Ampeg BR4 low output

[nosaj]

i've got a Ampeg BR4 with low output in mono bridge I might be getting 300watts out of a 1000.
The rail voltages look in the ballpark.
But looking around the amp shows c34 someone tacked a axial cap in a radial spot with goop all over the leads. And R168 missing with a burn mark on the board.

C34 I will just replace cause it looks bad.

Can anyone tell me what might cause r168 to burn out . It's a 3.3ohm 1watt.

Thanks,
nosajPower Amplifier PCB Schematics (442SCH_8).pdf

[g1]

R168 would burn out from oscillation or feedback.
What kind of power do you get from the channels separately? One side weak, both?

[Jazz P Bass]

"i've got a Ampeg BR4 with low output in mono bridge I might be getting 300watts out of a 1000."

What load value are you using?

The manual states 1000 watts continuous at 4 ohms.

Note: I have a hard time believing this.
The back panel states 800 VA max current draw.

[nosaj]

"i've got a Ampeg BR4 with low output in mono bridge I might be getting 300watts out of a 1000."

What load value are you using?

The manual states 1000 watts continuous at 4 ohms.

Note: I have a hard time believing this.
The back panel states 800 VA max current draw.

4ohms and I'd expect to at least get 800watts reasonably out of it. If I'm wrong please explain.
Gotta wait for the storm to pass before I can get wattage on the amp A and amp B.

Thanks,
Jason

[g1]

Spec sheet says those are RMS values: https://ampeg.com/products/b/b4r/
However, you can't make 1000W continuous using only 800VA, so that may be burst measurements or something.

[nosaj]

Spec sheet says those are RMS values: https://ampeg.com/products/b/b4r/
However, you can't make 1000W continuous using only 800VA, so that may be burst measurements or something.

Ch A getting 34volts same for Ch B into 4ohms makes 289 watts a channel. I will now have to make that measurement again for the Mono portion.

Thanks,
Jason

[Jazz P Bass]

The manual states 340 watts each channel @ 4 ohms, continuous.
Of coarse there is not a distortion figure attached to that rating.
That's 36.9 Vac RMS output.

So you are in the ballpark.

Have you checked the ripple on the main rails?

[nosaj]

The manual states 340 watts each channel @ 4 ohms, continuous.
Of coarse there is not a distortion figure attached to that rating.
That's 36.9 Vac RMS output.

So you are in the ballpark.

Have you checked the ripple on the main rails?

No not yet I have. To be sure Checking the ripple would be meter on positive and negative of cap on AC setting correct or AC mV?

When I have a speaker attached it is nowhere as loud as i think it should be. What is the function of the missing resistor?
Thanks,
Jason

[Jazz P Bass]

"What is the function of the missing resistor?"
It is 1/2 of the zobel network.
C117 is the other half.

If the R goes I usually change the cap as well.

[g1]

When I have a speaker attached it is nowhere as loud as i think it should be.

Did you have to put in a lot of signal to get it to full power on the load when you measured it?

[nosaj]

Did you have to put in a lot of signal to get it to full power on the load when you measured it?

Yes i did. Load being a 4ohm dummy load.
Are we thinking Coil problem?
nosaj

[g1]

No, I was thinking loss of voltage gain somewhere, so it can do full power, but the input sensitivity is wrong. This would make it seem weak with an instrument input.
Have you tried putting signal into the FX return?

[J M Fahey]

If tghe amp is making *real* 300W RMS per channel then itīs fine and should be putting out 600W RMS into 8 ohm, wall cracking power.
And IF it could drive 4 ohm bridged , it would easily meet the 1000W rating.
So Iīm not worrying very much about thye power amps.
"But it does not *sound* like 1000W (or 600W at least)"
Ah, thatīs something else, very different, and probably leading to a gain problem, weak Bass, wrong setting, other stuff, which of course must be properly detected.

* what is the speaker cabinet used for the test?
* controls setup? Isnīt a Passive Bass plugged in an Active Bass input? Or is -10dB pad switched on?

In a nutshell: does, say, 100mV 440Hz or 1kHz drive amp to full power?

I don't mention actual "clipping" because if it has the classic Crate/Ampeg Opto limiter it will never ever clip, it is that good.
Of course, it makes amp never reach rated power either, some measurements require disabling it.

[nosaj]

If tghe amp is making *real* 300W RMS per channel then itīs fine and should be putting out 600W RMS into 8 ohm, wall cracking power.
And IF it could drive 4 ohm bridged , it would easily meet the 1000W rating.
So Iīm not worrying very much about thye power amps.
"But it does not *sound* like 1000W (or 600W at least)"
Ah, thatīs something else, very different, and probably leading to a gain problem, weak Bass, wrong setting, other stuff, which of course must be properly detected.

* what is the speaker cabinet used for the test?
* controls setup? Isnīt a Passive Bass plugged in an Active Bass input? Or is -10dB pad switched on?

In a nutshell: does, say, 100mV 440Hz or 1kHz drive amp to full power?

I don't mention actual "clipping" because if it has the classic Crate/Ampeg Opto limiter it will never ever clip, it is that good.
Of course, it makes amp never reach rated power either, some measurements require disabling it.

i will get those measurements shortly for you. One question is there ever a reason to use 440Hz Vs 1kHz?

G1 no I have not. I used a drum machine on the 0 db input to get the 34 volts probably not ideal but I guess did show the power section could do it.

The speaker I have is a Behringer 15in bass speaker in an old 70's Carvin cabinet non ported. With other amps I could shake the ground with it.
Will follow up with Juans suggestions.

G1 What voltage should be inputted inthe Fx return?

If you had a kid would you call him G2?

nosaj

[g1]

No, h1. My dad was f1. g2 is my sister.

Somewhere on that schem. it shows that 680mV at the fx return should give 40V into 8ohms.