FirstWatt F6

[JANKAR]

Hi, i have build F6 amp and i need advise how to set bias voltage. I now this ( starting with a meter across the 0.47ohm source resistor ) but which is source resistor? ( R?).
How i now when trip pot is turned all the way down before turn power on?
Thanks.

 

[ColinA123]

R2 0.47 (they are in different places so be sure.
You must start with a current limiting device (bulb tester)
As an example my pots work backwards so be ready for that!
If you have 6.2v zenners fitted start with the adjusters set about half way.
Switch on with the current limiter fitted and watch the voltage across R2, this will rise slowly as the caps charge. (If it seems to run away switch off and try adjusting the pots.)
Just look for enough voltage to start the mosfets getting warm.
Make sure that you know which way the adjuster is working.

Turn down the bias and remove the current limiter.
Start again raising the bias slowly and balancing offset.

It is all in the build guide.

 

[JANKAR]

Thank´s , working fine and mine pots work backwards too.

 

[ColinA123]

Well done, now enjoy it while letting it stabilize.
I would check again in a couple of days.

 

[Bare]

Congrats!
Note that IF? you used 1st world quality parts there is small to no need to revisit bias settings.
Good insurance no doubt... but. You should find that little has drifted

 

[JANKAR]

Just finished and i also have build B1 and they sounds great.
My speakers is Cain&Cain Abby but i also have Magnepan 1,6 but i don´t know if F6 have enough power to drive them.

 

[Zen Mod]

at least put Clone somewhere

 

[JANKAR]

at least put Clone somewhere

I have thinking about it, course these are made for my self

 

[vdi_nenna]

Let us know how the F6 drives the Magnepans.

 

[JANKAR]

Just finished and i also have build B1 and they sounds great.
My speakers is Cain&Cain Abby but i also have Magnepan 1,6 but i don´t know if F6 have enough power to drive them.

Hi i have a problem, i try to adjust bias a bit higher and something goes wrong. I can bias only less than 0,1v (left channel) right is ok.

 

[Zen Mod]

post exact schematic how you build it , and write which output transistors you're using

 

[JANKAR]

I bought PCB and transistors from DIYAUDIO STORE

 

[ColinA123]

Hi i have a problem, i try to adjust bias a bit higher and something goes wrong. I can bias only less than 0,1v (left channel) right is ok.

Sorry, but I would suggest that you have caused a short with a test probe.
You are far from the first, I did it!

Time to test the Mosfets, and hope that the Jfets are still Ok.

 

[JANKAR]

You maybe right, so how i do the test?

Sorry, but I would suggest that you have caused a short with a test probe.
You are far from the first, I did it!

Time to test the Mosfets, and hope that the Jfets are still Ok.

 

[JANKAR]

I have test mosfets and there are no connection between drain and source so i think it´s ok
I can adjust bias voltage to 0 but not over 0,1V

 

[Zen Mod]

post schematic here, I can't be sure that my search will be valid

 

[2 picoDumbs]

Measure voltage drop across each zener diode.

 

[JANKAR]

Left channel board where problem is (upper PCB)

post schematic here, I can't be sure that my search will be valid

 

[JANKAR]

Left channel board where problem is (upper PCB)

Problem solved, 1 resistor and Q1 transistor burned now it´s working

 

[JANKAR]

Let us know how the F6 drives the Magnepans.

Hi
F6 has no problem to drive Maggies and sounds great, course if you listening very loud i think F6 don´t have enough power