Jfet BOZ

[Zen Mod]

J Fet BOZ

Bwana - mA ?

10 /pch ?

which exact schematic ?



naah .......... just joking ........... I'll post little later

edit :

one Shiny for both channels ?

 

[Manu]

one Shiny for both channels ?

Are you kidding?

 

[Zen Mod]

 

[Manu]

That was fast
Thanky you very much Zen Mod.

Manu

Thats funny but I like this pre so extremely very much (despite of my loosy PSU till now) ...

 

[Zen Mod]

That was fast
Thanky you very much Zen Mod.

Manu

Thats funny but I like this pre so extremely very much (despite of my loosy PSU till now) ...

stack 6 of them (JBoozes) in cascode and feed them with Shunty

 

[apassgear]

This is my latest shot to it. Lots of added amenities and some extras.

P.S. Too big, let me see if I can reduce it

 

[Zen Mod]

This is my latest shot to it. Lots of added amenities and some extras.

P.S. Too big, let me see if I can reduce it

seems that pictures are pretty well reduced these days in Mehico ?

 

[apassgear]

Here we go again...

 

[apassgear]

If bigger is better, no way...😀

 

[Manu]

Description of added goodies by the master?...
🙂
Manolo

 

[Zen Mod]

Here we go again...

now - that's really fugly ......... 😉

dual mono with 9V Batteries 😉

 

[apassgear]

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?

 

[apassgear]

uhhhh, forgot...

Available pad also for grounding the metal case of the vol pot

 

[Manu]

 

[Tolu]

uhhhh, forgot...

Available pad also for grounding the metal case of the vol pot

when can we buy your PCBs? 😀

 

[tschrama]

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!

 

[tschrama]

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...

 

[tschrama]

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

 

[thomasfw]

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😕 😕

 

[tschrama]

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