[kool bubba ice]

Quote:

Originally Posted by Torm I plan on changing the Green caps also (i believe they are panasonic caps). However on the underside of the PCB two of the four "green caps" are shorted from leg to leg with a diode?! I dont understand why they have done this and im hesitant to mess with them. It seems those two caps are related to the digital section. Any of you who already have a moded GM - does the underside of the PCB have these diodes? (the diodes are the only components on the underside as far as i remember - and they look like they were added as an afterthought).

Do all of these mods take soldering skill?..

 

[Torm]

Changing op-amps - no, they are sitting in a socket so you just pull em out and put in new ones.
Changing caps - Old caps must be de-soldered and new ones soldered in.

 

[peelax]

Quote:

Any of you who already have a moded GM - does the underside of the PCB have these diodes? (the diodes are the only components on the underside as far as i remember - and they look like they were added as an afterthought).

I do have the diodes, I changed the green caps for 2200uf 16v black gates and left the diodes in, I can confirm all is working well. I guess the exact values of these caps isn't actually too important.

Quote:

So then i took out two of the 827 and put back in two 2604 so that i was left with only a 827 " in the middle". This is how i see Pacific Valve configure their moded GMs and i wanted to try that. This sounded HORRIBLE - i mean shockingly bad! The bass was gone and it was very bright and brittle sounding. I thought i was imagining things so i passed the DT990s to errr.

I can't say I noticed a lack of bass, in fact the opposit compared against the micro DAC.

I would be interested people's experiences with changed out other op amps/caps though.

 

[Torm]

Good to know Peelax - ill change those too then.
I will change the four "green's" for 2200uf 16v Nichicon Muses tonight.
I will also put 0.1uf NX-HiQ blackgates over them - unless somebody tells me this is a really bad idea.

It will be interesting to see if the OPA2604x2 + AD827 will sound different after changing the caps (all the other caps will also be changed).

 

[Horizons]

Quote:

Originally Posted by Torm I will change the four "green's" for 2200uf 16v Nichicon Muses tonight. I will also put 0.1uf NX-HiQ blackgates over them - unless somebody tells me this is a really bad idea.

A great idea and I will probably do the same. I think Nichicons are 99% of the performance of the BG without the high price.

I just wish someone that has analyed this dac from a technical perspective could weigh in here. Judging by the way PV modded this dac, I'm not sure what all four of those green caps are for.

 

[bluemeteor]

Quote:

Originally Posted by Torm I got a stock GM as well. Today i replaced the three OPA2604 with 3x AD827JN and the sound signature changed considerably - far more than i anticipated! The 827's made the bass far more punchy and controlled. Hard to describe but the entire bass register changed, to the better. However, it took away something from the treble. It sounds slightly veiled - like cotton was stuffed in the earcups. I like the bass now but not so sure about the treble. So then i took out two of the 827 and put back in two 2604 so that i was left with only a 827 " in the middle". This is how i see Pacific Valve configure their moded GMs and i wanted to try that. This sounded HORRIBLE - i mean shockingly bad! The bass was gone and it was very bright and brittle sounding. I thought i was imagining things so i passed the DT990s to errr. co worker (well dont ask - i do some modding at work ) who had already hear the unmodded version. He imediatly responded that the treble was hurting his ears! In conclusion the "left and right" 2604 op-amps are def. NOT for the XLR outputs but have great impact on the sound signature for the single ended output. I also got a bunch of black gates and some Nichicon Muses and i will spend the weekend replacing all electrolytes in the analogue section of the DAC. It will be interesting to see if this affects the sonic characteristics of the op-amp configs.

They did more than just leave the 827's in middle. I have one of the original GMs and then bought the Pacific Valve modded one. It does not sound horrible but appreciably better. I did not get the bass response problems that you reported.

Pacific Valve does more to these DACs to get them to sound a certain way than they are admitting to on their web site.

I would like to try the March Madness bubt in all honesty, it has to come down in price.

