CSPP With Vertical-Fet 2SJ18 - diyAudio
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Old 1st February 2009, 01:51 PM   #1
frankln is offline frankln  Italy
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Question CSPP With Vertical-Fet 2SJ18

See this amplifier
http://www.ne.jp/asahi/evo/amp/CSPP/2SJ18.htm
somebody know the working principle of this amplifier and knows me explain?
The trimmer should be set as?
V-fet: what will be happening here?
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Old 2nd February 2009, 07:55 AM   #2
Elvee is offline Elvee  Belgium
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It is a semiconductor variant of the "circlotron". You can redraw the supplies, output stages, ground and load in a different order to understand what's going on.
VR2 & 3 set the Iq and VR1 sets the DC offset.
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Old 2nd February 2009, 07:24 PM   #3
frankln is offline frankln  Italy
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thank you Elvee.
can you recommend a procedure for adjusting the trimmer?
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Old 3rd February 2009, 07:37 AM   #4
Elvee is offline Elvee  Belgium
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Obviously, you should adjust Vr1 to get 0V at the speaker terminals.
For Vr2 and Vr3, it is less clear: they both have a similar effect, and I don't quite see the purpose of biasing the current source with a FET. Anyway, you should adjust them to get the recommended quiescent current.
Somebody else may be more inspired than I am.
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Old 4th February 2009, 08:26 PM   #5
frankln is offline frankln  Italy
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thanks for the information.I have four 2sj18 (and they were not cheap) and I would try to build this amp possible without burning them
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Old 5th February 2009, 08:43 AM   #6
Elvee is offline Elvee  Belgium
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Start with VR2 at its highest resistance, and VR3 at its lowest. This will give the minimal current possible.
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Old 5th February 2009, 10:19 PM   #7
frankln is offline frankln  Italy
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Quote:
Originally posted by Elvee
Start with VR2 at its highest resistance, and VR3 at its lowest. This will give the minimal current possible.

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