synth circuit - output to amp? different waveform?

If you don't hear anything, it's probably because speakers are low-impedance devices, so the voltage available at a speaker output is low. I don't know what a guitar pickup puts out, but you could try using a small audio output transformer driven backwards to get a better impedance match.

If the output is a square wave, you can low-pass filter it to knock down the nasty-sounding high harmonics. There are volumes published about waveshaping using active filters, but a simple RC section will probably make an audible difference.

Shouldn't matter. The input to a guitar amp is high impedence(usually) and usually just around 100mV. Chances are you might be output to much(or not enough). You definitely should hear something. Guitar amps are not the best amplifiers though and depending on your signal you might not get what you expect.

Chances are your either driving it with a DC signal(which shouldn't matter as it should be capacitively coupled) or its just to much voltage(But then you would probably hear something like clicking). If the freq is too high then chances are it isn't going to work on a guitar amp.... try your computer's mic input first and see if that works.

not sure what you mean here. The timbre of a sound is the simultaneous frequencies being heard. Most musical instruments use the overtone series(search on google) to form a harmonious sound. Different strengths of the individual overtones produce the different timbre's that you hear.

A frequency, BTW, is a pure sinusoid. So if you have a circuit that can generate one then you can duplicate it a few times and combine each one using an op amp sumer to get a timbre of something more realistic... the more overtones you add and the more real it will sound but only up to a point. Real instruments are not perfect and they have inharmonic overtones that give them character(and the fact that the timbre depends on time too(plus a multitude of other factors)).

If you disconnect the speaker there is no load on the circuit. The 2-transistor tone generator needs that to function. But you can easily find a resistor value to replace the speaker (and the 10 ohm resistor). To get started, connect the input of the guitar amp to the top lead of the speaker, and the amp connector shield/ground to the bottom of the 10 ohm resistor. I'm assuming here that the guitar amp is AC-coupled, which is pretty standard. (If not, you will need a series capacitor.) You should get plenty of sound from the amp. Now (turn down the amp first to avoid a "pop") replace the speaker with a resistor. A very low value (like 10 ohms) will probably work, but you might want to see what happens if you go higher... you should expect that this will change the operation of the circuit, so you might need to tweak other values.

In the Olde Tyme days, synth circuits almost always started out with a sawtooth (ramp, not triangle) that sounded pretty harsh, then used filters to mellow it out. They used voltage controlled filters (VCFs) so they could change the timbre of the note dynamically. That may be a bit much to start with, but you can easily make simple low-pass filters to alter the tone. After you get the circuit modified to drive the guitar amp, you can add a series resistor between the tone generator and the amp, and a parallel capacitor at the amp input to ground. The "cutoff" frequency of the filter is given by f = 1 / (2 * pi * R * C), so pick some appropriate R and C values. Say, if you want the filter to start cutting frequencies above 500 Hz, and you want to use 0.1 uF for C, then rearrange the above to get R = 1 / (2 * pi * f * C) and plug in 0.1*10^-6 for C and 500 for f. R comes out to be 3183 ohms. Pick the closest value you have on hand... this is just to get you in the ballpark. You might want to use a 10K control pot for R, to make playing around easier.

As it turns out, the real key to synthesizing different sounds is surprisingly not the waveform or harmonic content, so much as the envelope - the way the sound builds up (attack) and dies away (decay) as well as any sustain portion. (If you've ever seen an old-fashioned organ with voice tabs, you may have wondered why none of them sounded much like their names. That's because the envelope was always the same, not because the voices didn't have the proper harmonics.)

So, if you want to proceed beyond tone generation, you have to look up envelope generators.

Best regards,

Bob Masta D A Q A R T A Data AcQuisition And Real-Time Analysis

If you disconnect the speaker, you've broken the circuit, and there's nothing to pull Q2's collector low. leave the speaker connected. Connect a wire from Q2 collector (and the top of a speaker) to the "top" of a

Google "Oscillator circuits", oscillator tutorial, that sort of thing.

Have Fun! Rich

The first circuit won't work without the inductance in the speaker. The second one will work, but you get a square wave, which sounds ugly.

There are various sound generator ICs you can use to generate cool sounds. You could also use a PC to generate the sounds in mp3 format, and buy a cheapo MP3 player to output them. There are mp3 mini-boards at

If you want to build a nice adjustable sine wave, try a wein bridge. I found one that you might like after a search of the internet here:

It only takes a few more parts than yours, but I'm guessing that it works much better, particularly into a high impedance like a guitar amp. Make sure you don't forget to start with the amp turned down to 0, and slowly turn it up.

If it sounds like your 555 circuit, you are probably overdriving the amp. In that case, use a high value potentiometer (100k?) on the output of your circuit to lower the amp input voltage to something that the amp likes.

Regards, Bob Monsen