Adcom GFA-545 distortion light and hiss/buzz

[vr6ofpain]

I have had this Adcom GFA-545 amp for just about 2 years now, which I bought off ebay. It has run well every since I got it up until this weekend. I usually leave it on for long periods of time, even when not using it, because it doesn't get hot.

Well I walked by one of my speakers Sunday morning and I heard a very quite hiss/buzz coming out of the Left speaker. I was surprised because I had never noticed that before. I put my head next to my right speaker and it was doing the same thing, but at an even lower level. So I was like, "Never noticed that before", and I shut the amp off, figuring maybe the circuit in our house was bad or I just never noticed this noise floor or whatever.

This morning I woke up to see that the Left channel "instantaneous distortion indicator" light was glowing and the right channel was kind of glowing. This was after the amp had been shut off for ~24 hours. I was confused, because I had never seen these lights come on before and especialy since it was shut off for so long. I noticed if I disconnected the RCA's (input) nothing changed, but if I disconnected the left speaker wires (output) the light went out. I was confused so I connected the left speaker wires again and the light came back. So I decided to run the amp, and it seemed to sound fine, but the light for the left channel would glow somewhat, with the right channel still barely glowing.

I decided to shut the amp off again and unplug it. Strangely the light stayed on. So I then disconnected the speaker wires from both channels and the RCA's again, so nothing was connected to it and the amp was not plugged in to the wall. Guess what, the Left distortion light came on again very dim. I watched it for the next minute or so, and it was still glowing (now being unplugged for ~2 minutes).

My question is this, how can this light still glow when the capacitors have already drained (or maybe not completely) and more importantly, does this amp sound like it has gone into the toilet? Obviously it still works, but if the distortion lamp is glowing when in extremely light use or even off and unplugged ( I assume the lamp should be off when I get home after work, because there couldn't be any juice left in the unplugged amp) there must be something seriously wrong. You think this can be repaired and/or serviced?

sucks. might just give up on speaker audio and stick with headphones. I'm considering picking up some Grado SR-325i 's sometime soon.

[Geoffcin]

What you've just discribed is classic, and not in a good way. It sounds like a filter capacitor has gone south on you, but I'm not nearly as good at diagnosing something like this as Woodman. I would PM him to see if you can get some pro advice.

2 min is not that long for a big cap to stay charged. My old PS Audio 200c amp was lethal for up to a half hour.

[kexodusc]

That's what I was thinking Geoffcin...though I'm no pro either...if you smell anything bad (burning), hear anything sizzling, or take the cover off and see anything melted a bit you'll have your answer.

I needed a new cap in an old Kenwood a couple years ago, the bill wasn't much at all. Are you handy to NJ? I think Adcom is still HQ'd there, they might service it back to snuff too.

[Geoffcin]

That's what I was thinking Geoffcin...though I'm no pro either...if you smell anything bad (burning), hear anything sizzling, or take the cover off and see anything melted a bit you'll have your answer.

I needed a new cap in an old Kenwood a couple years ago, the bill wasn't much at all. Are you handy to NJ? I think Adcom is still HQ'd there, they might service it back to snuff too.

But I vote for a local fix. If it's just a cap or two it might be less than $100. Shipping it back and forth to Adcom might cost that by itself!

[vr6ofpain]

THANK YOU ALL FOR RESPONDING!

I think I could replace a capacitor....what could be so hard. I'm gonna take the cover off right now, as it has been unplugged the whole day while I was at work. Gonna take a look around for anything ~melted. Nothing smelled bad, well I didn't notice anything, but I didnt have my noise over the vents. Taking the cover off in T MINUS, TEN, NINE, .....

[vr6ofpain]

Now what exactly is a filtering cap (I understand it is a capacitor), and where would it be. I'm going to take some photos of the inside. Maybe that would help locate it. Man was there some dust in there. I think I have black lung....

