A guide to building the Pass F4 amplifier

Jean-Louis: for output wiring between the PCB and the speaker terminals, use heavy gauge stranded wire such as 12-14ga. For input wiring between RCA and PCB, use thin gauge, solid core wire, such as 24-30ga. A single twisted pair from telephone/CAT5 wire will work well. A few here will advocate for 30ga silver wire, which also works well.
 
Would a 5U big chassis be enough for a "mono block" F4 build? Two F4 boards per side, with parallel/balanced inputs?
It is quite smaller and somewhat cheaper than a true mono block construction.
With a balanced BA3 preamp we could have a nice 50-100W class A system in a "compact package."
Would the BA3 power amp be able to supply the same power output as such a solution?
 

6L6

Moderator
Joined 2010
Paid Member
Would a 5U big chassis be enough for a "mono block" F4 build? Two F4 boards per side, with parallel/balanced inputs?

Yes. it will be a fairly tight fit, and your PSU requirements obviously double, but it's possible.

You may need slightly reduced bias.

It is quite smaller and somewhat cheaper than a true mono block construction.
With a balanced BA3 preamp we could have a nice 50-100W class A system in a "compact package."

Yes.

Would the BA3 power amp be able to supply the same power output as such a solution?

Yes. The BA-3 is a F4 with a gainstage in front of the power stage.
 
As I'm waiting for PE to get more parts in I thought I'd start making a BOM for an F4. That way if I really the ACA amps I can start gathering bits. A couple of questions on the F4 though. I'll be using the PSU board from the store and see that I most likely do not want/need to use input/output snubbers. Is that correct? I'll be shooting for the Antek AS4218 trafo and using monolithic rectifiers along with the soft start/protection pcb's.. Also, I noticed a difference between Mr. Pass's schematic and the store schematic for R8. Any suggestions there?
 
I've just built my f4 and got it up and running.
My psu rails are +-24.5v.
I've biased to just over 200mv.
Do these amps take a while to burn in?
Whilst on my bench the heat sinks went up to just over 50C but don't seem to be getting anywhere near that warm whilst playing.
Possibly because on my bench it was up on end in the front panel. But wouldn't think it would have made as much difference as it seemed.
Was wondering what people thought I should bias this to. The stock spec is 200mv but most people seem to be running these much hotter. The build guide suggests 270mv to 300mv was optimum but that was with a 22.5 v supply.

My g&w t2.6f headphone/preamp will go loud enough to listen to music but enough to go loud in case any ones wondering. So will order the impasse kit.