Manu said: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?
Nelson Pass said: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!mpmarino said:Mr Mod,
You are a devilishly nice guy
-something like this - right??
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
I don't understand Nelson Pass said the best "Supply Voltage" is 16Vtschrama said:
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
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
Red = THD in %
Blue = Voltage supply/10 in Volts
