Apr 18, 2009 20:26:57 GMT
Simon Keep us all posted how you find it after the other JLH is made. I have always been tempted to make another one to fit in my Class A amp, so there would be one for each channel, but I always seem to find another use for any spare JLH. Alex Well I've just spent an interesting afternoon playing with the V-DAC, my JLH board and my reference KW250S setup. Source was a 24/96 feed from an Imac. I have to be honest and say that I didn't like the V-Dac with the JLH fitted.....but before you think I've gone deaf I need to explain why The problem is that the V-DAC + regulated bipolar psu + JLH board justs sounds too good. So good in fact that I had to remove the JLH board and fit it into my KW250S which I have been meaning to do for a long while but never quite got around to... its now clamped onto the +-15V rails feeding the DAC output stage opamps. The V-Dac was getting precariously close to the KW250S DAC stage, which just wasn't on. The effect of adding the JLH was immediately noticeable when fitted to both the V-DAC or KW - much more full, expansive and effortless bass with sweeter and better focussed treble. I think others have noted that despite their claimed high PSRR, the LM4562/LME49xxx opamps really do only perform at their best when fed a decent clean DC supply and I'd have to agree. I really do need to knock up some more JLH boards now..... simon |
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oldson
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Older than a well used glove
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Post by oldson on May 23, 2009 0:08:43 GMT
when you lot are finished meddling with the v-dac, and are happy with it, let me know where i can send mine to have it modded. as this thread is waaaay above my head! |
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Post by theadmans on Jul 14, 2009 15:57:24 GMT
I was thinking of getting one of these V-Dacs as I get it for £129 from Acton Gate Audio.
However, before I pull the trigger can someone tell me if you can connect digital outputs to both the toslink and coaxial inputs on the V-Dac at the same time. I see there is a switch provided to switch between coaxial and USB but no switch between coaxial and toslink?
I want to connect 2 devices one optically and one via coax is this possible?
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Post by traf on Jul 17, 2009 21:25:44 GMT
I was thinking of getting one of these V-Dacs as I get it for £129 from Acton Gate Audio. However, before I pull the trigger can someone tell me if you can connect digital outputs to both the toslink and coaxial inputs on the V-Dac at the same time. I see there is a switch provided to switch between coaxial and USB but no switch between coaxial and toslink? I want to connect 2 devices one optically and one via coax is this possible? You can have both connections made at the same time but you can't have them both 'live' at the same time. One source will need to be powered off so the VDac can lock on to a single digital stream. I can't lock onto 2 at the same time. |
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) and don't really want to use two transformers.
I now need to knock up another JLH board to see if that makes a further improvement.
