I need the schematic of a very simple sinusoidal signal generator

[gigimarga]

Hello,

I want to fine tuning my fuzzes/distortion using a software oscilloscope and i think i need a schematic of a  signal generator.
Because i need it very fast, i want the simplest possible, but good for my purpose - maybe one which uses a 555 IC?

Thx a lot!

[gez]

A 555 circuit wouldn't be my choice of oscillator to test a fuzz circuit as you can't easily see how said circuit is shaping the wave form.

IIR, there's a simple sine-wave oscillator somewhere over at Geofex.  Perhaps somebody could link to it?

[Auke Haarsma]

Check out this topic, Stm posted an improved version of the Quick n Dirty Oscillator at GEO here:

http://www.diystompboxes.com/smfforum/index.php?topic=53596.0

I've build that one last week and can confirm it works.

[jpm83]

And here you can find verified PCB layout and PNP. http://www.aronnelson.com/gallery/main.php/v/jpm83s-Gallery/album176/PCB+layouts/?g2_page=2

Janne

[jalien21]

i had a lot of fun with that signal generator a couple weeks ago. had the frequency vary by the resistance of graphite on a piece of paper and stuff. anyone know how to change the general range of resistances that produce an audible signal? i want it to vary by really big resistances so i can change the frequency by moving the leads around fruits and stuff

[gigimarga]

thx a lot...but...don't exist an easier schematic?
i have no chance to buy vero/perf today...

[George Giblet]

Look up phase-shift oscillator and find a one transistor version.  That's the simplest circuit for getting a reasonable quality sine wave.

Go here and look at the "Original EA Tremolo Schematic", the oscillator is the part on the right of C14.  You will need somewhat smaller caps for C5, 6, 7.  Replace the pot (R14) and R11 with 15k.

http://www.generalguitargadgets.com/index.php?option=com_content&task=view&id=142&Itemid=26

You haven't mentioned if you want variable frequency.  The coventional phase-shift oscillator and twin-T oscillator have limited frequency adjustment range.  The Wein-bridge is better for variable frequency.

To compare apples with apples realize that the quick and dirty oscillator uses an extra transistor for buffering, which you could remove if you don't need low impedance output.

[gigimarga]

thx a lot!!!

you give me a nice ideea: i have built a kay tremolo that i don't use (i don't like it...) and, as i saw in his schematic, his oscillator seems to be a twin-T one.
it is possible to modify only the caps of the twin-T filter and to have an oscillator for audio?
how can i calculate the value of the caps for a 1kHz frequency?

thx again!

[Paul Perry (Frostwave)]

When I tune a fuzz, I prefer to use a triangle wave.
That is because, with a triangle wave, it is much easier to see exactly when the tip of the wave is being flattened, and by how much.
Now a sine will be better for HEARING what is happening - but if you are watching on a scope, I very much prefer the triangle.
And, happily, it is much easier to generate a nice triangle!

And if you do make a triangle generator - you can run it to half a LM13700 OTA arranged as a simple amplifier & if you overdrive it by just the right amount, you get (very close to) a sine! Certainly close enough for rock and roll tweaking.

Of course, in the final analysis, a musician & a guitar is what you need. And ears.

[George Giblet]

> it is possible to modify only the caps of the twin-T filter and to have an oscillator for audio?
> how can i calculate the value of the caps for a 1kHz frequency?

Stm's circuit is already set-up for 1kHz.

To increase the frequency by a given factor you decrease all the caps in the filter network (twin-T + added filter cap) by the same factor.

[Processaurus]

When I tune a fuzz, I prefer to use a triangle wave.
That is because, with a triangle wave, it is much easier to see exactly when the tip of the wave is being flattened, and by how much.

Yessir!  Started using the triangle wave after years of using the sine wave, much easier to spot unwanted clipping and filtering.

[gigimarga]

thx a lot for your answers...how can i generate a triangle wave in the simplest way?

[R.G.]

The standard LFO source with two opamps is a square-triangle generator, just a very low frequency one. It generates a fine square wave at higher frequencies if you change the integrator cap (that's the one from output to inverting input on one opamp) smaller by a factor of about 100-1000. Frequency is inversely proportional to that cap.

[gez]

And with the addition of another amp, and a dual-gang pot, it's possible to get a pretty reasonable sine as well as the other two options (see the simple sine-on circuit in the members section*); although you'd need a scope to set things up.

*  Last post of the last page.

[jpm83]

Here is one link to schemo. http://www.electronics-lab.com/projects/test/010/
What kind of values for that R and C you gurus would suggest if one would make that R a pot so you could adjust the frequency?

Janne

[gez]

http://www.play-hookey.com/analog/triangle_waveform_generator.html

[gigimarga]

thx a lot for your kindness!!!
i will try it tomorrow...

[jpm83]

I think these two links have different opinions on what effects what ( the amplitude resistor and timing resistor). http://www.electronics-lab.com/projects/test/010/
http://www.play-hookey.com/analog/triangle_waveform_generator.html Which is correct?
And is the value of C in here in farads or microfarads?
http://www.play-hookey.com/analog/triangle_waveform_generator.html

Janne

[gez]

Using this schematic:

http://www.play-hookey.com/analog/triangle_waveform_generator.html

Amplitude = (R1/R2) X Vsupply

In reality, it's the output swing of amp which determines amplitude, but for back-of-envelope calculations 9V will do (assuming 9V supply - check out the simple sine-on, or schematics of commercial pedals, for single supply version).  R1 should be smaller than R2.  If you make amplitude too large, you have to pay attention to common-mode input range, otherwise the thing will latch (no oscillation).

C is in uF

[gez]

PS  Andy Flind's book, "Practical Oscillator Circuits" is worth buying (Babani publishing).  Very cheap, very informative.