F5 power amplifier

[dhole]

Originally posted by Nelson Pass


Matching P to N channel devices is not practical, but using the same
selection codes (BL, GR, V) is desirable.

I don't match P to N devices, just like types.

Thats the general idea I was getting , as it dosent mention matching in the F5 article. Looks like imight be powering up a channel later today then !
cheers
dave

[mike_diy]

Pass DIY
7/1/08

Watch this space - Pass Labs will shortly be offering PC boards for some of the DIY design projects.

First up is the DIY First Watt B1 buffered passive preamp, to be followed by the DIY First Watt F5 power amplifier.

Mr. Pass,

When can we expect B1 and F5 PC boards.

Thank you

[Nelson Pass]

You can expect a B1 as soon as the PC fab house gets them done,
probably 3-4 weeks.

I have not yet laid out the F5, and do not have an ETA.

[amp-guy]

Originally posted by jackinnj
Erno Borbely also has a pair of articles archived on his site -- which includes a JFET tester circuit.

http://www.borbelyaudio.com/adobe/ae599bor.pdf

and

http://www.borbelyaudio.com/adobe/ae699bor.pdf

Somewhere in this mess of an office I have a USB Based JFET analyzer based on the Measurement Computing data acquisition card -- it's written in VB.net

You got my interest, I have measurement computing DAC's
laying all over the place. I also have .net.
Tell me more please.

[bubba177]

got my F5 fired up today--1amp fuse, used variac, got to 115v,checked rail voltages +- 26volts-all looked good-turned the pots alternating- 1/2 turn at a time went to .25v 0 offset-all good-put in 1 1/2 sloblo fuse hooked up to speakers and preamp-played music for 1 hour-got warm -turned bias to .40v 0 offset all good-set bias to .59v o offset-did fine.i then bolted the amp all together and hooked to a different set of speakers turned it on and lost the right channel-dang!! took it apart-slightly melted the fuse but still had conductivity.put in 1a fuse and used variac--left channel okay but right has 22vdc offset p-fet has .4volt bias and n-fet has 0 and the pots don't seem to have any effect--what did i blow up?????helppppp!!!!

[Nelson Pass]

You did not specify your voltages and parts adequately for a
diagnosis, however there is a limited number of parts possibilities.

[bubba177]

i measure .4v across R11 and 0v across R12 when i have the variac at 115v. when i have the variac set at zero and start to increase to 20v the offset increases and the pots have some effect but past 20v the offset shoots up and the pots have no effect-the offset reads 22v when the variac is set to 115v--please tell me what else to measure and i'll sent back the info-thanks mark

[udailey]

Are you connecting your variac to a transformer/power supply of your F5 or just straight to the F5 circuit ?

[bubba177]

variac to the complete amp--took board off and had a look around and put back on-have the pots at minimum-turned on the variac when i got to 60-70 volts the offset was at 20v and R1 the 10 ohm resistor was smoking!!!!! that should narrow the search down-any clues to what part is defective? ( besides R1 )

[bubba177]

replaced the sk170 -didn't have any 10 ohm resistors but had a bunch of 4.7 ohm --biased up great and playing music again-in the spirit of educating the uninformed-what exactly did the faulty jfet do?