Peavey CS800H Buzzing

[JP-Stereo]

After it trip the breaker, i've removed and test all the ouputs, they all test good on the diode check.
So i just look for short around without removing anything else.
The resistors, the diodes and the caps around are normal and all test symetric between channels.

I just had these SBS14 looking odd.

[g1]

Have you checked for DC on the output with the Triac's removed yet?
You can deal with the Triac circuits after the rest of the amp is verified OK.

Can someone post the schematic please.

[JP-Stereo]

I did not get there yet.

With a 100w bulb in serie on the power LINE side.
Only the transformer = No bulb no trip.
When i plug ONLY the BIAS supply connector (P53) from the transformer, the bulb doesn't glow.
But, I have only 12 volts dc at C67+ and -20 volts dc at C68-, it should be +/- 25 volts.
And U1 get hot and have no output

I will desolder U1 just in case it is a dead on installation (short to ground)
Otherwise it must be something down the +15 volts that load the line very bad...

[JP-Stereo]

Now i am there...
0.003 vdc at the output : )

Everything power up and nothing gets hot.
It was a Bias 7815 reg, input completly short to ground.
Once replaced all voltages are fine for the bias and the rails.

But i still have a noise on both channel,

All 8 power supply's big filtering caps have been changed.
The 2 filtering caps and the regulators from the Bias supply have been changed.
All outputs and immediate components have been checked too.
(new heat sink compound)

Back at signal tracing...

[JP-Stereo]

I have a 50 mv AC noise at the bias regulators.
It is also present on each rails between 600 & 800 mv of AC noise, but the DC voltages are fine.
And the big tumb at power off is also back...

I think i will have to remove some surface mount components to isolate the preamp/crossover circuits from the power amp itself.

[JP-Stereo]

Another detail, the 7915 reg (U8) get a lot hotter than is 7815 (U1) mirror.
Even if the 7815 (U1) is also powering a 7805 (U12) downstream, the 7915 don't have such additionnal load.

[JP-Stereo]

Hi, i have locate a burned resistor (R17), it is in serie with a Low Freq filtered line level output.

If someone plug an output there instead of a link to an input by mistake, it may have blown the resistor and damaged the OpAmp in line.


It read in the megohms instead of 100 ohms.





Not easy to desolder some components to isolate the noise source.
It seam to affect all these opamp via the +/- 15vdc.
Any idea ?

[The Dude]

Well, obviously replace the burnt resistor. Also check D35 and D34. Check voltages on the op amp to see if it's shorted before replacing it. I presume your power supplies are now all good?

[g1]

If you suspect an IC is doing something to the +/-15V lines, just lift it's power pins. It's easier than replacing the whole IC. For 5532, that is pins 4 and 8.
If it makes the problem disappear, you can replace the IC. If not, you can reconnect the pins and look elsewhere.

[JP-Stereo]

Hi, did some tracing again.
I have lifted the power leg on U202, U201, U200 and U210 without any improvement.

For U205, it's bizarre.
At speaker B output, i see the noise on the scope but it's barely audible through the speaker.
Speaker A have a lot less noise on the scope but i heard the noise through the speaker half loud as before...
Getting confused...

[g1]

Maybe what you see on the scope is some different inaudible noise. What is the frequency of the noise on the scope? What does the frequency you hear sound like?

[JP-Stereo]

Hi, here are more details:
I did a video of the scope view for each channel at power up and going.

At power ON both channel have a period without signal corresponding to the output relay delay.
Once fully on:
Channel 1 have 0 v dc but 200mv of high pitch highly annoying audible ac noise.
Channel 2 have around 3 v dc with 400mv of barely audible low pitch ac noise.

[JP-Stereo]

Finally here is the shematic for this amp.
Still stuck at the crossover level.

I hope this can help

[x-pro]

Disconnect the crossover from the amplifier again. On the rear panel of the cabinet, turn the "Function" switch to the "full range" position.
Check the output DC voltage and noise with no load and no signal on channels A and B.