That is, where the guitar signal is sampled such that an amplitude representation is translated into a pulse width/time representation. Basically, pulse-width modulated guitar signal that can be demodulated with a simple low-pass filter/ AM envelope detector setup.
The tremolo part comes by putting these pulses through a comparator (or a simple single stage BJT amplifier) and modulating the upper voltage rail with a Tremolo LFO.
If anyone has heard of this, who makes it? I'm contemplating trying this for a simple volume swell effect I want to make, as this whole PWM thing does not require any typ of voltage controlled resistance, but I wanted to know if anyone had tried it or heard of it to see if it's actually a reasonable idea. THX
sounds complicated, but is an interesting idea...
never seen that before.
voltage controlled resistor
There's a R Penfold schematic which does something similar (though your idea sounds more complicated). He just uses a envelope follower to drive a VCO.
The speed of the trem is determined by the amplitude of the input signal.
The first part of what you're describing, the PWM bit, sounds like the operation of a Class-D amplifier. One of Robert Penfold's books describes an experimental class-D using a 555 timer to generate the PWM signal. He reckoned the sound quality was rather good. The tremolo bit sounds interesting, but a heck of a complicated way to modulate a guitar signal...
Quote from: Ge_WhizThe first part of what you're describing, the PWM bit, sounds like the operation of a Class-D amplifier. One of Robert Penfold's books describes an experimental class-D using a 555 timer to generate the PWM signal. He reckoned the sound quality was rather good. The tremolo bit sounds interesting, but a heck of a complicated way to modulate a guitar signal...
Out of interest, which Penfold book is it? I'd like to read that!
I find the hard part, is to get enough range in level variation, because it is difficult to get a simple PWM circuit to give really narrow pulses. Whihc is probably why you see PWM for filter control in fx, rather than for level control. Would work with say a PIC though, all the difficult stuff being done internally.
QuoteOut of interest, which Penfold book is it? I'd like to read that!
I knew someone would ask me that! You'll have to wait until I get home and check - I'll get back to you on this one.
Quote from: 'Ge_Whiz'The first part of what you're describing, the PWM bit, sounds like the operation of a Class-D amplifier. One of Robert Penfold's books describes an experimental class-D using a 555 timer to generate the PWM signal. He reckoned the sound quality was rather good. The tremolo bit sounds interesting, but a heck of a complicated way to modulate a guitar signal...
Actually, this is exactly it. This is more or less a Class D amplifier with the supply rails modulated to control the overal output power. My circuit design works quite well on PSPICE, but given the way PSPICE has treated many other circuits that I have made, I'm not so sure that the components I plan to use are adequately modeled for this application. It's really not as complicated as it seems at first thought, and I'll argue that the parts count and such is comparable to most LDR/LED tremolos based on my current PSPICE design.
The Robert Penfold book is "Electronic Projects for Experimenters", Babani BP371 (1995). He describes what can best be described as a Class-D 'demonstrator' using an op-amp and a 555, and then goes on to describe a 'true Class-D amplifier' of moderate complexity. I'd wondered if the simple 555 version might introduce some 'interesting' distortion; I got as far as designing a stripboard layout some months ago, but have yet to build it.
If you get hold of the book, the LED stroboscope is a useful circuit too.
Thanks. The interesting non-linear effects are always welcome with me.
Quote from: Ge_WhizThe Robert Penfold book is "Electronic Projects for Experimenters", Babani BP371 (1995)
Thanks G-W! I love the Babani range of books, especially all the Penfold ones - informative, cheap and all the circuits are complete modules that can be used as simple building blocks for larger circuits.
I'm pretty sure that my library has this book so I'll check it out next week (I'd ask for a photo-copy, but I wouldn't want you to get sued!!!) :D
Much as I have had my disagreements with the Babani company (see earlier post somewhere), they have done much to keep hobby electronics alive in the UK in the last couple of decades, and I wouldn't wish to harm their modest profits. On the other hand, should you find the book is no longer available, let me know... :D
Hey, maybe we should meet up some day - I'm based in the Kingston-upon-Thames area... Unless, by chance, you happen to be a big Prince fan... :wink:
Are you planning to attend the London Guitar Show on the 8th May?
Quote from: Ge_WhizHey, maybe we should meet up some day - I'm based in the Kingston-upon-Thames area... Unless, by chance, you happen to be a big Prince fan... :wink:
Are you planning to attend the London Guitar Show on the 8th May?
I'd love to meet up! I've sent you a PM.