[sdiy] lfo

[Jim Patchell]

    It is always tough to diagnose a problem like this remotely...but, you are
right, this is a very simple circuit...(I am looking at the ASM-1 schematic).
The most likely mistake is how you have U1A connected (the comparator).  Make
sure you have the +/- inputs of that amplifier connected as shown.  The feedback
should be from the output to the + input of the amplifier (positive feedback),
and conversely, U1B the feedback,through C1 goes from the output to the - input
of the amplifier (negative feedback).

    Also, are your power supplies connected up correctly?  For a TL082 (or
TL072), +15 to pin 8, -15 to pin 4...I know this may seem basic, but remember, I
can't see what you have built...for this circuit, power supply bypassing and
compoent layout will not be at all critical...in other words, if every thing is
connected correctly, it should work.

    There is also the posibility the op-amp is bad...pop a new one in the socket
if you can't find anything else (I hope you used a socket :-) ).

    Sorry I couldn't be of much more help...

    -Jim


TheMysticSatin wrote:

> I'm building an lfo out of electronotes that is pretty much identical to the
> asm lfo.  I've wired it up and, not to pose the stupidest point in the world
> but, it doesn't work.  I can never measure any voltage on the triangle outs
> and the square out produce all kinds of voltages based on the settings of
> the pot but none of them are useful.  occasionally i can measure oscillation
> but it is not controlled in frequency by the pot it just appears at certain
> pot settings and is not really consistent with the circuits purpose,
> occasionally it is close to supply (15v) in its amplitude.  The thing i
> can't get my head around is that this is such a simple circuit it doesn't
> seem like anything can go wrong.  The supply is bypass capacitored and all
> and geez, what else is there?  Is the distance of the cap from the op amp an
> issue?  or is there something that needs do be done that i just don't know
> about? any leads much appreciated.
> gavin