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Old 28th March 2011, 05:50 PM   #1
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Default Zenotron. Minimalist FET power amplifier. Improvements?

Zenotron is a power amp with only 2 JFET and 2 MOSFET.
It has lots of distortion.
Can it be improved, maybe?

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Old 28th March 2011, 06:04 PM   #2
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it can be

then is called F5

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Old 28th March 2011, 07:56 PM   #3
sajti is online now sajti  Hungary
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Quote:
Originally Posted by lineup View Post
Zenotron is a power amp with only 2 JFET and 2 MOSFET.
It has lots of distortion.
Can it be improved, maybe?
If You apply emitter follower between the 2 stages, will increase the performance. Most of the distortion resulted by the nonlinear Cdg capacitance of the output devices.

sajti

Last edited by sajti; 28th March 2011 at 08:13 PM.
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Old 28th March 2011, 08:19 PM   #4
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I have one easy mod that lower distortion much.

The feedback resistors which set gain is high 5.6k and 180 Ohm.
When make it 180 Ohm and 10 Ohm it lowers distortion
at 1 Watt from 0.775% to THD 0.245%

See schematic.
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File Type: gif zenotron_mod1.gif (4.6 KB, 731 views)
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Old 28th March 2011, 08:44 PM   #5
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Quote:
Originally Posted by lineup View Post
Zenotron is a power amp with only 2 JFET and 2 MOSFET.
It has lots of distortion.
Can it be improved, maybe?

Link: 2A & DIY
Schema:
Click the image to open in full size.
If you want to minimize the number of active components, how about two? Is it too many?
Zero Feedback Transformer Audio Power Amplifier
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Old 28th March 2011, 08:56 PM   #6
MiiB is online now MiiB  Denmark
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The Transformer audio Power amplifier...has not two but four active devices....

where especially the last High Current transformer is a limiting factor...

besides it has really nothing to zenotron...

I agree with Saity... A Stage in between the input and output would do some good....Some better drive of the mossfets would be good...

Thinking something like the current mirror in your J-fet-amplifier (mirrored to each rail and ...made from 2SA970 SC2240) with a resistor in the center to give the right bias spreading....
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Old 29th March 2011, 07:17 AM   #7
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I added two drivers 2N5551/2N5401 to the MOSFETs.
This lowered the THD wiith a factor 6.
THD 0.035 at 1 Watt.

If one is not concerned about 1% THD at 16 Watt
then my change of feedback resistors will do.
After all, there are TUBE amplifiers with such figures.
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Old 29th March 2011, 08:08 AM   #8
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Originally Posted by MiiB View Post
Thinking something like the current mirror in your J-fet-amplifier (mirrored to each rail and ...made from 2SA970 SC2240)
with a resistor in the center to give the right bias spreading....
MiiB.
I did a mirror.
It is absolute the perfect solution. Gives easier load onto JFETs.
The distortion became better with a factor of more than 10 times.
See Image.
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File Type: png zenotron_mod2.png (16.9 KB, 659 views)
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Old 29th March 2011, 08:27 AM   #9
sajti is online now sajti  Hungary
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Quote:
Originally Posted by lineup View Post
I have one easy mod that lower distortion much.

The feedback resistors which set gain is high 5.6k and 180 Ohm.
When make it 180 Ohm and 10 Ohm it lowers distortion
at 1 Watt from 0.775% to THD 0.245%

See schematic.
With this action You increase the open loop gain. So more feedback, means less THD.

Sajti
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Old 29th March 2011, 08:28 AM   #10
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Here using 2SK170BL/2SJ74BL and run mirror at 5 mA.
THD at 1 Watt is now 0.014%
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