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Dynaco 4-Dimensional Amplifier

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Posted on September 9, 2009 at 20:46:20
saeger
 I have a Dynaco transistor amp that buzzes loudly in one channel but not the other and is not effected by the volume control. A friend told me its the power supply. Which makes scene since it broke when I turned on a VCR that was connected to the same outlet. Would a broken power supply cause buzzing in one channel but not the other? What are the specs for the power supply? Where can I get a new one, if that's the problem? Is there anything else I could test for?

Thank you.

RE: Dynaco 4-Dimensional Amplifier, posted on September 10, 2009 at 04:10:22
JonM
 Joe's correct - it's unlikely that it's the power supply in that amp - the Dyna SCA-80Q (which is what I assume you have) used a common power supply feeding both channels. (I think the VCR incident is a pure coincidence.)

Try Joe's idea of switching cables, since that will help you determine if it's inside or outside the amp. (If the buzz stays in one channel when you swap cables, the problem is probably inside the amp.)

Since the buzz is not affected by the volume control, I bet the problem is inside the amp. From your description, it doesn't sound like you are technical - there's nothing wrong with that, it's just that the Dyna amp does have some reasonably high voltages inside, and if you don't know what you're doing, you can seriously injure yourself.

If I were you, I would find a friend who knows what he's doing (it doesn't sound like your friend has the right background, since I think he misdiagnosed the problem up front), or a local electronics repair shop that has experience with old audio equipment.

Unless this amp has real emotional significance to you, it may not be worth fixing. (Honestly, they weren't all that good when they were new, and I say that as someone who has built, owned, and repaired more than a handful of them, and whose career in technology got its start looking at SCA-80 schematics as a kid.)

Good luck!

RE: Dynaco 4-Dimensional Amplifier, posted on September 10, 2009 at 09:47:27
saeger
 Obviously I have tried switching the cables. The buzzing comes from the speakers weather the is something connected to the amp or not. I am very familiar with electrical theory, although not terminology. The buzzing sounds like a disconnected ground. I would like to start testing the circuits in amplifier, do you know which components, if they were to malfunction could cause the problem? Thanks.

RE: Dynaco 4-Dimensional Amplifier, posted on September 11, 2009 at 02:35:07
JonM
 Look for corrosion, a loose connection, or a cold solder joint on anything that connects to the chassis (which is ground in this amp). You can find the schematic at the link below.
RE: Dynaco 4-Dimensional Amplifier, posted on September 9, 2009 at 21:08:25
Joe Curcio
Manufacturer

Posts: 1094
Location: Northern CA
Joined: October 10, 2001
Contributor
  Since: July 1, 2002
 The power supply is common to both channels so it is likely that the power supply is NOT the problem.

Buzzing can have several causes - check you interconnecting cables. Try reversing the cables _one at a time_. If the buzz changes channels, you have found the cause

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