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Adcom amp has no bass

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CJ Payne

CJ Payne

Well-Known Member
So the search bar is not helping me address this one, though I doubt not there are other threads about this subject with likely other amplifiers.

I scored an Adcom 5500 a couple weeks ago and the owner told me it had some grounding issue or something...he couldn't recolect exactly, it had been sitting on a shelf unused for a long time. I thought I'd be getting a buzz or hum of some kind.

I plugged it into a pair of Klipsch CF-3's, used the pre-out from an HK-3490 stereo reciever that I know makes the Epic speakers bump pretty loud as is...and NO bass.

It's like a 100 Htz High Pass is on it. No hum, no buzz, really clean power with the dial up high. Just no bass. I had to turn the bass knob up on the receiver all the way just to make it sound like it should naturally.

I have a Crest amp that was ripped out of a High School gym that's actually a very solid clean amp...I switched to that to be extra sure, and the speakers sang. Tons of thump. So it's the amp.

Anyone have thoughts on what to look for if I open the hood? Electricians I'd trust to know their stuff around here are scarce...I'm more likely to do it myself. Thought I'd throw it out there before I started digging deep in the bowels of the coveted GFA-5500.
 
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Sounds like a good lead.

And, of course, double check the speakers were not inadvertently connected out of polarity with each other.
 
Btw, if you google "Adcom 5500 no bass" you'll get several other hits on the same subject, both on AK and other forums.
Seems like it might be a fairly common problem with these amps.
 
opnly bafld said:
Might want to try it the "wrong" way just in case it may have been reversed during a repair.
Click to expand...
good thought, but I simply tried one speaker at a time, nothing came back. I think I was searching incorrectly, because 45rpm I think is right, that this is a common problem with that series, and the thread link posted above goes into some detail about the caps that are prone to go over time.

Going to download the schematic and start looking.
 
This may sound silly, but where do you all source your capacitors? Brand's that can be trusted, or best places to order from. My mind goes sideways looking at these sites and I don't know a good cap from a cheap one. I find it hard to believe the problem could be fixed by a $0.69 capacitor, just because it matches uf and V rating...especially when I see posts about $70+ ones.
 
I use Digi-Key. They are close to me, ship fast, and will ship small orders by USPS which is about 1/2 the cost of FedEx or UPS ground.

But, Mouser, Newark, Arrow, et al are all reputable suppliers.
 
That will work just fine. Any good capacitor will be better than what's in it. You might as well order C7 and C9 while you're at it.
 
Ok I just didn’t want to order something that would risk affecting the original Sonics of the amp. If this affects the bass output I wanted something of equal or greater reliability/quality
 
I got backed up with other things, but finally ordered the capacitors to replace in this unit. Going to replace the C3, C7 and C9 caps on both sides.
 
I got the Right channel board out and off the heat sink, there is some browning around the backside where C3 is a little, but doesn’t look like a total blow out. The amp still had audio just no bass...should I be concerned the board is junk? Or keep going?

Also, the C9 47uf 25V nichicon caps I got in the mail are 3 times as big as the one on the board, I'm going to have to leave the leads really long or it won't fit, the C3 47uf 50V cap I got from Panasonic is a bit smaller than the original...?...I guess it just matters how well it works. I have to re-order the C7 4.7uf 50V because like a dummy they got here and I realized I had ordered bi-polar.
 

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That's a bad burn! Looks like the transistors next to the diodes got totally fried.

Would be best if you could figure out why, before replacing them and hoping they won't instantly burn out again.
 
It looks like the copper piece that I assume is a heat sink that goes across those two transistors fell off, and I'll need to glue it back on. Not sure if that was the reason.
 
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