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3PDT Pop:

EricssonB

EricssonB

Apr 5, 2011
1,287
630
CO
#1
Forgive me for posting a subject that's been hit on before, but the remedies offered before aren't quite doing it for me. I built a clone of a Stingray 2-band preamp into an enclosure, affectionately dubbed "Fæpbœx II" and had a thread dedicated to it.

To the point: the 3PDT pops like no other when switched ON. Obviously there's a current buildup, but I can't dissuade it with pulldown resistors on either side, input or output of the circuit.

I started at 1MΩ and worked my way down to 20kΩ.

The circuit is contained on the loop side of the 3PDT. The pulldowns as I soldered them in were to the left of "IN FROM THE PICKUP" and right of "OUT", both to the main ground.
MusicManStingRay.jpg


Should anybody have experience in this and could perhaps offer something that I haven't found through piles of research, please, contribute.
 
#4
Skrogh said:
Woopse didn't see this before I posted in the other topic. Look for my response there.
Click to expand...

I actually trigger only three LEDs on this pedal. The blue one (the FBIII model, different schematics) with many more LEDs has no clicking at all. Same thing happened before I even put them into enclosures.

Lol, had a false "ah-ha!" before I remembered the prototype stage.
 
#6
I'm surprised the pulldown resistors didn't help. To clarify, yes they should go between the input to ground, and the output to ground. Anyway, a couple of things to try:

1) there doesn't appear to be any power filtering on the pre-amp. Of course there was really no need for it on the original because it was powered by a battery and didn't have an LED. I'd add a 100 ohm resistor in series with the power supply to the preamp, then a 47uF electrolytic cap between the V+ and ground. With the tiny amount of current used by the circuit, the voltage drop from the 100 ohm resistor is insignificant. The LEDs should have their own dropping resistor(s) and get their power "upstream" from the 100 ohm resistor and filter cap.

Here's an example of a fuzzbox with similar power filtering, it also has a reverse-polarity protection diode and a film cap paralleled with the electrolytic for extra filtering. [Invalid or Expired Link Removed] R24 is the series resistor, C14 and C15 are the filter caps.

2) Wire up the 3PDT switch so that the preamp's input is grounded when the unit's in bypass. Link HERE. - Use "offboard wiring #5".
 
#7
Crater said:
I'm surprised the pulldown resistors didn't help. To clarify, yes they should go between the input to ground, and the output to ground. Anyway, a couple of things to try:

1) there doesn't appear to be any power filtering on the pre-amp. Of course there was really no need for it on the original because it was powered by a battery and didn't have an LED. I'd add a 100 ohm resistor in series with the power supply to the preamp, then a 47uF electrolytic cap between the V+ and ground. With the tiny amount of current used by the circuit, the voltage drop from the 100 ohm resistor is insignificant. The LEDs should have their own dropping resistor(s) and get their power "upstream" from the 100 ohm resistor and filter cap.

Here's an example of a fuzzbox with similar power filtering, it also has a reverse-polarity protection diode and a film cap paralleled with the electrolytic for extra filtering. [Invalid or Expired Link Removed] R24 is the series resistor, C14 and C15 are the filter caps.

2) Wire up the 3PDT switch so that the preamp's input is grounded when the unit's in bypass. Link HERE. - Use "offboard wiring #5".
Click to expand...

Now that's some practical advices. I'll be soldering sometime this week and try this out. Sounds just extensive-yet-straightforward enough to work.

I'll look between the two options when I get on my PC.
 
#8
Your output signal is out of phase with the input signal, which will increase the pop. Also, any leakage in that 1uF output cap will increase pop - best to use an electrolytic rated for low leakage (like the Nichicon MUSE series) or even better, a film cap.
 
#9
After trying many suggestions and passing through many websites, nothing worked. Thanks for the input.

Speaking of input, in THIS case there's positive DC coming from the input side of the circuit. Surprised me. 0.06VDC.

Said "NYAAAH" and stuck a 10k resistor between it (outside of the input cap -- could I try inside?) and ground. Pull down resistor, I know, but I hadn't gone that low before. Pop is now all but eliminated, and so is the tone of the bass!!!

So I either balance between acceptable pop and tone loss -- what? No!!! It's a preamp that I use to turn my three passive basses into zingy funk machines before they get a bit of dirt on their ears.

Any other ideas, now that I've isolated it? I guess this is the price I pay for taking something that's usually crammed into a 9V batteried bass, sticking it in an enclosure and plugging in 12V. Hmm. Maybe I should try 9V.
 
#10
The pull down resistor is in no way intended to pull the input down that "hard", it's there to prevent the input of the input-cap to drift in voltage, if nothing is connected to it, it works kinda like an antenna. 1meg ohm should be sufficient.
Have you tried to exchange the input and output caps with film ones? does it pop with the volume of your bass all the way down?
 
#11
Skrogh said:
The pull down resistor is in no way intended to pull the input down that "hard", it's there to prevent the input of the input-cap to drift in voltage, if nothing is connected to it, it works kinda like an antenna. 1meg ohm should be sufficient.
Have you tried to exchange the input and output caps with film ones? does it pop with the volume of your bass all the way down?
Click to expand...

Sounds like a trip to RadioShack. I'll have to drop in this weekend.
 

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