[Nayyte]

Yesterday I received a great condition Adcom GDA-700 DAC. My first experience with the PCM1702 chip, I like it! I have a Audio-GD R-1 NOS already and while it is pretty amazing, I've never felt like I completely vibed with it, mainly because the sound stage is so very in my face all the time. Now with the Adcom, I am hearing pretty much all the same detail but with a much more dispersed and pushed back soundstage. And for about third of the price, this is a win for me.

So I figure now that I have it, it would be worth it to tinker with OP amps and replace some parts since this guy is from 1995 .

The tools I own already:

• Soldering iron
• Good Rosin solder, solder wick
• Decent Multimeter w/ clip and point leads
• Cheap pcb holder

I should probably get a chip puller, can't think of anything else tool wise. I have good experience I believe since I have completed a BHC amp and various diy cables.

I figure the sound quality can only go up from here. Problem is I don't know/don't really understand how to choose replacement OP amps. I get the general principle but frying my new dac would really suck. I did some digging and found this post for modern OPA alternatives: https://www.diyaudio.com/community/threads/adcom-opamp-semiconductor-replacements.339904/

The ones in the GDA-700 are ADCOM 6AA 9439. According to the chart I can use OPA604 or AD711. I would love to use some sparkos SS3601 OPAs but I need to know if they aren't compatible.

Other than the OPAs, is it safe for me to order all new caps with matching uf/V ratings as the ones already installed? A quick search led me to these caps:

https://partsconnexion.com/products/elna-capacitor-10uf-35vdc-roa?_pos=1&_sid=c38316f85&_ss=r

The only schematic I found was pretty rough but still legible:

https://akdatabase.org/AKview/displayimage.php?album=20&pos=6

This is a big step for me but it's got me pretty stoked! Any and all advice is greatly welcome.

Photos below

 

[Nayyte]

 

[miketlse]

If you are 100% sure to be throwing those opamps away, you could cut the legs off near to the body, and then solder a socket like this to the legs.
You could then roll opamps to your hearts content, with no risk of damaging the circuit board.

 

[Nayyte]

If you are 100% sure to be throwing those opamps away, you could cut the legs off near to the body, and then solder a socket like this to the legs.
You could then roll opamps to your hearts content, with no risk of damaging the circuit board.

Thanks, I almost forgot that I need these to roll amps. I ordered 6 new OPA828s in SOIC to DIP8 adapters from brown dog as well

 

[Nayyte]

Progress, power supply board desoldered and flux cleaned

I now have all the parts and the soldering will commence!

 

[Waterclocker]

Nice project! Certainly worth the work! I had the Reimyo DAP-777 in house for a while (also PCM1702). It sounded really great after I bypassed most of the output section. I was able to come straight off the opamp and skipping some additional stages of filtering. Playing around with a DIY PCM63 build, I ended up using some OSCON caps on the digital side of the DAC chip and some ELNA Silmic II on the analog. Might be something to try with the 5 caps surrounding each DAC and the 4 by each pair of opamps. Sparkos voltage regulators might be an option to try also.

 

[Nayyte]

Nice project! Certainly worth the work! I had the Reimyo DAP-777 in house for a while (also PCM1702). It sounded really great after I bypassed most of the output section. I was able to come straight off the opamp and skipping some additional stages of filtering. Playing around with a DIY PCM63 build, I ended up using some OSCON caps on the digital side of the DAC chip and some ELNA Silmic II on the analog. Might be something to try with the 5 caps surrounding each DAC and the 4 by each pair of opamps. Sparkos voltage regulators might be an option to try also.

Thanks! Yeah I had mine in my system for a few hours and it sounded really close to my other DAC which is twice the price. I went with Panasonic eca-m caps for the entire DAC board. The lead spacing on the board is 2mm and I'm not comfortable stacking caps in all directions to make larger caps fit. If I really like the end result then I'll consider better caps in the future. I focused on upgrading the power supply board with nichicon UPW and rubycons zlg caps plus replacing all the vregs with new ones.