Is the filter cap one of the 4 large 10,000 microfarad caps in the center? I hope not, because if I am gonna replace one, I would probably have to replace all 4, if I wanted it to sound as best as it could...and to keep up with maintainence as far as the other ones pooping out. This thing is coming up on it's 20th birthday (circuit board says Adcom 1986).

[kexodusc]

I had an old 545 fixed maybe in 1999 or so when I was in Atlanta....Think Adcom charged me $120 including round trip shipping...they also replaced some older components and return it to spec (so says them)...it came back all shiny and clean and new...better than I ever took care of it up to that point. Sold it eventually for a 535II and a pair of speakers...

Geoffcin's probably right though, from California to NJ you're gonna pay through the teeth for shipping.

[vr6ofpain]

Now what exactly is a filtering cap (I understand it is a capacitor), and where would it be? I'm going to take some photos of the inside. Maybe that would help locate it. Man was there some dust in there. I think I have black lung....

Is the filter cap one of the 4 large 10,000 microfarad caps in the center? I hope not, because if I am gonna replace one, I would probably have to replace all 4, if I wanted it to sound as best as it could...and to keep up with maintainence as far as the other ones pooping out. This thing is coming up on it's 20th birthday (circuit board says Adcom 1986).

Anyone?

[psonic]

Yes that is a filter cap - they store lots of electricity, even after the unit is shut down. Do not attempt to service it yourself if you do not know what you're doing. 10000uf is the energy stored by the cap. You can get shocked bad if a cap dumps on you. They need to be discharged before they can be desoldered / removed. I assume you do not know how to do this...take it to a local shop who has audio experience...they will have no problem finding replacements and installing. If you want to get the parts, go for it, but don't attempt to install them...JMHO

[vr6ofpain]

Yes that is a filter cap - they store lots of electricity, even after the unit is shut down. Do not attempt to service it yourself if you do not know what you're doing. 10000uf is the energy stored by the cap. You can get shocked bad if a cap dumps on you. They need to be discharged before they can be desoldered / removed. I assume you do not know how to do this...take it to a local shop who has audio experience...they will have no problem finding replacements and installing. If you want to get the parts, go for it, but don't attempt to install them...JMHO

I have charged and discharged 1 farad capacitors in car audio environments. All you need is a resistor. for discharging you can even use a light bulb (i did that to discharge a cap before storage, when i couldnt find a resistor).

Well I need to find a source of good sounding caps with both the positive and negative terminals on the top (R type). Any ideas?

[vr6ofpain]

here are the pics:

4x


'Innards':

[psonic]

Oops sorry, I figured you had little electronics experience since you weren't sure what power supply filter caps are. Yes, that's them and if you have experience with discharging them, go for it - although I honestly don't know if that is what has failed in your amp. Could be a number of things, but it they would be a prime suspect...

you may want to try one of the audioasylum boards...

[vr6ofpain]

Oops sorry, I figured you had little electronics experience since you weren't sure what power supply filter caps are. Yes, that's them and if you have experience with discharging them, go for it - although I honestly don't know if that is what has failed in your amp. Could be a number of things, but it they would be a prime suspect...

you may want to try one of the audioasylum boards...

I think I am going to call Adcom's service people. See if they would be willing to give me any advice. I really don't think I would be willing to spend the money it would take to ship it to them and back. There are a few Adcom auth. service centers in southern California. Maybe I'll try some of them. Honestly though, if the repair(including shipping is going to be ~$150....or more. I would rather try to source some replacement caps (this could be hard) and just swap them out anyway...to see if that was the issue. I have read that capacitors can start to 'die' after ~20 years. This amp is 19.5 years old. Maybe it was its time...though I might try to bring her back. Definately going to be boxed up for some time, since I am moving in a week and won' have time to deal with it. Guess I will just keep listening through my Grado's as I usually do.

I need to see how much smaller the filter caps in my Kenwood receiver are...just for kicks. I know they are not 10,000 microfarads because these are about as tall as the receiver itself. Then again....maybe I will just splurge on a newer receiver....and kick the 2 channel way. Time and money will dictate I guess.

Thanks for the info.