Why is this relay based circuit popping?

[sfr]

So I had some relays kicking around for something or other, and decided to rewire my A/DA Flanger (built from Charlie's boards) for two-button operation - one for momentary, one for latching. 

I wired up a momentary switch to a transistor driving circuit for the relays, and all worked well.  Wired up a CD4049 for a latching circuit using another momentary and everything worked fine, but I'm noticing some clicking as I switch. 

I've been messing around and haven't had much luck.

things I notice: 

• It isn't the really loud pop I'm used to in cases where it's simply a matter of adding a cap to ground to avoid large differences in voltage.

• The board already has a pulldown resistor/cap network on it.

• The relay isn't switching "hard" - at least, being driven by the transistor, you can't hear the relay itself clicking like you could driving with just a switch.

• I don't think it started doing it until I added the second (latching) part of the switching, but removing it doesn't seem to help.

• I disconnected the LED (which was also being switched by the relay, at a higher voltage than the relay circuit operates of off.)  Makes no difference. 

• The thing is only half-boxed - it's pulled out of my all-in-one unit, so it's attached to a front plate, but not shielded in the back at all.
  

• Upped the value of the capacitor in the transistor relay driver, assuming this would slow down the relay action more (possibly?) and help alleviate any induced clicking from the relay.  no luck.

[/list]

So I'm thinking it may the mess of wiring - that the in/out lines are picking up either something from the relay or the associated circuitry.  Before I go to the trouble of replacing those wires with shielded (it's a tight fit in there, won't be a fun job)  I thought I'd ask if anyone here can point anything else out that may be resulting in clicking:

Here's the circuit I wired up, am I missing something obvious?  I'm getting noise with either switch.  I'll double check, but all connections test good. 

[soulsonic]

The relay coil should have a protection diode across it with the cathode end pointed towards the +5v connection. This prevents the sharp pulses of energy that the coil can kick back into the circuit during it's charge/discharge cycle. That may be a cause of the popping, and it's something that should be done anyway with any relay unless it already has the diode built in (some do).

[sfr]

Thanks.  I'll give that a try tomorrow. 

Looking at my notes - that was present in the original descriptions I was looking at - I must have left it out thinking it was part of the LED drive bit (the LED was attached to the +V and the collector of the transistor - I attached mine to an extra set of switches on the relay, as that was easier for physical reasons)

could neglecting the protection diode have damaged my relay or circuit in any way?  (I assume no, as it still works, and we're talking low voltage, but I'm curious)


EDIT:  That did it.  Thanks!  I hate when the answer is I missed something silly, but I love when the answer is also something simple.

Thanks again.

[soulsonic]

Glad to be of service.

[sfr]

Hrm -

Playing with the vibrato switching, decided against it, did a last test before boxing the whole thing up again, and yes - it is still popping on switch.  Pulled the diode, still checks good - can't tell if it's quieter than originally (so maybe I missed it last night) but it's definetly still there. 

I'm working through checking connections - with things spread out more, physically moving the wires around doesn't seem to help, maybe shielding would - I'm not thinking of anything else. 

Checking connections.  Again. 

Should I change that 10uf cap?  It had been 4.7 originally, but I changed it to 10uf before coming here with my first question.

Hopefully it's just a connection I messed up mounting the perf.

EDIT: used a 4148 for the diode across the relay.  can't imagine it matters what kind I used, however, but FWIW.

[sfr]

This might sound kind of dumb; but something this makes me wonder :

I've had a couple of situations, this is one, where I've wondered if using shielded cable would help or not (I really should just start using it to begin with) and it's a hassle to implement - would running my signal through unshielded wires passing physically around the same are as the wires I'm questioning replacing, and then powering circuit in question, switching it on/off or whatever, would that tell me anything?   Like, if it's noise being radiated out, I've now removed the circuit itself from the equation?  Maybe connect the grounds?  Or is this a dumb idea?

I'm not finding any bad connections and I'm beating my head against the wall on this one; I dislike these kind of problems.  I need to take a step back.

[soulsonic]

I'm sorry, I'm not very familiar with the A/DA Flanger circuit - I'd like to see some other people jump on this thread to help, because I'm not real sure about what's going on in the circuit normally.

[sfr]

That's the part that's weirding me out - I'd like to think it's not the circuit being bypassed that's in question - I never had any problems like this when I was using regular stomp switches.  I'd also think it's not a large DC change in the audio path itself - there's input and output caps and pulldown resistors on the circuit, and on the several pedals after it (it's part of my large all-in-one board.)  Does bring up a good point though - I'll have to try separating the relay bypass circuit from the flanger, maybe try it as a bypass for something else.

All in all, it's noise that's livable with - it's not that super loud pop you get when you cut the input to an opamp or switch caps in a wah or something, but it's not really something I want to deal with. 

My next plan is to re-breadboard the relay switching circuit, hook it up to the scope and see what switching those cap values around does - maybe if I can slow the voltage change even more I can improve this - I'm hesitant though - even slowing that down, the relay has to switch at some point, and that seems like it's my problem.  Maybe a solid state solution is in order here.

FWIW - I'm using an Omron relay, part # G6A-474P-ST40-US-DC5 

http://www.mouser.com/search/ProductDetail.aspx?R=G6A-474P-ST40-US-DC5virtualkey65300000virtualkey653-G6A-474P40-DC5

http://oeiwcsnts1.omron.com/pdfcatal.nsf/PDFLookUpByUniqueID/4C0C931D86929DE586256FC7006173ED/$FILE/D20G6A0305.pdf  (data sheet for the whole relay series)

It's a "low sensitivity" relay - should I have used a high sensitivity one?

Anybody with any advice, it's much appreciated!  And thanks for all your help, Soulsonic.