Switch popping in AC circuit

[skern]

Hi guys. I have a synth pedal called the AVP Polyrhythm which uses 12V AC @ 400mA. There is a loud pop when engaging the pedal using the SPDT toggle switch. After researching on these forums it seems like I have to add a capacitor somewhere, but I'm not sure where exactly to add it, and I'm not sure which value capacitor I need and whether it's different because I'm dealing with AC.

It's currently wired up using a 3-prong power jack with the shunt going to ground, though I'm not sure that's relevant here. Any advice would be much appreciated. Thanks!

[iainpunk]

i suggest you measure DC voltages on the switch pins, both on and bypass, then we can determine what and where,

cheers, Iain

[skern]

i suggest you measure DC voltages on the switch pins, both on and bypass, then we can determine what and where,

cheers, Iain

Which pins, exactly? Across the two non-pole pins, you mean?

This switch seems to behave strangely. When it is off, the middle pin connects to one side, but when it is on, all 3 are connected. Is this normal?

[Rob Strand]

I have a synth pedal called the AVP Polyrhythm which uses 12V AC @ 400mA. There is a loud pop when engaging the pedal using the SPDT toggle switch.

If the SPDT is a power switch as opposed to a bypass switch you will need to redesign/modify the power supply a bit.

Devices powered from AC adaptors often have voltage doublers to create dual supply rails inside the unit.   The doubler powers up one side of the dual rails then the other and that creates a power glitch and a thump.

The way to reduce the thump is to put some resistance in series with the 12V AC line.    Say 10 ohm to 47 ohm.   What that does is slows down the rate the power rails come up.   Increasing the filter caps on the supply rails can also help.

However if the device is pulling a lot of current, like  the full 400mA,  a 10 ohm resistor is going to introduce too much voltage drop.   So you will have to reduce that resistor perhaps as low as 1 ohm.   When you do that it becomes less effective.   You can increase the caps without too much problem but it might not be enough.

You really need to trace out the supply and know how much current you are pulling and how much voltage you can throw away across the resistor.     All fiddly stuff and you need to know what you are doing.  If the resistor which works is too small the whole idea is useless.    The other thing is the resistor's power rating needs to handle the current.

Often you can only tame the thump not remove it.  Removing needs a different idea altogether.

[PRR]

Are you "engaging" by turning power on and off? That is sure to pop.

You need to leave the power on, and switch the audio. If I have found the right box, it doesn't have audio switching?

[skern]

Are you "engaging" by turning power on and off? That is sure to pop.

You need to leave the power on, and switch the audio. If I have found the right box, it doesn't have audio switching?

I'm engaging by flipping the switch that says "On / Power." I'm not sure what you mean by 'audio switching,' but what I do know is that this power switch certainly doesn't work like any other pedal I own, i.e. the level knobs still affect the signal even when switched 'off.' So it's definitely not a normal bypass switch.

There are two other switches for the two sections of the pedal. These say "Bypass" and these don't cause any pops. I suppose the pedal is intended to be used with the power switch always "On", and using these Bypass switches to enable/disable the effect.

[davent]

Are you "engaging" by turning power on and off? That is sure to pop.

You need to leave the power on, and switch the audio. If I have found the right box, it doesn't have audio switching?

I'm engaging by flipping the switch that says "On / Power." I'm not sure what you mean by 'audio switching,' but what I do know is that this power switch certainly doesn't work like any other pedal I own, i.e. the level knobs still affect the signal even when switched 'off.' So it's definitely not a normal bypass switch.

There are two other switches for the two sections of the pedal. These say "Bypass" and these don't cause any pops. I suppose the pedal is intended to be used with the power switch always "On", and using these Bypass switches to enable/disable the effect.

Yes, and turn your amp on last after powering up all the other bits, reverse to power down, amp off first,  avoids amplifying all the various pops and noises.
dave

[anotherjim]

I don't think this AVP is made anymore. As such, it could become more valuable and modifying it will harm the value.

The neatest way to use it as a stompbox would be to get a bypass loop pedal. This basically is the footswitch circuitry you would need to add in the AVP in its own box with 4 jacks sockets and you only need patch cables to connect the effect up from the "send" and "return" jacks.
Probably one of the simplest DIY pedal projects.
http://ashleyjsaunders.com/blog/build-true-bypass-loop-pedal/