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-   -   Adcom 2A IC for GFA 565 (http://www.diyaudio.com/forums/solid-state/84639-adcom-2a-ic-gfa-565-a.html)

CompNut 13th August 2006 07:50 AM

Adcom 2A IC for GFA 565
 
I am in need of of a good replacement for an opamp IC labeled Adcom 2A that is used in a GFA-565. It is a single opamp and appears to be a low power piece. Would a TL061 work, or could any one suggest other suitable replacements? There was an old thread about the orginal poster never did reply with what IC worked.

Thanks,
James

Leolabs 13th August 2006 09:03 AM

First you need to figure out the pinouts and related function/connections,ie V+,V-,OUT,IN+,IN-...........

EchoWars 14th August 2006 05:06 AM

What's it doing? The GFA-555 has an opamp used as a DC servo. Last dead one I fooled with, I used a AD820 to replace it.

CompNut 14th August 2006 10:15 AM

It has about 2 volts DC offset on the speaker terminals. The IC is part of the servo circuit. The cap next to it leaked electrolyte all over it, after replacing the cap and many other bad caps and cleaning the PCB very well, the IC is bad. It is very temperature sensitive, heating or cooling it a little will make the output voltage go crazy. I am placing an order with Mouser tomorrow and they don't stock the AD820, I was trying to find something equivalent that they stocked, they carry ALD, Fairchild, Intersil, NJR, ON Semi, ST Micro, and TI brand op amps.

aparatusonitus 14th August 2006 05:46 PM

I would try LF411 or OP(A)27.

anatech 14th August 2006 06:08 PM

Hi James,
The IC is an AD 820 as EchoWars said. Watch the supplies as well!

If it is very temperature sensitive, you may not have cleaned the board and parts well enough. I used an ultrasonic cleaner and a degreaser (aqueous) to clean both the board and parts. I removed everything in the area, anything "saveable" went into the bath.

You really have to scrub these things.

-Chris

CompNut 14th August 2006 10:02 PM

I am going to order an OPA27 and try that as the specs look good on that chip. I have been a consumer electronics tech for >20 years and have seen plenty of leaky caps and damaged PCBs. This cap leaked but didn't corrode anything except the IC. The board is now nice and clean and without it in the cirucit I get only about .1V offset.

Thanks,
James

anatech 14th August 2006 10:12 PM

Hi James,
I am not doubting your abilities as a tech. Take it from me, the board may still have residue on it. This stuff is very difficult to remove. If you don't believe me, ask the folks at Adcom. I was a warranty shop for them.

-Chris

Edit: It could just as easily be on the chip you have too.

EchoWars 14th August 2006 10:58 PM

Quote:

Originally posted by CompNut
I am going to order an OPA27 and try that as the specs look good on that chip. I have been a consumer electronics tech for >20 years and have seen plenty of leaky caps and damaged PCBs. This cap leaked but didn't corrode anything except the IC. The board is now nice and clean and without it in the cirucit I get only about .1V offset.

Thanks,
James

The perfect chip for the job is the AD820, and I'm pretty sure that anatech is the one who suggested it to me a few years ago. The specs needed for a good audio IC are a lot different than those needed for a good DC servo.

For instance, the typical input bias current for the AD820 is 2pA. For the OPA27 it is 7,500 times that much. Input offset current is 20x higher on the OPA27 than the AD820.

It's just a matter of using the best part for the job.

RE: Your current offset. On the 555 II, the IC supplies the bias current for the input differential stage...the amp won't even operate without it. If your amp is similar (and I admit that I do not know), any measurement you take with the chip removed will be meaningless. Besides, with a good IC in place offset should remain well under 1mV.

CompNut 15th August 2006 12:30 AM

OK, I am going to get the AD820, I just hate ordering parts from 3 places to get what I need. I was already placing an order with Mouser and Antique Electronic Supply to get some parts to fix a customers MC275 and also build some knockoff QuietLineII noise filters. I guess I will also place an order with Newark and get the AD820.

I checked with Adcom a few minutes ago and they want $32 for that IC, that is a little steep!!

Thanks,
James


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