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

[harrybissell]

now we're getting somewhere.

The 10n / 10K between the second and third transistors ???

When the second transistor (Q2) conducts, the base of transistor
three (Q3)should go low almost immediatly. Q2 might be trying
to dump the 2.2uF cap through the 220 ohm resistor at the same time...
so it might be slow if it is not slammed on.

One change I'd try for 9V is make the collector resistors like 2.2K
instead of 4.7K... and possible make the 22K base resistor in Q2 10K
instead of 22K. This will increase the base drive to Q2 and Q3

I'd also try adding a 100K (or higher) resistor at the 10n / 10K
junction to ground, to be sure that Q3 eventually turns off.

What kind of capacitor is the 10n ??? It should be something fairly
decent like a mylar, imho.  A good ceramic would probably work but
a crappy one might be trouble...

H^) harry



Karl Ekdahl wrote:
> 
> 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
> >
> >
> >