[sdiy] 555-based ADSR that refuses to work with 9v

[René Schmitz]

Hi Karl and all,

Karl Ekdahl wrote:
> Hi all, i'm currently trying my luck adopting another
> René Schmitz design to 9v. The 555-based adsr2;
> http://www.uni-bonn.de/~uzs159/adsr2.png
> 
> I don't get the ADSR to work, it seems like the
> reset-pin doesn't like the non-reset VCC feed it gets
> from the transistors. It resets fine with the circuit
> given but it can't be set again unless i manually move
> the wire from Reset to VCC. Of course, i've measured
> the collector tied to Reset, and it is approx. 8.8V
> which should be more than fine as i understand it.

I suspect a wireing error, or a dead component. (hey that covers 99% of 
all problems...)
The entire part with the transistors and the 555s should be powered by 
+Ub and GND, the negative supply is only used for the OP. (And if you'd 
use a single supply type there, it could be also operated from Ub to GND.)

I've used this circuit quite a lot, infact it's my favourite ADSR 
circuit. I used different kinds of both bipolar and CMOS 555s (Philips, 
ST, Grizo-noname-brand...). They all worked. Never tried with 9V, but I 
don't see any reason why it wouldn't work.

Normally the RESET should be *LOW*, when the Gate is also low (or 
unconnected). And High, when the Gate is activated.
So maybe just one of your input transistor is bust. The reason why the 
pot-resistor-diode combination also connects to that pin, is that in the 
release-phase, where the second transistor would be turned on, this 
transistor also discharges the timing cap.

> I just thought there might be some "magic" as with the
> noise source that i had to tie to -9 instead of GND.
> Btw, could someone explain that a little closer? JH
> mentioned the reverse breakdown voltage or "zener"
> voltage, BE, but that is stated to be 6V for a
> BC547...  ??

The only place where the base might be more negative than the emitter 
would be at the input. But then there is a diode protecting it from ever 
becoming more than -0.7V.

Cheers,
  René

-- 
uzs159 at uni-bonn.de
http://www.uni-bonn.de/~uzs159