Audio Virtues of JFET Transconductance Amplifiers

Status
This old topic is closed. If you want to reopen this topic, contact a moderator using the "Report Post" button.
.

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
 

Attachments

  • lineup_syfetemi-3d_080617.png
    lineup_syfetemi-3d_080617.png
    7 KB · Views: 2,621
:cool:
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.
 

Attachments

  • nicole-duncan_lownoise-jfet-test.png
    nicole-duncan_lownoise-jfet-test.png
    7.7 KB · Views: 1,927
Basic JFET OTA - by Lineup Audio LAB

Hi.
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.

Note
.. 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 ;)
 

Attachments

  • jfet_ota_2d_public-version.png
    jfet_ota_2d_public-version.png
    19.3 KB · Views: 1,932
Nelson Pass said:

As is you have a balanced input if you want it, but yes, you
could have a balanced output that way, I believe.

:cool:

jam.
Thanks for reading my posts. And analysing/minding my circuits posted.

Of course you can balance. As much as you like ;)
Now I have my own likings.
I never use any balanced transfering of my audio signals.
And never will :cool:
It is not worth the trouble and matching.


Anyone using my circuit suggestions are of course totally free to modify.
More free than even with Nelson Pass diy amplifiers!

Because he has got his good name & amplifiers reputation to care about.
But if you modify a Pass DIY design, beyond the original,
without refering to his name as the designer of your specific circuit,
I am 100% sure Nelson never minds you take his schematics
as a a starting point for your explorations.


Lineup regards ;)
 
Nelson Pass said:
Lineup, you are a wildman :cool:

what's wrong Nelson

We have here one complementary JFET output stage
and
2 complementary JFET stages with precise mirrors

all useful in many ways and combinations
I have here only shown a few great ways to use
JFET based complementary OTA

Examine the FFT harmonics spectra
will tell some really good things ...... :cool:
 
I am still fond of OTA Operational Transconductance Amplifier.
But I am not so sure no more that the circuit in first post is useful.
A more traditional OTA is probably the way to go.

Now, I do not really know how to implement this circuit
for a simple volume control ....

This version uses Wilson mirrors. With 3 T.
I think this will do.
But I also have one version using Full Wilson mirrors - with 4 T.

Can anybody help me to arrange a simple bias volume control
in this following circuit:
 

Attachments

  • ota-2.png
    ota-2.png
    43.3 KB · Views: 463
A question for Nelson :

Suppose one builds a balanced version, but the two halves are not 100.0000000% well matched.
i.e. the output of one phase is not exactly -1.000000000x of the other.
Since both current outputs are connected to a single load, where the hell of the difference in the two currents should go to ?


Cheers,
Patrick
 
Status
This old topic is closed. If you want to reopen this topic, contact a moderator using the "Report Post" button.