Anyone have an answer for this. I know you can build and oscilator with two opamps, and about 10 other parts, and get a square, and triangle wave with variable frequency, but I was hoping there was something simpler.
any ideas?
Twin T osciator is fixed frequency right?
Quote from: Brian MarshallTwin T osciator is fixed frequency right?
Fixed frequency yes, but not necessarily fixed amplitude (assuming you want the thing to be variable frequency). Especially op-amp versions which need some form of auto gain control.
RG has a simple phase-shift oscillator over a GEO that might be just the ticket.
This miniosc is not that simple, but maybe you decide to go for it!
I think it's pretty complete.
http://sound.westhost.com/project86.htm
there's always the famous 555 timer.
1 8pin ic.
wide range supply voltage.
mainly square wave out @ pin 3.
if U add fet input/buffer opamp, u can tap off the
charge capacitor that has a sawtooth wave.
Constant current source 2 charge cap and
U have a triangle.
google 4 555 circuits.
:)
T
One wild efkt...put a vol control on it !!!
Oscillates by itself using the 555 timer and an OA. Does env fil type and octave down and etc too...
Does a very low tone and goes like past hearing'? on the high end...Fun to try out efkt too...
This was answered a few months back.
A Wein-bridge oscillator will give you variable frequency sine-wave and is used in many commercial generators - it requires a dual-gang pot. You add a Schmitt trigger after it to produce a square-wave. Tri-wave isn't really practical.
Both the Twin-T and the Phase-Shift oscillators can be made to vary over a small range of frequencies but generally aren't suitable for test oscillators. (Phase-shift oscillators used on Tremollo's only operate over a small range and the output wave shape is poor).
For rough Sine + Square + Triangle use a function generator chip like the XR2206 or ICL8038 or MAX8038 (last one is more expensive). There's a few opamp circuits which attempt to do this too, you could do it with 2 or 3 opamps and a few transistors and diodes.
Check the simple 1kHz sine wave generator at geofex.com - it's only 2 transistors. There's a resistor to ground in one of the "T"s. I put a pot across that resistor and found I could vary the frequency from under 1kHz up to about 5kHz. Simple and effective, but not a wide range.
Ok, thanks for the ideas guys.
I dont really want to use a 555. for some reason they seem cheesey to me, and i want something that will make me learn something.
Can the xr2206 or icl8308 run off of 9 volts.. i was under the impression that they could not.
hmmm voltage doubler....
Yes, minimum is 10V on both the XR2206 and ICL8038.
A doubler would work.
You might be able to find an opamp job on the web - it's likely it will need +/- rails but it can be modded to single rail.
Yes, minimum is 10V on both the XR2206 and ICL8038.
A doubler would work.
You might be able to find an opamp job on the web - it's likely it will need +/- rails but it can be modded to single rail.
The PAiA Fatman analog synthesizer uses 2 555s.
One 4 each VCO(VoltageControlledOscillator)
8038s are pwr hungry.
Max038 are $20.
XR2206 too difficult to find.
Either a dedicated VCO or a 555.
The 555's in the Fatman are run on an unusual voltage setup.
The V+ pin is connected to gnd, and the gnd is connected to Minus.
This is for the clever way PAiA found to do a linear voltage-2-current
converter to charge the 555's timing capacitor.
The schematic is posted @ PAiA web site.
Check it out---where else?---
http://www.paia.com
Check out their complete line of kits while U R at it.
They have a complete monophonic synthesizer,
compressors, tube preamps, guitar effects and whole LOTS! more.
Their older 4700 series schematics are several places on the web.
Their 4720 VCO has sine, tri, sawtoth, square and pulse simutaineously.
Can U tell i'm a big PAiA PHan? ? :D
staytuned
tone
The xr2206 or icl8308 won't teach you much useful. And they won't be any simpler than the two op amp oscillator. They're really not well suited to 9V power, either.
If you want simple, and will be satisfied with a square wave, almost nothing will beat a CMOS Schmitt trigger oscillator. A single Schmitt trigger chip, one cap and one pot (if you want variable freq).
You can hack a variable pulse width using a extra inverter and a RC network. You can also hack a saw by buffering the signal from the cap/pot junction.
I think the thread has deviated in all directions.
The only thing that's clear is you want 9V battery operation.
What is the purpose of the oscillator?
What waveforms do you really want?
What frequency range?
Will any old waveform quality do?
i want audio frequency in the guitar range.... say 100hz to 2000hz or so.
Wave form.... dont care, but dont really want square.
Purpose 1 signal generator to test audio circuits
2 learn something new.
It's by far the easiest to make a square wave-You could use 2 transistors, or even one PNP, I believe, to make a square wave oscillator, a la multivibrators. But I would have to say in my experience the most stable, simple and useful is the dual op amp version. Especially since you should test your circuits with more than one waveform. It'd be ideal to use a sine wave, because that's what most closely represents the guitar, but sine wave generation isn't that simple at all. So, I'd most certainly go with the dual OA pattern.
