mosfet opinion?

tadiam · 29th March 2007, 12:17 PM

Diy opinion of this mosfet amplifier......

http://www.pcpaudio.com/pcpfiles/pro.../Schematic.pdf

tomahauk · 29th March 2007, 05:32 PM

looking quite good ;]

Tube_Dude · 29th March 2007, 06:00 PM

Quote:

Originally posted by tadiam
Diy opinion of this mosfet amplifier......

Hi tadiam

If you connect R 17 (22K) to ground instead the negative rail , you get much more PSRR...

tadiam · 29th March 2007, 08:52 PM

thanks tube dude

tadiam · 29th March 2007, 08:56 PM

when up all volume have an motor boating in tha bass and one fet are more hot (no modification original circuit)

CBS240 · 29th March 2007, 09:16 PM

Do you think Q9 is saturating and causing the bias of Q5 to change? Maybe a base resistor on Q9 would help this.

davidallancole · 29th March 2007, 09:30 PM

Is R17 even required?

Tube_Dude · 29th March 2007, 09:37 PM

Quote:

Originally posted by davidallancole
Is R17 even required?

No!

Without R17 the distortion will be lower.

But some people think that lower open loop gain is better...

Another tip , use two 1N4148 diodes as voltage reference for the CCS of the LTP, a Zenner is a very noisy reference...

jaycee · 30th March 2007, 01:17 AM

I'd say R17 is a silly idea...

Why bother with the diode in the VBE multiplier... the BD139 on the heatsink alone will be plenty. Also, don't wire the bias pot like that - an open circuit wiper will spell disaster.

I agree about the zener in the CCS, although I would use an LED (better temperature stability). 1K in the base of Q9 will also help prevent saturation in that transistor killing the CCS.

Ipanema · 30th March 2007, 02:02 AM

For better thermal tracking and stability, you can replace BD139 with a Hexfet.

29th March 2007, 12:17 PM	#1
tadiam diyAudio Member Join Date: Mar 2007	mosfet opinion? Diy opinion of this mosfet amplifier...... http://www.pcpaudio.com/pcpfiles/pro.../Schematic.pdf __________________ audio

29th March 2007, 08:52 PM	#4
tadiam diyAudio Member Join Date: Mar 2007	ok thanks tube dude __________________ audio

29th March 2007, 08:56 PM	#5
tadiam diyAudio Member Join Date: Mar 2007	when up all volume have an motor boating in tha bass and one fet are more hot (no modification original circuit) __________________ audio

29th March 2007, 09:16 PM	#6
CBS240 diyAudio Member Join Date: Aug 2005 Location: K-town	Do you think Q9 is saturating and causing the bias of Q5 to change? Maybe a base resistor on Q9 would help this. __________________ All the trouble I've ever been in started out as fun......

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29th March 2007, 05:32 PM	#2
tomahauk diyAudio Member Join Date: Dec 2005 Location: Ruda Œl¹ska // Poland	looking quite good ;]

29th March 2007, 09:30 PM	#7
davidallancole diyAudio Member Join Date: Nov 2005	Is R17 even required?

30th March 2007, 01:17 AM	#9
jaycee diyAudio Member Join Date: Apr 2004 Location: Norwich, UK	I'd say R17 is a silly idea... Why bother with the diode in the VBE multiplier... the BD139 on the heatsink alone will be plenty. Also, don't wire the bias pot like that - an open circuit wiper will spell disaster. I agree about the zener in the CCS, although I would use an LED (better temperature stability). 1K in the base of Q9 will also help prevent saturation in that transistor killing the CCS.

30th March 2007, 02:02 AM	#10
Ipanema diyAudio Member Join Date: Jun 2004 Location: KL	For better thermal tracking and stability, you can replace BD139 with a Hexfet.

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