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Old 23rd February 2005, 07:57 PM   #1
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Default pioneer SA-6500 II problem

Hi all,


I hope you can help me with this one...

I have an old pioneer stereo amplifier from the 70's.
The model is SA-6500 II.
It's working ok, and it sounds extremly good, but there is
one problem: when I turn it on I have a big thumb for a second
or two...like big mmmmmm, so I always turn it on with the speakers' switch in off position, waits few seconds, and then turn the switch back on....

I think it's a dc offset problem, or maybe bias problem,
anyone has a clue on how to fix it? or anyone knows
where can I find the schematic?


Thanks in advance,

Udi.
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Old 23rd February 2005, 08:21 PM   #2
K-amps is offline K-amps  United States
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There's a good change the electrolytic caps on that have dried up. They may need replacing. DC offset does not cause "MMMMM" for a sec or two... neither does bias... they usually cause it for a long time of out of whack.

Try replacing the samller caps around the input stages, seems like the input bias circuit has a defective capacitor.
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Old 23rd February 2005, 08:32 PM   #3
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Hi K-amps,

Thanks for the reply...


In fact, I have this problem for a few years now, and last year
I replaced all the electrolitic capacitors in the amp
(except for the power supply capacitors), and it didn't help,
and in fact the sound got worse , but I guess this
is because I used cheap capacitors.

You think maybe it's the power supply capacitors?


Udi.
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Old 23rd February 2005, 08:42 PM   #4
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Doesn't that model have a relay? If so, it should take about 3 or 4 seconds to kick in.
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Old 23rd February 2005, 08:45 PM   #5
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Hi,

I think it doesn't have a relay, but it has inductors with resistors
in parallel at the outputs.

Maybe I should add a relay (or two) ??

Udi.
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Old 23rd February 2005, 09:06 PM   #6
K-amps is offline K-amps  United States
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The 6500II did not have relays. Yes the larger caps might need replacement.
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Old 23rd February 2005, 09:23 PM   #7
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Thanks guys,

I'll try replacing the supply caps.

Udi.
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Old 20th October 2005, 08:28 PM   #8
munja is offline munja  Croatia
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Hello udip,

do You solve that problem about bad sounds through switching amp on?
I received Pioneer SA-8500 with similar problem (left channel only), but here at me it works fine, I should wait until it sounds would appear!
I think the problems lying in some active component (diode or transistor), amp is very old and semiconductors change their characteristics.
Let us find it!!!

Regards, Munja
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Old 12th March 2009, 07:06 PM   #9
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hi,

I got the same amp but a different problem. i have distortion in the right channel. The left one sounds fine.

could that be Dc offset ?

thx
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Old 11th March 2011, 10:06 AM   #10
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Default Help

I have a 1974 Pionner SA-6500 II amp that was givin to me 12 yrs ago and it has worked fine all these years but a few years back a friend of mine fliped it on and i guess was listing to rap and roasted the speakers to the point of setting them on fire the board isnt burnt any where i have been able to find but it still will not put out any sound on a loud buzzing noise any one that help me i would be greatfull
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