PASS 50W single ended mosfet amp.

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pre65
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#346 Re: PASS 50W single ended mosfet amp.

Post by pre65 »

My Photobucket image of the circuit is unavailable for some reason. :(

I'll see if I can find one elsewhere.
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#347 Re: PASS 50W single ended mosfet amp.

Post by Ant »

Ta phil
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#348 Re: PASS 50W single ended mosfet amp.

Post by ed »

Hi Ant

I think this is the hockey puck circuit you're thinking about:

50w-single-baf2015-schade-enabled-50wseschade-jpg.jpg
although current flavour of the month for SE is the choke loaded source follower that Michael Rothacher is playing with. It uses standard Hammond chokes and in its present form is being used with IRFP250s but there is talk of beefing it up with hockey pucks...

check this out before the thread goes viral and it reaches the usual 500 pages:

http://www.diyaudio.com/forums/pass-lab ... -mofo.html
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#349 Re: PASS 50W single ended mosfet amp.

Post by pre65 »

Thanks Ed, that looks a lot easier to build than my Pass effort.

If anyone is getting the PCBs for this can they get me two as well ?
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#350 Re: PASS 50W single ended mosfet amp.

Post by shane »

Just thinking around something I don’t really understand. This circuit has no voltage amplification so needs a hefty voltage input to drive it. The old WAD PRE2/3 with its transformer outputs was often criticised for having far too much voltage gain. Would this be a match made in heaven?
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#351 Re: PASS 50W single ended mosfet amp.

Post by Paul Barker »

isn’t that a line level inout transformer? So no, cant ramp up the input voltage as if it were a valve amp. I dont know how these solid state things work, but must be using current amplification instead of voltage amplification to end up with power for the speakers.

im content to work with what I comprehend and leave the blind ignorant building of circuits they don't understand to others.
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#352 Re: PASS 50W single ended mosfet amp.

Post by pre65 »

Paul Barker wrote: Tue Nov 07, 2017 6:36 pm and leave the blind ignorant building of circuits they don't understand to others.
That's me. :(
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#353 Re: PASS 50W single ended mosfet amp.

Post by shane »

If I only built things I understand I’d never build anything and never learn anything.

AFAIK the pre2/3 is a valve amplification stage with a step up tx on the output.
The world looks so different after learning science. For example, trees are made of air, primarily. When they are burned, they go back to air, and in their flaming heat is released the flaming heat of the Sun which was bound in to convert air into tree.
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#354 Re: PASS 50W single ended mosfet amp.

Post by Nick »

Its a step down TX on the end of the pre2

The pass amp has all the gain it needs in the mosfet with its transconductance of around 10S (1v change on the gate == 10A change on the output),
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#355 Re: PASS 50W single ended mosfet amp.

Post by ed »

As with all Nelson’s breadcrumbs they are the genesis of a learning process. I should have been clearer and qualified the circuit with a link to the accompanying thread. All and every question regarding items not understood are usually answered in the threads by those more learned, or Nelson himself. I doubt there are very few builders who get to the end of one of these projects. or variations of the original, that do not fully understand the concepts. Of course there will be those without the interest or inclination to learn, and they may just build blindly, but I don’t think that is Nelson’s raison d’etre.

http://www.diyaudio.com/forums/pass-lab ... abled.html

end of sales pitch. I must point out I wasn't interested personally, just sticking my big nose in.
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#356 Re: PASS 50W single ended mosfet amp.

Post by Paul Barker »

shane wrote: Tue Nov 07, 2017 7:04 pm If I only built things I understand I’d never build anything and never learn anything.

AFAIK the pre2/3 is a valve amplification stage with a step up tx on the output.
No problem with people starting out not understanding.

My first attempt was a circuit with chokes and valves in and output transformers. First I found out what the components were what they did and this lead me to carry out more research as I clearly didnt understand sufficient to build the circuit.

When by asking questions reading books and asking more questions I had gathered more comprehention I started searching for components and built a valve amp.

If I wanted to build a pass amp I’d do likewise.
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#357 Re: PASS 50W single ended mosfet amp.

Post by pre65 »

Thiese amps have languished in the spare room since last used at Owston 2017, nearly forgot about them to be honest.

But after tripping over one of the power supplies earlier today, I've decided to do something with it.

I'm fed up with amps on the floor, so these are being modified to fit on my rack. On amp A I've trimmed 1.5" off the base side, so two can fit together side by side with a small gap. Just got to reorganise all the parts now to fit and have the on/off switch at the front.

Main reason is I think the Quads need a bit more oomph.

Work in progress.
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#358 Re: PASS 50W single ended mosfet amp.

Post by pre65 »

One power supply is now modified, and work on the second one has begun. :)
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#359 Re: PASS 50W single ended mosfet amp.

Post by pre65 »

Both power supplies finished, now working on the amp bits.

Because of the way the heat sinks are orientated it's got me thinking how to mount them on a shelf, the shelves are too close together at the moment. I have a plan A to investigate. :wink:

Whilst checking the wiring I found a badly soldered wire (just a loose fit :oops: ) on the input transformer, so that's sorted now. Also need to order 100 more M4 stainless nuts and 300 flat washers.
The only thing necessary for the triumph of evil is for good men to do nothing.

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#360 Re: PASS 50W single ended mosfet amp.

Post by pre65 »

I've got the B pair on test at the moment, rigged up an old speaker and a portable CD player as source.

Got the test voltage as near to the recommended 28v as I can, stable now it's warmed up.

I'll do the A pair later on if I get time.
The only thing necessary for the triumph of evil is for good men to do nothing.

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