Behringer A500 power amp problem, please help?

[AKN]

Hi emperor,

I have not auditioned nor seen this amp in real but judging from opinions on the web there is mixed impressions. Seen that some has reported sound improvements by upping bias a bit.

On the other hand, you said sound is fine provided pots are positioned close to end positions, this speaks for something different than bias issues I think.

Just some thoughts....

With your volume pots at approx mid position they have the greatest source impedance into next coming stages.
Could it be that signal in the long screened leads to/from the potentiometers gets inductively affected by high current leads located to close?

If you run the amp non bridged does the same issue occur on both amps/channels?

[emperor]

If you run the amp non bridged does the same issue occur on both amps/channels?

Yes it does, and i have two of them, that do it in stereo mode or monobridged, which would indicate, poor design, or (I swear i would have noticed before , the piano), failing components.

I personally am a technological dunce, and am asking for ideas, so i can get somone in the UK to fix it for me.

[geminni]

Originally posted by KISS
english translation: Stand by currrent = bias current. Stand by current could have different meanings depending on context. Interesting fix.

Thanks!

[KISS]

A bigger phrase might be "quiescent current".

Definition: quiescent: being at rest; quiet; still; inactive or motionless from www.dictionary.com.

You can stick to "bias current", so that people don't have to pick up the dictionary. <G>.

[beppe61]

Originally posted by emperor
Hi guys ...
If i take the gain potentiometers on the A500,s very low, and turn the preamp up full, no problem.
Also i put the gain on full, it sounds fine again, but because the gains up full, the noisefloor is higher, and so its a bit noisy.
....
if you had Any ideas i would be grateful?

I have one A500 myself.
I noticed that with the A500's front control at max (zero attenuation) and its inputs shorted with a resistance (please excuse my bad english) the amp is completely silent from the speakers.
This means for me that the amp is silent in itself.
Nevertheless when I connect the preamp and the source I get some noise (maybe a ground loop ?).
By the way I have not understood well in which conditions you get the distortion.
I never get distortion with the A500 front control at max, just some noise.
I read some test report very positive about this unit, also in terms of distortion.

Thanks and regards,

beppe

[SSassen]

Sorry for bumping this thread, but wanted to post the schematic of one of the Behringer A500 channels, it indeed is using flying rails as a topology for lack of a better description. I was expecting something like a standard Miller approach, maybe with some refinements (folded cascode etc.) so was somewhat dissapointed.

Cheers,

Sander.

[bomellberg]

There is a video on youtube showing distorsion problems if the A500 is NOT at max volume. So, keep it at max, and attenuate it at preamp.

If there are any A500 wizards out there, I could use some help. My amp is faulty on channel one. As soon as I turn the volume knob, it starts hissing in both speakers. At approx 5 sec intervals, both speakers produce a loud thump (lika a heartbeat). Speaker 1 begins thumping inward and speaker 2 outward.

If I keep the faulty channel at 0, the other channels works fine.

Best regards,

/Bo

[KISS]

Look coupliing caps. In other words look at the DC voltages and compare them with no signal to the other channel.

[bomellberg]

Ok, I'll do that! Thanks for the tip!

The reason for both speakers hissing was that the amp was set to bridged mono mode. With the switch set to stereo, only the faulty channel was affected.

Best regards,

/Bo

[KISS]

I'd suspect C11. Replace with a NP cap such as Amazon.com: 10uF 100V Non-Polarized Capacitor: Electronics