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Old 26th November 2005, 09:58 PM   #1
Variac is offline Variac  United States
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Default Pass JFET Amp- I'm making one!

Yes it happened!!! I gave my friends who are in the electronics industry here in Silicon Valley a list of cool parts I expected them to get for me cheapo or free. This was precipitated by me seeing a business card from a friend with the Vishay logo!

Welll....... no luck for awhile, then I got some stuff - including these !!! YES !!a pair of Loveltech power jfets!!!

The DIY Audio equivalent of crack cocaine!

There is no way I can get more- I have already asked...

Even though I'm a mod, people that have gotten to know me online realize that I am a mod more because of my enthusism for cruelly mistreating misunderstood members than my technical chops.

So far I've made some speakers, some ambitious and some not, a few chip amps, and have been working on about the simplest amp in the universe- the Pass SOZ, for about 3 years now...Hey!, it requires a pretty sturdy setup for all those heatsinks!

1. So, I've got 2 of the these and it looks like I only need one per channel to get 15 watts?

2. Can I use one IRF P140 per channel as Q2?

3. Can I use an unregulated power supply with a pi filter putting out 50v to run it?

4. I'm planning to make the circuit on perf board, then attach it to a heatsink. Another idea is to have the power devices separate from the rest of the circuit by about 6".
Is this OK? Should the resistor r4 be kept close to Q2?

Helppp me!!! I'm sure I will make mistakes that will spare you from making the same! We can accumulate construction info here, and when your ship (full of jfets) comes in, you will be ready to go!





thanks,
Mark
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Old 26th November 2005, 10:19 PM   #2
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I think it's imperative that the first thing you do is send the jfets to me for testing. This, of course, so you know your devices are good. I'll simply reply by email to let you know if they work or not.
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Old 26th November 2005, 11:11 PM   #3
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Quote:
I think it's imperative that the first thing you do is send the jfets to me for testing. This, of course, so you know your devices are good. I'll simply reply by email to let you know if they work or not.
Naw, We have much more comprehensive semiconductor testing facilities here in Utah.. cause of Hill AFB. I suggest you send them to me for a more comprehensive run down on them than the guy from Massachucets can give you... I am also closer to you so you'll know faster. I will also reply quickly by E-mail so you know exactly whats with them and where they've gone to(or into).....

Mark
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Old 27th November 2005, 01:54 AM   #4
Variac is offline Variac  United States
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All very generous offers-typical of the selfless spirit here on DIY Audio!

If they are bad it would be a problem, but I'm counting on you guys getting the order in soon so worst case I'm ready for their arrival. I promise to give you guys a report on how utterly fantastically GREAT they sound!

Here's a blurry photo showing the devices to prove I'm not making this up.. They DO need to be clamped or something to attach them to a heatsink...


I am looking forward to answers to my questions- I have plenty more...
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Old 27th November 2005, 09:30 AM   #5
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Default Re: Pass JFET Amp- I'm making one!

Quote:
Originally posted by Variac
my enthusism for cruelly mistreating misunderstood members
Speaking about swine throwing pearls.
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Old 29th November 2005, 03:48 AM   #6
Variac is offline Variac  United States
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Well, I DON"t think I mistreat people actually- Its just the ones taking the "long vacation" that seem to express this opinion
Then again, my avatar seems to fit.


Here is an example of some heatsinks. I was planning to use one for each channel of the amp Nelson describes with one jfet and one mosfet. The power resisters will be lightbulbs so not on the heatsink.
Is that gonna be enough?
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Old 29th November 2005, 03:49 AM   #7
Variac is offline Variac  United States
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And this view
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Old 29th November 2005, 04:10 AM   #8
Raoul is offline Raoul  United States
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Its just the ones taking the "long vacation" that seem to express this opinion
What ever happened to Fred anyway?
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Old 29th November 2005, 05:48 AM   #9
Variac is offline Variac  United States
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I think he's on holiday...
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Gotta get the 50v power supply up and going....
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Old 29th November 2005, 09:59 PM   #10
Buhl is offline Buhl  Denmark
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Congrats on getting your hands on the holy crown jewels of DIY audio - I would love to offer you testing of your devices under extreme climate conditions here in the cold scandinavia, but sadly, I have no time due to my masters assignment, so you'll have to do with mark or mpmarinos offer ;-)

About the heatsink, I think you should consider cutting it in half - assuming the fins wil be vertical, thus giving you a sink that is twice your present hight - I write this, based on a suggestion I got when asking the same question as you, just for a A30 - to look at some graphs over heatsinks, that shows hight and cooling effect - about 15 centimeters the efficiency declines very, very rapidly. A heavy duty alu cabinet to mount the sinks on, will also help the amps contribution to the global warming.....
Or mabye a slow running fan, should your test run of the amp prove to hot ?


Cheers !
Buhl
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