A guide to building the Pass F4 amplifier

[valvesound]

I think I confirmed 6L6 's answer. I didn't like the sound with the caps on the amp boards. There is more 'depth' as standard.
Just shows again.... Mr Pass does really know what he is doing

Thanks for your how to thread 6L6 it helped me a great deal and I have to commend you on your listening impression you posted at the start of this thread. You have it spot on!

 

[6L6]

What do you suggest as 'big' ?

15,000uF or whatever you have on the PSU board as a single cap.

 

[valvesound]

Thanks 6L6!

Just a little more info on my F4, I am driving it with a valve (tube) amp I put together. A Constant Current Draw Amplifier with a mu follower addition to give it a 20Vpk output with a standard line level input. I just love it!

 

[6L6]

That sounds like an ideal driver! Do you have a schematic?

 

[valvesound]

That sounds like an ideal driver! Do you have a schematic?

will post soon!

 

[valvesound]

 

[Zen Mod]

drekload of wasted gain

one 6Н6П will dance in circles around it

even one 6DJ8

 

[valvesound]

its not actually that much gain, about 26dB. The positive feedback resistor R14 takes care of that. The design is very quiet and very low distortion and drives the F4 well with some headroom.

The 2nd order distortion can actually be adjusted by changing the value of R14.

 

[Triodethom]

its not actually that much gain, about 26dB. The positive feedback resistor R14 takes care of that. The design is very quiet and very low distortion and drives the F4 well with some headroom.

The 2nd order distortion can actually be adjusted by changing the value of R14.

R 14 is a negative feedback resistor I do believe. 12au7s are not on my list of usable tubes. Regards

 

[valvesound]

R14 feeds back to cathode resistor of input tube creating a CCDA. would you suggest a 12AT7 rather than 12AU7?

 

[Triodethom]

6sn7 or 12sn7 is more linear than 12au7 . As for 9pins I like 5755 close to a 5751 in gain different pin out and very linear. If you have a good sounding at7 try it . for that mater all 6dj8s .

 

[valvesound]

it could be reduced to this following cct but it has higher noise and THD. Probably nothing to be concered about though.

 

[valvesound]

6sn7 or 12sn7 is more linear than 12au7 . As for 9pins I like 5755 close to a 5751 in gain different pin out and very linear. If you have a good sounding at7 try it . for that mater all 6dj8s .

I also like the 5755

 

[BigE]

Can the diyaudio store speaker protector be used on this amp in balanced mode?

 

[Zen Mod]

generally yes , if you connect it floating (that demands separate complete PSU)

read this :

http://www.diyaudio.com/forums/pass-labs/28336-aleph-x-builders-thread-122.html#post3915715

 

[BigE]

Thanks!

 

[bjorgens]

Finished my F4... Thanks to those who offered their assistance along the way. Is using Antek 500VA transformer, soft start, and speaker protection boards. So far so good running behind my 300B SET monoblocks. Surprised at how long this thing takes to warm up

not much listening time in yet, but what I can say is that nothing struck meas being markedly different...until I turned things up... then yeah... there was a difference there

cheers,
bryan

 

[6L6]

Not much listening time in yet, but what I can say is that nothing struck meas being markedly different...until I turned things up... then yeah... there was a difference there

Yep, that's the F4 - invisible. It sounds like the device driving it. So if you ever wanted to find out what a 300B amp would sound like with 50WPC/4ohm and an output impedance pf 0.02ohm, now you know.

Love the power switch BTW, complete overkill is always awesome. I bet it has a great solid klank when engaged.

 

[Zen Mod]

Fugly!

 

[bjorgens]

Thanks!
B