i need to make my relays quiet!

[youngb4]

Hello all, glad to finally be part of this community, I should have joined long ago seeing as how often I'm here.

Anyways, my problem is this: I am building a guitar pedal switching system that will allow me to true bypass any number of pedals that i have selected by toggle switches with one foot switch tap. (after doing some research online I found that Carl Martin makes something called an Octaswitch .... same idea if any of you are familiar with that product) My switching logic works fine, its just that I cant get rid of this relay "pop" every time i switch the effects in and out. It seems to only do it in the effects loop of my amp (egnater rebel 20), before the loop its quiet as christmas eve at nannas house. Im using fairly high quality signal relays (telecom) that i picked up on digikey and i am using proper diode protection. Does anyone have any ideas of how to atleast muffle or quiet the pop? Here's the relay Im using--- http://search.digikey.com/scripts/Dk...me=255-1078-ND
Its a 5v DPDT relay and fits pretty nicely in a 16 dip socket so id prefer to stick to this kind of foot print and type.
Any tips and advice are very much appreciated and thanks very much for your help in advance!

[h_a]

Switching DC can cause this noise.

Also, do you switch also the ground connection? If not, this can also cause a DC-offset.

Have fun, Hannes

[woodturner-fran]

AS he said!

Most likely one of your pedals is injecting DC into the circuit.
I had this on a preamp one time. Took me ages to figure out that when I disconnected the tuner, the clicking went. Turns out the tuner was passing on DC that it was taking in on its aerial/cable connection.

Put a meter on the outputs of the pedals and see what happens.


Fran

[AndrewT]

is it the mechanical noise of the relay switching?
or
an electrical signal that is being sent through the amplification system to the speakers?

[youngb4]

Thanks to all who have replied so far!

h_a: I am currently not switching the ground connections, all the input and output grounds are just tied together. I assume I would have to implement another relay for each channel in order to switch the grounds?

Andrew: Im pretty sure its the sound of the relay switching that is getting amplified thru my speaker because i can hear the click and a pop thru the speaker (but only when the system is implemented in the effects loop?!?!) I'm not sure if any DC is getting passed thru or not

[amc184]

It is most likely to be what everyone else says; you're switching DC. Something upstream of your relay is producing a signal with a DC component. You'll always get a pop trying to switch it.

You're best bet is to put a high pass filter right before the relay. This will block the DC part of the signal, but let the AC part through. Chose a filter with a suitably low roll off frequency, something less than about 5Hz. C=1uF and R=47kR should work. Preferably use a film capacitor.

[head_spaz]

As mentioned above... use dc blocking caps on the input/outputs, and then place a 1M resistor on each outboard end of these caps to your Vbias/signal-ground.

The caps will block any DC offset... and since the caps have slight leakage and will partially charge (milivolts) when the circuit is open, the resistors will drain whatever charge builds up without affecting your impedence too much.

Works like a charm.

[youngb4]

Thanks guys for the tips!

So do you think i should just include a high pass filter before each input to the relays and not the outputs, or should I do both? Im in the process of designing a PCB and dont have too much more room so the bare minimum is preferable.

Also head_spaz, do you mean I should substitute amc184's suggestion of a 47k resistor for a 1Meg or use both?

Thanks again in advance

[youngb4]

attached is a picture of what I've gathered from the last 2 posts, would this be correct?

Thanks again

[youngb4]

can anyone verify that this configuration would be appropriate before I order the parts?

Thank you in advance