Help: Adcom Power Amp

[Xenogear]

Hi,

I have an Adcom GFA 545 amp. The left channel started making a slight "scratchy" sound. It started getting worse over the course of time. Right now, that channel will sometimes drop-off and produce much less sound or volume than the other channel.

I won't send it to Adcom for repairs. The cost to do so would be about $350, at least. Does anyone have any suggestions on what might be causing this problem?

Thanks

 

[bandit]

I've got a 545 that I'ved had many good years of use from.

As far as what could be wrong - a few questions may help understand what is wrong.

Is it any way suseptable to vibration? Does it get change in any way with a tap (non-destructive of course) to the cabinet? If it does change I would look for a cold solder joint or other bad connection.

Does heat seem to affect it? If so - your more likely looking at a failing component. I had a GTP-500 that I lost one channel of the tuner to (made bad sounds) and it turns out it was a very inexpensitve coupling capacitor.

I think other repair shops may be able to fix your unit for much less than $350. Good luck.

 

[JoeE SP9]

At first guess I would look for a cold solder joint or a loose one.

 

[jeffsg4mac]

Also, switch your cables around and see if the noise follows and check your preamp. It might also be the cause. If that don't do it I will sell you my 535II for 150. I had it rebuilt by adcom about a year ago and have not used it since.

 

[Xenogear]

Ok, I'll try those tests

Thanks, I'll try those tests and let you all know the results. I didn't think about the possibility that it could be the pre-amp. I need to look into that also.

From my understanding, all of the parts inside can be replaced except the "boards". Is that true?

 

[Xenogear]

How do you fix a cold solder problem?

Does that mean the joint needs to be resoldered?

 

[mtrycrafts]

Does that mean the joint needs to be resoldered?

Yes, if you know which one.
Does this happen with volume control changes? The left ch pot could be the issue, or any number of other issues

 

[audiofox]

I think a failing capacitor could also cause the scratchy sound, similar to when the unit is shut off but sound is still going through it. Sounds like an opportunity for a BlackGate and Schottky diode mod-then you can turn your misfortune into a benefit.

 

[Xenogear]

tests

Ok, I did some tests. I checked the cables and connections. I checked the solders visually and also touched them lightly. I connected the amp and the same drop outs and scratchiness happened. I switched the connection, left to right and right to left coming from the pre-amp. After this, the problem hasn't returned. I think it is just a matter of time though. The problem is intermittent to begin with.

The unit passed the shake and rap tests. I noticed what audiofox is saying. After turning off the amp, 5 to 7 seconds later, a moaning sound comes from the left speaker. Is that the capacitor emptying itself?

If it is the capacitor. Where and how much would it cost to replace all four?

 

[bandit]

My 545 makes the same sound on shutdown - I've read about it somewhere in the Adcom manuals although that was a long time ago. Basically speaking it is because the output is directly coupled to the speakers with out relays or other protection devices. I suspect this is one of the reasons the adcoms are stable into very low impedences. The sound you hear is some noise that happens as the power supply collapses. Adcom uses a large amount of power supply capacitance. You will notice the red light on the front (power indicator) stays on for some time after you push the power button or remove power by other means. If it is what I suspect (which is not a problem) you will hear the sound close to the time that the red light extinguishes.

Bandit.

 

[Xenogear]

Bandit

That is what it does. My amp does exactly what you said. But only on the left channel. In that case, the other problem may not be related to that. I will look at the solders again. If that fails, I will take it to an electronics shop and get an estimate to fix.

 

[bandit]

Just an FYI... mine doesn't do it every time - and sometimes the left, sometimes the right. Unpredicatable when it would make that noise. It seems to me and I have no idea why that it was more likely to do it if I used the "lab" outputs on my GTP-500 preamp vs. the normal outputs. Go figure.

Best of luck.

 

[PENG]

Hi,

I have an Adcom GFA 545 amp. The left channel started making a slight "scratchy" sound. It started getting worse over the course of time. Right now, that channel will sometimes drop-off and produce much less sound or volume than the other channel.


Thanks

As bandit said, the noise at the end of a shutdown (when the red light is about to fade away) is normal. Other than that, the way you describe it, something else is wrong and your best bet is to consult Adcom. Did they give you the estimate of $350, or you were just guessing?

 

[PENG]

Hi,

I have an Adcom GFA 545 amp. The left channel started making a slight "scratchy" sound. It started getting worse over the course of time. Right now, that channel will sometimes drop-off and produce much less sound or volume than the other channel.


Thanks

As bandit said, the noise at the end of a shutdown (when the red light is about to fade away) is normal. Other than that, the way you describe it, something else is wrong and your best bet is to consult Adcom. Did they give you the estimate of $350, or you were just guessing? It seems unreasonably expensive to repair one channel.

 

[Xenogear]

Peng

They rebuild the amp for $350. It's a flat fee. I can't get it lower but they also won't charge higher.

Right not, the amp is running fine. Has been for a few days.