problem with Ray's Multi Noise and Random Gate/Trigger Gen.

[PHOBoS]

I just finished building the MFOS Multi Noise and Random Gate/Trigger
Generator and most of it seems to work correct. I did have some problems
with getting the amplitude of the initial noise generator stage high enough.
Tried several 2n3904's but I kept getting an average of only 2-3Vpp with a
6V peak. Breadboarded it with the same results so tried a BC547 and that
worked great.

White noise works, digital noise seems to be find too, roaring noise
sounds, well, roaring (and looks like a sort of triangle wave on my scope)
so no problems there.

But then I get to the grainy part which kinda works but only the first 20%
of the pot seems to be usefull, beyond that point it doesn't do anything.
(the gate ouput stays high/low). I measured the voltages on the pot going
to the inverting inputs of the opamps, and they are what I calculated they
should be. Also breadboarded it but get the same results, so I'm kinda
stuck right now. Hopefully someone is able to help me out

edit: oops, forgot to mention that I'm using a -/+ 15V PSU

[post #250]

[PHOBoS]

I've tested a bunch of transistors and found a better one which pretty much
solved it. I found a 2n3904 that was better but not quite 'loud' enough, also
tried some BC547C's which gave a very high output but settled on a BC547B.
I still have to turn the 10K trimpot almost to GND to get the full range of the
100K pot but it works

[jordroid]

I think the explanation for the lack of resolution of R20 has to do with the +/-15 volt power supply. IC1-D and IC2-C are comparators, whose threshold is determined by the voltage appearing on their inverting inputs, since your power supply rails are 6 volts farther apart it makes sense that a potentiometer referencing those rails would act differently.

You could try making R17 and R22 bigger, or make a little sub regulated +/-12 volt supply for just that pot, or any other way you can think of to reduce the range of the voltage appearing at the inverting inputs of IC1-D and IC2-C. Messing with R17 and R22 is probably the easiest thing, a sub regulated supply that eliminates the need for R17 and R22 is probably the "best" solution, but maybe overkill for a noisemaker.

regards,

jordan

[PHOBoS]

Thanks for the info

you are correct about the supply voltage/comparator but I did try it on
+/-12V and it only improved slightly so the transistor plays a part in it too.
I'm probably gonna add some 12V regulators anyway because I noticed that
it's very sensitive to noise . It does have some ferrite beads, though I
have no idea if the ones I'm using really have much of an effect. I tried
adding some 10 resistors followed by some 100uF caps, that seems to work
but it's still not enough. So I hope some regulators will do the trick.

[Snaper]

Sorry about stealing this old thread, but just finished this board, home etched.
Everything works...but have a few issues :

- ground hum on every outputs
- gate and rigger outs are not working

Used 3904 for the noise tranny, 084s and 4013.

Gate and trigger are on bananas, everything else on banana and jack aswell.

Tips?

[Snaper]

Well, hum problem solved : noise transistors emitter to ground instead of -15V.
Gate and Trigger out still not working

[wackelpeter]

Already tried boosting the noise Level? It schould be around +/-5V... Maybe exceed that Level a bit to see if it's working then...

Also ray suggests some changes in the passive filter before the comparator when it doesn'T work properly...

Had some issues too after i build this... mostly picking up noises from the power rails, which i only got solved by adding Regulators and further 100nF caps before the beads and caps of the original power Input of my module...