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Old 16th June 2006, 07:09 PM   #1
TerryC is offline TerryC  United States
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Default ADCOM Amplifier Experiences

I've been looking at the prethora of used two-channel Adcom power amps on the market, and am curious what people think of these amps. Specifically I would like to know if the older models are considered better/worse (sound, reliability) as the newer models. I would also like to know how easy they are to work on. I've been inside a few Adcom pre-amps and found them challenging to very difficult to work on. I would like to purchase several moderately powered two-channel amps for a tri-amplified project that has been on my mind for some time. The ability to modify these amplifiers is a requirement.
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Old 16th June 2006, 07:30 PM   #2
anatech is offline anatech  Canada
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Hi Terry,
These amplifiers are reasonably reliable. I don't find them hard to work on, but they can be a lot of work. Having said that, I like working on Carver amps also.

The early models are bipolar designs. The newer ones are almost completely mosfet.

You really need to understand how the amp you have works before attempting to modify it. If you have to replace output transistors, be prepared to buy many and match them. The same should be done for all amps.

-Chris
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Old 16th June 2006, 07:55 PM   #3
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Hi,
My experience is nothing like Anatech's but I have had a couple of 555 series 1 and 2. A couple of things I've noticed is:

1. although the PSU caps seem to be of very good quality and last very well, they can only last so long and I've had more than 1 vent on me. Not bad being 20 or so years old.

2. The 555's of this series (and possibly others) used toshiba output transistors that are obsolete and usually hard to get (expensive). I have found that a failure is best served with a complete replacement of all output transistors with one of the ONsemi (or equiv.) gems.

3. There is more space in a 555 than a '76 cadillac trunk. (Mafia amp? )

overall I've found them to be a great value and easy to work on, just try to get one at the right price if your interested in this age of amp, as it may need some work. Why are they easy to work on? well...because Anatech and others that know them so well are around! Like I said I've had a few come and go, but I always have one around, and it's not like I have a ton of amps.

my 2 pennies...
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Old 16th June 2006, 08:17 PM   #4
anatech is offline anatech  Canada
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Hi mpmarino,
You've been around the block ...

Bipolar Adcom outputs, use On Semi. MJ15022/23, MJ15024/25 pairs. The newer MJ21193/94 and MJ21195/96 work very well also. But you have to replace the entire channel and match them.

One problem I am running into more and more are amplifiers that poor technicians have been into. They are a pain in the *** to work on. Always somethings that are never blown - are blown.

The first clue - mismatched transistor numbers. Or my favorite idiot sign, NTE or ECG parts. Pretty much forces a complete rebuild to the output assembly and driver board assembly.

I haven't had any caps vent on me yet. I shouldn't have said that 'cause now I'm jinxed.

-Chris

Edit: Didn't you find part of Jimmy Hoffa in one?
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Old 17th June 2006, 04:02 AM   #5
TerryC is offline TerryC  United States
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Thanks for the valuable info. I would also be interested in opinions on the sound of the bipolar vs. mosfet designs.
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Old 17th June 2006, 07:28 AM   #6
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Sorry,

I've never given the mosfet models a good listen. Of the older bipolar models I think the 535 and 545 sounded best, no experience working on them however. Most seem to thhink the mk2 models were better than the mk1 in that series.
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Old 17th June 2006, 06:06 PM   #7
anatech is offline anatech  Canada
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Hi Terry,
Both sound good, but different. What more can I say?

-Chris
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