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PostPosted: Tue Oct 25, 2011 7:42 pm 
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Could someone look at my voltage readings and tell me if anything looks off?

Readings taken with a DMM referenced to ground using a regulated supply at 9.05v, with input and output grounded, all control knobs on minimum and switch in the on position.

Something wrong in the oscillator section. It only oscillates for half a second or so and won't sustain oscillation. I did substitute 2N3904s for the 5088s at Q2 and Q4.

Q1-g: 4.30v
Q1-s: 9.05v
Q1-d: 5.03v

Q2-b: 1.46v
Q2-c: 5.80v
Q2-e: 0.81v

Junction R8,R9,C3: 0.69v
Junction R11, D1: 6.10v

Q4-b: 0.64v
Q4-c: 4.30v


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PostPosted: Thu Oct 27, 2011 9:16 am 
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Before we worry about voltage readings, any info on why you subbed the 2n3904s for the 2n5088s? They are not equivalent. While they are both NPN, and can both be used as small signal amplifiers, they are not the same.

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PostPosted: Thu Oct 27, 2011 3:33 pm 
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tonedeaf wrote:
Before we worry about voltage readings, any info on why you subbed the 2n3904s for the 2n5088s? They are not equivalent. While they are both NPN, and can both be used as small signal amplifiers, they are not the same.


Laziness, really. I already had all the parts except the 5088s and one resistor value, so using the 3904s saved me having to place an order for $.80 in parts.

Since then, I've done some research on the differences between the 3904 and the 5088 and have come to the realization I think that I'm going to have to suck it up and get the right parts. The 3904 works well enough in the front part of the circuit, but the LFO section seems much less forgiving on part values.


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PostPosted: Fri Oct 28, 2011 4:57 am 
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The voltages you have for Q1 are wrong. Q1's drain should have 9V on it not the source. I'd suggest going back and make sure you have the leads of the transistors correctly identified and take another set of readings.

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