Pass Labs 1.2 Amplifier

[GeeVee]

Hi all

After scouring the internet, and this forum, there appears to be quite a few people that have started to build this monster amp, but unfortunately few that have completed one.

I would very much like to hear from diyaudio members, or anyone else that has completed one.

Looking forward to responses.

Kind Regards

George.

[GeeVee]

Hi all again

Looks like there's not to many in this camp.

What I was after, was to hear from members, with particular reference to what issues they had, what construction difficulties occured and generally what lessons they learnt, to stop me from making the same.

My reasoning is, that at this level, you probably dont want to make to many mistakes as failures could be costly, not to mention possibly spectacular.

I have looked at the Aleph 2.0 threads, as it would appear that several members have built this one.

At this stage, I have determined:

Power requirements,
Thermal considerations,
Protection measures,
Physical case logistics,
Soft start,
Matching of O/P devices,

I have completed the P1.7 preamp, and the X-Ono phono stage, and I am every happy with them

Now just to complete the final missing link.

Anyway, would be delighted to hear from members.

Regards

George.

[sakellogg]

i made a set, and love them.

i got 4 800?va 65v torids and unwound the secondarys for good voltage. 150kuf per block.... kinda small, but under .08v ripple @ .5A per fet.

only trouble i had was blowing a few fets....forgot to change from current to volts on my fluke.
and matching the blocks... i was anal about getting signals to match one side to the other.
i ordered 150 irfp240pbf from newark (i get a discount) and about 2 times the parts needed for just in case. but it wasnt all that bad.
i etched my own boards and made my own case.
i added rail fuses and small indacator led for the same,and a bias cir.
the bias cir just is relay controled. a standby and normal setting, controled either by manual switch or preamps 12v out. it was so while not using the amps the bias went down to keep the blocks warm but not so much power drain. both normal and standby are fine tuned with a small pot inside, with the normal side having a extra pot in series ecsesable from outside the case for jacking up the bias up to .8A per fet.
there again matching one side to another was hard. i didnt want to have to get out a meter every time i jacked up the current to make sure r&l matched.
at stock current, sinks are hot, 45-50c ish. at my normal mode .5A/fet sinks are no higher than 57c and at max current i allow with the external pot, .8A/fet sinks are no hotter than 60c-65 ish. i dont run them that hot offten or for long.

i love them. i dont use them very often due to kids, only in the winter and when im listiening for crickit farts in the recordings of lps late at night.
but ive got 3 kids, 2 under 4 so time to sit and enjoy is not often.
they get the most use when people ask what the big blocks of metal are next to the speakers, they roll their eyes then listen.....i uasualy have to ask them to leave around 2am. and then help them find audio bliss cause there bestbuy bose and sony dosent cut the cake anymore.

i hope u finish them and love them as much as i.

1 peice of advice...if i may.
build them together. IE power sopply for both so on and on..
its a big undertaking.
i did one and then the next..with a year inbetween.
cause i let other projects start.
good luck happy jamming

[Andersonix]

Originally Posted by sakellogg

the bias cir just is relay controled. a standby and normal setting, controled either by manual switch or preamps 12v out. it was so while not using the amps the bias went down to keep the blocks warm but not so much power drain.

I've been thinking of creating some kind of stand-by function as well, as I want a quick warm-up for instant bliss.
Any pics?

[Nelson Pass]

Originally Posted by sakellogg

i made a set, and love them.

Inspirational description.

[sakellogg]

Originally Posted by Andersonix

I've been thinking of creating some kind of stand-by function as well, as I want a quick warm-up for instant bliss.
Any pics?

pic of amp or relay cir?
ive got my notes and my multisim scematics if you want them. amp pic here i go....to try to post.
these are of the first block at my office without the top

IMAG0071.jpg

[sakellogg]

im going to do these 1 @ a time
hope i dont break any rules....

[sakellogg]

front

IMAG0062.jpg

[sakellogg]

rear input and selector switches
one for bal/unbal other for bias nor/stndby

IMAG0048.jpg

[Andersonix]

Thanks, sakellogg! (I guess you also get a discount on aluminum? -- Those rectangular tubes remind me of NP's BA chassis...)

I think I can imagine the bias stand-by relay circuit.