Transistor switching causes popping?

[tnecniv]

So I figured for fun I would see if my idea for a tremolo type effect would work. Basically, my idea was that I would put the guitar signal in parallel with the source of a JFET and connect the drain of the JFET to ground. I would then hook the gate of the JFET up to a 555 timer which would send a pulse that would essentially mute and unmute the signal by sending it to ground. This idea seems to work, but there is a very loud popping noise as the transistor turns on and off. After playing around with it and doing some reading, I added a resistor in series with the gate and a cap in parallel with the gate that leads to ground, but this doesn't seem to be doing it. The idea was to create an RC circuit to slow down the voltage change from high to low so the JFET isn't flipping quite so fast.

Any other suggestions? My knowledge of transistors is somewhat rudimentary.

[PRR]

> a JFET

N-type or P-type?

N-type are MUCH more common.

To turn an N-type on and off, you take the Gate to Source voltage or 5V *negative* of Source.

Your '555 is probably powered to swing the Gate +Positive+ of ground and Source.

When the Gate is taken Positive, the internal Gate diode conducts, and throws the '555's high level (+5V) into the audio path; otherwise not. (Either way the FET is ON.)

5V is 10 or 20 times larger than guitar level, so yes that is a POP!

Ten-cent fixes (maybe not worth that much):

Use a 1Meg resistor Gate to ground, a 0.01u cap from Gate to '555. The first pulse will POP but the capacitor quickly charges-down to make a mostly-Negative swing.

Replace the FET with an NPN. Collector to signal, Emitter to ground, 5K resistor from Base to '555.

BTW, you are trying to "short-out" the signal. Naked guitars are fairly easy to short-out. Some effect box outputs short nicely, others have enough muscle to force large ugly currents through. In general you ought to have "some" resistance between the signal source and the switch. 10K is a fair trial value; 1K to 100K for further experiments.

[tnecniv]

Thanks for the response, I will try this after work and post the results.

[tnecniv]

I got it working, thanks a lot. I used the second method but there was still some popping so I added a cap in parallel with the base to create an RC circuit and that removed the popping.