op-amps, Poly's

[Andrew Schrock]

On Fri, 16 Oct 1998, LMVogue wrote:
> First, what should be a simple question - how do you test whether an op-amp
> is still operational, with only a multi-meter to go on?  I've got no idea.
> All this talk of Poly800s reminded my to start trying to see if I can fix
> my beast - someone suggested the op-amps could be a problem (lowdown - the
> CPU was fried, this was replaced, the next chip in line was tested, nothing
> coming out, replaced, still nothing.  I get no read-out on the LEDs, and
> someone suggested that something else blown is probably blocking the system)

I think there was a thread a while back on testing op-amps... the way
op-amps work isn't really condusive to simple testing with a multimeter.
You would need to first see a schematic and figure out what the said
op-amp is doing. Best to bone up on electronics theory. 

> Speaking of the Poly800, here's a thought - they (synth makers) went from
> analog interfaces to digital to make the thing programable, right?  Well,
> why didn't(?) anyone come up with free-wheeling knobs with readouts under
> them (eg. LEDs), with all knob-twirling leading to a programmable setting?
> ie.  kinda like the virtual analogs now, but using real analog - shouldn't
> have been very expensive, surely?  I can see why everyone's now going back
> to analog interfaces - digital are a pain in the arse, and no fun to tweak!
> I wonder if all that made sense to anyone ; )

The Waldorf pulse does this, as well as a few others. My only complaint is
that I wish it was absolute and not relative... or another route would be  
to be able to push a knob to see the current setting. (The pulse is now an
essential part of my semi-feeble studio! Fantastic box...) 

> PS hey, if you had a simple oscillator with it's envelope controlled by an
> envelope follower running off a mic, would you get a very basic vocoder
> thing?  Hook up a little keyboard to give you a bit of frequency control,
> play a melody and sing into the mic... ????

Remember, the envelope follower follows amplitude, not frequency. So the
louder you sing, the higher the frequency would be. Not quite what you
want.. although you could probably do some nifty percussive sounds. 

Andrew

| Andrew Schrock							|
| Network Programmer, Synthesizer and electronic music enthusiast	|
| aschrock at cs.brandeis.edu						|