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555 based Tremolo

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2/2/2001 7:27 AM

555 based Tremolo

Since I had some time, I started to fool around with the 555 timer chip. Though instead of distortion I'm trying for tremolo (I may go back to the distortion again, if I could find out how to lower the threshold for (more/any) sustain.) Well as you said Steve, you get nice clicking sounds...and when the "rate" is up high a nice square-wave organ sound. What i tried was to use the voltage coming out of the 555 (set as an astable multivibrator) to bias a transistor. The funny thing is, I don't know how to bias a transistor, but i got it to work somehow. At first I was getting distortion, so that told me it wasn't in it's linear range, right? But a few tweaks and a turn of a pot and it seemed to work. So without any knowledge of how to take out the clicking, i think the 555 would work well as an LED/LDR tremolo.

A few questions though, what is the proper way to set up a transistor that can be biased (then turned off) by 3/4 supply (then 0V, even if it should still click)? Second, how would i go about biasing a transistor with an LDR? And thirdly, is it possible to ramp-up/ramp-down the voltages (using caps?) from the 555, in order to get triangle or sine-like waves from the square oscillator? (i'm guessing that if we were able to ramp up the voltages, it would work for the LED/LDR trem, but not the straight to tansitor trem.)

Thanks for everyone's input,

Krusty

2/2/2001 3:07 PM
Steve Daniels	Hi Krusty-- I have done a design for a 555-based circuit, called the Tremulous Bear, and I'm working on getting it into a magazine. Doesn't mean other people can't take a crack at this, but I will be waiting till my print article comes out before I publish anything on my site.

2/2/2001 4:57 PM
Krusty	I figuered as much when you mentioned your project a little while back, but I thought I'd go ahead and at least try it. In the process, I've learned more about the 555, which was also my intention of this excercise...now to learn more about biasing transistors. Looking forward to the Tremulous Bear with wanton anticipation....Thanks as always Steve. Krusty

2/2/2001 9:59 PM
Dev	I built a clicking tremolo with a 555 flashing LED circuit I got from a model train site. But I ran the gutar signal straight through the LDR no buffers at all, without light it all but killed the signal. I also but a pot across the LDR to pass as much of the unaffected signal as I wanted. That's how I kept it from being a square wave chopper. Still couldn't get rid of the clicks. Dev

2/2/2001 11:14 PM

So you still got clicks even though it was isolated from the 555 via led/ldr setup? With that pot, It semse to me that you would still have a square wave, though the depth wouldn't be 100%...loud --> not as loud, but still in a squarish pattern...though i guess the led/ldr's slow the reaction time so you get a curved waveform.

I'll try that soon, if you used a pot with the ldr i think you might be able to get a less "totally killed" signal...so the signal wouldn't be totally grounded out when it's at its extreme low.

Thanks Dev,

Krusty.

2/3/2001 12:24 AM

I'm still playing with it, the wierd thing is that the 555 must give off some noise because when it's on and oscillating, even when it's not remotely attached to the circuit (i unplugged the led) it still is able to send the clicks through the air.

My LDR isn't sensitive enough to go to 0 ohms resistance and thus kill the signal, and it's max is 15k. I'll have to find the other one i took out of a light-sensitive night-light. I'm just running it from live to ground.

One other query: how do the other tremolo circuits (like the Kay and pulsar) load the signal, and what is happening?

Thanks,

Krusty.

2/3/2001 3:41 AM

Steve Daniels (Small Bear Electronics)

The edge on the 555 square wave is sharp enough to have harmonics into the megahertz. Yah, as you see, it does radiate. When connected to a common power source with a modulator circuit, the switching action makes things worse. Some things I learned--painfully--if you want to keep fiddling:

1. Decouple the 555 section from other parts of the circuit.

2. You will probably also need a small cap on the output to round off the edge of the square wave.

3. You may have to physically isolate/shield the oscillator and modulator sections.

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