My trusty Pioneer A-9 has a problem on the right channel. If I listen on the
headphones the sound is great, on speaker the sound is fuzzy but only on the
right channel. The headphone ouput actually comes from the speaker output,
not the preamp, so it seems that fundamentally the signal is getting through
but under load it gets fuzzy. I can hear the distortion in the headphones
when I click the speakers on but when I click the speakers off the sound is
fine.

The power supplies feed both channels in parallel so I doubt it's a power
supply problem.

I have a scope and a little audio probe gizmo that lets me listen to audio
signals with an earphone. I can generate signals from my PC and feed them
into the amp, if that helps. I also have the schematics so I can trace the
signal but I'm not quite sure how to go about it.

Any tips?

Thanks,
Andrew Queisser

andrew queisser wrote:
My trusty Pioneer A-9 has a problem on the right channel. If I listen on the
headphones the sound is great, on speaker the sound is fuzzy but only on the
right channel. The headphone ouput actually comes from the speaker output,
not the preamp, so it seems that fundamentally the signal is getting through
but under load it gets fuzzy. I can hear the distortion in the headphones
when I click the speakers on but when I click the speakers off the sound is
fine.

The power supplies feed both channels in parallel so I doubt it's a power
supply problem.

I have a scope and a little audio probe gizmo that lets me listen to audio
signals with an earphone. I can generate signals from my PC and feed them
into the amp, if that helps. I also have the schematics so I can trace the
signal but I'm not quite sure how to go about it.

Any tips?

One tip might be to reverse your speaker connections left to right and
see if the problem remains in the same channel.

It might not be a problem with your amp....

jak
Thanks,
Andrew Queisser

jakdedert wrote:
andrew queisser wrote:

My trusty Pioneer A-9 has a problem on the right channel. If I listen
on the headphones the sound is great, on speaker the sound is fuzzy
but only on the right channel. The headphone ouput actually comes from
the speaker output, not the preamp, so it seems that fundamentally the
signal is getting through but under load it gets fuzzy. I can hear the
distortion in the headphones when I click the speakers on but when I
click the speakers off the sound is fine.

The power supplies feed both channels in parallel so I doubt it's a
power supply problem.

I have a scope and a little audio probe gizmo that lets me listen to
audio signals with an earphone. I can generate signals from my PC and
feed them into the amp, if that helps. I also have the schematics so I
can trace the signal but I'm not quite sure how to go about it.

Any tips?

One tip might be to reverse your speaker connections left to right and
see if the problem remains in the same channel.

It might not be a problem with your amp....

jak

Thanks,
Andrew Queisser




Maybe it's a problem with the speaker?
Have you tried switching the speakers?
Carefully checked the speaker wires?
Maybe the right speaker is bad.
Maybe there is a frayed wire. maybe even a short at one of the ends.
A frayed end just barely touching the other wire could be causing the
problem, and if it is allowed to continue like that you'll blow the channel.

I did switch the speakers and the problem stayed on the right side.

thanks,
andrew

Jumpster Jiver wrote:
jakdedert wrote:
andrew queisser wrote:

My trusty Pioneer A-9 has a problem on the right channel. If I listen
on the headphones the sound is great, on speaker the sound is fuzzy
but only on the right channel. The headphone ouput actually comes from
the speaker output, not the preamp, so it seems that fundamentally the
signal is getting through but under load it gets fuzzy. I can hear the
distortion in the headphones when I click the speakers on but when I
click the speakers off the sound is fine.

The power supplies feed both channels in parallel so I doubt it's a
power supply problem.

I have a scope and a little audio probe gizmo that lets me listen to
audio signals with an earphone. I can generate signals from my PC and
feed them into the amp, if that helps. I also have the schematics so I
can trace the signal but I'm not quite sure how to go about it.

Any tips?

One tip might be to reverse your speaker connections left to right and
see if the problem remains in the same channel.

It might not be a problem with your amp....

jak

Thanks,
Andrew Queisser




Maybe it's a problem with the speaker?
Have you tried switching the speakers?
Carefully checked the speaker wires?
Maybe the right speaker is bad.
Maybe there is a frayed wire. maybe even a short at one of the ends.
A frayed end just barely touching the other wire could be causing the
problem, and if it is allowed to continue like that you'll blow the channel.

On Wed, 23 Nov 2005 12:28:03 -0800, "andrew queisser" andrew.queisser
at hp com wrote:

My trusty Pioneer A-9 has a problem on the right channel. If I listen on the
headphones the sound is great, on speaker the sound is fuzzy but only on the
right channel. The headphone ouput actually comes from the speaker output,
not the preamp, so it seems that fundamentally the signal is getting through
but under load it gets fuzzy. I can hear the distortion in the headphones
when I click the speakers on but when I click the speakers off the sound is
fine.

The power supplies feed both channels in parallel so I doubt it's a power
supply problem.

I have a scope and a little audio probe gizmo that lets me listen to audio
signals with an earphone. I can generate signals from my PC and feed them
into the amp, if that helps. I also have the schematics so I can trace the
signal but I'm not quite sure how to go about it.

Any tips?

Thanks,
Andrew Queisser


Try feeding a 400 HZ square wave into it and see what comes out
(compare channels)

If the leading or falling edges look funny describe the bad one.

