Simple remote Loop Switch

[duck_arse]

let's assume I know nothing of gt8's or channel switching amps for a moment. can you draw me a block diagram of your connections, guitar to ?, ? to gt8, amp to ? include jack names please.

do you have a different amp you  can try? have you tried different cables?

the next step is to start with nothing but the guitar and amp. any noise? now plug the guitar into the rat trap, the rat trap into the amp input. use the battery and shorting method for switching the rat trap. any noise? if no - and no - then - guitar into amp, rat trap in/out amp fx loop. move it from the top of amp to the floor. any noise? if no - then - try bringing the gt8 back into the room, and apply power to it. any noise? move things about, any noise?

I think you can see how this is developing, I'll leave you to your in-pluggings.

[Minty]

...steps ahead....

Tried:

Different cables - same
Moving Rat Trap to floor, 6m away - same
Guitar to amp, no noise
Guitar to Rat Trap, Rat Trap to Amp - slight hiss introduction
Add 9V (battery) - noise
Add 9V (wart) - mega noise
Add shorting lead - more noise
Change shorting status (open/closed) - noise change

Not tried another amp, haven't got access to one I'm afraid.

Block diagram:

[duck_arse]

"Guitar to Rat Trap, Rat Trap to Amp - slight hiss introduction"

can you try this again, add the rat itself (with a battery of its own) to the trap, and then work the relay? I can't remember if you said the switching actually passes audio in an appropriate manner or not.

also, different guitar? different mains socket? is the mains earthed, and earthed properly (can never tell with you americans, seems you people do odd things w/ mains power)? we have 50Hz here, so our earth loops sound bassier.

I'm about all tapped out for ideas. if built like shown, I can't see where the problem would be. I guess you'd be having to strip all the wiring from yr original, and re-do it nice and neat, see if any change.

[Minty]

American? Nah mate, I'm from UK. 

All of our plugs are three pin with an earth - but there is an extension lead in the mix so I'll check that it has an earth.

I'll try a different guitar too.

All test have been executed without a Rat connected (just a patch cable going from "to FX In" and "From FX Out").

[Minty]

Could it be that this relay is just not suitable for this function?

[Minty]

OK, so, here's another thing.

I've gone back to the original publication which gave me the first diagram I had and found the author's suggested diagram of a PCB print trace, things I note are:

- He's already placed a 47uF across v+ and 0v (C3)
- There is no D1 running parallel with R1





What do you make of that?

[duck_arse]

the uk? wit de funny fuses in the plugs?

the C3 addition is simply good practice, in any supply. it provides a "local bucket" as the experts call it, from which the circuit can get juice when it needs, and it also provides a low-impedance, smoothing path to ground for all the hash and noise long cables like to pick up.

from what I can see, without having built this myself, the D1 provides a bypass to the resistor in one direction only, so the resistor will allow a slow charge, but a fast discharge (I don't have the circuit in front me the moment, so this may be the other way round).

as for the relay, and as I keep hinting at, if it is wired as circuit-drawn, the switch contacts-ing has no common to the power section, so there should be no way the relay contacts can contribute hum. if the relay is chattering, it might make a hell of a noise, but it isn't, is it? and if there was a load of digital junk in the amp, the leads might pick it up, but there isn't any. with the gt8 in the next room, all the digital hash its internals will and do generate are too far away, and not connected anyway.

turning down the guit killing the noise may very well be a pointer to the rooot cause, but I'm not smart enough to know what that might be. so, all I can suggest is doing a nice tidy re-wire, so we can look in and say "yes, it's all wired as per the diagram". and then, if it still makes the noise, probably start a new thread, with a new title, to draw in some of the more knowledgable types. we'll get there in the end.

[Minty]

Sorry for the delays, having some auto trouble so this has taken a back seat - will test more asap.

[trixdropd]

Make sure your audio ground connects to power ground somewhere. I think that's your issue, is that it does not.

[duck_arse]

welcome aboard, trix! geeze, I hope that's not the problem, because I've been telling him exactly the opposite, all this time.

[greaser_au]

As the small-signal stuff is handled by relays, there is no 'electronic' need for mixing the signal with the switching.  In cases like this I'd say that the audio ground and the power ground can (and likely should) be isolated.

david

[Minty]

I made a new Rat Trap yesterday using the strip board - I took pictures (upload asap).

All tests with a meter were as they should be.

Results through the amp.....still the same.

[Minty]

Photos:

[duck_arse]

I notice on the original pcb that there is a ground looping around the switch contacts, but isolated from the switching section.

really, if the second one is  the same as the first build, we can draw one of 2 conclusions: either you've done the same wrong twice, or, there is something lurking in the rest of your gear. possibly the rat trap is allowing the something to show itself, but not actually causing the prob.

perhaps if you tried the rat trap and none of your other gear on a mate's guitar/amp/leads/room, and see if he's still your mate after.

[Minty]

I notice on the original pcb that there is a ground looping around the switch contacts, but isolated from the switching section

...and what might that do?

really, if the second one is  the same as the first build, we can draw one of 2 conclusions: either you've done the same wrong twice, or, there is something lurking in the rest of your gear. possibly the rat trap is allowing the something to show itself, but not actually causing the prob.

Same wrong twice is possible since I'm following the same diagram with my same interpretations.

perhaps if you tried the rat trap and none of your other gear on a mate's guitar/amp/leads/room, and see if he's still your mate after.

Good idea, I will.

I'm thinking about trying one more thing. taking out all of the switch quietening circuitry and the LEDs. Just test the relay on it's own withpower and  audio leads. Can't really go wrong with that. If it's still the same then I know it's not my bad workmanship.

[duck_arse]

ohh, and I forgot one thing: if you reused your sockets without rewiring them, they may contain the lurker.

the earth around the relay may provide some small protection to/from very high impedance circuits being interfered with/to, but mainly it just demonstates the isolation-ing principle.

you could do your test idea using your wired sockets and a double pole double throw toggle, or a stomp switch, anything you can solder as replace the relay contacts. this would flush the socket-wiring devils out. (don't forget your audio earths.)

[Minty]

Well, it's been a while!

I had a family tragedy and everything had to be shelved.

I'll be looking into starting this project again, maybe from scratch. Not sure yet.

I think the DPDT stomp switch is going to be the first thing I try - this will isolate the noise to either the audio or switching circuits anyhow.

[duck_arse]

welcome back. sorry to hear the bad news.