Can a Fisher ca-276 be made 'safe' for speakers?

drwatson32

drwatson32

New Member
Apologies as I'm new here, but I've been feverishly looking for an alternative to my 80's era ca-276 as one of the channels sometimes hisses and makes other odd sounds when there are idle periods of the amplifier being on but no/not much in the way of music playing. I suspect that this is from a dying transistor? At any rate, I also suspect that this is potentially lethal for speakers (and I just picked up a pair of restored DCM TF-600s)

I tried a brand new Yamaha a-s501 and hated it, sent back. I'm considering my options and might go the route of separates, but I know that I really like the way this old Fisher sounds (briefly tried with TFs, they seem to love the horsepower) so going through the trouble of troubleshooting (or sending off for service) is tempting.

In your guys' opinions, is this a piece worth putting time and/or money into given that, as I understand, the circuit design is liable to destroy speakers if fails? Some protection safeguard that could be added in case this really s--ts the bed? lol
 
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put a fuse inline with the speaker , not 100% protection still better than nothing at all , try a fast blow fuse and go a little under your speakers wattage rating at first , see if you can get to volume you like before the fuse blows speaker fusing.jpg
 
its actually kind of amazing the variety of amazingly cheap but functional stuff you can get from China now. I'd probably want to do some testing to verify it does what it should, but that would be easy enough to install inside a lot of amps.
 
That amp is not worth repairing. It has several design flaws that guarantee eventual catastrophic failure. As I recall it does have a speaker protection relay to prevent large DC voltage going to the speakers in the event of failure, so it shouldn't damage the speakers. Having said that, the DCMs are much better quality than a BPC Fisher amp. You can get an Onkyo Integra integrated amp for not a lot of money that will blow that Fisher away. There are several models and they are all good. Any of the Kenwood Silver faced integrated amps would be great also.
 
Awesome replies! Much appreciated and gives me a lot to think about. I've pulled and ordered at least the main output transistors. Dr*audio, you replied since I've been typing this- duly noted, and I suspected this to be the case. If I can get this working, it'll suit the basement exercise area least hah!

Edit, hello from Barberton/Akron!
 
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We got about 9" in South Euclid.
If you're thinking of opening the amp up, replace the bias adjustment pots with sealed pots. They go open and the amp goes to full bias current.
 
we got hammered pretty good out here , with the winds and the snow , some dam big drifts , spent the better part of the day pushing and shoveling snow , daughter needed to be at work by 5 and our little farm all needed fed and watered , getting to old for this **** , feeling pretty beat now that its dark out and I got a chance to chill out with a few shots of cheap rum
 
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dr*audio, yikes! I do have it all apart, so I'll definitely swap those out. On the subject of replacement (+better) amplifiers, I'm seeing that most of the Onkyos and Kenwoods that you mention are in the same wattage neighborhood as the Yamaha that I returned (it generally lacked bass extension regardless of tone settings). I suspect that I'm missing or misinterpreting units of measure that might indicate how good the first few watts of an amp might sound. I believe you when you say that these will blow the Fisher away, but I'm not seeing many examples near the specs of it. Did you have certain models in mind? Thanks!
 
drwatson32 said:
dr*audio, yikes! I do have it all apart, so I'll definitely swap those out. On the subject of replacement (+better) amplifiers, I'm seeing that most of the Onkyos and Kenwoods that you mention are in the same wattage neighborhood as the Yamaha that I returned (it generally lacked bass extension regardless of tone settings). I suspect that I'm missing or misinterpreting units of measure that might indicate how good the first few watts of an amp might sound. I believe you when you say that these will blow the Fisher away, but I'm not seeing many examples near the specs of it. Did you have certain models in mind? Thanks!
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Mine is an Onkyo Integra A-8087.
 
Hey dr*audio, while I ended up going with an Emotiva preamp + restored Hafler 220, I'm still sort of interested in resurrecting the Fisher. It could be nice for maybe bass extension for the back of my living room with my Best Buy grade Polk t50 towers. (That or basement gym)

I replaced the output transistors on the offending channel (I think I realize now that a differential phase transistor was probably the crackling culprit) My foolish self forgot to put the mica insulators back between these and the heatsink and shorted them, popping the fuses. Replaced fuses and insulators. Now I actually have 60v dc center voltage on that channel (instead of 0). I almost threw the whole works away, I still might. Yet, with that channel board disconnected, it'll go out of protect mode and play through he left channel. I assume that there's a straight up open short on one or more transistors now. The trim pots don't seem to be shorted.

Let's say for conversation's sake, that I get the above issue straightened around, you seem to really know these units- aside from sealed pots, are there other design flaws that can be overcome to make these _ok_ ?
 
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