On Wed, 1 Dec 2010 10:53:06 -0800, Kele wrote
(in article ):
I fear my Adcom GTP-600 surround preamp ( http://oi38.tinypic.com/sfuxap.jp=
g
has a problem (mine is cleaner than the one pictured). It=92s about
15 years old, I like it allot and can=92t afford to replace it with same
level of performance.
Here's what happened and what I know... there was a single semi-loud
pop sound; I was not in the room at the time but heard it. Upon
arriving, noticed the overall volume level had diminished. After
fiddling, I found that just the two surround modes: Adcom's Cinema and
Dolby Surround are bad. The other modes: Stadium, Concert Hall, Club,
five channel, and 2ch stereo seem ok.
When switched to either of the Dolby modes, as I turn up the Master
volume (to about 9:00 position) the main speaker's woofers extended
outward about an inch and stays there=85 and that is with no source
playing. I can move the volume higher and the woofer extends
further. When extended, the woofers move in and out slightly and
slowly. It=92s ugly.
For now, everything other than Dolby modes sound good and appear
normal. I don=92t go to Dolby modes at all and continue to use preamp
daily=85 it=92s rarely turned off.
Wondering if the Dolby section is like a chip that can be swapped out
=96 If I could get the part, a DIY job? I=92ve only found scary
electronic repair options locally, but could get some soldering done
if necessary. Adcom says contact Auth Service Center in Jersey.
Jersey=92s response to my email was simply, =93call us=94. I=92m not in th=
e
continental US, Jersey is far. I haven=92t cracked the un-vented case
ever; have no idea of internal. Before I do, I=92m trying to get
advice.
Bummed,
Kele
One thing seems likely. You defiantly have a power supply problem. The
extended woofer cone indicates DC in the audio. The preamp is so busy
amplifying a slight DC offset that it's using up all the power supply to do
so . Obviously, your preamp and power amp are DC coupled. AS to the surround
functions not working, I suspect that whatever has put DC on your audio path
has also stopped your surround decoder from working properly.
Don't use it this way, Amplifiers aren't designed to amplify DC as it causes
1/2 of the output circuit to be driven "on" all the time. I'll bet if you
feel the amps heat sinks for the main channels, you'll find that they're very
hot (careful, now don't burn yourself). If you keep using the amp like that
you could destroy the output transistors. They aren't made to have their
duty-cycle exceeded in that manner.