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Old 2nd July 2008, 11:19 AM   #591
lohk is offline lohk  Europe
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The 2N3820 would be the equivalent P-version.
But that is only theoretical, I do not know how good they are compatible in practice.
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Old 2nd July 2008, 11:26 AM   #592
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Thanks, Thijs, for that series of tests. I will try to make a 2N3819 version as soon as time (and outside temperature) permits.

Did you do some critical listening yet?

all the best
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Old 2nd July 2008, 11:29 AM   #593
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Quote:
Originally posted by lohk
The 2N3820 would be the equivalent P-version.
But that is only theoretical, I do not know how good they are compatible in practice.

Much higher capacitances in the 3820, but otherwise they seem fairly complementary, judging from the rudimentary datasheets I have found.
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Old 2nd July 2008, 07:32 PM   #594
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No listening tests yet... but I should defenitely do that ... the distortion character will change dramaticly when you adjust the power supply for low THD.. from allmost 100% second harmonic, to allmost 100% third harmonic....

PS
I also wondered about a 2N3819 complementary... so a bought a few and just received 50 2n3820 JFETs in my mail box today... 0.10$/piece
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Old 2nd July 2008, 07:39 PM   #595
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So ... because this Optimum Voltage, 2nd harmonic canceling, thingy that Nelson suggests works so marvelously... I got thinking...:

I have just completed a Pacific RIAA pre (with the MC pre) amplifier last month or so, and judging from my measurements, the suggested supply voltages are WAY to high.. so I hooked it up to my HP 339A (my pride and joy).. here goes:

Power supply +24Volt, as the circuit suggests:
1mV input, 400mV output, THD = 0.3% , purely 2nd harmonic

now with optimum power Supply + 13.7Volt
1mV input, 340mV output, THD = 0.0485% , purely 3rd harmonic


Yep...
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Old 2nd July 2008, 11:08 PM   #596
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Quote:
Originally posted by tschrama
So ... because this Optimum Voltage, 2nd harmonic canceling, thingy that Nelson suggests works so marvelously...

Can you draw me a picture? I'd like to see how you graph this out in order to cement, or jack-hammer, my ideas on how this is done.

I've been using the ID/VDS graph and adjusting my amp's values until the transistor's voltage/current falls on one of the graph's curves. Is this correct?

Many thanks,
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Old 3rd July 2008, 08:44 PM   #597
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Think about it as presented in ZV9. Working the load line is
something that the smarter tube guys have done for a long time.

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Old 3rd July 2008, 09:11 PM   #598
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Quote:
Originally posted by Nelson Pass
Think about it as presented in ZV9. Working the load line is
something that the smarter tube guys have done for a long time.

It's a great feeling when a newbie, like me, can learn something important.

Thanks Nelson,--this is so cool! When simming out a schematic that employs the LU1014D jfet, I've been staying on the lowest VGS curve and adjusting my voltage/amperage to match that curve.

That's what got me to wondering about the mosfets--could it be the same?

It's weird how much amperage some of the mosfets must have to stay on a VGS curve--I'm thinking IRFP044N as an example. When tracking the lowest (4.5V) curve, I have to have about 6 amps for anything over 10 volts. That's a lot of amps to add to the bias.

The big, bad situation I can't always resolve occurs when the bias wattage is around 100 watts per device! To keep the IRFP044N linear, I have to run high amperage, but low voltage... or switch to a mosfet that's more suitable.

Still, I have a bunch of these guys, so I'd better learn how to do this.
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Old 4th July 2008, 03:39 AM   #599
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Quote:
Originally posted by carpenter
That's what got me to wondering about the mosfets--could it be the same?
Not exactly, but I do have some very interesting stuff happening
there.
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Old 4th July 2008, 07:54 AM   #600
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Quote:
Originally posted by Nelson Pass


Not exactly, but I do have some very interesting stuff happening
there.

Hmmmm, I was wondering about that too this mornig... I have an original Bridge Of Zen, and I can manipulate the Voltage supply with my variac...Would like to see what happens t'night....
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