 

[Torm]

Finished the "cap mods" and it's a success!
As always it's hard to tell what is psychoacoustics and whats real when it is not possible to A/B against an unmodded version - but to me it sounds like detail/resolution has increased moderatly.
I seem to pick out details I have never noticed before. Maybe thats because im listening "harder"? I dunno, but on a couple of songs I can now clearly hear noise or pops on samples that have been inserted into the song (example; Patrick Cassidy - Vide Cor Meum, a second before the male vocal starts, i can hear a slight background buzz as if the male vocal was recorded separatly and with a slight background noise).
I'm pretty sure i couldnt hear that before!

My mod consisted of replacing the four "green caps" with same value Nichicon MUSE caps, bypassed by 0.1uf BG's. I also replaced the six elctrolytes in the analogue out section with same value BG caps.

 

[Horizons]

Quote:

Originally Posted by bluemeteor Pacific Valve does more to these DACs to get them to sound a certain way than they are admitting to on their web site.

I would like to believe that but looking at the photo of the PV modified unit, it looks pretty shaky to me. Mismatched caps looks sloppy. This is one of the main reasons I bought the stock one.

http://www6.head-fi.org/forums/showthread.php?t=190189

 

[Torm]

Agreed - i have examined that photo extensivly and compared it to my stock unit.

The changes i can see are:

The 4 "green" caps changed - but to three different types. I dont know why they would do this but i suspect they got their reasons (the two bottom Blackgates supply the analogue section, the two orange/gold ones supply the digital section).
They have also bypassed these with 4x WIMA 0.1uf 63v film caps.

Replaced the "middle" Op-amp in the analogue section with AD827JN.

Replaced the RCA connectors on the line out. Also replaced the 56ohm resistors here with...two "red" 56ohm resistors.

Finally they have replaced the two coax input RCAs.

And thats it - unless they have done something on the underside of the board also.

 

[Horizons]

Quote:

Originally Posted by Torm Agreed - i have examined that photo extensivly and compared it to my stock unit. The changes i can see are: The 4 "green" caps changed - but to three different types. I dont know why they would do this but i suspect they got their reasons (the two bottom Blackgates supply the analogue section, the two orange/gold ones supply the digital section). They have also bypassed these with 4x WIMA 0.1uf 63v film caps. Replaced the "middle" Op-amp in the analogue section with AD827JN. Replaced the RCA connectors on the line out. Also replaced the 56ohm resistors here with...two "red" 56ohm resistors. Finally they have replaced the two coax input RCAs. And thats it - unless they have done something on the underside of the board also.

Thanks Torm, this info is invaluable to me. Now, if we can just verify which dual opamps drive which outputs???

In my experience, it is less problematic to tweak the analog sections than the digital sections. So now I now I will focus on the analog areas first.

 

[Torm]

All three op-amps drive all the outputs! The RCA out, the mini XLRs and the minijack (which is mislabeled as headphone -- its just line out).

I'm not electronics expert but i diligently followed the traces and they all end up in one "set" that goes to all the above mentioned terminals.

It does make sense when you think about the little "click" you hear turning on and off the GM. This is a small relay (the "big" black square next to the RCA out) that protects anything connected to the outputs for the first half second after turning the unit on. Two wires go in - two wires go out and to all the mentioned outputs.

 

[Horizons]

Quote:

Originally Posted by Torm All three op-amps drive all the outputs! The RCA out, the mini XLRs and the minijack (which is mislabeled as headphone -- its just line out). I'm not electronics expert but i diligently followed the traces and they all end up in one "set" that goes to all the above mentioned terminals. It does make sense when you think about the little "click" you hear turning on and off the GM. This is a small relay (the "big" black square next to the RCA out) that protects anything connected to the outputs for the first half second after turning the unit on. Two wires go in - two wires go out and to all the mentioned outputs.

Interesting. Then it would make more sense to me to make sure all three duals are exactly the same but PV throws the AD827 in the middle of 2 2604s. Strange. I am going to use (3) 2107s for the audio duals and (4) OPA627s for the PS opamps. I have all these laying around here from other projects.

 

[Torm]

If you get the opportunity - test and see if you can notice any improvements from just replacing the PS op-amps!