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Old 21st October 2008, 05:40 PM   #21
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... lots of support & info for these MOSFETs in other arenas here at the Pass Labs Support Forums (diyAudio.com). But you knew that already ... ... I'll look at mine later for model/part numbers ... but I believe if memory serves I have the lower power sets.
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Old 21st October 2008, 06:36 PM   #22
PSz. is offline PSz.  United States
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I had decided not to take home anything after last years haul...
but a winning raffle ticket convinced me otherwise.

I made it home with a beautiful chassis stuffed with 6 complementary pairs per side (with 4 sets on one pcb and two sets on another). It also features a 40-0-40 trafo. I was instructed by Nelson to wire it for 240V operation giving a nominal 20-0-20, rectified to 28-0-28. Then build a nice little class a amp.

Thank You Nelson!

I am open to any suggestions on how to best utilize this wonderful stuff.

My speakers consist of two JBL 2226H woofers per side topped with JBL 2435H compression drivers on Edgar tractrix horns. These are currently driven by a mini-Aleph with regulated supplies for the horns and a Hafler XL280 drives the woofers. A Marchand XM1 splits the signal at 800 Hz.

I am fascinated by the idea of a First Watt B4 preamp driving step-up transformers into First Watt F4 amps. The B4 would replace the XM1 crossover and include boost to correct the low frequency roll off from the high efficiency woofers.

I suppose a current source amp could take care of the LF response without using EQ.

Any thoughts? What should I build?

best regards,
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Old 21st October 2008, 06:59 PM   #23
preiter is offline preiter  United States
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Looking in the chassis I am curious as to where people are going to mount the input stage and power supply. Everything else fits in there so nicely, but I can't figure out where the original design for these amps would have placed those boards.
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Old 21st October 2008, 07:22 PM   #24
gl is offline gl  United States
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One of the really cool things about those chassis is that they all came equipped with top notch Vampire RCA input connectors and output binding posts, and what looked like Neutrik XLR's, plus fuse posts and AC inlets - all brand new!

I think someone needs to calculate the number of square inches of heatsink area and make an estimate of how much heat can be dissipated. That will dictate how much power can be expected from the output section. Maybe Nelson has that info.

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Old 21st October 2008, 08:37 PM   #25
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Without having taken a side panel with the board and mosfets off,
I haven't figured out where you would solder in the driver and output
connections, but I would be inclined to mount perfboard/pcbs on the
rear surface with standoffs up far enough to be away from the AC
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Old 22nd October 2008, 12:18 AM   #26
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So I'm starting this thread to get a couple of designs together that can be put together easily. I figure that some F4 type follower systems will be the easiest, although there's no reason that we can't explore other stuff.
I've always wanted to hang some output followers on a BZLS. Maybe that will end up being one of the other things explored?

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Old 22nd October 2008, 12:53 AM   #27
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The chassis and parts were originally made to form test beds for
playing around with designs. I think it will be useful to continue
that approach.

Those concerned that the power supply voltages are too high will
find that a 240V input configuration will take care of that.

As far as front ends go, there are a lot of possibilities, but for starters
a nice follower configuration will form several interesting possibilities
for push-pull and single-ended class A designs.

Some of you are emailing me with regard to these things, but I think
it will be more useful and efficient to air questions and answers
publicly. You will be directed to this thread.

Also, I counsel patience. There are a lot of possibilities on the table,
and it will take time to work through them.

Also, a number of you out there (and you know who you are )
will be making your own contributions to this, and these will be
most welcome.

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Old 22nd October 2008, 01:12 AM   #28
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Originally posted by Nelson Pass

Also, a number of you out there (and you know who you are )
will be making your own contributions to this, and these will be
most welcome.

My contribution. . . ?
It might be becoming a quiet observer. . .


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Old 22nd October 2008, 02:32 PM   #29
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Default Burning Amps At The Ready

Hi All,

I was so disappointed that I couldn't make the festival again this year. But my mood over missing another year was lifted last night when a generous friend decided I should do something with amps 28 and 35. Now my mind is reeling.

What I know so far is that one has BJTs and the other MOSFETs. One has a transformer and one does not. No driver boards on either. I won't have time to look deeper until next week.

My thinking is that I may want to convert the BJT to MOSFET based solely on my positive experiences with MOSFET designs. Then I would set them as monoblocks though I wonder if the damping factor of 20 at 100W is low. Still need to read the F4 OM in detail though I skimmed it this morning.

I've got loads a of questions and plan to be patient and see what appears on this thread. Any specific guidance would be greatly appreciated.

Nelson, your generosity is staggering. Thank you.

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Old 22nd October 2008, 02:59 PM   #30
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Geez, next thing you know the big guy will come over to your kitchen table.
It doesn't count how one deals with winning, but how to handle a loss (© DjT)
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