New opamps as well, OPA828 x6 all in brown dog adapters. Super excited to hear them.

 

[Waterclocker]

Thanks! Yeah I had mine in my system for a few hours and it sounded really close to my other DAC which is twice the price. I went with Panasonic eca-m caps for the entire DAC board. The lead spacing on the board is 2mm and I'm not comfortable stacking caps in all directions to make larger caps fit. If I really like the end result then I'll consider better caps in the future. I focused on upgrading the power supply board with nichicon UPW and rubycons zlg caps plus replacing all the vregs with new ones.

New opamps as well, OPA828 x6 all in brown dog adapters. Super excited to hear them.

That should go a long way. Just recapping an old DAC PSU will help it sound more accurate and clear in my experience. I will be curious on your impressions when you finish. I might just pickup a DAC with the HDCD filter one of these days. I've only tried Burr Brown filters or running in NOS.

 

[Nayyte]

That should go a long way. Just recapping an old DAC PSU will help it sound more accurate and clear in my experience. I will be curious on your impressions when you finish. I might just pickup a DAC with the HDCD filter one of these days. I've only tried Burr Brown filters or running in NOS.

Yeah it's really interesting the HDCD filter. Some people say it really sucks but I have seen a couple say that it's all in the power supply. Problem is that replacements are non existent for either the HDCD chip or the ultra analog aes chip. Upgrading them would be not worth it especially if they work still. Be better off designing your own board from scratch.

 

[Nayyte]

 

[Nayyte]

Final update. Finished!
She sounds really nice

New parts:
Schaffner IEC/emi filter combo socket
Nichicon UPW 2200uf x6
Rubycon ZLG 56uf x9
Vishay wirewond resistor 47ohm 5W
All linear regulators replaced,
LM317/337 replaced with LT317/337AT
Power to DAC board umbilical cable
Panasonic ECA-M 10uf x20
6x OPA828 adapted to DIP8 from Cimarron technology

29 year old parts cya never!

 

[Waterclocker]

Final update. Finished!
She sounds really nice



New parts:
Schaffner IEC/emi filter combo socket
Nichicon UPW 2200uf x6
Rubycon ZLG 56uf x9
Vishay wirewond resistor 47ohm 5W
All linear regulators replaced,
LM317/337 replaced with LT317/337AT
Power to DAC board umbilical cable
Panasonic ECA-M 10uf x20
6x OPA828 adapted to DIP8 from Cimarron technology

29 year old parts cya never!

Looking good! Nice 6000CDT also, a great little cd player! What would you say the biggest improvement in the sound is?

 

[Nayyte]

Looking good! Nice 6000CDT also, a great little cd player! What would you say the biggest improvement in the sound is?

thanks!

My impressions are limited so far but I would say it would be overall speed and soundstage got turned up to eleven. The stock sound with all the old parts was good but with a noticeable veil of muddiness in the whole stage. The tone and timbre was great but the upper mid range was fatiguing along with having muted transients.

Now with it finished there is a lightning speed to every instrument and the veiled haze to the soundstage is gone. Percussive instruments have accurate attack followed by swift decay. Complex parts of jazz sound well controlled especially with guitar, very coherent. Honestly it's a amazing reference quality sound that is easily textured/toned by whatever amp/speaker/headphone you run it through.

Compared to my Audio-GD R-1 NOS, it doesn't have that extra lushness you get from a fully discrete r2r ladder/output stage. After listening to the R-1 for so long, this has a sense of actual realism that can be overly colored and in turn lost in the mix with the Audio-GD. Like I said, a superb reference sound.

No doubt this is due to the latest "next generation" OPAMP from TI, the OPA828, and all the work I did updating the power supply board.

I would love to compare this with more advanced R2R/FPGA Dacs in the future, and would love to see someone measure this Adcom. I do not have such equipment.