A guide to building the Pass F4 amplifier

6L6

Moderator
Joined 2010
Paid Member
(could certainly use more gain than the XP10 provides)

My experience with the F4 is that it's playing louder than you expect because it's so breathtakingly clean. I was mostly using an O2 which has a bit more gain the the XP10, but the same idea still applies. I bet its actually a little louder than you actually think.

That said, there's no question that for full power you'll need to do something different. (Might be a great excuse to try some transformers...)
 
Official Court Jester
Joined 2003
Paid Member
last time when I messed up ( recently ) , while doing some work wit friend's Nagra pre , I had funny acting balance pot

after some head scratching , I did leave it for a while , to make coffee and relax (clear head-fog) , I realized that I connected it not in stereo but in twice Left channel (interconnect between pre and amp)

:clown:
 
My experience with the F4 is that it's playing louder than you expect because it's so breathtakingly clean. I was mostly using an O2 which has a bit more gain the the XP10, but the same idea still applies. I bet its actually a little louder than you actually think.

That said, there's no question that for full power you'll need to do something different. (Might be a great excuse to try some transformers...)

With the XP10 I can listen to my preferred level when volume control is at 60-64 (64 being the max). Of course my wife always says I listen to music too loud. :rolleyes: First impression is the F4 is my favorite of the 3 I have done.
 
Getting close. Building the bulb limiter, double checking all wiring, and then powering up board by board tonight...
 

Attachments

  • 20190509_143832~2.jpg
    20190509_143832~2.jpg
    894.4 KB · Views: 239
  • 20190512_233307~2.jpg
    20190512_233307~2.jpg
    994.9 KB · Views: 233
With the XP10 I can listen to my preferred level when volume control is at 60-64 (64 being the max). Of course my wife always says I listen to music too loud. :rolleyes: First impression is the F4 is my favorite of the 3 I have done.

And you're still driving directly, or through your DHT?

I've got an 8W DHT SET that I'll be using for voltage. Will be trying the F4 on bottom of a bi-amp setup and driving everything with the SET running a resistor. Really looking forward to hearing it this week/end, I've been trying to solve a bass problem for a year. Any amp I try beats the SET in bass, but loses too many other places... And bi-amping with an active crossover killed coherency. Hoping the F4 solves all of that.
 
And you're still driving directly, or through your DHT?

I've got an 8W DHT SET that I'll be using for voltage. Will be trying the F4 on bottom of a bi-amp setup and driving everything with the SET running a resistor. Really looking forward to hearing it this week/end, I've been trying to solve a bass problem for a year. Any amp I try beats the SET in bass, but loses too many other places... And bi-amping with an active crossover killed coherency. Hoping the F4 solves all of that.

Not yet. Need to replace the binding posts with RCAs on the amp to make using it as a preamp easier. Will probably get to it some time this week. BTW, of the 3 I have built (M2, F6, F4) the F4 has the best bottom end (and also the most depth in sound stage).
 
Last edited:
Official Court Jester
Joined 2003
Paid Member
And you're still driving directly, or through your DHT?

I've got an 8W DHT SET that I'll be using for voltage. Will be trying the F4 on bottom of a bi-amp setup and driving everything with the SET running a resistor. Really looking forward to hearing it this week/end, I've been trying to solve a bass problem for a year. Any amp I try beats the SET in bass, but loses too many other places... And bi-amping with an active crossover killed coherency. Hoping the F4 solves all of that.

drive upper driver through high-pass passive xover with SET; take signal from SET output to F4 and drive lower driver through low-pass passive xover
 
Member
Joined 2011
Paid Member
I Agree 100%!
The F4 is a current monster which is why the bottom end is so great.
It images well because it basically lets you hear your preamp.
Ever wanted to see what your headphone amp sounds like driving your favorite speakers?
Build An F4 and find out!

Some IEC's have the jumper bars done from the factory, some need 2 some need 1.
 
I've got the same dual fuse iec inlet that 6l6 has in the build guide. Copied the wiring and dropped a fuse in the live/hot side. Can't figure out how to jump the neutral though. Aside from putting in a second fuse, I can't figure out how to complete the circuit... (Without soldering together parts that clearly aren't meant to be connected, like the end of the fuse holder)
 
Thanks ZM. I did that for testing purposes (at least).

Finished all wiring and used the bulb limiter to check the PS and both boards, everything looked good.

Then tried to set bias and could only get up to .06V. Switched out R9 for 47.5K and realized that I'd been trying to set the bias with the amp plugged into the limiter. ****. Plugged into the wall to test the left channel, immediately sent it well over .5V, smelled something (light, no smoke) and unplugged quickly. Switched back to the stock 10k resistor and now I get a bias of .000V (with power LED illuminated). Not real happy with myself tonight.

On the plus side, the right channel at least biased up to .13v when tested by itself.

Any thoughts would be greatly appreciated. I saw the "potentially blown tl431" thought earlier in response to a bias of 0V...

Thanks folks.