My good ole' mini stereo amplifier started to behave extremely weird
recently. Beyond not being able to use it, I'm really puzzled with the
symptoms:

There's a strong reverb effect and the vocals are canceled and slightly
to the right - seems like a phase shift. I put on a Beatles song to
better test it:
- The vocals are canceled even when I hold my ear against one speaker,
or when I flip the polarity for one of the speakers.
- I hear both channels in each speaker, and each channel on both
speakers.
- With balance full left, the left speaker sounds slightly louder, with
full right it sounds centered.
- I tried the two available inputs ("DAT" and "AUX"). Same thing.

I opened up the unit, and as far as I can tell, everything looks fine.
Nothing burnt or melted, no excessive dust (and they were smart enough
that no board is facing up). I vacuumed it just to be sure, didn't
change anything. You can see snapshots at
http://www.flickr.com/photos/3127847...7594269637399/

The unit is a Sony MHC-1600. Its amp, if that means anything, is
STK4132II. The only thing I did to it was to move it to another room
for one night.

So my only conclusion is that the unit spontaneously crosses (mixes)
both channels, with inversed phase, before splitting it back to the
stereo amp. How the hell can that happen, not to mention how to fix
it?!

Binba wrote in message
oups.com...
My good ole' mini stereo amplifier started to behave extremely weird
recently. Beyond not being able to use it, I'm really puzzled with the
symptoms:

There's a strong reverb effect and the vocals are canceled and slightly
to the right - seems like a phase shift. I put on a Beatles song to
better test it:
- The vocals are canceled even when I hold my ear against one speaker,
or when I flip the polarity for one of the speakers.
- I hear both channels in each speaker, and each channel on both
speakers.
- With balance full left, the left speaker sounds slightly louder, with
full right it sounds centered.
- I tried the two available inputs ("DAT" and "AUX"). Same thing.

I opened up the unit, and as far as I can tell, everything looks fine.
Nothing burnt or melted, no excessive dust (and they were smart enough
that no board is facing up). I vacuumed it just to be sure, didn't
change anything. You can see snapshots at
http://www.flickr.com/photos/3127847...7594269637399/

The unit is a Sony MHC-1600. Its amp, if that means anything, is
STK4132II. The only thing I did to it was to move it to another room
for one night.

So my only conclusion is that the unit spontaneously crosses (mixes)
both channels, with inversed phase, before splitting it back to the
stereo amp. How the hell can that happen, not to mention how to fix
it?!


I would suggest your speakers are now wired
L-C-R
where C is a common connection but not connected to ground G (black)
L-GG-R
properly

--
Diverse Devices, Southampton, England
electronic hints and repair briefs , schematics/manuals list on
http://home.graffiti.net/diverse:graffiti.net/

N Cook wrote:
Binba wrote in message
oups.com...

My good ole' mini stereo amplifier started to behave extremely weird
recently. Beyond not being able to use it, I'm really puzzled with the
symptoms:

There's a strong reverb effect and the vocals are canceled and slightly
to the right - seems like a phase shift. I put on a Beatles song to
better test it:
- The vocals are canceled even when I hold my ear against one speaker,
or when I flip the polarity for one of the speakers.
- I hear both channels in each speaker, and each channel on both
speakers.
- With balance full left, the left speaker sounds slightly louder, with
full right it sounds centered.
- I tried the two available inputs ("DAT" and "AUX"). Same thing.

I opened up the unit, and as far as I can tell, everything looks fine.
Nothing burnt or melted, no excessive dust (and they were smart enough
that no board is facing up). I vacuumed it just to be sure, didn't
change anything. You can see snapshots at
http://www.flickr.com/photos/3127847...7594269637399/

The unit is a Sony MHC-1600. Its amp, if that means anything, is
STK4132II. The only thing I did to it was to move it to another room
for one night.

So my only conclusion is that the unit spontaneously crosses (mixes)
both channels, with inversed phase, before splitting it back to the
stereo amp. How the hell can that happen, not to mention how to fix
it?!


