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logotrikes 18th October 2011 09:28 AM

Replacing output opamps in Adcom GCD575
Hi Folks,

I'm new to this forum, know precious little about electronics, and have a query about replacing the opamps in my ancient Adcom GCD575 cd player.

Reading the forums it seems that a useful sonic gain can be had by substituting the existing opamps with something a bit posher. I've ordered a pair of BB OPA627's since they seem, by many folks reckoning, to be the ducks nuts with regard to sonic value. I like the Burson discrete op amps too but feel that my old Adcom might not be worth the outlay, so for now I'll try the 627's in sockets so I can roll later.

The question I have is this... Is the BB OPA 627 a single or dual op amp? It says on the front of the amp that dual DAC's are used. Does that mean 2X dual opamps, or 2X single op amps, or are the DAC's something else entirely?

Is it possible, if it is the latter, that there might be a useful sonic benefit if I was to fit a double-up socket to carry 2 of the 627's per side ( 4x 627's in total)? Is that either possible, or necessary, or would it be best just to stick with the original plan of straight swaps?

I'm an absolute beginner in all this, so go easy anyone who is inclined to reply. We all have to learn:)

Cheers, Martin

ide2003 18th October 2011 03:43 PM

hi Martin, Adcom is using proprietary opamp for their player, and imo is good enough and
for this kind of tweaking best to have schematic or service manual, check out, 627 is single, and if memory serves me right so does the adcom opamp

wish you luck with this fine player

SoNic_real_one 18th October 2011 10:38 PM

You need to find out what kind of OpAmps you have - single/dual, if they are SMD or trough hole mounting...
There are adaptors (Brown Dog is one) that can fit 2 singles to provide dual connections, if you are set for the 627.

In my experience (other model, GCD600) they are using some single thru-hole OpAmps, labeled "6AA". I would bet those are relabeled NE5534...

pchw 19th October 2011 01:59 AM

GCD-575 has 6A which is LT1056.
6AA is AD711. 7A is LT1057, and as you can guess, 7AA is AD712.


SoNic_real_one 19th October 2011 10:06 PM

I am curious where did you get that information - not that I won't belive it.
If 6AA is AD711, that is listed by AD as "With a slew rate of 16 V/ms and a settling time of 1 ms to 0.01%, the AD711 is ideal as a buffer for 12-bit D/A and A/D Converters...". They continue with "Common-mode rejection of 88 dB and open loop gain of 400 V/mV ensure 12-bit performance even in high-speed unity gain buffer circuits."
LT1056 is slighty better (maybe one bit higher), but a far cry from something like LT1028...
Kind of sad...

On a positve note, being JFET, they can use for the OPA627 as replacements.

pchw 19th October 2011 10:31 PM

Here is where I found the info:

But one thing to consider, this CD player is close to 20 years old. They (Adcom) probably didn't have too much choice at that time. Yeah, mine is due for a refresh
of more modern parts as well :-)


SoNic_real_one 19th October 2011 10:40 PM

Oh, sure... My Phillips had LM833. Before I replace them with some LM4562 :)

pchw 19th October 2011 10:49 PM

I am filling my DigiKey order for a bunch of caps for the Adcom oldies: GCD-575, GDA-600, and GCD-700. Thanks to Martin to remind me that I still have these treasure, LOL. Yeah, will pick up a couple LM4562 along the way.

SoNic_real_one 19th October 2011 11:21 PM

Carefull, those 4562 are dual opamps. For singles you have the LME49710. Sligthly better specs.

logotrikes 30th October 2011 01:33 PM

Thanks for the replies guys,

Being short on expertise means I rely on suck it and see; do the mod, switch on and hope for a miracle. I have yet to get up to any mischief with it the new sockets but still waiting for the 627's. (EBay rocks!)

I've hung on to the Adcom but only just started reusing it after a number of years now I have most of my hearing back. I guess I've kept it rather than forked out on a new machine out of nostalgia, and having read the various forums I hope I'm right.

I also have an Adcom power amp ( I used the variable output from the GCD575 which saved the expense of a pre-amp, and the system worked very well till I retired the power amp...under the bed with the GCD575). A new though quite modest SET tube amp sits patiently waiting for me to flail into it with replacement signal caps (Russian pio's), and once I've done the various mods, we shall see, or hear...

The GCD 575 was a very good player in its day I understand, an '89 model which I bought preloved around '92, and I haven't had the remotest urge to let it go, so if I can improve things a little, maybe even replace a few of the tired old electrolytics on the way, and it goes up in smoke, I would be sad, but life is too short, and I would wing my way back to the excellent hifi emporium from whence it came, and buy another machine, maybe a middle range NAD or something.

Nothing ventured, nothing gained, as they say, so here's hoping...

I'll report back in due course...

Cheers, Martin

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