Zenotron. Minimalist FET power amplifier. Improvements?

lineup · 28th March 2011, 05:50 PM

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:

Zen Mod · 28th March 2011, 06:04 PM

it can be

then is called F5

sajti · 08:13 PM

Quote:

Originally Posted by lineup

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

lineup · 28th March 2011, 08:19 PM

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.

Nikolas Ojala · 28th March 2011, 08:44 PM

Quote:

Originally Posted by lineup

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:

If you want to minimize the number of active components, how about two? Is it too many?
Zero Feedback Transformer Audio Power Amplifier

MiiB · 28th March 2011, 08:56 PM

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....

lineup · 29th March 2011, 07:17 AM

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.

lineup · 29th March 2011, 08:08 AM

Quote:

Originally Posted by MiiB

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.

sajti · 29th March 2011, 08:27 AM

Quote:

Originally Posted by lineup

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

lineup · 29th March 2011, 08:28 AM

Here using 2SK170BL/2SJ74BL and run mirror at 5 mA.
THD at 1 Watt is now 0.014%

28th March 2011, 05:50 PM	#1
lineup diyAudio Member Join Date: Dec 2005 Location: the north	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? Link: 2A & DIY Schema: __________________ lineup

28th March 2011, 06:04 PM	#2
Zen Mod diyAudio Member Join Date: Jan 2003 Location: ancient Batsch , behind Iron Curtain	it can be then is called F5 __________________ my Papa is smarter than your Nelson ! tnx to clean thread ; Cook Book ; PSM LS Cook Book ; Baby Diyaudio FORUM ; BAF Forum & Gallery;I'm dumb

29th March 2011, 07:17 AM	#7
lineup diyAudio Member Join Date: Dec 2005 Location: the north	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. __________________ lineup

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28th March 2011, 08:56 PM	#6
MiiB diyAudio Member Join Date: May 2005 Location: Denmark	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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