[Steve Rogers]

"Mark D. Zacharias" wrote in message
et...

"RdM" wrote in message
...
TBerk in
rec.audio.tech1187834110.151986.223470@l22g2000pr c.googlegroups.com:

Was wondering if I should be concerned, adjust, ignore this 'new to
me' Sony amplifier I just hooked up.

It's the one I mentioned in a recent thread on driving a dvc sub.

When I turn the thing on it makes a click or snap (I expect this) and
then it hummmmms for about 30 to 60 seconds.

It seems to quiet down at it 'warms up' but I think there is a
persistent (if lesser) hum going on all the time.

Any care and feeding tips appreciated.


TBerk

Mark is certainly the expert on Sony gear, and has helped me personally
with a
couple of schematics in the past, (TX M!) but this is quite an older amp
from
the early 70's; I'd expect even the larger power caps to have
deteriorated ...

There's a nice page on it here
http://www.thevintageknob.org/SONY/s...30/TA1130.html
and if you scroll down, the first "More" button at the bottom shows an
interior view; there are two large and two smaller caps visible. (with
caps!)

Modern audio grade capacitors would probably be an improvement, I'd
think.

Some consultation or investigation of the diode rectifier current
capabilities
might be wise before dramatically increasing their values; no doubt
modern
equivalents will be smaller, but it may be worth putting some quality
ones in.

Certainly worth checking for ground loops too, especially if it has a
3-core
mains lead, ie is earthed, and also earthed back through the
interconnects.

But then, maybe the surround receiver has a chip for switching, rather
than a
mechanical switch, and there is a hum until it switches on ... I find
that,
with examples of both types connected through tape loops to different
rooms.

Does it hum with no inputs connected? Then probably power supply (and
other
decoupling smaller caps, as suggested) capacitor replacement is in order.

The order you turn things on when you have it connected might bear
thinking
about; perhaps the "pop" is from something else switched further up the
chain?

(Proceed carefully;-)

Regards,

Ross Matheson
Auckland, NZ.

Let's not forget the possibility of a ground loop. Try connecting ONLY the
Sony to the sub speaker with no connection at all to the surround system
or anything else. If there's no hum anymore, we can address the ground
loop issue.

Mark Z.

One more question. Does it hum on both channels or one. Seems a waste to
chase a problem in the
power supplies if it is in one channel only. Also, look for small amounts
of DC on the out put.
(or look at signal on a scope.)