Differential stage

brandes.cm · 27th February 2010, 06:45 PM

Working on a Fender guitar amp, the output stages are essentially the same RF amps. I show two red circles on the schematic(collector of Q8, and Q11), I assume the signal at those two points would be the 1Khz input signal pulsing the rail voltage. I see no sign of the 1Khz signal. The transistors seem to read ok. Is there an easy way to use DC rather than AC signal to trouble shoot this circuit?

thanks,
cory

Perry Babin · 27th February 2010, 07:04 PM

There's generally very little signal at those points unless the amp is driven to hard clipping. In what way is the amp malfunctioning?

brandes.cm · 27th February 2010, 08:09 PM

I have no output from it. It functioned at one point though. The output fets measure fine, no DC on it. I lifted the D20 and D10 thinking those are protection circuits, no help. Maybe I need to focus on the lower left hand side, muting pin.

27th February 2010, 07:04 PM	#2
Perry Babin diyAudio Member Join Date: Nov 2003 Location: Louisiana	There's generally very little signal at those points unless the amp is driven to hard clipping. In what way is the amp malfunctioning? __________________ Links >> Basic Car Audio Amp Repair --- Basic Car Audio Electronics --- Basic Transistor Testing --- Basic Switching Power Supply Design --- Basic Computer Skills << Links

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27th February 2010, 08:09 PM	#3
brandes.cm diyAudio Member Join Date: Sep 2009 Location: Wisconsin	I have no output from it. It functioned at one point though. The output fets measure fine, no DC on it. I lifted the D20 and D10 thinking those are protection circuits, no help. Maybe I need to focus on the lower left hand side, muting pin.

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