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Topic: Eliminating Relay pop in preamp/TVR (Read 1 time) previous topic - next topic

Nick_A

I have built a TVR controlled by a pro mini using relays to switch volume and source.

Source switching is quiet, but the volume relays are not.   The puzzling thing is that the noise is not consistent; it may be loud, or virtually inaudible from the same relay.   I had suspected contact bounce as the source of the noise, but it is only generated when there is a signal present on the input; if I mute the source, no pops or clicks.   I can also switch the source while music is playing and that doesn't cause any pops.

Because it is a transformer volume control, I don't think there is a DC offset on the seconday. (where the volume relays are)   There are snubber diodes on all of the relays, which are Takamisawa RY5W-Ks.   I prototyped the setup with a manual rotary switch, and that was silent, so I don't think any other bit of equipment is introducing a DC offset.

I have read of a possible capacitive coupling from relay to switch contacts, but I would have thought that this would occur even if there was no (or a very low) signal present on the contacts.   People have also talked of a high-pass filter on the input, or a 1M resistor on the output, but I would prefer to fix this on the coil side of the relays if possible, not in the signal path.

Any help would be appreciated.

Magician

Do you have a circuits schematics?

Nick_A

#2
Apr 09, 2014, 08:37 am Last Edit: Apr 10, 2014, 09:50 am by Nick_A Reason: 1
Here is a simplified schematic showing the actual switching.   I haven't included the digital side with the shift registers driving the ULN 2803s.   I also haven't included the other 25 relays for all of the other taps and inputs.   This is my first attempt at using the schematic layout package, so please pardon it's roughness.

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