F5 power amplifier

[Babowana]

Originally posted by Nelson Pass


A concept error

It seems "open" in the mid centre
between the upper and lower half.


...

[KSTR]

Tim,

I have to correct myself, your idea is working fine (I overlooked the 1k drain R's). Also with source degen.

X'ing R3 and R4 (exchange end points on one side) does even seem to give better results, after rescaling for the same bias current (but not changing R5 etc). EDIT: no it doesn't, simming error ;-)

- Klaus

[Nelson Pass]

Originally posted by TimS

J1 is biased through R1. The offset that would be caused at Vout+ is cancelled by the equal current drawn by J2 and R2.

I think I see the Biasing error that Nelson is referring too, I should have source resistors on my mosfets to help stabilise the bias currents.

Current through one hundred

Pinched the front end bias is

Output Source matters not

[traw]

Sounds nice... guess I'm a caveman.

Yowza, watch them pots to adjust bias - definitely start with them at zero as midway juicing 1.8 volt on 0.47 (3+ amps) bringin smoke, ehhe - gotta love how tough these mosfets are.

DC offset adjustment seemed painless.

Better get back and check bias... left out the thermasistor since didn't have on hand.

Can I insert a R0 between 100k ground/signal ground and the 2 - 10 ohm resitors to ground? Connecting the the ground point for those 2 -10ohm to power supply ground. I'm getting faint ground loop noise and using traditional technique for creating pure ground at center of power cap bank...

[Variac]

Can you make a power supply with just chokes and resistors and no caps? That would be thematically correct!

[Zen Mod]

Originally posted by Variac
Can you make a power supply with just chokes and resistors and no caps? That would be thematically correct!

wakoo Mod !

ya have Niagara in backyard ?

[TimS]

Originally posted by spencer
Assume supply is +/- 24v, current through R5, R1, R2, R6 will be :

48v / 2.2k = 2.2 mA max, assume J1 and J2 is not there.

I am afraid that 48V/2.2k = 22mA

[jackinnj]

Originally posted by traw

Yowza, watch them pots to adjust bias - definitely start with them at zero as midway juicing 1.8 volt on 0.47 (3+ amps) bringin smoke, ehhe - gotta love how tough these mosfets are.

I was gonna say the same thing -- and this just from the simulation. I set the pots to 1% per click and just a small change can really affect the bias. NP makes this point quite clearly in the AX article (it arrived yesterday afternoon) so everyone is recommended to start at 0.

I had a couple of prototype boards burned (don't have the time right now to make my own.) If I were to do it again I would put the output MOSFETs further apart since this thing really cooks. A 0.6 C/W heat sink is recommended.

[traw]

Notice article suggest fairly good size of heatsinking to satisfy the c/w details. I used borderline as myself running without the therm comp thus probably not good idea, for my situation, to run it like an aleph (sizzlin).

Only listened to for about an hour late last night. Ran warm-hot but not too bad. Will check steady state over weekend.

Nice immediate and natural sound. Can tell it's as stated in article, lowest distortion one yet. Gain feels higher than 15db, or seems good bit louder than my F3 (13.5db).

[jackinnj]

Usually I use 270 degree trimpots -- in this case multiple turn pots are probably to be recommended --