-Colin
Quote from: anonymousexperimentalistIt's by far the easiest to make a square wave-You could use 2 transistors, or even one PNP, I believe, to make a square wave oscillator, a la multivibrators. But I would have to say in my experience the most stable, simple and useful is the dual op amp version. Especially since you should test your circuits with more than one waveform. It'd be ideal to use a sine wave, because that's what most closely represents the guitar, but sine wave generation isn't that simple at all. So, I'd most certainly go with the dual OA pattern.
-Colin
I have a book called practical electronics for inventors, and it has an oscilator similar to the one your posted a couple months ago, but as far as i know you cant really get a sine wave out of it with out adding annother stage.
However in that same book there is a drawing for a relaxation wave generator... that might work... much simpler. I know the slope changers, because the cap discharges inverse to how it charges, and it actually gives me an idea on how to use 2 caps and 2 diodes to (maybe) make a sine wave..... maybe im on to something.
time to go back in to the dungeon.
For simple, Schmitt trigger, I tells ya.
Quote from: Tim EscobedoFor simple, Schmitt trigger, I tells ya.
doesnt that have something to do with flip flops?
Quote from: Brian MarshallQuote from: Tim EscobedoFor simple, Schmitt trigger, I tells ya.
doesnt that have something to do with flip flops?
Only if you want to add a flip flop.
http://www.musicfromouterspace.com/analogsynth/mmlogic.html
ok... i'll look in to that some day.... right now i want to concentrate on parts i aready own.
If i remember right a schmidt trigger is usualy on an IC, not a simple circuit.... right?
I'm too sleepy to google it right now... good night everyone
:roll:
A wein bridge oscillator can be built with one opamp and a small light bulb (~20mA to 40mA) (which doesn't glow - it's used as a resistor). The output is a sine-wave, the frequency can be varied with a pot, or switched with a multipole switch - the output quality is very good.
There's another version which uses a JFET instead of the light bulb.
You will find one on the web no problem.
There's a really nice pseudo Wien bridge circuit in the March issue of Everyday Practical Electronics. The auto gain control is done with a single transistor and a couple of diodes - very clever! - and has a low parts count, apparently low distortion (haven't tried it yet) and low current consumption. It's all transistor, but could easily be re-jigged using an op amp.
www.epemag.wimborne.co.uk
Quote from: Brian MarshallI have a book called practical electronics for inventors, and it has an oscilator similar to the one your posted a couple months ago, but as far as i know you cant really get a sine wave out of it with out adding annother stage.
You CAN add another op-amp stage to integrate the triangle to get a sine, and in my opinion it's worth it as the quality of the wave is surprisingly pure. The problem is keeping the amplitude stable over the frequency range you select, but I've had good results using a dual-gang pot with resistors wired in parallel here and there.
It's the sort of thing you need a scope for to set it up right, but I've designed some pretty mean LFOs using this method! :twisted:
Quotegain control is done with a single transistor
Be interesting to see if it is really low distortion.
Quote from: gezYou CAN add another op-amp stage to integrate the triangle to get a sine,
..I don't doubt you have a nice sine, but it isn't coming from integrating a triangle, or I wasted my time in that trig class :roll:
bugger, just found this link http://www.discovercircuits.com/O/o-sine.htm
now I won't get any sleep :shock:
Paul
I first found out about integrating a triangle to get a sine in ‘Practical Oscillator Circuits’ by A Flind. He mentioned that the sine is surprisingly good and he’s not bloody wrong! - I’ve got extremely pure sine waves using this approach!
He uses a op-amp and 7556 for the triangle generator then feeds the output to another op-amp wired as an integrator. His version is fixed frequency but uses a input resistor to control the amplitude of the sine. I did an all op-amp version and used one half of a dual gang pot (plus a resistor from wiper to outer lug) instead of a input resistor, to keep the amplitude stable over the whole range of frequencies. The other half of the pot is used for the frequency control, and the whole thing is wired up so that as it’s resistance increases (slower frequencies) the input resistance of the integrator increases, thereby keeping the amplitude of the sine constant. It works a treat and is remarkably stable (used a regulator to power everything).
At the very lowest frequency (less than 1Hz) there’s some triangulation of the signal granted, but only for a miniscule portion of the pot’s travel, once you’re into useable range the sine wave is as good as the one on my function generator - I was amazed when I scoped this!
The beauty of this circuit over Wien bridge is that it allows for pulse-width modulation, plus you get a triangle and square wave output.
Quote from: BoofheadBe interesting to see if it is really low distortion.
It's the diodes that do the job of keeping distortion to a minimum not the trannie.
I hope it does what it says on the tin as it's a nice little circuit, ripe for modding! (and not a dual-gang/trim pot in sight!)
thanks for the explanation gez! I'v been making my sines from triangles by overdriving CA3080s, good for 2% distortion but that is about it (of course for a LFO, or fo normal audio testing a 2% distortion sine is no problem).