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lineup 17th June 2008 08:12 PM

Audio Virtues of JFET Transconductance Amplifiers
2 Attachment(s)

Audio Virtues of JFET Transconductance Amps.

Now you will ask me, what are the benefits, the virtues,
of using transconductance amplifiers for Audio.

Let me say there are some very good things I have found.
And some other more normal audio amplifier characteristics, too.
I leave it to your own exploring mind to find this out ....

The V-gain in my amplifier below, is roughly R12/R9.
There are some % losses, as always is in No Global Feedback amplifier (NGFB).

Lineup :) Sweden June 2008

Nelson Pass 17th June 2008 08:28 PM

Lineup, you are a wildman :cool:

Vix 17th June 2008 09:21 PM

If you count a Zen V9 without feedback as a JFET transconductance Amplifier, then I can say that it sounds very good! :D

jam 18th June 2008 06:03 AM


Nice circuit. Did you have any stability issues with the output buffer?

Mr.Pass is right. You are a wildman.:D


lineup 18th June 2008 06:53 PM

2 Attachment(s)
hi jam
nice to see you post

here todays finding :cool: for my friends .. & who ever else ..
See attachment - for more info.


Nicole Duncan
Summer REU 07
Advising Prof. Scott Robertson

Noise in electronic circuits has origins both inside and outside the system.
External interference comes from 60 Hz wall sockets, cell phones, other experiments and many devices which transmit and collect signals.
Often, these sources of interference can be identified and eliminated from the signal by shielding.

Internal sources of noise are more difficult to eradicate and come from three main sources;
- thermal noise,
- shot noise and
- flicker noise.

Thermal noise results from the random motions of charge carriers within a material.
This intrinsically noisy property of molecules cannot be eliminated above 0K


Lineup comment:
0K = absolute zero temperature = 0 Kelvin = -273 C
... and so Nicole Duncan goes on
... etc. etc.

jam 18th June 2008 09:19 PM

2 Attachment(s)
Hi Lineup,

Have you considered this as a buffer? I was curious how it compared to your buffer.


lineup 21st June 2008 12:06 PM

Basic JFET OTA - by Lineup Audio LAB
2 Attachment(s)
Part 2.
Basic JFET OTA, Operational Transconductance Amplifier.

Very easy to build
I used 100 Ohm for all resistors, except for the Load + Cap at output.
Extremely good performance .. and harmonics spectra.
Considering the pure simplicity of this design

At gain x100, +40 dB,
you can get like 500.000 Hertz -3 dB bandwidth.
Phase angle, without any kind of compensation, is -45 degrees at same frequency!!!!
Distortion can be as low as 0.03 % .. for my first test circuit 0.029 %
Totally dominante is 2nd harmonics dist.

.. these figures are without any feedback
Which of course can be added, if you like it so.

Transistors used:

- 4 x 2SK170 JFET
- All NPN: PN2222A
- All PNP: PN2907A
.. basically common standard general transistor, all the way
Enjoy ;)

jam 21st June 2008 12:24 PM


Could you not replace Q9 and Q10 with current sources and have a true balanced circuit?

Waiting for Part 3....................:up:


electrofan 22nd June 2008 04:04 AM

couple of questions

1. in first your posted schema is load 1000 ohm or 100 ohm?
think not this amplifier can make good with 100 ohm. maybe too much load to prefer
2. what recomended n-jfet + p-jfet you use? other transistore?

thank you

Nelson Pass 23rd June 2008 07:37 PM


Originally posted by jam
Could you not replace Q9 and Q10 with current sources and have a true balanced circuit?
As is you have a balanced input if you want it, but yes, you
could have a balanced output that way, I believe.


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