F5 power amplifier

[tinitus]

hmm, with raised power, wouldnt you need stronger source and feedback resistors ?

 

[wuffer]

Im also going to make the F5. Got pcb and some of the parts.
Have looked in this thread but im not sure how big the heatsinks should be.
Bias i think should just be standard.

I see 2 options.

modu
or something from

HeatsinkUSA

 

[Neutrality]

That looks nice! Have you noticed that psu board looks like a bomber plane?

Btw you might think about have optional off-set legs on the trimpots - most I have bought came with middle leg not in line with the rest.

Buying trimpots form farnell, they have the correct version with in line legs.

 

[tinitus]

I see 2 options.

modu

5U, 400mm

500mm heatsinks appears to be made of two each side, and not so good
400mm looks like one piece each side, and much better

 

[Neutrality]

hmm, with raised power, wouldnt you need stronger source and feedback resistors ?

Hmm, maybe?

Havent really thought about that.

 

[wuffer]

5U, 400mm

500mm heatsinks appears to be made of two each side, and not so good
400mm looks like one piece each side, and much better

Thanks.

 

[bobodioulasso]

Think I finally found a configuration I am happy with.
CRC PSU 3 x 18,000 uF - 4 x 1R0 - 4 x 18,000 uF, one for each channel

I almost win.
http://www.diyaudio.com/forums/pass-labs/121228-f5-power-amplifier-988.html#post2432118

 

[Neutrality]

I almost win.
http://www.diyaudio.com/forums/pass-labs/121228-f5-power-amplifier-988.html#post2432118

Almost.

 

[bobodioulasso]

hmm, with raised power, wouldnt you need stronger source and feedback resistors ?

Wise!
I forgot that too.

 

[Neutrality]

Hmm, should one change from fast on connector to a through-hole mounting pad instead?

Fast on is easy to work with but the most optimal solution would be to solder wires to the PSU and Amp PCB.

Regarding feedback and source resistors with higher power levels, what would a reasonable size be?

 

[Nelson Pass]

hmm, with raised power, wouldnt you need stronger source and feedback resistors ?

If you're going to be pumping continuous waves at full
power you probably will. Panasonic makes 5 watt versions
of the same resistors.

 

[Neutrality]

What resistors are we talking about exactly? The source resistors the JFETs and the 4 x feedback resistors?

 

[tinitus]

What resistors are we talking about exactly? The source resistors the JFETs and the 4 x feedback resistors?

source power outputs, from supply
and feedback to Jfets, from output

 

[Neutrality]

source power outputs, from supply
and feedback to Jfets, from output

Offcourse, dont know what I was thinking.

Hmm, hope I have room for 5 watt resistors. Better do a small redesign.

 

[bobodioulasso]

Input jfets source resistors. (feedback current to ground)
As there are three outputs, current is divided into the three source resistors.

 

[Neutrality]

The 4 100 Ohm 3 watt feedback resistors are now 5 Watt, the same goes for the 0.47 Ohm Source resistors.

 

[Neutrality]

Input jfets source resistors. (feedback current to ground)
As there are three outputs, current is divided

I dont think the JFET source resistors are a problem.

 

[bobodioulasso]

The jfet source resistors and feedback resistors form dividers. They share the same current.
Or, if you prefer, the same current flows through both.

 

[Neutrality]

The jfet source resistor and feedback resistors form a divider. They share the same current.
Or, if you prefer, the same current flows through both.

Yes, but the voltage drop across them is alot smaller than the 4 100 Ohm resistors.

 

[Neutrality]

Yes, but the voltage drop across them is alot smaller than the 4 100 Ohm resistors.

JFET source resistors, increasing them to 2 watts, would be ok I think.