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Old 10th April 2011, 12:55 PM   #11
Jay is offline Jay  Indonesia
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Quote:
Originally Posted by bear View Post
this is not a new configuration, and doesn't seem to change anything...

_-_-bear
The JLH? It is all designers' reference.
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Old 10th April 2011, 01:38 PM   #12
jam is offline jam  United States
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lineup,

Do you not think it better to set the cascode voltage at between 10 to 15 volts?

Jam
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Old 10th April 2011, 03:10 PM   #13
jam is offline jam  United States
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lineup,

In the 100w version would the current help reduce distortion?

Jam
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Old 10th April 2011, 03:54 PM   #14
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Quote:
And I don't understand why BD139 for the input current source?
10mA and 50V

That's the reason why I have doubt. It is quite high for the difference amplifier. Thermal drift and noise could be a problem.
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Old 10th April 2011, 05:08 PM   #15
MiiB is offline MiiB  Denmark
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If you make a LED based current source the thermal balance will be better...
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Old 10th April 2011, 06:47 PM   #16
Jay is offline Jay  Indonesia
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Originally Posted by MiiB View Post
If you make a LED based current source the thermal balance will be better...
I don't believe that it has something to do with thermal tracking (linearity), but LED based current source has been long known for its good sound.
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Old 25th April 2011, 12:42 PM   #17
lineup is offline lineup  Sweden
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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
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Old 25th April 2011, 01:08 PM   #18
Dr_EM is online now Dr_EM  United Kingdom
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The 2SK/2SJ pair certainly are rare now, but maybe these could work as an alternative:

Mosfets/Modules - Lateral MOSFETs - Class D

or

ECX08N16-Z
ECX08P16-Z

These seem to be readily available laterals. Your first circuit modelled as very nice performance.
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Old 25th April 2011, 01:29 PM   #19
MiiB is offline MiiB  Denmark
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Diving the Jfet right at the limit...a 10-12V cascode would be good....
What is the reason for the bipolar driver stage....can't you just pull enough current through the mosfets to drive the laterals directly..??

M

ohh sorry didn't see you changed to IRF's....

Last edited by MiiB; 25th April 2011 at 01:34 PM.
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Old 25th April 2011, 01:31 PM   #20
ontoaba is offline ontoaba  Indonesia
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Quote:
Originally Posted by lineup View Post
The good thing is that 2nd harmonic is very dominant at all levels.
The sound is probably very MOSFETish!

Enjoy
Umm., could you explain that MOSFETish? What kind is it?

This one using cheapo MOSFETs, but this prototype is best sounded that I have, and best sounded among all amplifiers I ever tried and heard. I listen it almost all few day long (still play when I sleep) without listening fatigue. Best sound reached when driving headphones directly (most beautiful high frequency), but my motorola earpiece burned by this amp when crack input from bad connector happen. Finished in last few days.
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