The lone pop(per)

[aettin]

Hi there-
I built a ggg envelope filter (DOD 440) pedal recently and while I've built a couple successful diy pedals before, this one has a rather odd problem. I've seen pedals consistently pop when switched on, but this one pops only the first time it's switched on after getting power (I have a 9V switch so the pedal doesn't drain power when plugged in). After that initial pop, I can stomp as much as I want, and there's not a pop to be heard. What's going on? Does it have something to do with this weird VTL5C4/2 Vactrols LED/LDR unit thing? This single pop makes me think a pull-down resistor may not do much good? What do I do?

Here's the schematic and parts layout if it helps.
http://www.generalguitargadgets.com/pdf/ggg_ef440_sc.pdf?phpMyAdmin=78482479fd7e7fc3768044a841b3e85a
http://www.generalguitargadgets.com/pdf/ggg_ef440_lo.pdf?phpMyAdmin=78482479fd7e7fc3768044a841b3e85a

Thanks so much folks. I'm a bit out of my depth here, and would really appreciate your help

[Gurner]

such popping is down to all those caps in your circuit charging up & opamps biasing up at once, which is likely to be a challenge to address if you're not used to such designtechniques, so I'd be inclined to go for 'masking' techniques...for example, a basic one would be slowing the supply voltage to the opamp with a large resistor & cap  - this means it doesn't get to output much until the rest of your circuit has settled at initial power up etc.

[ayayay!]

After that initial pop, I can stomp as much as I want, and there's not a pop to be heard.

That's good and mostly common.  Only one initial pop is acceptable, to me at least.  I always plug my pedalboard in and cycle every pedal at least once before I turn my amp on. 

Always use a pull down resistor. 

[aettin]

Thanks so much for your input guys.
ayayay!: I'm glad to her that a single pop is normal.. for a moment I thought it may have been my fault and I was feeling a bit embarrassed. Also.. I think R18 (the 1M5 resistor functions as the pulldown in this circuit). Cycling's a really good idea.

Gurner: thanks for going into the details about what causes this abnormality. I'm very interested in your solution, but have no idea about how to implement. I don't want to presume too much on your time, but is there any way you would be able to tell me exactly and specifically what and where I need to solder to slow the supply voltage to the opamp with the resistors and capacitors you speak of?

Cheers.

[PRR]

> pops only the first time it's switched on after getting power (I have a 9V switch so the pedal doesn't drain power when plugged in). After that initial pop, I can stomp as much as I want, and there's not a pop to be heard.

Pop it, put it back in bypass, and wait an hour, a day, a week. After some time, it will again pop when engaged.

You can live with this "fault", as long as it doesn't discharge much before the gig is over. Pop it in setup and enjoy.

In this case: the output cap is not drained. When powered-up but not connected, this cap's right end will rise to 4.5VDC. The first time you connect it to something, 4.5V POP! and then the right end is at zero. Disconnect, and the cap right end will (typically) s_l_o_w_l_y rise toward 4.5V again. If the cap leaks, perhaps in a minute. If the cap's leakage is very low, maybe a day.

If it bothers you, do this:

[aettin]

This is fantastic! What an easy fix. Gonna try it this evening, thank you. If you don't mind, just for my own edification, how did you determine that the resistor needs to be 220k?

[Gurner]

In this case: the output cap is not drained. When powered-up but not connected, this cap's right end will rise to 4.5VDC. The first time you connect it to something, 4.5V POP!

Maybe it's how I interpreted aettin's initial description, but I read this popping as still happening with something connected to the effect output all the time.....aettin, can you confirm, if this is the case, then your follow on connected effect will likely be pulling down the voltage that PRR descibes (if the follow on effect is well designed in itself!).

I'd read this problem as more aligned with initial circuit 'power up' popping with everything already connected (input & output) vs the output floating due to no pulldown.

[ayayay!]

Paul, while I've got your attention (sorry to hijack from you aettin) what's your remedy for the Orange Squeezer pop?  Seems every other one I build pops, and I once saw a great explanation by Mr. Hammer that I can no longer find. 

Thoughts?

[aettin]

Gurner thanks for bringing that up. The EF440 is the first pedal in my chain. Followed by a rebote delay and then a tremolo. All three pedals have pulldown resistors after the input. I think I understand what you're saying about the following pedal acting as the pulldown, but if the pedal isn't on, with true bypass wiring, isn't the current not going through the following circuit, and therefore not getting the benefit of its pulldown?

So I guess to answer your question about clarification, there is something always connected, but it's not always on, and it all (should) be connected in true bypass.
Initial pop occurs after I plug in the output, switch on the 9v and stomp the first pedal in the series with all other pedals off.

To be a thorough as possible, before sending this I did a liittle experimentation, and plugged in the chain, powered up the 9v, switched on the last pedal in the chain and then powered up the EF440, in hopes that the pulldown of the last pedal will pulldown the pop of the first (with it being on as per my theory above)..... and still POP. Damn, I guess I'm not as good as I had hoped. Haha.. Any thoughts?

[PRR]

Engaged or power-up?

These circuits always POP at power-up. The transistor or opamp rises from zero to some DC voltage, often "instantly".

> resistor needs to be 220k?

Low enough to drain the cap, high enough to not add much load. In this case the opamp can pull load but the 0.047u cap can't put bass into a low resistance. More than 100K, less than 1Meg? You have a 220K elsewhere and I thought you might have another nearby. If not, 150K, 470K, what ev er.

[aettin]

Worked like a charm!! What a great suggestion PRR. And thank you to everyone else who helped me through this.. I can't tell you how happy I am.
All I had lying around was a couple 10K's, a 1M and a 22M, lol, so tried the 1M. Quiet as a mouse!! Will the 1M kill my battery significantly enough for me to go to radioshack and pay $5 or whatever for a 470/ 220k?

[PRR]

> Will the 1M kill my battery

Not in the least. It's only draining the cap's stray charge. Like draining the dew off your porch: I suggested a 1" drain to be sure, you tried a 1/4" drain and find it entirely sufficient for your dew; life is good.