Loud squeal/hiss from Smash Drive

[zener]

I'm a newbie and this my first attemp to build one.

I had a Smash Drive wired into a breadboard. It is working now, but I have some problems with it.

When I push the switch on, there's always a sudden short (less than a second) burst of strong sound, then it will go to its normal level. While playing with the circuit on, I always get a fading in loud squeal or hiss whenever I stop playing. :x  Another thing, the tone seems to be lower than usual though the treble pot is at full. I actually use a karaoke which mic input was modified by my dad so that I can use it as guitar amp. I don't any problem with it putting my guitar straight into it.

By the way, the circuit is still in the breadboard and the wires are kinda tangled but I looked a lot of times for any shorts and there was none.

Is this normal? Does the loud noise disappear if I put into a PCB then in an enclosure? If not, what might be the reason and what can be done?

Thanks for any help  :wink:

Zener

[Paul Marossy]

It sounds like the circuit is starting to oscillate when there is no input. Try changing the value of the pot to a 10K and see if that helps. You could also try reducing the value of the 47uF electrolytic cap, maybe a 22uF. I seem to remember that there was a difference between the chips available at RadioShack, something to do with different manufacturers of the same chip. This was a while ago, I just don't remember all the details...

I remember having a similar problem when I built mine. I think I ended up soldering a small value cap between the wiper and one of the lugs on the on the pot to stop the oscillation in mine. I think it was in the neighborhood of 560pF or so. Putting a tone stack on it may also help some, too.

Anyhow, putting it in an enclosure probably won't stop the problem all by itself. However, sometimes a breadboarded circuit will be much noiser than an actual soldered up version of the same circuit.

[Peter Snowberg]

By the way, the circuit is still in the breadboard and the wires are kinda tangled but I looked a lot of times for any shorts and there was none.

Is this normal? Does the loud noise disappear if I put into a PCB then in an enclosure?

This could easily be the cause. High gain/high impedance circuits are succeptable to signals bleeding in from other places.

In tube amps, if you want the best tone you have to be very careful about how the wiring and components are laid out. Out of phase signals should not be running on parallel paths; ideally out-of-phase wires should cross each other at 90 degrees. It's interesting to note (at least to me) that some of the best tube amps get much of their "mojo" by careful placement to minimize this crosstalk in some places and to actually accentuate it in other places.

Take care,
-Peter

[Ansil]

not only the above mentioned but if you used the non inverting input  when the inputs and outputs are brought close together at the switching for on and off it can oscillate at extreme settings.  if you use the inverting input then it is probally something else