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Wah Sequencer for ZV and others


 
1/14/2001 7:03 PM
R.G. on the road Wah Sequencer for ZV and others
For you, Zachary, if you're interested.  
 
 
 
I just uploaded a wah (and other effects) sequencer design to GEO. Uses three CMOS chips, and provides left-right, right-left, and random selection of one of eight wah pot settings.  
 
 
 
I did some thought about how to do the sequencer simply and easily, as we discussed below. The up/down/load counter was a natural. It occurred to me that you don't really have to blat 1MHz into a counter to get a random setting, you can load all of its bits from a much lower set of frequencies in parallel with a loadable counter. This lets you get away from the "zzzzp" you heard, as all the selector bits go directly to a new random setting at once, not through a blast of RF counting.  
 
 
 
While it's not exactly minimum-parts, three CMOS packages is pretty cost effective. I think you could marry this pretty well with the twin-t wah circuit or even with an inductor-style wah circuit by twiddling pot values. I think I'll mess with putting this on a surface-mount postage-stamp PCB when I hit the road again... tomorrow... 8-(  
 
 
 
I DC-isolated the selector switch with caps because that's the simplest way to tame switch feedthrough with these. Other techniques that you already know may work just as well.
 
1/14/2001 9:12 PM
zachary vex
your method may result in aliasing problems that will result in noticable repeating patterns, but i admit it looks like it might sound very random. i wonder about clicking problems with your approach. with the same chip count i could have four interacting frequencies (mine uses 3 too). i see mine produce patterns for a few seconds and then wizz off to some completely unexpected set of wahs... it's musically exciting, like another person is present. i wish there was a site that let one test three frequencies at once, but this one lets you test two:  
 
 
 
http://www.ceet.niu.edu/faculty/kostic/aliasing.htm  
 
 
 
the noise i heard was continuous, not momentary. it resulted from leakage due to proximity and limitations on filtering the power supply (for me, space is at a premium and i have to cut certain corners), and by raising my operating frequency to the higher level i pushed it out of the human hearing range, obviating the need for improvement. 8^) i love obviation. it always results in a lower parts count!  
 
 
 
i can visualize a way to use your circuit to steer a series of 8 3-lead pots or even two of them at once. the bilateral switching gives you this opportunity, if you use two or four of the 4051's in parallel to lift outside legs simultaneously. in fact, your circuit could be easily adapted to select 8 loops or 8 different effects at random. i know some rockstars would love that effect.  
 
 
 
thanks for the inspiration. i'm still wary of the clicking problem with those bilateral switches. but there's always a solution.  
 
 
 
zachary vex
 
1/14/2001 11:04 PM
R.G. in Austin for the moment
quote:
"your method may result in aliasing problems that will result in noticable repeating patterns, but i admit it looks like it might sound very random."
 
 
Yeah, short length repeating patterns are always a possibliity whenever you do anything but a true random noise generator or a maximum-length sequence generator. The three-generator trick will definitely have a rhythm to it. I went to over 100kHz to hide that a bit. For three more chips you could put in a sixteen bit maximum length shift register that would have 65535 states before repeating, and you could clock it with the sequencer clock, so that with 10Hz on the clock, it would only repeat every 6553 seconds, just under two hours. But that's a lot of chips.  
 
 
 
The repetition of the sequence is influenced heavily by the relative frequencies of the counters. I picked 100kHz, 150kHz and 250kHz as being 2, 3, and 5 (first three primes) times 50kHz. The sum frequencies are even higher, and the differences are still above audio, so the patterns are likely to be determined by the synchronicity of the system 0.1 to 10 Hz clock with any patterns. Could happen, but it would probably drift away in short order.  
 
 
 
quote:
"i wonder about clicking problems with your approach. "
 
 
Always a consideration. CMOS is good because it uses little current to cause ground-injection noise. Good layout will keep down capacitively-induced clock clicks.  
 
 
 
If you meant clicks from the analog multiplexer, then yes, there is the potential for that; however, again if you bias the ins and outs of the 4051 properly and feed them from impedances under 100k, it's pretty darn minimal. Maxim makes a chip that's the same pinout, but is optimized for low charge injection.  
 
 
 
For a bit more randomicity, you could use the remaining unused 40106 inverter section to run a 4 second or so oscillator that changes the timing capacitors on the "random" oscillators. That would reinforce the "changes a lot every now and then" action.  
 
 
 
quote:
"the noise i heard was continuous, not momentary. it resulted from leakage due to proximity and limitations on filtering the power supply "
 
 
Ah. Yep, that could be problem.  
 
 
 
quote:
"i can visualize a way to use your circuit to steer a series of 8 3-lead pots or even two of them at once. "
 
 
Yep. That would work just fine. I actually envisioned a setup I didn't show that uses eight pots in parallel, hot and cold lugs all bussed. The selector just picks off the wiper of interest. Works for voltage control, or the classic inductor wah circuit, any time you have a low enough impedance to drive eight pots in parallel. A second selector chip would give more freedom, as well.  
 
 
 
I've been working on a multichannel fader for quiet a while. I have a setup where the circuitry cross-fades to a new loop every so often, but it's a bit complex for the average DIY'er. I'm working on simplifying it down. The random trick works there, too, as you recognize.  
 
 
 
Of course, the real answer to all this is - use a PIC. Microchips' PIC microcontrollers would do any and all of the digital part of this nicely. Some of these things are available for under $3.00 in ones, and the programming could easily support long-sequence random, "rhythmic" random, sequence up, and sequence down. It would also directly read a speed pot for how often to change state. You might even get it into one of the 12xxx series with only eight pins.  
 
 
 
Here's a thought - use the 12xxx PIC for a digital controller, but buff off the numbers and get a rubber stamp made with "JRC4558D" on it to stamp on working units... >8->
 
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