robertkd
Been here a while! 
Electronics Engineer from sunny Queensland
Posts: 111
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Post by robertkd on Apr 24, 2009 13:09:36 GMT
Yep bang for dollar this PCM1793 is pretty damn good people  it's essentially a reference BB build wrapped with a single ended PSU, which if you follow the thread it is fairly easy to remove the rail splitter and milk quite a bit of extra performance  Robert |
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Post by rbrook on Apr 26, 2009 16:37:40 GMT
Yay!!!
Finally got the DAC back from Hong Kong and after intensive testing for a couple of days to make sure this one is OK I'm ready to start doing a few mods.
So i take it i want a 8-0-8 Supply into the DAC removing the onboard rail splitter. I have a spare LM4562HA sitting around to drop in, any other recommended changes?
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Post by PinkFloyd on Apr 26, 2009 19:39:38 GMT
I'm not using my "el cheapo" so if anyone wants it then £40 will secure it.... extensively modded with high quality parts (ELNA Cerafine, NoVer for audio caps, WIMA film caps etc.) This is it:  Please note, the DAC comes without a PSU it is up to the buyer to supply a PSU. Mike. |
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robertkd
Been here a while!
Electronics Engineer from sunny Queensland
Posts: 111
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Post by robertkd on Apr 27, 2009 0:32:27 GMT
Yay!!! Finally got the DAC back from Hong Kong and after intensive testing for a couple of days to make sure this one is OK I'm ready to start doing a few mods. So i take it i want a 8-0-8 Supply into the DAC removing the onboard rail splitter. I have a spare LM4562HA sitting around to drop in, any other recommended changes? You got the PVM um PCM1793 right? Ok preparation rockgrotto.proboards.com/index.cgi?board=c&action=display&thread=3736&page=6#44761some parts I have changed/added rockgrotto.proboards.com/index.cgi?board=c&action=display&thread=3736&page=6#44850I've tidied this up a little since this rockgrotto.proboards.com/index.cgi?board=c&action=display&thread=3736&page=7#46437here still a work in progress  sports a transformer in the coax i/p and mounted the optical in on the back panel, added a 0.1 poly and 47uF 16V (iirc) to decouple the B+ to the optical pickup. so all digital i/p has no electrical connection to this unit. soldering/desoldering is a little challenging especially some to the larger stuff I usually work on minimising damage as much as possible. By this I mean it may be better to destroy the component and remove the bits not so good if you want to reuse though. Watch out on the plated through holes and pads there on. Robert PS I think this voids any warranty ;D |
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Deleted
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Post by Deleted on Apr 27, 2009 0:39:20 GMT
Yay!!! Finally got the DAC back from Hong Kong and after intensive testing for a couple of days to make sure this one is OK I'm ready to start doing a few mods. So i take it i want a 8-0-8 Supply into the DAC removing the onboard rail splitter. I have a spare LM4562HA sitting around to drop in, any other recommended changes? You got the PVM1793 right? Ok preparation rockgrotto.proboards.com/index.cgi?board=c&action=display&thread=3736&page=6#44761some parts I have changed/added rockgrotto.proboards.com/index.cgi?board=c&action=display&thread=3736&page=6#44850I've tidied this up a little since this rockgrotto.proboards.com/index.cgi?board=c&action=display&thread=3736&page=7#46437here still a work in progress sports a transformer in the coax i/p and mounted the optical in on the back panel, added a 0.1 poly and 47uF 16V (iirc) to decouple the B+ to the optical pickup. so all digital i/p has no electrical connection to this unit. soldering/desoldering is a little challenging especially some to the larger stuff I usually work on minimising damage as much as possible. By this I mean it may be better to destroy the component and remove the bits not so good if you want to reuse though. Watch out on the plated through holes and pads there on. Robert PS I think this voids any warranty ;D rbrook If you want something a little less complicated, follow Robert's DAC mods ,then check out my posted photo. Eventually, I will incorporate the SPDIF transformer, but it is pretty damn good without it. Alex |
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robertkd
Been here a while!
Electronics Engineer from sunny Queensland
Posts: 111
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Post by robertkd on Apr 29, 2009 8:30:59 GMT
Alex,
the SPDIF transformer essentially interfaces where the RCA would have delivered the SPDIF in the original circuit and I have retained the 75R termination and so forth. I hadn't done a comparison of with or without the transformer but to me it made sense to electrically isolate the ground from say a computer with possible high levels of noise on the ground or CD/DVD transport with obligatory caps to case.
Robert
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Post by Deleted on Apr 29, 2009 8:47:55 GMT
Alex, the SPDIF transformer essentially interfaces where the RCA would have delivered the SPDIF in the original circuit and I have retained the 75R termination and so forth. I hadn't done a comparison of with or without the transformer but to me it made sense to electrically isolate the ground from say a computer with possible high levels of noise on the ground or CD/DVD transport with obligatory caps to case. Robert Robert I have done that, but didn't notice any obvious improvement when I tried the DAC in my main system using the Oppo DV981HD which has a SMPS., where it was clearly outperformed by the X_DAC V3. But that is to to be expected because of the huge price differential. Alex |
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robertkd
Been here a while!
