Adcom GFA-555 fuse stuck

Hi there,

I've got an Adcom GFA-555, which I use with a pair of Infinity Kappa 8 speakers.

I was running pretty loud on some low frequencies, and I lost all power from the amp. I figure the Kappas were just drawing too much current, since the woofers can dip down to around 1 ohm with low frequencies.

The power light doesn't turn on, so it shouldn't be thermal shutdown or the transistor fuses. I opened up to check, and they are all fine (I put in 4.5 amp fuses instead of the 6 amp ones spec'd to give me a little safety room). After cooldown it still won't turn on.

I didn't see any scorched components either, but I know from personal experience that that doesn't necessarily mean that there aren't any burned out components. I don't smell anything, at least.

So I'm pretty sure the problem is that the power fuse is blown. The problem is, the screw-in plastic holder is cracked in a couple of places, making normal extraction with a screwdriver impossible.

I thought about trying to super glue it, but I doubt that would hold (and I don't have any on hand any way). I suppose I could epoxy an old screwdriver on to it...

I'm pretty stumped as to what to do - I generally tackle this kind of stuff myself, although at this point I know I need a replacement holder in addition to the fuse anyway.

My only thought is to take it to a general electronics repair shop - there's no real audio repair shops in town AFAIK, and the nearest Adcom authorized repair shop is an hour and a half drive away. As long as it's just the fuze, it shouldn't be that difficult of a job - which is why I'd like to do it myself if possible.
It's hard to tell what's wrong from your description...a picture certainly would help. I'm sure a call to Adcom would either turn up the fuse holder part...or a suggestion on what to get. Most fuse holders use the same size hole, so if you don't care about it being "authentic" you could probably buy a replacement most anywhere.
Here's a photo of it. You can see that there are four cracks in it as well as it being partially stripped. When I try to turn it, the parts just separate from each other.
I would take a disk of plastic and cut a slot in it that will accept a screw-driver, then glue it flat to the outside face of the fuse holder, making sure that each of the pieces of the old fuse holder are bonded to the plastic disk. Epoxy might be the best bet; you can always heat it to break the bond if you cannot get a new fuseholder, then epoxy the pieces of the old one together (or maybe just keep it glued to the old one and use it that way).
That's a great idea. I didn't think about epoxying something else to it - I've got a spare knob that might work well. That way I'd never have to worry about using a screwdriver for it again.
Good suggestion...just be very careful not to get the glue/contact cement you use on the outer ring.

Alternatively, instead of cutting a slot for a screwdriver in a plastic disk, you might use a plastic cylinder about 1/2-3/4" long and the right diameter..and then turn it with a pliers or your fingers.
If anything take the fuse holder completely out of once you remove the cover and can access it. Go to a local electronics store e.g.Radio Shack, etc and buy a replacement fuse holder. That is a very standard fuse holder. It is most likely using a plastic nut on the inside of the rear panel to keep it sandwiched to the panel. Take a sharp utility knife or a Xacto knife and cut the nut, push the holder out undo the solder connection and wah-la, put in the new one and it will still look OEM.
Heat up a standard screwdriver hot enough to melt plastic and melt it into the rear of the fuse holder, remove, let cool, then insert the cooled down screwdriver into the new (now hardened) slot, and unscrew.

Well, I extracted the whole fuse holder after the cover split apart on me - the nut and washer holding it in were brass, actually. It also turns out that there was a crack in the holder body as well. It must have been overtightened last time the fuse was replaced. I never actually got the fuse itself out though.

The hardest part was working around all the wires - I worked from the bottom to minimize that.

I had to cut the wires that were soldered in - there was no way I was going to unsolder them as they were rock solid with wires wrapped around very well. I suppose I shouldn't expect anything less for a power source that's supposed to handle up to 1000 Watts.

