Adcom GDA-600 tweaking

Thermionics

Post Whore In Training
Got a good deal off of CL for an Adcom GDA-600 multibit (ladder) DAC (uses a pair of Burr Brown PCM63P-J 20-bit DAC chips). After a few recommended modifications (recapping the analog stage, replacing the stock Adcom 7AA dual-channel op-amps with dual OPA627s per channel, recapping the power supply), it is singing sweetly (120uF Panasonic solid caps not visible in the PS photo below as they hadn't arrived yet):

20190309_222511996_iOS.jpg20190309_222503597_iOS.jpg

I may end up replacing the Burr-Brown DF1700P and Cirrus CS8412 input stage with a DF174 and CS8414 respectively in order to get 96/24 on the S/PDIF inputs (I've got a couple of 28-pin sockets, but the upgrade daughter boards are a bit spendy), but for now, I'm simply enjoying the RedBook playback. If you come across one of these for a decent price and don't mind a little solder-slinging, I highly recommend giving it a shot - at the very least you'll end up with a true r-2r DAC with laser-trimmed resistors in a single chip (rather than SMD daughter-board r-2r DAC which will never be as accurate), and who knows, you might end up deciding it is a keeper. :)

[Edit: title changed to be more specific and not bury the lede]
 
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BillWojo

Junior Member
I like the PCM63P chip myself and use a stock Parasound D/AC-1000. Very musical and since I don't stream, just play red book there isn't a down side.
It seems the latest DAC trend in the high end world is building discrete R2R to get back some of the musicality that the newer non R2R chips are missing.
A lot of folks think that the Burr Brown PCM63P DAC chip is the best sounding DAC chip ever produced.

BillWojo
 
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