I would suggest your speakers are now wired
L-C-R
where C is a common connection but not connected to ground G (black)
L-GG-R
properly

the other possibility is an o/c connection on the balance control

NT

o/c as in open-circuit? can you elaborate?
The source is a laptop, I tested it with other amp systems and the
balance control works perfect, so this part of the chain is functioning
properly. The Sony amp doesn't even have balance controls...
If you know these units, they're very simple - no settings to spoil.

Binba wrote:

o/c as in open-circuit? can you elaborate?

if you disconnect the balance pot's wiper you get mono output, in
phase.


- With balance full left, the left speaker sounds slightly louder, with
full right it sounds centered.

The source is a laptop, I tested it with other amp systems and the
balance control works perfect, so this part of the chain is functioning
properly.

Someones sure confused.


NT

Interesting... I'm still wondering how something like that can just
happen.
And if I'm trying to think of a workaround...should I try to ground the
speakers? Perhaps run a jumper wire from one (--) (black) terminal to
the unused AM antenna's GND? Or is that just gonna cause one big
short-circuit...?
The amp's mains connection is 2-prong.

N Cook wrote:


I would suggest your speakers are now wired
L-C-R
where C is a common connection but not connected to ground G (black)
L-GG-R
properly

--
Diverse Devices, Southampton, England
electronic hints and repair briefs , schematics/manuals list on
http://home.graffiti.net/diverse:graffiti.net/

"Binba" wrote in news:1157473246.298395.192480
@d34g2000cwd.googlegroups.com:

N Cook wrote:


I would suggest your speakers are now wired
L-C-R
where C is a common connection but not connected to ground G (black)
L-GG-R
properly
Interesting... I'm still wondering how something like that can just
happen.
And if I'm trying to think of a workaround...should I try to ground the
speakers? Perhaps run a jumper wire from one (--) (black) terminal to
the unused AM antenna's GND? Or is that just gonna cause one big
short-circuit...?
The amp's mains connection is 2-prong.

First thing to do is *test* to see if this is the case.

Disconnect the G leads (both speakers) from the unit, tie them together,
and then temporarily connect them to any known ground on the unit (such
as the one you mention).

Listen to tell whether the problem goes away. If it does, then you can
open the unit and figure out why the G speaker connectors aren't
connected to ground, and fix it.

If the problem is still there, this is not the solution. Reconnect both
G speaker leads to the speaker connectors on the unit. Continue looking
for cause elsewhere.

You could try turning the karaoke switch off!
John.

"Jim Land" wrote in message
. 3.44...
Disconnect the G leads (both speakers) from the unit, tie them together,
and then temporarily connect them to any known ground on the unit (such
as the one you mention).

Listen to tell whether the problem goes away. If it does, then you can
open the unit and figure out why the G speaker connectors aren't
connected to ground, and fix it.

If the problem is still there, this is not the solution. Reconnect both
G speaker leads to the speaker connectors on the unit. Continue looking
for cause elsewhere.

I'm not familiar with the particular unit, but I wouldn't attempt this if it
uses bridged amplifier outputs like some do.
There aren't any "G" connectors in that case of course, but then most amps
don't have terminals actually marked "G" in any case.

MrT.

Actually, I found the whole datasheet for the amplifier (unless there's
more than one STK4132II amp in the world), the system is a Sony but the
amp is made by Sanyo...whaddyaknow.
http://service.semic.sanyo.co.jp/sem...=%22STK4132%22
From my basic electronics knowledge, it doesn't look like it's a
bridged amp.
But if someone is actually interested in examining the circuit diagrams
and verifying, that'll be cool. Maybe you could spot some design flaw
that'd explain this behavior :-)

Thanks for the replies, I'll try the grounding workaround.

-D


Mr.T wrote:


I'm not familiar with the particular unit, but I wouldn't attempt this if it
uses bridged amplifier outputs like some do.
There aren't any "G" connectors in that case of course, but then most amps
don't have terminals actually marked "G" in any case.

MrT.

And yes, there's a chasis ground terminal, actually 2, for the AM+FM
antennas.

Oh and it totally sounds like the kareoke switch is on... except that
there's no such feature in this system :-)