I'll go to Radio Shack in the morning and pick up a new one and the 10A fuses I need. It shouldn't be too hard to solder it back in - I'm used to soldering on delicate PCBs rather than thick wires.
The big question remains.
Why and HOW do you melt a fuse holder? Can the amp 'take it'? Sure doesn't seem like it. You are apparently running this at redline for long time periods.
Sounds like you are on your way to a solution. If you can't find the fuse holder at RS you might check eletronics stores but I am afraid they will all be closed today(saturday). If not look at I am sure they will have it and also you might check an audio dealer in the area, he may have one battin' around if he does any repairs.
The fuse holder didn't melt - it was cracked already so I wasn't able to remove the fuse, which has presumably burned out since I don't even get the power light to turn on.

I didn't hear any clipping (or see the distortion lights come on) until just a few seconds before I lost power, but it was some bass heavy electronic synth stuff so I think the continuous bass frequencies brought the overall power consumption above the max without exceeding the ability of the output transistors.

Like I said in the OP, I have 4.5A fuses instead of the 6A spec fuses for the amplifier stage - and they were all fine. The previous owner used 3A fuses for an even bigger margin of safety, but one of those blew the first week that I had the amplifier. Those Kappas are really power hungry, and other than this the Adcom has taken it without any hiccups.

Well, I went to Radio Shack today and they indeed had the right size fuse holder. It cost me $3, so my total repair cost was under $7 including new fuses.

Installing it was a snap - there was just enough wire left on the leads to strip and solder without making them too short.

Thankfully, it performs great now.

Unfortunately, for a short while I hooked up my second amplifier, a Carver TFM-15CB, and I heard a relatively quiet crackling noise from both channels.

It gets marginally louder as I turn up the volume on the amp itself, but it's still quiet and drowned out by moderately loud music. The input level doesn't affect it at all either. It runs fine at high power as well.

I'm pretty sure it's not the volume pots - I've heard that before, and it's working fine otherwise so it shouldn't be a fuse. Both output channels (A & B) show the same symptoms. I never heard it in the past, although it's been months since I've used the amp for more than a few minutes. It's just hooked up to another pair of smaller Infinity RS-5's from the same preamp.

Hmm... Maybe this is a good project to start learning audio troubleshooting and repair? I've got some experience with basic circuits, op-amps, and electrical troubleshooting, but I've never done anything more with audio components than what I did with the Adcom.

I suppose I could just take it to the electrical engineers' audio club (I'm a graduating mechanical engineer at Michigan State), they do some good work - even so far as designing and building their own preamps, amps, crossovers, etc.
I know you found a simple solution to your problem already, but since the internet's eternal, I thought it best to include this information here for the next guy searching.

From Adcom's website:

"Parts are available form ADCOM's parts distributor Affiliated Electronics. Contact them as follows:
Affiliated Electronics
216 Route 206, Suite 15
Hillsborough, NJ 08844
PH: 908-874-3799

Regards all.
Cool, that's good to know in case I ever have any trouble in the future. To be honest, I'm kind of looking at getting a pair of GFA-565s or maybe a Mac sometime in the future.

Unfortunately, I've had more trouble with the Carver (actually, now I have three of the same - picked up one for just $80 from the local used music store). I inadvertently shorted one of them causing one of the channels to go out (replacing the fuze didn't fix it), and something went wrong with one of the others too (I can't remember what it was since I've been in Sweden for graduate school since August.).
I guess I should mention that I've since moved up to a pair of Infinity Renaissance 90 speakers. Wow - what a difference they make (although the Kappas are still excellent).

I had to bi-amp them though - the 555 alone was almost entirely bass-less when powering them. I put one of the Carvers on top, and use the gain controls to match them (about 60-75% of max on the Carvers gets a good balance, which goes to show the incredible current requirements of the woofers).

That (or any potential bigger upgrade is why I'd like to try an even more powerful amp. Maybe a tube amp for the top end, like the ARC amps Infinity used for testing. I of course don't have the money now, being a poor graduate student and all.