Frequency Divider Waveform

[J. Larry Hendry]

----- Original Message -----
> From: Mitchell Hudson <mitch at sirius.com>
> So the frequency divider is working! The amateurs have
> successfully modified a module!

Well, I guess I'll chime in here since I fall into this same catagory
"amateur that successfully modified a Blacet FD."

> I have to thank Mr. Blacet, the FD is one of the most useful
> modules I have built before the modifications.

Ditto.  I especially love the divide by 1.5 and 3.0 which is a feature I
don't currently have on anything else.

> Now that I am playing with the frequency divider I am
> curious what is happening with the wave form that is coming
> out of the FD. Is it a chord? or is it a more complex single
> tone? I am not sure how to describe what I am thinking here.
> But is the output like hitting multiple keys on the piano or is
> it like playing a single note on an instrument that has overtones?

That question comes from an interesting perspective. I've never heard it
asked that way.  When mixing the original tone with one of the square waves,
you certainly have two different tones and see the resulting wave (my
perspective).  However, when mixing the square waves, I see it differently.
Since one edge of each square wave lines up with the others at some point
(at the multiple frequencies), I look at adding of the square waves more
like your other description (single note on an instrument that has
overtones).  I say this because you can cause one frequency to partially
mask or cancel out the others.  When you examine the square waves output on
a scope (with none of the original signal mixed in) you can see this effect.

Conversely, I have a MOTM sub octave module.  Those square waves are
somewhat out of phase and do no mix the same way.  I like the diversity of
the difference between the two.

On the subject of modifications, I will throw in one and suggest another I
have not tried:

Mr. Blacet included a couple of smaller caps on the circuit board (in the
feedback loop of the mixing op-amp) to taking the edge off the square wave.
I tried larger cap sizes and found that the wave could be tamed to a
"sine-like" tone.  So, instead of leaving the jumpers on the board, I put a
rotary switch on the panel with several capacitor selections.  I can have no
filtering, all the way to sine-like.  I find this useful.  I cannot however
take credit for the idea.  The idea belongs to Ken Tkacs from the MOTM list.
Now that it is complete however, I wonder if could not have made that a
continuously variable control by putting a pot in series with my largest
value cap in that feedback loop?  Experts?  I may try this sometime.  My
other mod simply took advantage of the left over buffers for individual outs
for the divide by 1.5, 2.0 and 3.0.

If I ever build another, I plan to modify the output buffering.  As
designed, the circuit gives the square wave outputs as pulsing DC, 0 to ~15
volts positive.  This is great for sync pulses and such.  If you are using
it for AC though, it effectively injects some DC offset into your audio.  I
suppose two outputs could be provided, one through a cap to strip that off.
However, I was thinking if op amps were used on the output, that a bais
could be summed with a fixed voltage to shift the pulsing DC back to AC.  A
switch could be provided so that the pulse output could be selected to AC or
pulse DC since both are quite useful.  That's probably an overkill way to do
that.  But, it sounded like fun.  And, using the amp out would allow one to
scale the output voltage if something different than 15 V peak to peak was
desired.

Another sinple but useful function of this module is a reversing attenuator
is you need another for a patch.  Mix nothing but the original signal since
it is inverted by the module.

I enjoy this module a lot.  Although Mr. Blacet has provided a fine product
without modification, this is one that screams out "modify me" to amatuers
like me since it is not rocket science to do so.

Larry H