Spontaneous phase inversion?!

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

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 in news:1157473246.298395.192480 @d34g2000cwd.googlegroups.com:

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.

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.

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:

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 :-)

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

Someones sure confused.

NT

The problem will almost certainly be that the grounds to the speaker " black " connectors have gone missing - it's a common problem. The really big clue to this is that the vocals disappear on a Beatles recording. Most of their stuff was produced in the early days of stereo recording, and was studio-made rather than genuinely recorded with multiple mics. The vocals were almost always just a mono-split across the two channels, to help with keeping them 'bright' and defined with mono pickup cartridges that were billed as " stereo compatible ". The effect of this when you lose the ground to the speakers is just as Cook-y from Diverse Electronics said at the top of the thread - you get almost total phase cancellation of the vocals due to the L-C-R connection that's left when the ground goes ( it's almost like having the two speakers connected in series across a bridge connected amp, but with each half of the amp being driven by different signals ). Most likely bet is a bad joint or cracked print right behind the connector block.

Arfa

black

clue

ground

to

block.

I think this was the weirdest sympom I ever saw. I thought the customer was winding me up initially. Kit was a play only car cassette player and whatever tape you put in it , self recorded or shop bought, it recorded the sound of a cracked vinyl record over the music, permanently.

If no one gets the answer I will post back in a few days time.

There used to be a Panasonic answer machine that used to do the same thing in that it recorded a rythmic "crack - crack - crack " when certain tape types ( mostly of their own manufacture, oddly ) were used. Problem was caused by a static build up on the head's surface from the passage of the tape over it. The head as I recall, was mounted on plastic, so 'floating'. This may not be exact as it's been some years ago, but something along those lines anyway. Cure was to add a ground wire to the head. Something similar to this perhaps ??

Arfa

vocals

due

like

,

those

A tiny piece of magnetic material squashed into the rubber of the pinchwheel

-- Diverse Devices, Southampton, England electronic hints and repair briefs , schematics/manuals list on

Also note that the *inputs* to the amp can cause a similar problem, I repaired an amp that was doing this intermittently. It turned out the phono-RCA-jacks

*in* to the amplifier had no ground connection. This was due to them being dual phono sockets, stacked vertically, with no physical support other than the solder joints (not good), coupled with super tight fit, gold plated, heavy cable interconnects -- the insertion force required to get the line-in to go in was such that it broke the amp input.

Either at the input, or output :)

--
--------------------------------------+------------------------------------
Mike Brown: mjb[at]pootle.demon.co.uk | http://www.pootle.demon.co.uk/

Yep ! That's a good one ...

Arfa

Hi Mike

This is absolutely true, as a general rule. I too have seen this many times on even high end Yammies and Teacs. I assumed it not to be the reason in this case, because the unit has a built in CD, which I took to be the OP's source when playing his test Beatles track. [ " I put on a Beatles track to better test it " ] It sort of reads like the available input sockets on the back secondarily produce the same result, [ " I tried the two available inputs, ( "DAT" and "AUX" ) - same thing " ] so this would indicate an output rather than input issue. It is a shame that he did not post just one more picture looking down on the print side of the output connector PCB, which he has otherwise completely exposed. It may have been possible to see whether or not the joints were bad there.

I wonder if the OP has got anywhere with it yet, as a result of all the advice offered so far ?

Arfa