freq doubler

[Grant Richter]

You can also use this trick to provide high frequency clocks to things like
top octave chips and voice synthesizers. You can use a 4046 PLL to phase
lock an SC-01, SPO256 or top octave chip to standard VCO outputs. They then
track at one volt per octave. The PLL locked top octave circuit is what the
EML "Polybox" was about.

You can hang a 4040 in the 4046 loop and generate x2, x4, x8, etc up to as
high as you want to go. A 74HCT4046 VCO will clock up to 45 Mhz with a 5 pf
timing cap.

Just for fun I have been overriding the clock on DSP instruments like a
Yamaha CS1X (11 Mhz). If you inject an RF square wave through a 10-100pf cap
into the clock input side of the DSP, it will "swamp" the crystal frequency
and you can push the clock around. You will lose MIDI communication as the
clock is changed but loops already playing will be under voltage control.

> From: Scott Gravenhorst <music.maker at gte.net>
> Reply-To: music.maker at gte.net
> Date: Fri, 12 Jan 2001 07:20:18
> To: synth-diy at node12b53.a2000.nl
> Subject: Re: freq doubler
> 
> <PLL whoring mode>
> So I'll mention the 4046 micropower PLL, yet again.
> 
> Yes, there are disadvantages.  It is not instantaneous,
> however a proper loop filter can diminish the slewing
> time and overshoot, which are the main "problem".  I
> use this feature to my advantage as an effect.  A PLL
> used in this manner is very musically useful.  One thing
> it does very well is outputing a 50% duty cycle square
> wave, and within the lock range (which can be very
> wide) and while locked, it will output at *precisely*
> twice the frequency (or whatever ratio you like depending
> on the dividers in the loop).  It's very inexpensive and
> quite simple.  BTW, any reasonably clean waveform seems
> to drive it well.  Any of the rectangular waveforms are
> just perfect for it.
> </PLL whoring mode>
> 
> 
> 
> Toby Graves <carpet8 at mac.com> wrote:
>> 
>> Hey folks.
>> 
>> Does anybody know how to take a nice, pristine, 50% duty cycle square wave
>> and double its freq and still have a nice 50% duty cycle square wave?  I
>> know I mention this about every other month, but I swear I'll never mention
>> it again if I can get something to work.  The D word isn't out of the
>> question. "digi..."
>> 
>> toby
>> 
>> 
> 
> -- Scott Gravenhorst : Done the Edge, Now What?
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> 
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