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Audio Virtues of JFET Transconductance Amplifiers
Audio Virtues of JFET Transconductance Amplifiers
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Old 15th May 2018, 07:43 PM   #31
jam is offline jam  United States
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Old 15th May 2018, 09:44 PM   #32
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Audio Virtues of JFET Transconductance Amplifiers
(wanna pcb , to make XA25 killer ?)

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Old 15th May 2018, 11:13 PM   #33
Nelson Pass is offline Nelson Pass  United States
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Audio Virtues of JFET Transconductance Amplifiers
Yes, Jam admires himself in the current mirror every morning....

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Old 16th May 2018, 01:00 AM   #34
jam is offline jam  United States
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Old 16th May 2018, 06:37 AM   #35
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Quote:
Originally Posted by jam View Post
Everyone seems to forget about the Early Effect...............

Eliminating the Early effect in the... (PDF Download Available)

Jam
I dont understand what can be done to eliminate early effect.
That paper does not say.
It just shows a Wilson current mirror at the end.
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Old 16th May 2018, 07:08 AM   #36
jam is offline jam  United States
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An enhanced Wilson (4 transistor goes some way to reduce the Early Effect) but this situation can be reduced further by adding helper transistors (base current compensation). This is particularity helpful if you are using a Widlar Mirror.

Adding resistors to the emitters of the upper mirrors usually helps the accuracy of the mirror.

Cascoding can also help by reducing heating of the mirror transistors.

If you are using transistors of the same lot numbers I find that beta matching is usually less important, besides you could add a trim pot to balance the mirror in a complementary circuit to zero the dc offset, but I digress.......

Jam
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Old 16th May 2018, 07:39 AM   #37
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Audio Virtues of JFET Transconductance Amplifiers
oh yeah , we know that Jam likes mirrors , current or past , whatever

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Old 16th May 2018, 10:17 AM   #38
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> If you are using transistors of the same lot numbers I find that beta matching is usually less important,

Do not agree.

I bought recently 200 each 2SC3324BL and 2SA1312BL.
Supposedly already preselected.
hfe is all over the place, and almost no N-P match.
The Pioneer Super Linear Circuit
See PDF in Post#1, also post #127, 132.

> besides you could add a trim pot to balance the mirror in a complementary circuit to zero the dc offset,

For me a must. I have not been able to do without.
But then I also do not have any NFB.

> oh yeah , we know that Jam likes mirrors , current or past , whatever




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Old 16th May 2018, 03:20 PM   #39
jam is offline jam  United States
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Hi Patrick,

I have to admit I use feedback in my circuit. I have compared the circuit I use with matched transistors and without and I don't see much difference on the AP
analyzer, maybe a slight reduction in second harmonic but not much else.

I agree that without feedback matching is much more important but if you are direct coupled without a servo you still have to trim dc offset somehow.

I find that matching the input fets I use much more important.

Nice headphone amplifier design.


Last edited by jam; 16th May 2018 at 03:49 PM.
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Old 16th May 2018, 03:33 PM   #40
jam is offline jam  United States
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Patrick,

Great circuit that Pioneer promoted (Their new new stuff is not nearly as good).

So how about taking the front end up a notch ..................... Ignore the feedback.

Jam
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