Using CD4016 CMOS switch in an A/B box

Axe_meister

I have a schematic for a FX bypass system that uses CD4016 CMOS switches. Anybody have experience with these. Now this schematic is for a simple bypass. Q if I interrupt the bypass path with a pair if jacks will I turn it into an A/B box?

Sporky

Iirc you need to be careful with biasing with those switches.

Axe_meister

Now the schematic includes a switch which interrupts the bypass path when FX loop is enabled. Would I put a loop before or after the switch?. I'll try and up load on here

Sporky

I think uploading the schematic might well help.

Axe_meister

http://i241.photobucket.com/albums/ff297/Axe_meister/null_zps302d14d1.jpg

Axe_meister

Also what the best way to do pcb boards these days? Last time I did it was in 1989. Using UV light and some nasty chemicals

Sporky

CNC router/engraver.

Not sure about that schematic - it seems to leave the send hanging when in bypass mode, which is very poor practice.

Axe_meister

Given I don't have a CNC router to hand what would the ocational hobbiest do? When you say leaves the send hanging what do you mean? is that not why you have the R7 to ground?

Sporky

Press N Peel seems to be the popular DIY option.

When the system is in bypass the send is not connected to anything - R7 looks to be a pulldown resistor but there's no decoupling capacitor and (unless I'm missing something) nothing to bias the switch inputs and outputs so I don't think it'll work very well - it relies on the external systems having appropriate decoupling. They ought to, but you can't guarantee it, and most systems in guitar electronics that don't have their own bias and decoupling don't play well with others.

Axe_meister

You have any other schematics that may do the same sort of thing? I'm trying to create a remote switchable a/b box to stick in a rack, the controller being a g-system. Turning the 4 loops into 8

Sporky

I would do it with relays then - the G-system's four relays can each control one loop or an A/B. Use a DPCO relay for each function. There's loads of stuff at geofex about relay switching. Most importantly you'll need back EMF protection diodes across each and a well decoupled power supply in order to prevent any clicking when the switches happen.

Axe_meister

Sounds like what I want to do is way beyond my limited knowledge. Will have to go with a midi solution I think

Sporky

The relays are very simple, honest. You use the relays on the g-system to trigger them, then each is effectively a DPDT switch so you can wire it up as an AB or a TB loop or whatever else you want.

thermionic

Axe_meister said:

Given I don't have a CNC router to hand what would the ocational hobbiest do? 

I've never tried it myself, but apparently good results can be had if you have access to a laser printer.

Sporky

This sort of thing can be easily put together on stripboard if you can't make a PCB. Also saves drilling the holes.

Axe_meister

Sporky said:

The relays are very simple, honest. You use the relays on the g-system to trigger them, then each is effectively a DPDT switch so you can wire it up as an AB or a TB loop or whatever else you want.

Won't I have to put some circuitry in to prevent popping?

Sporky

Yes - the back EMF protection diode and some power supply decoupling caps (though these are more about making sure the thing works than avoiding popping).

That should be all you need. If you want to go belt, braces and sock-suspenders then you could put decoupling caps and pulldown resistors on each input and output, but that's not normally needed because there's no internal bias - same as you wouldn't bother with that sort of thing if you were using a footswitch for the same job.

The back EMF protection is just an IN4004 or similar across the relay coil, and the power supply decoupling is just a big electrolytic across the power supply rails - have a look at Geofex for some remote relay circuits.

Axe_meister

Would you recommend this circuit?
Not much detail on it however in terms of what transistors to use or what hex inverters

Sporky

What circuit?

Axe_meister

Oops forgot to link
http://i241.photobucket.com/albums/ff297/Axe_meister/null_zpsf22289ad.gif

Sporky

I'd use simple non-latching relays and just have the g-system control them directly - no need to make it more complex.