I'm not familiar with the A-9 but some discrete amps used to use fuses
on the speaker terminals so if the amp shorts it won't set fire to the
speaker cones. The fuse holders or fuses would corrode and cause
distortion when the current was higher (speakers versus phones).
--

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"andrew queisser" bravely wrote to "All" (23 Nov 05 12:28:03)
--- on the heady topic of "Attempting audio amp (Pioneer A-9) repair - any
tips?"

aq From: "andrew queisser" andrew.queisser at hp com
aq Xref: core-easynews sci.electronics.repair:349443

aq My trusty Pioneer A-9 has a problem on the right channel. If I listen
aq on the headphones the sound is great, on speaker the sound is fuzzy
aq but only on the right channel. The headphone ouput actually comes from
aq the speaker output, not the preamp, so it seems that fundamentally the
aq signal is getting through but under load it gets fuzzy. I can hear the
aq distortion in the headphones when I click the speakers on but when I
aq click the speakers off the sound is fine.

aq The power supplies feed both channels in parallel so I doubt it's a
aq power supply problem.

aq I have a scope and a little audio probe gizmo that lets me listen to
aq audio signals with an earphone. I can generate signals from my PC and
aq feed them into the amp, if that helps. I also have the schematics so I
aq can trace the signal but I'm not quite sure how to go about it.

aq Any tips?

aq Thanks,
aq Andrew Queisser


Connect the scope to bad channel and inject a 400Hz triangle wave test
signal, increasing the amplitude until the buzz is obvious. If the
triangle wave is mishaped at the zero crossings then it is crossover
distortion. This is most likely due to a defect of idle bias
circuitry. If instead the triangle wave is clipped then positive
clipping means a defective NPN output, and negative clipping a
defective PNP output. Perhaps intead one of the drivers or supplies.
A triangle wave is a good test signal because it consists of straight
lines and it also stresses the output devices less than a sinewave or
squarewave.

A*s*i*m*o*v

.... A stereo system is the altar to the god of music.

"andrew queisser" andrew.queisser at hp com wrote in message
...
My trusty Pioneer A-9 has a problem on the right channel. If I listen on
the headphones the sound is great, on speaker the sound is fuzzy but only
on the right channel. The headphone ouput actually comes from the speaker
output, not the preamp, so it seems that fundamentally the signal is
getting through but under load it gets fuzzy. I can hear the distortion in
the headphones when I click the speakers on but when I click the speakers
off the sound is fine.

The power supplies feed both channels in parallel so I doubt it's a power
supply problem.

I have a scope and a little audio probe gizmo that lets me listen to audio
signals with an earphone. I can generate signals from my PC and feed them
into the amp, if that helps. I also have the schematics so I can trace the
signal but I'm not quite sure how to go about it.

Any tips?

Thanks,
Andrew Queisser





I've seen mainly controls and switches need cleaning on these, including the
speaker switches, and speaker relay.

Mark Z.

On Wed, 23 Nov 2005 12:28:03 -0800, "andrew queisser" andrew.queisser
at hp com wrote:

My trusty Pioneer A-9 has a problem on the right channel. If I listen on the
headphones the sound is great, on speaker the sound is fuzzy but only on the
right channel. The headphone ouput actually comes from the speaker output,
not the preamp, so it seems that fundamentally the signal is getting through
but under load it gets fuzzy. I can hear the distortion in the headphones
when I click the speakers on but when I click the speakers off the sound is
fine.

The power supplies feed both channels in parallel so I doubt it's a power
supply problem.

I have a scope and a little audio probe gizmo that lets me listen to audio
signals with an earphone. I can generate signals from my PC and feed them
into the amp, if that helps. I also have the schematics so I can trace the
signal but I'm not quite sure how to go about it.

Any tips?

Thanks,
Andrew Queisser


The channel can be blown and the headphones will still sound fine. Check for an open output transistor or resistors. Chuck

Jumpster Jiver wrote:
jakdedert wrote:

andrew queisser wrote:

My trusty Pioneer A-9 has a problem on the right channel. If I listen
on the headphones the sound is great, on speaker the sound is fuzzy
but only on the right channel. The headphone ouput actually comes
from the speaker output, not the preamp, so it seems that
fundamentally the signal is getting through but under load it gets
fuzzy. I can hear the distortion in the headphones when I click the
speakers on but when I click the speakers off the sound is fine.

The power supplies feed both channels in parallel so I doubt it's a
power supply problem.

I have a scope and a little audio probe gizmo that lets me listen to
audio signals with an earphone. I can generate signals from my PC and
feed them into the amp, if that helps. I also have the schematics so
I can trace the signal but I'm not quite sure how to go about it.

Any tips?

One tip might be to reverse your speaker connections left to right and
see if the problem remains in the same channel.

It might not be a problem with your amp....

jak

Thanks,
Andrew Queisser




Maybe it's a problem with the speaker?
Have you tried switching the speakers?
Carefully checked the speaker wires?
Maybe the right speaker is bad.
Maybe there is a frayed wire. maybe even a short at one of the ends.
A frayed end just barely touching the other wire could be causing the
problem, and if it is allowed to continue like that you'll blow the
channel.
My thoughts exactly....

jak

Yes, the outputs, one or the other on the affected side is open in such a
way that allows the driver to power the output. The driver will pass
enough current to operate the headphones, but not the speakers... which
quickly clip the output of the driver. Check the outputs with a vom and
you'll find one of them open. Replace in pairs, adjust bias, and offset
voltage measured at speaker outputs. Check associated resisters for
opens. Power up with variac, watch current rise at low voltage to ensure
everything is good before applying full line voltage.

I've seen mainly controls and switches need cleaning on these, including the
speaker switches, and speaker relay.

Mark Z.

Yup, I've been unable to use the balance and tone controls due to dirt
or corrosion on this amp for years. I can only run it in
"straight-through" mode where it works fine.

And after cleaning the connector that goes to the power amps everything
works fine again.

Thanks!
Andrew

Thanks to everyone who replied. My amp is working again but the
solution was a bit anticlimactic. I took everything apart and when I
hooked up the scope the signals looked ok and the sound over the
speakers was clean again.

I think the problem was in the connector between the main amplifier
board and the board with the power amp for the right channel. After
cleaning the connector everything started working again.

Andrew