Oscillator issues causing me pain

[DrinkyCrow]

Hi Everyone! This is my first post here, and I hate to start by begging, but I got a problem. I've gone through my textbooks, looked online, and found nothing that will help. I'm designing a variation on the classic tremolo effect, and want to do it the old school way. Don't ask me why, I like making thing hard on myself.

I need help building a Triangle Wave generator with the following parameters:
Must use LM324 Quad Op Amp (because I only have 45 of those and nothing else close)
0-+5Vdc supply
Variable output Freq. .5-20Hz
I don't think output V range is important, I can throw another stage in to boost it to rail to rail, but rail to rail output would be nice.

Any ideas or pointers? I'm at the point of just throwing components at the circuits I've seen so far, and it's a huge stumbling block on my progress. Hey, I'm just a tech, not some kinda fancy engineer, lol, so be nice.
Anyway any help would be greatly appreciated.

[DrinkyCrow]

Woot! Finally got a clean triangle out. Wrong voltage, wrong freq., but a little more shotgunning and I got me my generator! woohoo! Couple extra stages/tweaks to adjust F range and levels, and I'll have my ramp generator to feed the pulse width modulator

[MrAl]

Hi,


How do you intend to get rail to rail output?

[DrinkyCrow]

actually, I don't need the triangle to be rail to rail, I just need to limit my comparator bias range to whatever output the triangle wave puts out (0-4Vdc, it turns out), the comparator puts out the rail to rail control signal I was going for. I just need to add in a couple of resistors, and buy myself some linear, much smaller pots, and restrict the control range to my needed specs. I'm all happy, it works now, and I know how to fix the remaining issues.

[MrAl]

Hello again,


Oh ok well you mentioned rail to rail output so i asked about that. The LM324 i think goes to within 1.5v of the Vcc rail, so that would mean 0 to 3.5v operation or thereabouts.

I guess you are all set then

[Bob Scott]

actually, I don't need the triangle to be rail to rail, I just need to limit my comparator bias range to whatever output the triangle wave puts out (0-4Vdc, it turns out), the comparator puts out the rail to rail control signal I was going for. I just need to add in a couple of resistors, and buy myself some linear, much smaller pots, and restrict the control range to my needed specs. I'm all happy, it works now, and I know how to fix the remaining issues.

Hi DrinkyCrow,

You have the output you wanted? It sounds like you send the triangle wave to a comparator. That output would then be square wave to modulate the frequency modulator.

Do you think it might sound better, more like old school, if you built a triangle oscillator that has a constant amplitude while the frequency is adjusted? (2 opamp stages: One an integrator for perfectly linear triangles, the other a toggle.) Hmm. If you are already using the comparator as a toggle to switch the oscillator's voltage direction, then you may have already made one.

How about a depth of modulation control? (Just a pot.)

I do like the old LM324. It's not rail-to-rail or FET input, but it does work half decently at PS voltages lower than the standard FET models' rated minimum supply voltage.

[DrinkyCrow]

I don't think I need rail to rail, just enough to switch a 4053 or 4051, if I need higher voltage I'll put a transistor amp stage in. I'm just using it as a control voltage, the key need is independently variable frequency and duty cycle from .5Hz to 20Hz, 0-100%. I got it working last night, but only in a very narrow band, I'm going to have to use some fixed value resistors and much smaller value pots to keep my parameters in the right range. And all the pots I have on hand are audio taper. Boo..... off to Radio Shack again to pay 3$ for 14cent parts.
Anyway even though I solved my problem, thanks much for trying to help me!

[MrAl]

Hello again,


Oh that's ok really, you're welcome.
Yes Radio Shack has a bit of a markup on parts but sometimes you need one in a hurry so im still glad they are there. Just wish their prices were up to date

[Dean Huster]

A 566 function generator chip is a lot easier to use for a triangle output, especially if you want to vary the tremelo frequency. But I thought tremelo cirucits were driven with a low-frequency sine wave, not a triangle.

[DrinkyCrow]

Not the one I'm making The classic 60 Tremolo was indeed an LFO amplitude modulating the source, newer ones have a hard/soft setting with the hard setting being more of an on/off effect, and the soft the classic sine.

[DrinkyCrow]

Let me restate that, not on/off, but a square wave that drops the volume to a certain level, that level being controlled by an "Intensity" setting. Gives a choppier sound.

[Bob Scott]

Not being intimately familiar with musicians' effects, I looked up tremolo and vibrato in the good old Webster's dictionary, the great source of all knowledge. Apparently, vibrato is a tremolo effect and tremolo is a rapid frequency variation. I guess the guitar amp manufacturers misnamed their AM modulation effect. They would need to incorporate way more expensive FM circuitry to simulate real tremolo using '60s era analog circuits.