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I was recently messin round with some of my old equipment and i was doin some mods to my adcom dac. Its the gda-600. Im curious about the opamps they use in the dac. its a regular 8pin opamp, and it looks like its made by adcom, or at least has adcoms name printed on it. It says..
Adcom
7AA
9349Can anyone give me any info on these opamps?? are they any good?? Are they made by adcom or are they just a BB or AD chip relabeled by adcom?? Any ideas on an upgrade??
Follow Ups:
They sound wonderful in the GDA600. Big step up IMO.
Magnetar
Have you actually used this opamp in the GDA600?? The reason i ask is cuz this dac has a circuit that biases the opamp into class a, and im not sure if u can just swap opamps in?? Would u have to worry about how the clas a biasing circuit would work with a opamp it wasnt designed for??
thanks
Yes, with the 2134 it surpassed the sound of my tweaked Audionote DAC 1.1. A friend upgraded his too and loves it.I sold the Audionote.
Now I listen to a Curcio CD-12V in my big system. It's a better in some ways but not by much. ie - warmer more dimensional, ect.. It's a 3800.00 DAC.
Magnetar
Magnetar
I was looking at the schematic for my brother's Adcom preamp a few years ago. There were a couple dual opamps in the circuit that looked like good candidates for replacement. But as I studied the schematic I saw that Adcom had biased these opamps into class A. Because of this, swithcing opamps wasn't a simple remove and replace procedure because the biasing was no doubt specific to the device they chose. Replacing these devices would necessitate changing the biasing circuit or removing it altogether.In the end my brother decided to leave well enough alone. Too bad, I saw a lot of room for improvement in there.
David
tHANKS FOR THE INFO, I WILL PROBABLY LEAVE THE OPAMPS ALONE. i HAVE SOME MORE OASCONS TTHAT IM PLANNIN ON USING AROUND THE DAC CHIPS , TYHERE ARE 5 ELECTROLYTICS 10UF AROUND EACH DAC. wOULD CHANGING THESE TO OSCONS BENEFIT THE SOUND IN ANY WAS?? i ALREADY DID THE CAPS IN THE POWER SUPPLY AND THE SOUND GOT BETTER. BETTER BASS AND SMOOTHER OVERALL SOUND. ALSO NEAR THE RCA OUTS,THERE ARE TWO RESISTORS NEXT TO THE OUT PUT RELAY AND A 2 TINYS ON EACH CHANNEL. wOULD IT BE A GOOD IDEA TO CHANGE THESE TWO RESITORS AND 4 CAPS TO SUMTHING BETTER?? i WAS THINKING OF SOMEVISHAYS OR CADDOCKS FOR THE RESITORS AND MAYBE SOME STYRENE CAP TO REPLACE THE 2 SMALL CAPS ON EACH CHANNEL. i READ A POST ABOUT THE MSB LINK WHERE THESE SMALL CAPS WERE REMOVED??
THANKS
THHANKS
If I remember correctlly the GDA-600 used the same opamp as the 565 preamp. These ops were manufactured to Adcoms specs, and were highly regarded, much like the 565 pre. I bet you can do better now, Not too sure if it would be worth it with the GDA-600 (old technology)
Julien Therrien
jntherrien@msn.com
If the 600 used the same parts and circuitry as the 565 ....I beleive at the time, Adcom was using some Linear Technology parts.
The RIAA section used the LT1115 + LT1010 buffer, pretty much as you see on the LT1115 data sheet (complete with JFET hanging on the LT1115 for class a biasing) and the line stage used either the LT1022 or LT1122 BiFET + LT1010 buffer.Adcom gave Linear Technology a little extra $$$ change to label the parts in a less than easily recognizable way to help cut down duplication :-), no specially built for Adcom parts. Adcom may have paid for LT to select stock for noise or DC offset criteria, etc. however.
Adcom used Linear Technology 3 terminal regulator ICs also.
I ordered the service manual for the Adcom 565 preamp years ago. It's a bad habit of mine (according to my wife :-) )
Not bad at all, but you can do better....
Thanks alot for the info. That really helped me alot. I guess adcom has the opamps biased into class a, so it would be tough to just swap in another opamp. Did u do any mods to the Adcom pre-amp u spoke about?? I have done a few simple mods to the DAC. I swapped out all the elctrolytics in the power supply for Panasonic FC(2200uf) and Oscons(33uf). I also wanna change the 10uf electrolytics around the two dac chips. I think thees about 5 for each channel, i think im gonna try some 33uf oscons i have layin around. After that I may swap the two 100ohm resisitors near the rca outs to vishays, think this would be worth it??
thanks
Gpt any ideas on an opamp that would be better?? Im using the adcom in a second system, so im not abpout to go spend alot of money on new technology. I just figured a few inexpensive tweaks could make it better. Its already a pretty damn good dac for the price i paid($100 used). I already changed out all the 2200/35v caps to panasonic FC and the smaller 10uf caps to some oscons i had layin around. Just wanted to know if some better opamps would make it sound any better. Are these opamps single or dual opamps? And whats a good replacement?? I have some bb 2132's and some 2604's layin around, i might try those and see what happens.
thanks
I am not familiar with the piece of gear you speak of, but Adcom commonly relables parts with their own numbers. Dunno why..If the pinout is right for a single or dual opamp (the Adcom's I've seen used single channels opamps), then check the voltages. That will tell you what you can use.
If the voltage is higher than +/-15V, then you are looking at a TI/Burr-Brown OPA604/2604 for a replacement. +/-15V or less, then a Analog Devices AD797 or a TI/Burr-Brown OPA627 (expensive) or OPA134 or OPA604 for a single, or a TI/Burr-Brown OPA2134 or the OPA2604 for a dual (the OPA604/2605 work best at the higher voltages though). Selections are a bit limited because most of the best new opamps are in a SOIC package...
Thanks for the input. But im not sure how i would tell if its a dual or single opamp. Also is it worth it to swap in a bb or ad opamp?? Im guessing that adcom prolly relabeled a BB or AD chiop in the first place. Is there any way to find out what the chip really is??
thanks
If it's single channel opamp, you should measure +v @pin#7 and on pin#8 if it's a dual.
A single channel opamp will have the '+' power at pin 7, and a dual at pin 8.No way to tell what they are now, but I'd bet on something like a 5532/34 or a TL072. Not terrible, but you can do better if you want to fool around.
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