[sdiy] new noisetoy design from ray wilson

[Seb Francis]

Hi Harry,

Thanks for your reply .. it wasn't so much that I was 'worried' about 
reverse biasing the transistor, but that when running this circuit on 
15V the square wave output of the inverter becomes totally 
non-symetrical - the down period is much shorter than the up period, and 
as the frequency is lowered (R11 increased) the down period does not 
lengthen and it eventually stops oscillating at all.  I assume this is 
somehow because of the reverse breakdown of the transistor as I can see 
the tops of the 'curved-triangle' signal (the inverter input / 
transistor emmitter signal) appearing at the base.

Adding a diode in series with the base does help (same effect as 
temporarily disconnecting R18 from the base) - at least the inverter 
keeps oscillating at lower frequencies, but the square wave is still 
quite non-symmetrical (not as bad as without the diode).

I don't really understand what's going on here, but I'm guessing it has 
to do with some current being able to flow from emmitter to collector 
when the transistor gets reversed biased  .. is it possible that a 
transistor will behave like this?

Anyway, for now I've resorted to running the 40106 from a 7809 regulator.

Seb (learning more about transistors every day)

Ref:

http://www.musicfromouterspace.com/analogsynth/YOUR_FIRST_SYNTH/YOUR_FIRST_SYNTH.html




harrybissell wrote:

>Run it on 15 V
>
>If you are worried about reverse bias on the tranny, add a diode in
>series with the base. Then no reverse bias current can flow.
>
>Probably no big deal anyway with the 100K resistor in series with the
>base... but if you're shy...
>
>H^) harry
>
>Seb Francis wrote:
>
>  
>
>>This is a very cool little circuit :) .. I'm just about to build a
>>version with MIDI->GATE, AR Envelope + VCA circuitry.
>>
>>.. but I want it to run from 15V supply (this is what is available), and
>>I'm a bit stuck how to modify Ray's circuit to do this - it seems that
>>if the supply voltage goes too far above 9V then Veb of the transistor
>>exceeds 6V and reverse breakdown occurs.
>>
>>I'd appreciate it if anyone can see a solution to this .. the only thing
>>I can think of is to power the 40106 from a potential divider or a
>>voltage regulator .. but maybe I'm missing a more elegant way?
>>
>>Seb
>>    
>>