Double D / Fuzzy Dicer - Looking for input!

[Cyeos]

Hi all,
I'm working on a Fuzzy Dicer from the Nicolas Collins book, but am looking to make it better as a pedal.
Essentially I took part of the Double D from Runoffgroove / the Anderton Tube Sound Fuzz 4049 designs and stuck that on front of what feeds the 4093 NAND gate.
This essentially works, but I am looking for feedback, corrections, or just ideas to improve upon this design. My EE has a long ways to go...

Note there is switching to go between high rate and low rate oscillator stages.

Curious why some designs ground the extra 4049 stages, but some short them to V+? I've gone with grounding them so far.
Also curious if the J201 input/output buffers on the Double D are needed, or what they are improving.
Lastly wondering what's the difference between using 100K or 10K log pot for the volume control? Is that just for output impedance?

[PRR]

Curious why you added gain in front of the '4093. That's a Schmitt Trigger, which has a very drastic action already.

> some designs ground the extra 4049 stages, but some short them to V+?

If you leave them disconnected, CMOS inputs are "infinite" impedance and WILL make trouble by catching stray signal and static out of thin air. If you nail them high OR low they do as they are told and make no trouble. Choice of high or low is whatever is convenient, which bus is closer.

[Cyeos]

Thanks for the reply!
The idea for the gain in front of the 4093 is to make a weird oscillator setup by clipping a guitar signal enough that it looks to the CMOS like a digital square wave, and having it gate the guitar sound.
Or something like that... 

[Cyeos]

Corrected the 10uF output capacitor.

[duck_arse]

the first half of the hi/lo switch should be not necessary. joining the two gating inputs to the R12 should be fine (and will terminate those hanging inputs). and you could use a spare gate connected to the two outputs, and get some weird gatings. maybe.

[Cyeos]

Thanks!
Like this?


Actually sounds like I might have too much gain on the front, so I think I'll try going down to just two of the 4049 stages.

[anotherjim]

The 3 inverters may be doing a fair job of rolling off harmonics so the triggers see mostly fundamental pitch from the guitar. Maximum gain isn't that high - about 200?

An unselected 4093 has a floating input so I'd suggest  removing R12 and have 100k pull-down on each gate input instead, so each oscillator is "off" when deselected.

The output signal is huge at close to the full 9v peak to peak , and if you don't want it to heavily overdrive whatever it's feeding, the volume control will spend most of it's life at about 10%. So I'd pad it down with 33k or 47k resistor before the 10k pot. That way you also have some output protection should it be plugged into something it shouldn't be, and have better range on the volume control.

[duck_arse]

go with jim's suggestions over mine. but, for that extra series resistance in the output, you can add a tone control, and still come out ahead.

[Cyeos]

The 3 inverters may be doing a fair job of rolling off harmonics so the triggers see mostly fundamental pitch from the guitar. Maximum gain isn't that high - about 200?

An unselected 4093 has a floating input so I'd suggest  removing R12 and have 100k pull-down on each gate input instead, so each oscillator is "off" when deselected.


The output signal is huge at close to the full 9v peak to peak , and if you don't want it to heavily overdrive whatever it's feeding, the volume control will spend most of it's life at about 10%. So I'd pad it down with 33k or 47k resistor before the 10k pot. That way you also have some output protection should it be plugged into something it shouldn't be, and have better range on the volume control.

Thanks!
Confused what you mention about the floating inputs. Did you mean floating output? Did you mean going back to the earlier version with switching before the gates?

Yeah, the volume control sounds like a good idea : )

[Cyeos]

go with jim's suggestions over mine. but, for that extra series resistance in the output, you can add a tone control, and still come out ahead.

Yeah, tone control would be a good idea!
Let me see if I can figure out what the best arrangement to avoid floating ins/outs is first.

[Cyeos]

How about now?

[anotherjim]

Yep, R12 & R14 as you have it now make sure the gate input is connected when its HiLo switch is open. By "floating" we mean left to chance as opposed to "pulled". Without a connection to ground via the resistors the gate input could float high and the osc will keep running. It looks like it would have it's output disconnected by the other switch pole, but you might still hear it due to leakage & pickup from the wires etc.

The R13 you added should be in series with the volume pot, not in parallel, to act as a voltage dropper. 47k+10k should give a maximum output from the pot of around 1.5v peak to peak. This will fall a bit if fed into a line input of about 50k input impedance, but should still be strong enough. If it works right, you should have similar volume between the pedal on or bypassed with the volume knob at about 12 o'clock.

[Cyeos]

If I were to incorporate a 'stupidly wonderful tone control' from AMZ (http://www.muzique.com/lab/swtc.htm) based around that 47k in series, would it work out properly?
I assume I would need to switch my volume pot to 100k instead of 10k(?)

[anotherjim]

I would definitely test any tone control on a breadboard circuit first. The effect you're making is going to have a lot of high frequency content, so the original Mark Hammer SWTC idea might be best as it will always cut highs . The AMZ idea can also boost high frequency - but will you want that? Depends on what sounds you're after of course. The AMZ with suggested values cuts about half at full volume, still leaving you with a hot output level. Reducing that means increasing R2 which changes everything for the cap value and control range.

Going with the original SWTC...

If R1=1k, R2=47k tone pot, R3=10k vol pot.
Then C1=22n gives a high cut range of 127Hz to 7kHz from the tone pot.
When you cut any frequencies, it will also make it sound a bit quieter, so my original plan for cutting the maximum level might now be by too much. If so, increase the volume pot to 22k or 47k.

[Cyeos]

Tone control worked out great!

Do you think there is advantage to adding the input/output buffers as found on the Double D (of runoffgroove)?

[anotherjim]

As the description of it on ROG has it...
" The second goal was to have 1M or better input impedance. The third goal was to have a buffered output to avoid loading the inverters."
Your inverters aren't driving the output line and there's no significant load from the 4093 & 100k pull-downs, so an output buffer shouldn't be needed.
The input buffer of the DD gives it a normal high 1M input impedance to suit passive guitars. As you have straight into the inverters, the 100k input resistor is the input impedance. This will affect the tone of the signal from the guitar - reducing highs going in. This is often a good thing in circuits where the aim is to square up the guitar signal. So it might be best as is, but its something you may have to try just to settle the question!

[Cyeos]

Here's where I've ended up:
I put the output buffer on after all because I needed a connection for the 4th position on the selector switch, and I made it a bypass for the 4093 ("no dice").

[anotherjim]

Nice options. Any sound samples?
If the 4way switch clicks/pops when you change it, 1M resistor from its common SW_A to ground might help.