F5 bias question

[richD]

Does anyone have a “ How to Bias the F5 for Dummies”?
I’ve read Mr. Pass’s article and it’s still not clear to me on how it is done.
Thanks

[audiorob]

Originally posted by richD
Does anyone have a “ How to Bias the F5 for Dummies”?
I’ve read Mr. Pass’s article and it’s still not clear to me on how it is done.
Thanks

Maybe the scope of this issue could be narrowed if you could tell us
more specificly, what problem you're having (what is going well, and
what isn't). In general, you might find the Zen 5 paper helpful, as the
Zen 5 amplifier's bias is set by the same method.

[juluska]

don't worry, it's easy:
1.- Turn off your amplifier
2.- put the pots to 0 ohms position (measured between legs 1-2 and leg 3)
3.- turn all the pots about 5-7 complete turns
4.- then turn on the amplifier (with no speaker connected) and begin adjusting one channel, with one multimeter in the speakers output and other multimeter in R11 or R22.
5.- Now all you have to do is to turn P1 and P2 in half turns alternately until achieve a value near 0V DC at the output and .59V volts across R11 or R12

[richD]

Thanks juluska, I think I can handle it now!

[juluska]

Originally posted by richD
Thanks juluska, I think I can handle it now!

take care with heat, it runs really hot but you can touch the heatsinks for 4-5 seconds.

[richD]

Thanks again. I have not build it yet. I just want to make sure I understand everything before hand.

[vdi_nenna]

Hi juluska,

What you're saying is you can monitor R11 or 12 for .59v?
One doesn't have to monitor both at the same time? Let's say I monitor only R11. R12 will end up at .59v also?

3.- turn all the pots about 5-7 complete turns

Also, in the above are you saying that there should be some resistance above zero before turning on the amp? What happens if I start the amp at zero on the pots?

I ask because I've had problems with my F5 build.

Thanks,

Vince

[cviller]

Originally Posted by vdi_nenna

Hi juluska,

1. What you're saying is you can monitor R11 or 12 for .59v?
One doesn't have to monitor both at the same time? Let's say I monitor only R11. R12 will end up at .59v also?

2. Also, in the above are you saying that there should be some resistance above zero before turning on the amp? What happens if I start the amp at zero on the pots?

3. I ask because I've had problems with my F5 build.

1. Exactly - you might not end up with precisely the same voltage on both R11 and R12, but that is not as important as DC offset.

2. That suggestion just saves you a few turns while the amp is ON. Do it the way you feel most comfortable.

3. Is it working now?

[vdi_nenna]

Hey thanks. Not trying to hijack this thread...but here goes.

Not fixed yet, just got the replacement parts yesterday. I planning on removing the active components, marking them e.i., value and channel, then test them outside the circuit to see what went wrong. It's bugging the $#!+ out of me! Will also recheck all resistor placement and values. Something has to turn up. It's too simple a circuit and nothing burned up! I'm betting on a semi gone bad somewhere, but keeping all possibilities open.

thanks,

Vince