tremolo switch pop

[m-theory]

This is the first time I've encountered a switch pop, so I'm a bit stumped.  I've read through the threads on the subject, and have followed recommendations I've read, but haven't yet resolved the issue.

This is on the Hearthrob trem, on nokaster's vero layout (which I cannot find in the gallery right now). 

I installed a 2.2m resistor at the input, just assuming that would resolve it.  No luck.  Then, I took some voltage readings.  I have a scant .03 mA at the switch input, but a rather hefty amount at the output.  When I first put the meter to it, I read 19.7 mA.  That quickly drops to about 4mA, where it stays.  I would think that anywhere from 4 to 20 mA would be enough to make an audible pop. 

Once I verified that C4, which is 4.7uf elec cap at the output, was oriented correctly, I assumed it was leaking, so I replaced it.  Same results. 

I'm not sure where to go from here.  Obviously, I have to find a way to get that DC off the switch, but I really don't know what to do.  Can I install a 2.2m resistor at the output as well, or will that hose up the output impedence of the circuit? 

[darron]

hmm... can't find a schematic on it right away. i could find markm's pcb layout here, but that doesn't help much:
http://www.aronnelson.com/gallery/main.php/v/MarkMs-Gallery/album15/album76/Hearthrob_Tremolo_PNP.gif.html

there's only so much that you can try. regarding putting a 2m2 on the output cap, you CAN do that without causing any problems whatsoever. if there's already any resistance to ground after the cap you don't need to though, such as if there's a volume pot which has a leg tied to ground.

another thing you may want to try is to remove the LED (just desolder one leg) to see if that makes a difference.

when you test it for pop, i reckon testing it inside the enclosure with the bottom panel on actually makes a difference.... maybe that's in my head? hehe.

if all that fails, then i'd try replacing the 4.7uf electro at the end with a 1uf film cap, such as an MKT.


if you find it was the led, then maybe put a larger limiting resistor or try the suggestion here:
http://www.muzique.com/lab/led.htm

failing all that, i suppose you could go fro millennium bypass switching? i've never used that though.

good luck. pops are very frustrating.

[m-theory]

if there's already any resistance to ground after the cap you don't need to though, such as if there's a volume pot which has a leg tied to ground.

There's not.  The negative leg of that cap goes right to the output. 

Here's the populated version of the layout you found (still not the vero I built on, but the same circuit, as far as I can tell)
http://www.aronnelson.com/gallery/main.php/v/MarkMs-Gallery/album15/album76/Hearthrob_Tremolo_LAYOUT.gif.html

I'll try a 2.2m resistor on the output first, and if that doesn't resolve it, look at that LED.  I've never had a switch pop issue before that was intolerable like this, and it just blows me away that, after the scores of boosters and dirt circuits I've built, it was a seemingly innocuous tremolo circuit that brought it into my life! 

Thanks!

[darron]

nobody suspects the butterfly... 

[m-theory]

No luck...

I tried the 2.2m resistor on the output jack, and still had the pop, so I moved it right to the board, between C4 and ground, and it still popped.  I clipped one side of the LED, and it still popped. 

I'm officially frustrated now. 

[darron]

try a 1uf film cap on the output for lower leakage?

edit: or anthing above 0.1uf that you might have lying around... you can swap it out for a 1uf later if it helps.


i just looked on the layout.. there's also no power supply filtering??? put an electro across the +9v rail to ground as close to the board as is convenient. anything from 100uf-1000uf couldn't hurt. if there's no LED on the circuit then i don't think this could be a problem, but supply filtering is generally a good idea anyway especially on a shared supply (non battery), so consider it an *upgrade*/custom mod (:

out of curiosity, are you powering it from battery or DC supply?

[darron]

grounded input won't fix the problem either.... but it never hurts for true bypass switching. www.dazatronyx.com/support/true-bypass-technique.pdf

hopefully someone who's built the circuit will be able to suggest a cure.

[m-theory]

I'll try the 1uf cap on the output.  Are you referring to replacing the 4.7uf electro w/1uf film, or an additional cap? 

It's currently powered w/battery, but I've included an adapter jack as well, so that's an option.  I'll throw a 100uf cap on the power rail as well.

Here's the switch wiring I use:  http://www.generalguitargadgets.com/diagrams/switch_lo_3pdt_ig_dcjack.gif

Here's a (slightly blurry) shot of the build:



Thanks again. 

