Tube Amps / Music Electronics
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|1/12/2001 5:28 PM|
|R.G. on the road||Re: Question for Zachary|
Did you get any use from the Pseudo-random LFO stuff at GEO? That was one of the intended uses of that article.
I have no idea if that's the way you did the seek-wah, but the analog sequencer circuit at the end of the article is a two-chip way to select eight adjustable set-points for a wah, either as eight different resistor-sets or using a voltage to control a voltage-controlled wah as noted in the "Technology of the Wah" article.
From there, if you've set up the wah as voltage controlled, you can combine the first part of the article on the pseudo-random voltage generator with the eight way sampler to get the ooh-wah function.
|1/12/2001 9:39 PM|
i built the seek-wah 8-stage sequencer and started selling that original design over 3 years ago. the random generator is based on a variation of my probe rf circuit that sends short bursts of frequency-modulated rf into the clock input of the sequencer. i take it this is not the method you used. i haven't studied your pseudo-random voltage generator. my piece was commissioned by henry kaiser. he sent me a cd-r filled with samples of "ship ahoy" and other zappa songs with the effect he was attempting to achieve. i had considered making a random wah for a long time, called the "mumbler", but i decided to go with ooh-wah because i have a lot of international sales and it's an international-sounding phrase.
my first attempt at this effect on monday was built around a zener pure noise source, random s&h, but i decided that i needed more control over the emphasis on particular wah frequencies, so i went with the random channel selection instead. it is much more pleasing to the ear.
i can mod old seek-wahs with a second board and some patches and parts replacement, to do exactly the same thing as the new ooh-wah, which has a selector switch on the bottom for sequenced wah and random wah. it all fits neatly in a 1590B (nine knobs, 3 switches, 8 led's) and it draws less than 2 mA average, 6 mA with all settings on their brightest level (a non-varying setting no one would use). it is silent when bypassed. no clock leakage is observable. the wah is a current-controlled single-transistor variable twin-t filter. the unit continues to function well even with a carbon-zinc battery drained down below 7 volts. current consumption compared to the original seek-wah is reduced by more than half.
|1/12/2001 10:00 PM|
re: "ship ahoy" and other zappa songs
so did you nail that effect? I love that piece - especially when the section from disc 3 of 'Lather' blows in...
|1/13/2001 3:20 AM|
well, i can't duplicate the high-resonance sound of an arp or moog synth filter with a one-transistor wah, but the spirit of the sound is completely captured.
|1/13/2001 5:02 AM|
No, it wasn't. The sequencer is a CMOS analog selector switch that selects one of several anythings according to the selection bits. I actually had in mind driving the sequencer with a sample/hold just like you mention, but a sudden blat of running the clock at much higher frequencies would do as well. Another way is to use a short CMOS pseudorandom generator to generate the clock bits. That would get the clock down to the sequencer frequency as well, no rf needed.
Many ways to skin felines.
|1/13/2001 2:40 PM|
i've never considered that one, but i have a different approach in mind that i plan to use on a project in the future... a voltage-controlled sequencer using a bar/dot driver. i was about to start building one when i found the exact approach used at tom's synth cookbook site, and i got that sinking feeling in the pit of my stomach.
i suppose i should look at this pseudorandom generator your're talking about. is it on your site?
i found i had to run the fm bursts near 1MHz because at the reset pin on the sequencer chip the action of dividing lower fm frequencies by 8 was dropping clocking noise into the audio range, where it appeared as a zippy sweeping spittle at the output. the limit of 2MHz for cmos is quite real, by the way. up there, you can just eliminate the cap in your clock oscillator and let the thing free-run. the worst problem i've found with messing around with hf in the cmos realm is with mixing diodes. i routinely use diodes with cmos to steer instructions around and your average 1N4148 has to have a brick put on it's head to get it to drain off between clock pulses once you hit the rf range.
yeah, it's amazing how many ways you can get similar results. i tend to immerse myself in the low-current minimum-parts approach. i know i wouldn't end up designing this way if i didn't focus on that stuff so much.
|1/13/2001 4:00 PM|
|R.G. in Austin for the moment|
I've used the LM3914 in a couple of things, and yes, it does make for a great voltage controller for most things. I also saw it used in another synth module for a voltage controlled waveform or tone control selector.
There is a PR generator there, but it's not the synchronous version that you'd want for this approach. The one that's there in the LFO article is non-synchronous with anything, so you'd have to sample/hold. If you have a copy of Lancaster's CMOS Cookbook, the right one is in there. I can post a version of the most appropriate form if that would help.
Hmmm... OK, how about using three CMOS counters, each with an independent clock. All you're looking for is three uncorrelated bits, so with three bits on different clocks in the 100-200khz region, you'd get uncorrelated, and you only have to gate them for a millisecond to get another uncorrelated word.
Also, you could simply leave a high frequency counter(s) going, and periodically gate in the next sequencer word with a follow/hold latch. As long as counter was kept running fast (again, 100-200khz), the periodic gating would get you the same uncorrelated outputs.
I'm hacking on an article on what different approaches to design do to the results. Your minimum parts approach is one of the main veins of engineering design; conserves space, cost and packaging, but requires a lot of design work for elegance. Other approaches are
- design to available parts
- design for least design effort
- design for minimum cost (which may be and usually is different from design for minimum parts!)
- design for fastest time-to-market
- design for easiest manufacture
and there are others. All of them will make for a different design, even if they all do exactly the same thing on the outputs.
The *real* primo way to do a sequencer is with a PIC microcontroller. Program the $3.00 chip, and it spits out any computable sequence of ones and zeros you'd like, including pseudo random sequences of arbitrary length. All the RF is encapsulated inside the chip, you only get out the bits you need.
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