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JFET input, MOSFET VAS, LATERAL output = Perfect!!
JFET input, MOSFET VAS, LATERAL output = Perfect!!
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Old 17th October 2015, 10:42 AM   #2371
horizonrays is offline horizonrays  India
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Join Date: May 2010
Quote:
Originally Posted by lineup View Post
Here a new take on JFET input, MOSFET vas and MOSFET output.
It does 48 Watt RMS before clipping in Class AB (bias is 200mA).

The only bipolar are the drivers: 2SC2911/2SA1209
I use them drivers to get 12 mA onto gates of IRFP240.

Power supply are trafos 2x24 VAC, 200VA for +/-35 Volt rails.
One trafo for each channel.

To setup you need to seek a resistance R8 that give ~5 mA through your JFET 2SK170BL at 35 Volt
Then chose feedback resistor R9 for gain like x20
After this you can adjust R1 (632 Ohm) for zero at output.

Then adjust R4 (4.95 kOhm) for 200 mA in the output devices.

Performance.
THD at 1 kHz is low.
0.0008% at 1 Watt
0.0060% at 42 Watt

The good thing is that 2nd harmonic is very dominant at all levels.
The sound is probably very MOSFETish!

Enjoy
would like to know the name of simulation software which you have used to create this schematic .
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Old 17th October 2015, 10:57 AM   #2372
kees52 is offline kees52  Netherlands
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Location: Sprang-capelle Holland.
Quote:
Originally Posted by horizonrays View Post
do you have any idea about which simulation software has been used ?
I did use multisim.
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Old 25th November 2015, 04:26 PM   #2373
lgqliu is offline lgqliu  China
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Location: chengde
Quote:
Originally Posted by lgqliu View Post
IH5020-SRPP
IRF610
2SK1058/2SJ162
Attachment 508714

Attachment 508715

Attachment 508716
JFET input, MOSFET VAS, LATERAL output = Perfect!!-jpg
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Old 25th November 2015, 04:30 PM   #2374
lgqliu is offline lgqliu  China
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Join Date: Feb 2005
Location: chengde
Crude heard about, because time is short, may not be accurate, the first impression is good:
****Basic circuit is single-ended tube amp sound at the end, Naiting not noisy people, the density of the sound is good, small volume under can still have a good performance, but better than the kind of advanced single-ended tube amp tube amp just does not unique "Empty inspiration." More balanced tri-band, low frequency control better, voluminous music appears, musical interpretation of the relatively clear, high-frequency a little dance movement, seems sound and energetic.
****Because the circuit is not yet fully open burning, high-frequency slightly rough, loose bass are somewhat less degree. In our listening more than one hour, the feeling evident in the positive development of the low-frequency loose gradually improved, high-frequency gradually delicate up, but have not heard enough, it was the machine he hold back.
****In addition the machine a little quiescent current, the source resistance of the output tube using a 0.33 ohm, then forget the quiescent current test, but feel quiescent current should be less than 120MA. Then drive 4 ohm speakers, working more than one hour small volume, there is little cooler temperature, it seems have heard for some time, we have to adjust the quiescent current.
****Coupling capacitor using the ROE 1UF green film capacitors, may require a oil capacitors in parallel polish it.
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Old 14th January 2018, 12:58 PM   #2375
rhythmsandy is offline rhythmsandy
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Join Date: Aug 2012
Quote:
Originally Posted by lineup View Post
This is the most perfect amplifier I have spiced.
It is simple but yet very, very good.

- JFET input with minimal offset problems.
- MOSFET VAS for speed and gain
- LATERAL output for be a light load to VAS

When CLass AB operation, 350mA bias, it shows only
THD 0.00018% at 1 Watt
And there is almost no increase of THD at 25 Watt output

Enjoy!!
---------------------------
EDIT:
For more building the final stuff and details, look for FETZILLA
in this AKSA forum: AKSA - diyAudio
Can we use this like a preamp with +/-20V with IRF610 and IRF9610 in output and a hexfet based Vbe Multiplier?
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Old 15th January 2018, 11:29 AM   #2376
kees52 is offline kees52  Netherlands
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Quote:
Originally Posted by rhythmsandy View Post
Can we use this like a preamp with +/-20V with IRF610 and IRF9610 in output and a hexfet based Vbe Multiplier?
Poor 2sk1058 mosfet, he wil glow red Ohh it is one watt I see.
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Old 18th January 2018, 03:05 AM   #2377
a1greatdane is offline a1greatdane  United Kingdom
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Location: Cornwall PL15
Default @kees52

Dear kees52,

the topology could be utilized for pre-amp driver stages.
I would recommend to use different MOSFETS to the IR's though. (I find them 'fuzzy' sounding..).
Zetex has some good parts as well for this purpose.
You basically need some with relatively low on Vgs-Voltage and they do not have to have 'outrageous' high Vds-voltage ratings for Your intended +/- 22V use.
50 Vds types will do just swell here.
More importantly - You should look for the most linear transfer curve 'ones', without to much Gate capacitance - as to not make life to difficult to the presiding stages.

Best for it
a1gd
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Old 18th January 2018, 03:13 AM   #2378
a1greatdane is offline a1greatdane  United Kingdom
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Join Date: Oct 2005
Location: Cornwall PL15
Dear all,
please look at having a gate resistor for the Vas MOSFET instead of the Band limiting C2-Capacitor. The overall stability pole is better employed at the input LTP pair.
This all best done by simulating Circuit in OL-Open loop response mode.
Just me humble '2-cents suggestions'...
Best 4 it
a1gd
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Old 10th December 2018, 10:04 AM   #2379
lineup is offline lineup  Sweden
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Quote:
Originally Posted by a1greatdane View Post
Dear all,
please look at having a gate resistor for the Vas MOSFET instead of the Band limiting C2-Capacitor. The overall stability pole is better employed at the input LTP pair.
This all best done by simulating Circuit in OL-Open loop response mode.
Just me humble '2-cents suggestions'...
Best 4 it
a1gd
Good idea having a gate stopper resistor onto MOSFET U7.
Capacitor should only be used as the final choice.
Because they are un-linear.

Better use the input capacitance in the MOSFET together with Resistor to shape the circuit behavior.
__________________
lineup
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Old 10th December 2018, 11:34 AM   #2380
kees52 is offline kees52  Netherlands
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Join Date: May 2009
Location: Sprang-capelle Holland.
Quote:
Originally Posted by a1greatdane View Post
Dear kees52,

the topology could be utilized for pre-amp driver stages.
I would recommend to use different MOSFETS to the IR's though. (I find them 'fuzzy' sounding..).
Zetex has some good parts as well for this purpose.
You basically need some with relatively low on Vgs-Voltage and they do not have to have 'outrageous' high Vds-voltage ratings for Your intended +/- 22V use.
50 Vds types will do just swell here.
More importantly - You should look for the most linear transfer curve 'ones', without to much Gate capacitance - as to not make life to difficult to the presiding stages.

Best for it
a1gd
This is a time back? I am busy with a circlotron with mosfet vas, can you guys take a look? I have low output distortion, but it does have high distortion on the vas side and even more on the long tail pair input.

Maybe I did something wrong, or can do better.

I have use the phillips bsp225 types, have 2 volts gate on voltage. I have 65 + 65 supply on prestage because it needs 16 volts above circlotron output, maybe the cascode vas has high impedance and can not drive output well.

Practice is not problem for me, but the dieper knowledge is, I never had school for electronics, I did learn on mine own, en still see new things, class D is not a problem for me.

thanks in advance.
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