2. amps-preamps
  3. 1406857519

Audio Research M100 Thumping

I just picked up a pair of ARC M100 mono blocks. When I turn them on, all is good. They operate fine for about 15-20 minutes, then the output cuts on one, and it begins a three-beat thump which sounds like a loud heartbeat. This occurs even if the volume is all the way down on the preamp. It also bleeds over to the other channel, but if I pull the speaker wires from the offending channel, the other channel is clear.

Ideas? Should I simply try replacing some of the output 6550s?

Thanks,

Brian.
bkrpdx

Showing 3 responses by bifwynne

bifwynne
2,206 posts
 
Bkrpdx ... call Kalvin Dahl at ARC. He can properly advise you.
bifwynne
2,206 posts
 
If your tubes are not fresh, it's alwasys a good idea to freshen them up. If that solves the problem, you are good to go.

I have another suggestion, regardless of whether a retube fixes the issue. Your amp is long in the tooth. Some parts do degrade over time, like caps.

I suggest that you call Kal at ARC and ask him if he thinks it would be a good idea to have the amps checked over. If he says "yes," depending on where you live, you could take it to an authorized ARC service tech, like Gary (Hifigeek1) in LA, ARC if you live in the Midwest, or if you live on the East Coast, there's a fella near me who makes house calls.

I strongly believe you should only use an authorized ARC tech. There was a story running here on A'gon about a well meaning and I'm sure talented tech who tried to fix an older ARC amp. He just started replacing parts. After the job was done, Gary picked up the thread and told him exactly what and where the problem was. No surprise since this is what Gary does.

Just sayin.'

BIF
bifwynne
2,206 posts
 
Brian,

I am very glad that Kal set you right. Having said that, according to the ARCDB website, your mono blocks were introduced in 1984.

Not knowing the service history of your amps, if never serviced, the components could be upwards of 30 years old. I think it's worth letting Kal know the amp is operating ok, but ask him if he thinks it would be a good idea to do some preventative maintenance.

As an aside, my son owns an SP-9 preamp, which is of similar vintage. Kal sent me a kit of parts that he recommended replacing. The local ARC service tech did the job. All in, less than $100.

Btw, per the ARCDB site, your tube compliment is:

(2) 6DJ8, (5) 7044, (2 matched pairs) 6550, (1) 6550, (1) 12AT7

If you check back with Kal, ask him if any other tubes should be replaced.

It has been my experience that my ARC gear sounds best with fresh tubes. I follow ARC recommendtions and have never looked back. Didn't have to. ARC gear is great stuff.

Let us know what you decide to do.

BIF
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