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Old 22nd December 2012, 02:54 AM   #331
Mr. dB is offline Mr. dB  United States
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Quote:
Originally Posted by 6L6 View Post
Who is Spencer, and how can I contact him?
Indeed?
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Old 22nd December 2012, 03:59 AM   #332
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he's legit...
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Old 22nd December 2012, 05:02 AM   #333
jarkaa is offline jarkaa  Finland
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Originally Posted by juma View Post
BJTs as direct replacement - no way !

But if BJT is your weapon of choice, this can fit the bill (Zin is about 300k, gain about 3.5 V/V, Zout less than 300 Ohms):
Thanks Juma!, I will try this one.

I will keep hunting of those sj74:s still.

Audiosan, Who is this spencer? and how can I contact him?

I have bought a batch from ebay whih turned out to be fakes.
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Old 22nd December 2012, 05:09 AM   #334
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Originally Posted by 6L6 View Post
Who is Spencer, and how can I contact him?
he is a member on this forum
or use williams link.

Last edited by AudioSan; 22nd December 2012 at 05:15 AM.
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Old 22nd December 2012, 12:07 PM   #335
Marra is offline Marra  United Kingdom
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Spencer supplies well matched devices and gives good service with tracking number in fact some arrived this morning.Only one week from dispatch to delivered.
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Old 22nd December 2012, 12:17 PM   #336
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Spencer supplies well matched devices and gives good service with tracking number in fact some arrived this morning.Only one week from dispatch to delivered.
yes i got a package from him this morning too. a FDA-2 DAC kit.
and have earlier ordered a lot of J-fets from him.
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Old 26th December 2012, 02:13 PM   #337
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Hi!

I built the preamp from post #53 in this thread from juma.
(Now with the correct matched types of jfets)

But I can't get a stable output?
It's always going from -1100mV to 1500mV. If I adjust the 20R pot with a screwdriver, then the output value is changing faster to crazy values like 2.2V, then 0V, then -1.5V, until I put the screwdriver out of the adjusting screw from the pot.
If I blow a little air over the jfets, then everythings running out of control...

The Jfets arent fixed together yet, but very close and there is no air or wind in my room...

I have to say that input and output is open. Would it make sense to short the input (IN+GND bridge) and measure/set again or is there a mistake in my circuit?

Best Regards,
Matthias
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Old 26th December 2012, 02:35 PM   #338
Zen Mod is offline Zen Mod  Serbia
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you're having a problem , if there is no air in your room .......


pictures, pretty please ....
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Old 26th December 2012, 04:41 PM   #339
juma is offline juma  Germany
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GentryBa,
did you measure the new JFETs that you got from China?
Did you thermally couple them ?
When setting the DC offset shortcircuiting the input is a must.

BTW, please let some the air into the room, you risk suffocation ...
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Old 26th December 2012, 04:46 PM   #340
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hey zen and juma!

uuups, my bad english... sorry for that.
I think, there is some air in the room.

Sorry I have no pic in the moment... But tomorrow you will get it!

The value is changeing the whole time when its fired up.
Slowly when I do not touch it, but always from about -1100mV to +1500mV (both 12V mains are ok and stable).
Changeing the pots value doesn't show any effekt.
Waiting an half hour changed the output value a little bit to the range from -500mV to about +650mV or so....

Hmm, sometimes I hate me for those things...

@juma:

ooh, I saw your post tooo late...

ok, then I first try to shorten the input!
I didn't check the china fets, cause of christmas stress

I'll give it all a try and write back tomorrow!

THANK YOU!!!

Best Regards,
Matthias
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