A guide to building the Pass F4 amplifier

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PJN

Member
Joined 2004
Hi Everyone,

Good news, booked up Wayne's 2018 BA per to the F4, nothing but sweet music, clean and clear. Very nice combo. I guess The F4 doesn't play well with the Aikido. Next steps will to put in a good system and give it a good listen. Thanks for all the help, and thanks to Nelson for his generosity.

Paul
 
P

PJN

Member
Joined 2004
I let the amp settle in running for a few hours in the garage, then brought it inside to audition. I substituted into my main system replacing my F6. Using a Doug Self preamp driving sealed 3 way speakers. After two hours listening I can say that the F6 is not going back in. I really liked the F6, and used it for years, but to me the F4 sounds cleaner, a bit more refined. Great amp. I am very glad I finally built one.
 
amandarae

amandarae

Member
Joined 2004
PJN said:
I let the amp settle in running for a few hours in the garage, then brought it inside to audition. I substituted into my main system replacing my F6. Using a Doug Self preamp driving sealed 3 way speakers. After two hours listening I can say that the F6 is not going back in. I really liked the F6, and used it for years, but to me the F4 sounds cleaner, a bit more refined. Great amp. I am very glad I finally built one.
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Great to hear!
Is the Doug Self preamp 6SN7 based?
I would suggest if you can borrow a preamp with a Type 26 or a 01A output tubes to drive the F4 to try. You might forget about the 6SN7's.
IME, the F4 will sound better and better in time as you use it for the next month or so. Congratulations!
 
P

PJN

Member
Joined 2004
The Doug Self pre is SS, it was a design published in Linear Audio several years ago. Carl Huff did a group buy for the boards several years ago. The pre uses opamps and has balance and tone controls, nice functional preamp. Sounds very good and has more than enough omph to drive the F4.
 
P

PJN

Member
Joined 2004
The Doug Self pre is SS, it was a design published in Linear Audio several years ago. Carl Huff did a group buy for the boards several years ago. The pre uses opamps and has balance and tone controls, nice functional preamp. Sounds very good and has more than enough omph to drive the F4.
 
C

cal3713

Member
Joined 2014
mcandmar said:
Congrats, great to see another happy F4 owner. I 2nd the DHT preamp suggestion, currently running a 01a preamp on mine.. its just wonderful.
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3rd. I use a Shiny Eyes DHT pre built by Radu Tarta that's based on the EML20A tube (for maximum gain from a single stage design). It outclasses my previous 6sn7 based pre in every way. Amazing really.
 

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C

Chiptech

Member
Joined 2005
Paid Member
dill3000 said:
My F4 project with pics


Hi Guys,

Just posting my F4 project with pics from the early stages to the final F4.


I decided to build a dual mono F4 - this was my first DIY project ever. Had so much fun doing it!! :)



My dual PSU boards mounted to the 5U chassis front


— —

My dual transformers. (these were 400VA 230V to 2 x 24V)
I later discovered that I was going over board with the 24V. I ended up returning the transformers and going for 200VA 230V to 2 x 18V - as I’ll be using two transformers, 200VA is fine. Thanks to 6L6 for the tips :)





— —

My mounted F4 right board


— —

Almost wired up



— —

Close up of the right PSU wiring


Final wiring - this is where I got stuck. I’m from the UK so we use 230V the guide only had the 115V wiring with picture.

6L6 helped me out here, with a hand drawn diagram (it was a great help!) :)



— —


Testing

So I have replaced the transformers and successfully completed the final PSU wiring.

I tested the PSU boards first and all was working, so I connected the F4 boards.




— —


I had to replace my JFETs and MOSFETs for matched items, this is something I didn’t do at first and it was giving me problems.

Ordered my matched JFETs and MOSFETs - and managed to complete this F4. Its sounds amazing!!

It runs at 300mV bias and heatsinks get to around 45C average. It only went higher on the hottest day of the year but it still only got to 50C.

Just need a good preamp now! (I’m currently building the Pumpkin Shunty)

See final finished pics below.
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Dill3000,

Thanks for posting your photos. That is one beautiful amp build. It helps me start to envision doing a dual mono myself one day. First I have to finish my F6.
 
R

ra7

Member
Joined 2009
Paid Member
cal3713 said:
3rd. I use a Shiny Eyes DHT pre built by Radu Tarta that's based on the EML20A tube (for maximum gain from a single stage design). It outclasses my previous 6sn7 based pre in every way. Amazing really.
Click to expand...

Nice. The F4 is so good and it has opened so many possibilities. I recently assembled an 01a/26-based pre. It has all the bells and whistles. And the BA-3 is now kicking its butt. I can scarcely believe it. Try a BA-3 pre with the F4. You might be surprised. It is so simple to build, you could do it in an afternoon.
 
nkostop

nkostop

Member
Joined 2012
Hello,
I have build the F4 before some weeks and is a great sounding amplifier.
I have an issue that many members have helped me here.

I have o 50hz (I am in europe) hum when the amplifier is connected with other equipment or when I connect both inputs together. When both inputs are open there is no hum.

So I am thinking of a ground loop right?
When the amplifier is connected to other equipment and I am sorting the right input to ground the hum continues. When I sort the left input to ground it is less audible but audible indeed.

I am thinking of changes on the power supply:
1) Change transformer (does it make any sense)
2) Align the capacitors in a straight line instead of quads (I believe this was ZenMod indirect suggestion?)
3) Change the T bar of the ground with something with less resistance(now it is from thick wire maybe a copper bar)

What do you think about this? Do you think that maybe there is a problem with the channels (I have used the diyaudio store boards)
I am certain it is not RF EMI because I have made a lot of experiments by moving the components, adding shields etc

For everyone who'd like to help I am attaching a photo of the inside!

Also I am building the Impasse preamp which is a great fit, If anyone interested I am designing a schematic, you can follow here (ImPasse Preamplifier)
 

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