[sdiy] Sound Lab Mini Questions

[Ray Wilson]

Hi Rude

> osc 2 is still problematic. by itself, it isn't there. i've patched mine
> out, and if i give it a cv from osc 1, it sounds but very weakly. it
sounds
> like a weak copy of osc 1, but by also giving it an lfo in (long live
banana
> plugs)  i could determine that the sound was indeed osc 2 as osc1 was not
> affected by the lfo.

If you look at the output of IC6-D (pin 14 of IC6) you should see the raw
sawtooth wave
output of Oscillator 2. You should see a very narrow positive going pulse
wave (a few uSecs) at the same
frequency at pin 8 of IC6-C. If the sawtooth is there the pulse is
definitely there. If neither of them are
there then check all the components associated with Osc 2 for correct values
and good soldering. If you used
a sub for the MPF102 make sure the leads are oriented correctly.

Next look at the output of IC2-A pin 1. You should see a rectangle wave
whose width will depend on the setting
of of R85. The width should vary quite a bit as you adjust R85 and in
conjunction with the LFO switch turned on
may fade in and out as the bias at pin 2 of IC2-A becomes higher (or lower)
than the amplitude of the signal at ZZ.
By adjusting the level of the LFO and the setting of R85 you should be able
to get good PWM without the pulse
wave going away. With S15 off you should be able to get from 10% to 90%
pulse width variation using R85.
If this is not what you are seeing then look over the panel wiring to make
sure that R85 is connected on both sides to
+9V and GND through the correct value resistors.

Look at the bottom of the Sound Lab page for more trouble shooting info on
the PWM and noise circuits.

>
> it's only giving sound though when the frequency knob is sort of in the
> middle. when turned either way, it fades out almost like the pulse width
has
> gone too far. i can't get pwm to work either, but that's a later
worry..;-)

The pulse width should not vary so much as you adjust the frequency that it
disappears unless it is
adjusted to a very narrow pulse.

>
> i'm missing noise (also not a main concern) and the trigger knob doesn't
> work. vc in works, the gate input works, but i can only hear it when the
> vca's initial gain is open pretty far. it's there, but it seems to weak.

See the bottom of the Sound Lab page.

>
> any ideas on this before i start diving into the rat's nest? ;-)
>
> but even with one vco, filter, lfo and eg it's already one hell of a fun
> box!
>
> r./
>

I hope this helps

Ray