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Old 10th June 2008, 08:48 PM   #571
Zen Mod is offline Zen Mod  Serbia
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Quote:
Originally posted by apassgear
Here we go again...

now - that's really fugly .........

dual mono with 9V Batteries
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Old 10th June 2008, 09:04 PM   #572
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Quote:
Originally posted by Manu
Description of added goodies by the master?...

Manolo
Thanks for that, Manolo


Provision for a PCB mounted cheesy vol pot.
Provision for a low pass cap at the input
Provision for a resistor to ground the case
Pads for direct connections of the batt cables to the PCB
Provision for LED connections of each channel
Provision for switches for each channel
Pads for rail voltage testing

Do I miss something?
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Old 10th June 2008, 09:19 PM   #573
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uhhhh, forgot...

Available pad also for grounding the metal case of the vol pot
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Old 10th June 2008, 09:48 PM   #574
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Old 25th June 2008, 08:55 AM   #575
Tolu is offline Tolu  Germany
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Quote:
Originally posted by apassgear
uhhhh, forgot...

Available pad also for grounding the metal case of the vol pot
when can we buy your PCBs?
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Old 25th June 2008, 07:21 PM   #576
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Quote:
Originally posted by Nelson Pass
It really helps if you have any kind of distortion analyzer
for setting this up. There is a specific bias voltage/current/
gain/load sweet spot, and the figures I gave are approximate
due to part variations.

I have just received my HP339A last week, and this gave me a perfect oppertunity to play with it....I measured the original schematic as postec by Nelson on post#2 with a few JFETS.. 1Vrms out, 1KHz, here goes:

Idss=4mA, optimum Vsupply = 7.7Volt, THD = 2.5% mostly H3, some H2

Idss=8mA, optimum Vsupply = 16.3volt, THD=0.43% , pure H3, gain=26dB

Idss=14mA, optimum Vsupply = 24.5volt, THD=0.17% pure H3, gain =28dB

Idss = 16mA, optimum Vsupply= 28.9Volt, THD=0.115% pure H3, gain =28dB

JFETs with simmilar Idss measured the same THD, gain and optimum Vsupply...

cheers,
Thijs





HP339A... nice little machine!
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Old 25th June 2008, 07:34 PM   #577
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PS

forgot to mention that Vsupply for optimum THD is pretty sensitive... using 18.3 instead of 16.3 (Idss was 8mA) doubled the THD.....mostly H2 though...
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Old 25th June 2008, 09:37 PM   #578
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Quote:
Originally posted by mpmarino
Mr Mod,

You are a devilishly nice guy

-something like this - right??
Click the image to open in full size.


that looked like a good idea, so I tried it.. sing a 11k input R and 22K FB R...gain was a more sensible 5.5dB and now we're getting some real respectable figures...
at 1.0Vrms out, THD was 0.015%, pure H3,
at 0.3Vrms out, THD was 0.0027%...

chrzz,
Thijs
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Old 26th June 2008, 02:00 AM   #579
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Quote:
Originally posted by tschrama


I have just received my HP339A last week, and this gave me a perfect oppertunity to play with it....I measured the original schematic as postec by Nelson on post#2 with a few JFETS.. 1Vrms out, 1KHz, here goes:

Idss=4mA, optimum Vsupply = 7.7Volt, THD = 2.5% mostly H3, some H2

Idss=8mA, optimum Vsupply = 16.3volt, THD=0.43% , pure H3, gain=26dB

Idss=14mA, optimum Vsupply = 24.5volt, THD=0.17% pure H3, gain =28dB

Idss = 16mA, optimum Vsupply= 28.9Volt, THD=0.115% pure H3, gain =28dB

JFETs with simmilar Idss measured the same THD, gain and optimum Vsupply...

cheers,
Thijs





HP339A... nice little machine!
I don't understand Nelson Pass said the best "Supply Voltage" is 16V
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Old 26th June 2008, 11:41 AM   #580
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I think Nelson said that the optimum Vsupply depended on the individual JEFT.. His might have been +16Volt.. I'll attach a plot so you can more or less see what you optimum Vsupply is when you know your Idss.... as a bonus the THD is predicted too....

Red = THD in %
Blue = Voltage supply/10 in Volts
Attached Images
File Type: jpg jfetboz.jpg (41.9 KB, 2388 views)
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