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Old 15th April 2011, 09:54 AM   #1091
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Jacco, interesting comments on the ExtremeA.
I think this amp should get more attention.
Too bad there seem to be some "support" issues (not that anyone is obliged to give such support, but still...).
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Old 15th April 2011, 09:56 AM   #1092
AndrewT is offline AndrewT  Scotland
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completely different animal.
It might work. Can you simulate with it in lieu of the 170?
There is no information on level of matching !
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Old 15th April 2011, 10:25 AM   #1093
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Quote:
Originally Posted by koldby View Post
PMBFJ620
Phily : 10mS at 10mA
K170 : Gm at 3mA, a 10mA Iddss device does over 40mS at 10mA Id.
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Old 15th April 2011, 10:29 AM   #1094
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Hi
Could you advise me how to change the thermal compensation circuit of this amplifier to use Toshiba BJTs instead of thermaltrack devices?
Any help will be very appreciated.
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Old 15th April 2011, 01:55 PM   #1095
Sheldon is offline Sheldon  United States
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Quote:
Originally Posted by AndriyOL View Post
Hi
Could you advise me how to change the thermal compensation circuit of this amplifier to use Toshiba BJTs instead of thermaltrack devices?
Any help will be very appreciated.
Look up the symasym schematic. Replace the FC-100 diode string and pot with the symasym's BD135 (or similar) and the resistive divider to its base.

SymAsym5 - Project
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Old 15th April 2011, 01:59 PM   #1096
koldby is offline koldby  Denmark
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Hmm.
Maybe too low Gm, but that wouldn┤t that just mean, that the openloop gain would be a little less, and therefor maybe the distortion figures a very small amount higher, as the feedback amount is reduced?
The cool thing about the device is that the two FETs track each other temperaturewise.
But again the drawbacks may be too servere.
Another candidate (I have in house!) could be 2sk363. Gm: typ 60 mS @ 15mA and IDss 5-30mA.
My problem is , that from the many 2sk170 I have here only very few has IDss > 9mA so I cannot match them good enough. Almost all of the 2sk363 has IDss > 9mA and the Phily dosen┤t need to be matched, so they could be selected by highest Gm.

Hmmmm....
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Old 15th April 2011, 02:02 PM   #1097
Macleod is offline Macleod  France
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This design seems great!

Didn't yet read all the topic...

Is there a place where some measurements have been done?
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Old 15th April 2011, 02:32 PM   #1098
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Quote:
Originally Posted by koldby View Post
Hmm....Hmmmm
Stack 'm.
(and read Mr Popa's remarks on parallel JFETs)
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Old 15th April 2011, 02:47 PM   #1099
koldby is offline koldby  Denmark
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Stack the PMBFJ┤s to get higher GM ?
Maybe that could be a solution, and you would get better noise figure too, wouldn┤t you?
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Old 15th April 2011, 06:16 PM   #1100
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Quote:
Originally Posted by Macleod View Post
This design seems great!

Didn't yet read all the topic...

Is there a place where some measurements have been done?
RMI-FC100, a single stage audio power amplifier
RMI-FC100, a single stage audio power amplifier
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