Help with an idea: CMOS inverter-based octave up/down

[earthtonesaudio]

Here's my goal: One octave up, one octave down, and straight signal.
You could call it a Monophonic Octave Generator (MOG)... basically a wannabe POG, but all analog, simple, low parts count, low-fi, fuzzy.

Here's the plan:
Using a single CMOS hex inverter chip...
-heavy lowpass filtering at the input to improve tracking
-full wave rectification for octave up
-square up the signal
-flip-flop for octave down
-independent volume controls for each of these,
-plus a level control for a non-octave sound (maybe clean, maybe fuzzy depending on what works).

Full wave rectifier is easy, just a gainstage with a series diode, then another, like this:
http://www.geocities.com/tpe123/folkurban/fuzz/octupblend.gif

Sub-octave is harder, considering the limitation of using only a couple inverters.
Here's a couple schems for RS flip-flops:
http://electronicdesign.com/Articles/Index.cfm?AD=1&ArticleID=1370
http://hammer.ampage.org/files/dodswitch.gif

...but how to convert them to trigger/toggle flip-flops, I don't know.  Maybe someone can chime in...?


I think this could be really fun.  Your thoughts?

[dschwartz]

i´ve been playing with cmos inverters lately, and i love them..
i recommend you to use LTspice to simulate your ideas, i simulated an octave doubler using  inverters, but in a very unorthodox way..

something like this:

- signal enters the circuit and splits in two, one goes to a non inverting boost stage, to, let´s say a gain of  5..
- The other part, goes to the inverter with a gain of 10 and the output mixes with the other signal output through a diode..

that way, the inverter is only boosting the negative part of the signal and yielding a positive swing.. this positive swing cancells the negative swing, and since it is double the amplitude, it turns out like a positive swing...

gosh...this is so complicated to explain,.. i hope you got it...

[earthtonesaudio]

Took me a while, but I think I get what you're saying. 

[SISKO]

Its so much easy to achieve octave doubling with nands. Plus nands gates can be used  as inverter digitally. If anyone knows if in that fashon, nands gates can be used in the linear region, ill post a schematic

[Ben N]

Cool stuff. I can't rreally help, but I am very much interested.

[R.G.]

Sub-octave is harder, considering the limitation of using only a couple inverters.
...
...but how to convert them to trigger/toggle flip-flops, I don't know.  Maybe someone can chime in...?

You need two inverters and a JFET. Look at the circuit for the bypass flipflop on every DOD ever made. You do need the JFET or the equivalent to perform the floating-switch function. Otherwise, you'll spend a lot more circuitry trying to build R-C-D clock steering networks.

[earthtonesaudio]

So something like this:
http://www.geofex.com/article_folders/cd4053/cd4053-4.gif
...But with a JFET in place of the switch?

Sounds good!  But it still seems like you'd need cross-coupled diodes on both source and drain of the JFET to avoid the need for separate supply voltages for the control circuitry.  Otherwise you could never get the thing to turn off.  Probably not just any diodes, but LEDs to get enough of a voltage drop. 

But maybe I'm missing the point entirely, since you mentioned avoiding much extra circuitry...

Thanks for the help so far!

[R.G.]

http://www.schematicheaven.com/effects/dod525_compressor_limiter.pdf
Upper right hand corner.

[earthtonesaudio]

Huh.  I guess I was overthinking it. 

[R.G.]

You could also use a CD4013 dual flipflop.

[earthtonesaudio]

Breadboarded some stuff last night, with some limited success.

Converting Tim Escobedo's "Octup Blender" to CMOS was a piece of cake.  The only big difference was I used an inverter to buffer the signal going in.  Nice effect, even using the "bad" 4049B (unbuffered) chip.  Fuzzy octave, clean straight signal.  Some good sounds available.

Getting any kind of recognizable octave down from the same chip has thus far eluded me.  I've been able to get nasty, gated, sputtery octave down, but nowhere near as good as a Blue Box.

http://www.schematicheaven.com/effects/dod525_compressor_limiter.pdf
Upper right hand corner.

That's drawn like a JFET, but it's not a JFET.  Note the numbers by the pins, giving it away as one of the P-channel MOSFETs from the same 4007 chip, as shown more clearly here:
http://hammer.ampage.org/files/dodswitch.gif

You could also use a CD4013 dual flipflop.

That's a good idea. 

[R.G.]

That's drawn like a JFET, but it's not a JFET.  Note the numbers by the pins, giving it away as one of the P-channel MOSFETs from the same 4007 chip, as shown more clearly here: http://hammer.ampage.org/files/dodswitch.gif

Yep, in that one. I believe earlier versions used a discrete JFET.

But if you can bring yourself to use a 4013, you'll get more reliable operation.

[earthtonesaudio]

Yeah, I just have to wrestle with my aesthetic vision... 

[dschwartz]

i´ve seen 555 chips as frequency dividers..maybe is worth a shot

[Ben N]

Hey, Alex, ever get anywhere with this?

Even if you don't get the whole deal that you envisioned out of the single chip, it would be a cool addition to a TSF/Red Llama/Hot Harmonics to add the octave up option with a CMOS driven Octup Blender. How'd you handle the mixer part?

[earthtonesaudio]

Hey Ben,

Yeah I got the octave blend to work well enough.  I think what I ended up doing was using 4 inverters:
First as an input buffer/splitter
Second and third exactly like the Octup Blender (same values and everything)
Fourth as a mixer taking the output from the diode mixing pot and the clean output from the input buffer/splitter.

The mixer I just wired as a summing amplifier... a big cap and 10k resistor from the output of each volume pot (I used 100k for each of these) going into an inverter with a 10k feedback resistor.  Pretty simple.


...If you do that, you'd still have 2 inverters left over for whatever.  Personally I'd stick with the "Escobedo" theme and use one of his CMOS circuits, or maybe use one inverter as the second half of his "Tripple Fuzz."