MOTM

I finally finished building my 320 LFO and had a great time 
experimenting with the 420!  I decided to put a scope on it to 
determine frequency and amplitude ranges.  I verified that the shape 
control has the appropriate effect on the various waveforms as shown 
in the instruction guide.  I did not verify 1V/oct-in or shape-in.  
Also, as I do not have another "tunable" sound source, I cannot 
verify sync-in.  I'm wondering if these numbers look reasonable:

freq control at min: not measured, but REAL slow (a technical term)
freq control at max: 31.25 Hz

sine output (peak-to-peak)
shape=0: -4.9V to +3.75V
shape=5: +-4.9V
shape=10: -3.75V to +4.9V

tri output is +-5V
shape has no effect

saw output
shape=0: -4.9V rising ramp
shape=5: +0.2V to +5.2V fairly triangle w/slightly rounded top
shape=10: -5V to +5.2V falling ramp w/slight rise before fall

pulse output
shape=0: -4.4VDC
shape=5: +-4.3V fairly square
shape=10: +4.4VDC

Note: to determine if I could get a higher output freq, I set the 
rate to 10, plugged pulse-out into FM-in and set the shape to 10 
(thereby sending +4.4VDC to FM-in).  The new output freq was 588Hz.

Note: I tuned the 900 so that the +- supplies are at +5.00VDC and -
5.00VDC.

Ok, so I'm a perfectionist, but I'm a bit concerned about the saw 
output when the shape control is set to 10, as the waveform is not a 
clean ramp.  Another point: the actual center of the waveform shape 
adjustment is actually just a bit right of 5.  Since there are no 
tunables in the PC board, I'm not sure what to look for, possibly a 
resistor out of spec?

If anyone has some input, that would be great.

Cheers,
George

>
> Note: I tuned the 900 so that the +- supplies are at +5.00VDC and -
> 5.00VDC.


I am hoping you mean +15 and -15V!!

>
> Ok, so I'm a perfectionist, but I'm a bit concerned about the saw
> output when the shape control is set to 10, as the waveform is not a
> clean ramp.  Another point: the actual center of the waveform shape
> adjustment is actually just a bit right of 5.  Since there are no
> tunables in the PC board, I'm not sure what to look for, possibly a
> resistor out of spec?

It's OK. You are just looking at resistor tolerances. The ramp "clean-ness"
can
be set by R78. This may need to go up or down some.

Paul S.

Whoops...yea, I meant +=15VDC.  Thanks for the info.  At some point I 
will pull R78 and measure it.

GK

--- In motm@y..., "Paul Schreiber" <synth1@a...> wrote:
> >
> > Note: I tuned the 900 so that the +- supplies are at +5.00VDC and 
-
> > 5.00VDC.
> 
> 
> I am hoping you mean +15 and -15V!!
> 
> >
> > Ok, so I'm a perfectionist, but I'm a bit concerned about the saw
> > output when the shape control is set to 10, as the waveform is 
not a
> > clean ramp.  Another point: the actual center of the waveform 
shape
> > adjustment is actually just a bit right of 5.  Since there are no
> > tunables in the PC board, I'm not sure what to look for, possibly 
a
> > resistor out of spec?
> 
> It's OK. You are just looking at resistor tolerances. The ramp 
"clean-ness"

> can
> be set by R78. This may need to go up or down some.
> 
> Paul S.