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

[Karl Ekdahl]

Maybe i'm really confused, i've rewired the circuit 3
times on a breadboard and my conclusion is this: the
circuit triggers fine applying a +9v trig at the
junction of the 10n and 10k, though while trying to
trig it from the "actual" trigger it works spordically
every now and then. As i understand it, after
fiddeling a little, the 10n cap gets a charge from the
trig that it doesn't allways gets rid of before the
next trig thus not retriggering. My current setup is
that the 555 is configured in monostable operation as
examplified in the datasheet, thus Reset is allways
tied to VCC. I have, of course, tried the whole ADSR
setup but minimized it to this to be able to locate
the error. All components have been checked (except
the caps since i don't have a supply for my cap meter
right now) and should be working fine, transistors
used are BC547B.

Karl


--- René Schmitz <uzs159 at uni-bonn.de> skrev:

> 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
> 
> 
>