[[email protected]]

When I turn on the amp, I get bad "buzzing" type noise from the left
speaker. The noise soon stops and the amp then works fine. This power-
on noise has been getting worse recently. Can anyone suggest a fix
for this? I have some tech-savvy friends that could probably do the
repair. Thanks for any comments.

[Mark D. Zacharias]

wrote:
When I turn on the amp, I get bad "buzzing" type noise from the left
speaker. The noise soon stops and the amp then works fine. This
power- on noise has been getting worse recently. Can anyone suggest
a fix for this? I have some tech-savvy friends that could probably
do the repair. Thanks for any comments.

It may be oscillating - with the "buzz" sound representing only the lower
frequency portion of the oscillation. If so, this could be seen on an
oscilloscope.
If the power switch were arcing, I would expect it to show on both channels,
but this is something else to look at.
If it's more of a deep hum, maybe the initial bias is dangerously high -
something to consider.

Mark Z.

[Colin B.]

DeserTBoB wrote:
On Sun, 04 Mar 2007 23:29:35 GMT, "Mark D. Zacharias"
wrote:

wrote:

It may be oscillating - with the "buzz" sound representing only the lower
frequency portion of the oscillation. If so, this could be seen on an
oscilloscope. snip

Aging caps can cause this very thing on these.

Fix the amp. These were excellent MOSFET power amps for the money
(and even disregarding money altogether) both in their day and even
now.

Random question here. Since the MOSFETs that were used in these amps are
now unavailable, has anyone built a similar amp (or better, a derivative of
the DH-220) using modern parts?

Colin

[jack]

You can use lateral mosfets from Renesas (2sk1058/2sj162) or the Exicon
devices from Profusion in the U.K.

[[email protected]]

The DH200 style amplifier has been made for some years by

Smart Devices in the US. http://www.smartdev.com

Norm

[[email protected]]

Random question here. Since the MOSFETs that were used in these amps are
now unavailable, has anyone built a similar amp (or better, a derivative of
the DH-220) using modern parts?

Colin

The amp has been available for some years from Smart Devices in the
US.

http://www.smartdev.com

Norm