Build Your Own Clone Message Board

Hi All-
I searched quite a bit on the topic of switch popping but could not find a definitive answer. I've built the Chorus kit and LOVE the sound of it-with the exception of the very loud "pop" when switching it. The noise is very noticeable and I actually had to put my amp in standby to switch the unit in and out while playing with an orchestra PIT for a musical. The first time I hit it I could see the audience turn and look toward me )
Is there a way to address this? Running a Les Paul and Boss TU-3 & OS-12 before the Chorus-Phase 90 and Carbon Copy after it.

thanks so much- I really want to keep using the pedal but if I can't fix this I will not be able to.

There is no definitive answer to your question because there is no single cause of turn ON pops. Sometimes it's the switch that's responsible for the pop. Other times it's the LED. Sometimes it's the amp that causes the problem. It could even be a combination of any of the above. I have an AX84 High Octane tube amp that I built that is dead quiet with all my true bypass pedals. A few years ago I built a couple of different 18 watt amps (TMB, Lite, Lite II) and all my pedals that didn't pop with the HO popped with the 18 watt amps.

Thanks for the feedback - I have tried the unit with multiple guitars (active/passive/single or dual coil) and amps (all valve Fender pro/solid state Peavey) and in various signal chain configs ( or alone) there is no detectable change. The "pop" registers 68 dbA at 6 feet- in other words its significant. The Phase 90 is true bypass also and makes no noise. I will try a manual switch bypass - I have to say this is very disappointing as it renders the pedal un-useable. As an aside- I have a home-brew Germanium Fuzz that uses what appears to be the exact same switch (Mouser supplied) and is dead silent.
Lastly- I understand that turn on pops can be caused by DC offset or ground issues-but the turn OFF pop is just as loud.

thanks

wjl

I really can't think of a normal situation where an indicator LED would cause pops in a switched audio circuit.

Actually I think the explanation of switch popping is simple and fundamental. It is due to differences in potential between the two points being switched. The cure is straightforward - take steps to ensure there is no potential difference between the points being switched.

As far as i know popping is not normally due to the switch itself although flaws in real switches can make popping worse (switch bounce). It is perhaps possible for static charge to build on the body of the switch itself and since this results in a potential difference, be the cause of a pop.

Most audio circuits are coupled by capacitors. If one end of a coupling capacitor is connected to a jack connector or a switch terminal it is possible for this end of the capacitor to remain unconnected for significant periods of time. The jack or switch tag is simply a mechanical anchor for the capacitor wire, supported on an insulator. This means that end of the capacitor is floating and will tend to accumulate charge and potential. For example you might have a guitar amplifier input that just has the input capacitor connected to the input jack with no other components. If you then throw a switch to connect to the floating end of the capacitor it will suddenly discharge into the circuit you have connected to, causing in most cases, a pop.

The solution is to make sure that ALL points being switched are at the same potential by tying all floating capacitor ends to ground (on either side of all switches) using a high value (several megohms should work) pull down, or pop stopper, resistor.

There is another cause of switching artefacts and this occurs when you switch an audio signal. Unless the switching occurs while the AC signal is at a zero crossing you will normally hear an objectionable switch transient as the signal, on the far side of the switch, jumps from where it was to whatever instantaneous voltage the input signal happens to be at, at the exact time it is switched.

Looking at the chorus circuit diagram, while the circuit sides of the bypass switch are pulled down to ground - Input - pin 5 by R1 a 1M and Output - pin 7 by R24 a 100K, the jack socket sides of the switch are not pulled down. The assumption being perhaps that whatever the Chorus is connected to will pull them down. I would try fitting a 2.2M resistor directly across the input jack and perhaps a 1M across the output jack (although that does mean the circuit would no longer be a perfect true bypass). You might also want to replace R1 a 1M with a 2.2M if you are really concerned about input impedance / tone suck.

I had a pedal with very similar symptoms one time and it turned out to be that the input cap was leaking a full 1 vdc to the circuit input. If you have a DMM, measure the voltage on lug 5 of the stomp switch both in bypass and effect mode. There should be zero volts there.

Spot on Morgan, although leaky caps are covered by my description of the problem I did not explicitly mention them.
Electrolytic caps are perhaps the most prone to leakage problems, particularly if they are in, or have been at some point, in the wrong way round or are used in positions where there is no clear polarising voltage.