Cgs synth

Near as I can tell those all check out fine. These are the readings I
got on the meter w/common connected to ground:

Left transistor collector: 7.04 to 7.32 (freq pot low to high)
Left transistor emitter: -.64
Left transistor base: -22.6 to -.33

Right transistor collector: 5.60 to 5.80
Right transistor emitter: -.64

Center diode string: 4.86 to 5.06

So my suspicion was wrong methinks...what else might cause very little
signal to pass through the filter? Further clues:
If I switch off the power while a signal is still present, I get a good
spike of loud, clear sound through for a couple seconds as the power
fades. It's like the power supresses the output when it's on, and when
switched off allows a capacitor to briefly bleed out the correct amount
of power. Also, the res pot currently acts like a hiss control,
suggesting it is functioning, just not getting enough signal. The output
transistors test good...

Probably something very simple...again I'm new to this. Ryan, I really
appreciate your help. Little by little, I learn as I go. Thanks.


ryan williams wrote:

> the two non-output 2n2222s would be the differential pair. Those two
> transistors set the cutoff frequency. what happens if you connect a volt
> meter across the colloectors of these two transistors, then adjust the
> frequency pot. The voltage difference between the collectors (also
> across the diode string) should increase as the pot is increased.
>
> also, check the voltage at the center of the diode string. This should
> be around +6V and will only change a small amount as the cutoff
> frequency changes.
>
> check that the emitters of the 2n2222s (differential pair) are about
> -0.65V. make sure that the voltage at base of the 2n2222 on the left
> side increases a small amount as the frequency pot is increased.
>
> you can do all these tests with no audio input. These just check the
> biasing of the diode string. so, what results do you get?
>
> -ryan
>
>
>
> betweenpie wrote:
> > I have built the kit but is not yet functioning 100% - more like 10%.
> >
> > An audio signal does come through each input, with a very low output,
> > with the LP being the lowest (barely audible), BP the loudest. Freq
> > pot has no effect. Res appears to be functioning. TL071 is doing it's
> > job, there's just not much coming to it to actually amplify. I have
> > double checked all component values and orientations, tracks, etc.
> > Transistors check OK on diode tester. Note that removing the two
> > non-output 2222 transistors has no effect on sound moving through the
> > circuit, so I suspect that my problem is in that area.
> >
> > Any clues or ideas would be greatly appreciated! Thanks.
>
>
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