CSPP With Vertical-Fet 2SJ18

frankln · 1st February 2009, 01:51 PM

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?

Elvee · 2nd February 2009, 07:55 AM

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.

frankln · 2nd February 2009, 07:24 PM

thank you Elvee.
can you recommend a procedure for adjusting the trimmer?

Elvee · 3rd February 2009, 07:37 AM

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.

frankln · 4th February 2009, 08:26 PM

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

Elvee · 5th February 2009, 08:43 AM

Start with VR2 at its highest resistance, and VR3 at its lowest. This will give the minimal current possible.

frankln · 5th February 2009, 10:19 PM

Quote:

Originally posted by Elvee
Start with VR2 at its highest resistance, and VR3 at its lowest. This will give the minimal current possible.

1st February 2009, 01:51 PM	#1
frankln diyAudio Member Join Date: Oct 2005	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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2nd February 2009, 07:55 AM	#2
Elvee diyAudio Member Join Date: Sep 2006	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.

2nd February 2009, 07:24 PM	#3
frankln diyAudio Member Join Date: Oct 2005	thank you Elvee. can you recommend a procedure for adjusting the trimmer?

3rd February 2009, 07:37 AM	#4
Elvee diyAudio Member Join Date: Sep 2006	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.

4th February 2009, 08:26 PM	#5
frankln diyAudio Member Join Date: Oct 2005	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

5th February 2009, 08:43 AM	#6
Elvee diyAudio Member Join Date: Sep 2006	Start with VR2 at its highest resistance, and VR3 at its lowest. This will give the minimal current possible.

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