[darron]

wow. looks really well built. yeah, the output 4.7uf i was thinking to try replacing with a 1uf film. the pop has to come from a voltage change, either at the supplies etc. or on the caps. ideally we could always use a small 0.1uf film cap on the output for quality of sound and minimal capacitance and leak for pop, but we don't know what the effect might be next driving so we like putting massive caps on the output just in case, but these can cause pop problems. i think the healthiest compromise if it's just an effect pedal is the largest film cap you can et of practical size with true bypass...

how did you connect the battery clip? i've been thinking about using those for the larger enclosures but didn't want to put the screw through.

[m-theory]

Ok, I've got plenty of 1uf film caps that'll fit just fine there, so I'll try that when I get back to it.  Thanks again.  I found last night that, when I FIRST touched the meter to check switch voltage at the output, I had nearly 2 volts!  That seems more than enough to produce a pop, and that number only dropped as low as 4 mv, so that's likely where my pop is coming from. 

To attach battery clips and board standoffs, I use an epoxy that's made for fusing plastic.  I've tried many different types of adhesives, and, for whatever reason, this is the only thing that I've found that works.  I have a buddy who's had success with JB Weld, but that stuff didn't work for me.  I've also tried "normal" epoxies, with no luck.  The only products I've found that hold securely to cast aluminum are the plastic epoxies. 

[m-theory]

I tinkered with this some more yesterday, to see if I could eliminate that pop.  I first tried a 10uf electro in place of the 4.7u at C4.  That made it worse.  Then, I swapped that for a 1uf film cap, and the pop is less, and seems to all but disappear after a couple of switches in/out.  After a few switches on and off, all that remains is a very slight click.  I guess I can live with that, much more so than the horrendous, 24/7 "POP" that I had before, but this seems nuts to me. 

Is there NO way to completely eliminate the pop in this one?  A buddy of mine said his Demeter trem is the same way (he's converted it to TB, so it's not entirely stock, but he said that it had popped before as well)...he has to switch it on and off a few times before lifting the amp standby, and then it's good to go for the night, but if he forgets to do that, the first engagement is met with a horrendous switch pop. 

[darron]

i'm glad that removing the electro on the output helped out with the problem.

it seems that single transistor stages and inverting signal stages are more prone to pop than say a non-inverting opamp. i wonder if anyone can jump in and saw if that is more or less likely to be true?

as for the switch 'warm up phase', this is something that i'm just getting now. i had always bought my switches from smallbear and never noticed them needing 'warming up'. recently i bought a batch off a significant amp manufacturer that were RoHS and he swears his were better. i put them in a circuit and POP! wow. that was really fricken annoying. but then after 3 or so clicks it became something tolerable.

i once gave a guy a true bypass loop box for a tone-suck pedal he had. he reported back after a week of gigs and said "wow. and you even wore the true bypass switch in so that it doesn't pop and it has that nice click feel under your foot" to which i responded "nope.. it just slapped it in there..."

it could be a matter of lubricant at the contacts settling in, or mild corrosion or something that needs a scrape. i'm sure the experts like R.G. will know as they have been in the biz so long that they have had returned products and know what went wrong. it seems most the people who have the knowledge move away from true bypass.

i'll watch what people jump in and say with keen interest.

[m-theory]

This is definitely a "POP," and not the standard mechanical "click" that you typically have with any switch.  This is audible in the speaker.  My guess, although I haven't confirmed this with voltage readings, is that the POP I'm hearing is DC that's on the switch, and that after a couple of clicks on and off, the majority of the voltage drains off the switch and all is good after that. 

Why that happens isn't something that I understand, but I do recall reading about it in the past.  I also don't understand why it wouldn't drain off with the stock 4.7u or higher cap, either, nor why a drop-down resistor wouldn't take care of it. 

[darron]

This is definitely a "POP," and not the standard mechanical "click" that you typically have with any switch.  This is audible in the speaker.  My guess, although I haven't confirmed this with voltage readings, is that the POP I'm hearing is DC that's on the switch, and that after a couple of clicks on and off, the majority of the voltage drains off the switch and all is good after that. 

Why that happens isn't something that I understand, but I do recall reading about it in the past.  I also don't understand why it wouldn't drain off with the stock 4.7u or higher cap, either, nor why a drop-down resistor wouldn't take care of it. 

maybe we should start putting pull-down resistors on the pole side of the switch as well as the throw just to be safe    hehe