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:
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.