Making a noise? (Electronically)

[GHA]

As I said, the impedances are wrong. A volume control needs to feed a relatively high impedance, not direct to a speaker.

Would a pot on the input to the FET work? (In series with r3)

http://www.google.co.uk/url?sa=t&rc...=pcFIBaaktnpemS9LihwA8g&bvm=bv.50500085,d.aGc

 

[nigelmercier]

Would a pot on the input to the FET work? (In series with r3)

http://www.google.co.uk/url?sa=t&rc...=pcFIBaaktnpemS9LihwA8g&bvm=bv.50500085,d.aGc

Yes, good call, I hadn't seen the schematic.

Cut the track between R3 and Q2. Wire the ends of the pot to R3 and ground, the slider to the original connection to Q2. Probably best with a logarithmic pot, about 1k.

An example http://uk.farnell.com/bourns/pdb181-k415k-102a/potentiometer-rotary-1kohm-17mm/dp/1823540

 

[prv]

Cut the track between R3 and Q2. Wire the ends of the pot to R3 and ground, the slider to the original connection to Q2. Probably best with a logarithmic pot, about 1k.

Even better - thanks.

I think I have a 1k log pot from my experiments with the original piezo buzzer.

Pete

 

[pteron]

I'm afraid I don't think it will work very well. The FET has such a large gm that the smallest increment of gate voltage over its threshold voltage will pull the output fully down unless the load is significant.

It will be incredibly sensitive to pot position (you may well need a multi turn pot) and it will change volume dramatically with temperature and supply voltage.

Try it though, I may be wrong

 

[nigelmercier]

I'm afraid I don't think it will work very well. The FET has such a large gm that the smallest increment of gate voltage over its threshold voltage will pull the output fully down unless the load is significant.

I bow to your superior knowledge of FETs. If it doesn't work, perhaps substitute a BJT.