Can I do this with a uProcessor?

[Eeyore]

I did try breadboarding using a MAX 4622 (SPDT CMOS relay) and a dual
supply, but found it added and unacceptable amount of background noise. Each
switch added more and more noise, and by the time it was through 4 of them
(in bypass mode), it sounded like a windstorm.

That's very curious. I'm not familiar with that specific part (I'd more likely
use a DG series switch e.g. DG211 or DG308) but I can't think of any reason why
that should be.

A nice thing about using JFETs over CMOS switches though is the switching need
not be instantaneous. This can reduce, or eliminate 'Fourier clicks' when
changing signal paths.

Graham

 

[MooseFET]

TF's equipment does not have a negative supply or it would be an obvious choice.

LT1054 will supply enough.

 

[MooseFET]

I did try breadboarding using a MAX 4622 (SPDT CMOS relay) and a dual
supply, but found it added and unacceptable amount of background noise. Each
switch added more and more noise, and by the time it was through 4 of them
(in bypass mode), it sounded like a windstorm.

Was is SSSSSSSSSSSS or SHSHSHSHSHSH?

I suspect that you had a leakage current problem.

 

[Eeyore]

LT1054 will supply enough.

I'm sure but it is getting ever more complicated.

Besides jfets will 'soft switch' nicely wheras CMOS swiched can't / won't.

Graham

 

[tempus fugit]

LT1054 will supply enough.

I'm sure but it is getting ever more complicated.

Besides jfets will 'soft switch' nicely wheras CMOS swiched can't / won't.

Graham

When you soft switch, do you ramp up the control voltage? If so, why do
JFETs respond more nicely than CMOS? Also, Rich's schem shows the switch
configured as DPDT. How would one do this (or even SPDT) with JFETs? Or are
there JFET switches avaiable?

Thanks again

 

[Eeyore]

When you soft switch, do you ramp up the control voltage?

On the fet's gate itself.

If so, why do JFETs respond more nicely than CMOS?

Because you're using discrete parts and can get at the relevant terminals.

Also, Rich's schem shows the switch configured as DPDT. How would one do this
(or even SPDT) with JFETs?

Easy. Are you subscribed to alt.binaries.schematics.electronic ?

Or are there JFET switches available?

In IC form ? Not that I know of.

Graham

 

[tempus fugit]

..

On the fet's gate itself.



Because you're using discrete parts and can get at the relevant terminals.



Easy. Are you subscribed to alt.binaries.schematics.electronic ?

I am. Shall we move this discussion there?

Thanks again

 

[Eeyore]

Eeyore wrote
do this (or even SPDT) with JFETs?

I am. Shall we move this discussion there?

Absolutely.

Graham

 

[MooseFET]

When you soft switch, do you ramp up the control voltage? If so, why do
JFETs respond more nicely than CMOS? Also, Rich's schem shows the switch
configured as DPDT. How would one do this (or even SPDT) with JFETs? Or are
there JFET switches avaiable?

The level shifter inside the CMOS swich chip turns your smooth ramp
back into a sharp step.

 

[joseph2k]

I did try breadboarding using a MAX 4622 (SPDT CMOS relay) and a dual
supply, but found it added and unacceptable amount of background noise.
Each switch added more and more noise, and by the time it was through 4 of
them (in bypass mode), it sounded like a windstorm.

Those parts should not have been acting like that. I have used DG403's
which they are a replacement for and didn't have noise problems like that.
Either the parts were ESD damaged (rather easy to do) or there was some
other circuit problem.

 

[tempus fugit]

Absolutely.

Graham

OK, I'll keep an eye out there for your post

Thanks