A guide to building the Pass F4 amplifier

Official Court Jester
Joined 2003
Paid Member
you'll see numbers on DVM creeping up, then slowing ....... then almost stopping

measure a dozen or so , without writing values down , just for experience and getting feel sake

then measure for real

don't skimp on heatsinking and pressure

I'm using forced cooling , just to keep temp as steady as I can ....... in case that I do it more often than it\s already the case , I would invest my time in obtaining temp controlled plate instead of heatsink

anyway, it's close enough with simplest methods
 
Hi all. Just finished building my second f4 and have a question about paralleling the outputs...

As you can see below, I put in switches so I could link the inputs and outputs to switch from stereo to mono. The input switches are working like I anticipated, bridging the RCA's so that whatever I've got on one channel comes out both.

The output switch is not, however. In the manual, Nelson says you have to connect the red speaker outputs when paralleling. Flipping that switch, however actually kills any output on the cross channel, even if the RCA's are bridged with the top switch.

If I just use an external wire then everything seems to work as expected. Any thoughts would be appreciated.

Thanks for all the help, the stereo is sounding better than ever.
 

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Official Court Jester
Joined 2003
Paid Member
pull that garbage switch out and do it correctly , with piece of wire between terminals

switch is small and prone to melting if soldered by someone with less than 1K hours of soldering experience ...... so good for line level signals only

though , by pictures ...... Gremlins are in action , if there is no signal out if you engage that output switch

btw. invest some time in sorting that wiring - shorter, thinner, fatter and neater ..... if nothing else- matter of principle
 
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Now that both F4s are singing, I thought I'd post my corrected parts lists... As before, happy to send the excel document if anyone wants it.

Thanks again everyone. I love this site/community.

May I ask why you used Carbon Film 10K for R6 and R7? Is it because R6 and R7 directly in signal path?

One more thing, I noticed you used RN60 for metal film. Do all of them fit well on the PCB? RN60 is quite long and fat. Thanks.

~Kecap
 
May I ask why you used Carbon Film 10K for R6 and R7? Is it because R6 and R7 directly in signal path?

One more thing, I noticed you used RN60 for metal film. Do all of them fit well on the PCB? RN60 is quite long and fat. Thanks.

~Kecap

The cheaper carbon films were used for LED resistors. I think I chose them because I copied someone else's purchase. If I were to reorder, I'd just buy extra RN60s and use them there. As for the choice of RN60, I chose them because I had trouble finding RN55s and wanted Dale/Vishay resistors... just got forced into that size by mouser/digikey.

Here's a look at what a populated board is like. Everything there is RN60.
 

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The cheaper carbon films were used for LED resistors. I think I chose them because I copied someone else's purchase. If I were to reorder, I'd just buy extra RN60s and use them there. As for the choice of RN60, I chose them because I had trouble finding RN55s and wanted Dale/Vishay resistors... just got forced into that size by mouser/digikey.

Here's a look at what a populated board is like. Everything there is RN60.

I see, I made a wrong assumption then. It's a hassle to stock CF just for those LED. Thanks for the picture. Those RN60 looks like little sausage squeezed together.

~Kecap