Electronics Engineer from sunny Queensland
Posts: 111
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Post by robertkd on Apr 29, 2009 8:59:44 GMT
Alex, the SPDIF transformer essentially interfaces where the RCA would have delivered the SPDIF in the original circuit and I have retained the 75R termination and so forth. I hadn't done a comparison of with or without the transformer but to me it made sense to electrically isolate the ground from say a computer with possible high levels of noise on the ground or CD/DVD transport with obligatory caps to case. Robert Robert I have done that, but didn't notice any obvious improvement when I tried the DAC in my main system using the Oppo DV981HD which has a SMPS., where it was clearly outperformed by the X_DAC V3. But that is to to be expected because of the huge price differential. Alex Alex, well likely a fair point but again it was more a case of averting nasty earth problems rather then improving preformance specifically Don't forget not all SMPS are well implimented doubly so when they persist in the 50c each way trick and tie the case to some potential via caps form the PSU to case  Robert |
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Post by Deleted on Apr 29, 2009 9:09:41 GMT
Robert
I am well aware of the >100VAC via the 100nF from SMPS primary to secondary sides, and the RCAs of the Oppo are also earthed via the Class A amp. back through the preamp. Seems like existing precautions may have been adequate.
Alex
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Post by Deleted on May 2, 2009 5:11:09 GMT
I have managed to get a further improvement in soundstage via speakers, by installing a 100nF capacitor under the PCB between the now vacated +VE supply pin of the railsplitter I.C. and the adjacent Earth (0 volts) pin.This improves the input pin bypassing of the 3.3V regulator.
SandyK
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robertkd
Been here a while!
Electronics Engineer from sunny Queensland
Posts: 111
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Post by robertkd on May 2, 2009 12:40:24 GMT
Interesting result, I have added decoupling on input to 3.3V digital and 5V analogue regulators, TBH I can't say that it brings anything to the table. Still sounding pretty damn good  Robert |
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Post by Deleted on May 2, 2009 13:00:28 GMT
Robert
I was feeding it into my Class A preamp and 15W Class A amplifier which are quite a bit more revealing than average, partly due to the front end balancing modifications. I am also using JLHs in all 3 bits of gear, which further improves S/N. This combination helps to give quite a reasonable 3D soundstage with most sources if good quality material.
Alex
P.S.
This may sound like conceited BS, but ask the guy in the U.K . who used to have a Pussycat for an avatar. He has quite similar gear to mine,except for an even better DAC. (Buffalo DAC with Paul Hynes Regulators.)
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robertkd
Been here a while!
Electronics Engineer from sunny Queensland
Posts: 111
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Post by robertkd on May 2, 2009 13:23:24 GMT
Robert I was feeding it into my Class A preamp and 15W Class A amplifier which are quite a bit more revealing than average, partly due to the front end balancing modifications. I am also using JLHs in all 3 bits of gear, which further improves S/N. This combination helps to give quite a reasonable 3D soundstage with most sources if good quality material. Alex P.S. This may sound like conceited BS, but ask the guy in the U.K . who used to have a Pussycat for an avatar. He has quite similar gear to mine,except for an even better DAC. (Buffalo DAC with Paul Hynes Regulators.) Alex in that case the question is why with all the JLH goodness did you have to add decoupling to the regulators  Robert |
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Post by Deleted on May 2, 2009 13:32:54 GMT
If you look at the photo that I posted, (reply 149) you will see that the leads from the JLH are fairly long. I believe that a University trained Electronics Engineer would do something similar given those circumstances ? Alex P.S. I'm going to bed. Dodging friendly fire can leave you quite exhausted ! |
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robertkd
Been here a while!
Electronics Engineer from sunny Queensland
Posts: 111
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Post by robertkd on May 2, 2009 14:03:00 GMT
If you look at the photo that I posted, (reply 149) you will see that the leads from the JLH are fairly long. I believe that a University trained Electronics Engineer would do something similar given those circumstances ? Alex P.S. I'm going to bed. Dodging friendly fire can leave you quite exhausted ! Oh you know better, I'm just asking all those questions that need answers and well yes the obvious one here is what to do about lead length between PSU and circuit. lucky it's friendly fire PS I have to say I actually connected the PCM1793DAC to the main amp and I was intrigued as to the sonics, interesting Robert |
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Post by rbrook on May 21, 2009 10:27:07 GMT
OK.
Alex was kind enough to send me some capacitors for my PCM1793DAC so its given me a good excuse to lift the lid and neaten up my build a bit while i installed the 1uF MKT. I was going to take a few snaps and post them but my camera is currently holidaying with my lovely lady so they will have to wait a few weeks, a good time to finish the build properly.
Have you found any more worth while modifications? I've currently done the PSU (with JLH), 1uF cap, LM4562HA and toned down that blinding blue power led.
Richard
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