F6 Amplifier

[Zen Mod]

you need to be sure that both pots (P3 and P4) are on their minimum (or maximum - irrelevant in case when Rs is shortie)

check the gain of amp

whatever - this amp is of relatively highish output impedance , comparing to Symasym ; you can't expect same bass character from these two amps

[Tea-Bag]

Also make sure R1 is 100R, as that was a recent issue ian had.

[nicoch58]

dumping factor....play with reflex

[generg]

......make positive k2 by opening your shortcut wire on the negative side... and maybe I would make small wire directly from the sources to the caps not over the 10R pot... at least I have a better feeling to do this.... might be not necessary.

......are the SemiSouth very good matched, so we can suppose you have now k2 at the same level like k3 or even lower...

to have fun with the F6 you must learn to measure distortion....it can sound so different...!

very nice build...!

[cjkpkg]

OK,

I have my F6 finally up and running from using TeaBags boards.

Xformers are Cinemags
Output devices are IRFP240's
Unbuffered

So overall the sound is very nice and I am biased to 1A per device as of now.

Problem is REALLY bad what sounds like 60Hz hummm.

PSU is Peter Daniel's board stuffed with 22,000uF X 2 per rail and 3X panasonic 0.47 ohm parallel "R" CRC.

Initial startup is very quiet but then after about 1 minute the humm becomes overwhealming.

This PSU has been quiet in other amps - I used it in my F5 for a spell and it was very quiet.

Anything obvious I should try? Could buffering make a difference?

I tried to keep the wiring as simple as possible.

Ground scheme is IEC to chassis star. PSU to chassis star. Each board to PSU. Speaker output ground to PSU.

[Zen Mod]

fat wire from PSU gnd to F6 pcb GND
fat wire from G6 pcb to spk neg. post (NO wire from PSU to neg spk post !)
then bridge made of fat wire between two main GND points of two F6 pcbs
RCA isolated from chassis , coax or twisted pair to pcb

those mains connected NTCs are dangerous - flapping in space and non isolated ; make small pcb for them , place it with screws and extenders on bottom plate

[Marra]

Would it be ok to use 1500uf caps for C1/2 instead of the 1000uf's shown on the schematic?

[Zen Mod]

moi think that Divine Force would not be offended

[dimkasta]

cjkpkg I would also move the toroidal to the back and bring the CRC to the front. Having 220V AC wires running throughout the chassis is not such a good idea noise-wise.

[generg]

besides all what more competent ZM said.....

I would place the pcb with the Jensen xformer as much as possible the the backside, even if one SS more to the PSU xformer need some longer cables.....

look at the M2 pictures at 6moons......
Nelson placed the small xformer on the board completely on the back side, there is even a piece of Mu metal for shielding......
and on the pcb are long traces to the lonely SS direction PSU xformer...

So cables do the same, the 47R gatestopper of course directly at the gate of the lonely SS......