totallly silent switching circuit - soooo close

[tempus]

Hey all;

Here's my latest switch:



On my breadboard, this one is totally silent. I plan to use a PIC to control the switching action. The 2nd BS170 switches the signal to ground, and it will always be at ground when any switching occurs. This eliminates the need to ramp up the control voltage on the 1st BS170.

There is 1 small caveat: In bypass position, there is a tiny amount of leakage (sounds like a heavily compressed clipped signal) present. I can get rid of it with a bigger cap (100uF) but if I go much higher than 10uF, there is a noticeable thump. Any comments or suggestions?

Thanks

[R.G.]

Have you considered how you might use two MOSFETs, source to source, with a dual photovoltaic source device?

[tempus]

Have you considered how you might use two MOSFETs, source to source, with a dual photovoltaic source device?

No I haven't. What's a dual photovoltaic source device? Can you give me an exmple of a part number? Since I posted the last message, I thought the problem might be solved by replacing the 2nd BS170 with a JFET, since the leakage sounds a lot like the leakage I got when I used a single BS170 as a switch - you know the one that was the result of the drain-source diode?

Thanks RG.

[km-r]

LDRs?

[R.G.]

No I haven't. What's a dual photovoltaic source device? Can you give me an exmple of a part number?

It's an LED-solar cell in a package. You make light on the LED, and there is a stack of photovoltaic junctions that create a voltage. Not much current, but you don't need much to make a MOSFET gate change.  Toshiba TLB-590, International Rectifier PVI5033/PVI1050/PVI(others).

Since I posted the last message, I thought the problem might be solved by replacing the 2nd BS170 with a JFET, since the leakage sounds a lot like the leakage I got when I used a single BS170 as a switch - you know the one that was the result of the drain-source diode

I actually suspect that it is leakage, just in a way you haven't found yet. MOSFET switches are maddening that way.

[tempus]

Thanks again for the replies. Is this the same thing as an optocoupler like a 4N25?

[snap]

crosslink:
http://www.diystompboxes.com/smfforum/index.php?topic=76261.0