very strange bypass and popping problem

[beatnik]

Hi everybody,

I am experiencing a weird behavior on my newest pedal, an xotic bb preamp clone.

Firstly I wired it with two different millenium bypass boards, but both of them had the led that didn't light up (bypass worked ok)

Then I substituted the millenium with a standard 3pdt switching.

That worked but the pedal has a popping noise when pressing the switch.

I even added another 2.2M pulldown resistor from input to ground, but changed nothing, switch still pops.

I have no idea of what it could be. I think about some current flow to the switch, but actually I have not enough knowledge to solve this.

I hope in your help! Thanks in advance

[PRR]

> xotic bb preamp

What is that?

Schematic?

[beatnik]

Hi PRR thanks for posting.

Here you have the bb preamp schematic. It's just another tubescreamer clone, with two band active tone control.

[DavenPaget]

Hi PRR thanks for posting.

Here you have the bb preamp schematic. It's just another tubescreamer clone, with two band active tone control.

Use tinypic , imageshack is being a bitch .

[beatnik]

Ok here you have

[DavenPaget]

You should put another 1M pulldown resistor after the output capacitor , or you could try placing R1 after C1

[beatnik]

you mean after 10uF electro and before 47R resistor? I'll try and see if it works, thank you sir

[Tacoboy]

Is your effectinput switched to gnd when switching to bypass?
Also take a look here: http://www.diystompboxes.com/smfforum/index.php?topic=94871.msg819969#msg819969

[beatnik]

You should put another 1M pulldown resistor after the output capacitor , or you could try placing R1 after C1

that didn't work..still popping

yeah the circuit input is shorted to ground when in bypass.


I am thinking about something wrong within the circuit board that cause a current flow to the switch. I triple checked everything and it's allright.

Maybe a bad audio jack?

[beatnik]

Maybe a bad audio jack?

neither it is, replaced with no results.

i am sure that the strange behavior of the previously installed millenium bypass board can be a hint, but can't figure out what is actually causing the popping problem.

any voltage to check or something?

[Tacoboy]

Does the popping disappear when you disconnect your led circuit?

[davent]

In regards to Tacoboys question, you might want to explore this article on LED popping.  http://www.muzique.com/lab/led.htm

dave

[wesman26]

Hate to derail the conversation, but just for my own knowledge I'd love to be set straight on this.

Is R1 really all that necessary here?  Couldn't you just use a larger value for R2?  And does it really matter which side of the LED R2 is on since on either side won't it limit the current through the LED just as much?  Obviously C1 can't be on the grounded side of the LED because by the point the current has already passed through the LED, but I don't see a reason why the resistors can't move around.

Also with the capacitor where it is wouldn't it already theoretically be charged when the switch is thrown, rendering its placement useless?  Or is that not how it works?

Again, I apologize, these are probably silly/obvious questions, especially since the above picture functions, but regardless of how impractical it may be to know these things I'd still really like to know.

Thanks in advance,
--Wes

[snarblinge]

i'd like to continue down this path of derailment, I always use the above circuit as drawn, since i had popping issues early on. I find 33uf with 390OHMs on both sides works, never thought to rearrange them though. usually just add them to my layout.

[PRR]

> does it really matter which side of the LED R2 is on

No.

But the LED is on the panel and ground may be handy there.

But dumping LED spikes directly to signal jack "ground" is liable to click.

> Is R1 really all that necessary here?

Yes.

> with the capacitor where it is wouldn't it already theoretically be charged when the switch is thrown

Yes.

And that's why you need R1. LED off, C1 charges to 9V. Flip the switch, and a 9V cap is connected to a 1.6V LED and zero series resistance. Current will be (9V-1.6V)/0 which is infinity. Infinite current is bad for caps and LEDs. More exactly, LED has about 20 ohms stray resistance, current is 7V/20 or 350mA, still a lot.

With the suggested R1, peak LED current is ~~20mA dropping to 2mA steady. Power supply current rises slow from zero mA to 2mA, which is I guess the intended benefit (better than instant step from zero to 2mA).

[wesman26]

Yes. And that's why you need R1. LED off, C1 charges to 9V. Flip the switch, and a 9V cap is connected to a 1.6V LED and zero series resistance. Current will be (9V-1.6V)/0 which is infinity. Infinite current is bad for caps and LEDs. More exactly, LED has about 20 ohms stray resistance, current is 7V/20 or 350mA, still a lot.

With the suggested R1, peak LED current is ~~20mA dropping to 2mA steady. Power supply current rises slow from zero mA to 2mA, which is I guess the intended benefit (better than instant step from zero to 2mA).

Wouldn't that be where R2 comes in?  It seems to me that its resistance would add with the stray resistance of the LED so instead of 7V/20 we'd have more like 7V/410 or ~17mA.  Again I may just misunderstand.

Edit!!!
I just realized that I was referring to the resistors wrong.  I thought the resistor closer to the 9V source was R1 and the one closer to the LED was R2.  Upon closer inspection I was very wrong in that assumption.  So to reword my questions with appropriate labels:


Is R2 really all that necessary here?  Couldn't you just use a larger value for R1?  And does it really matter which side of the LED R1 is on since on either side won't it limit the current through the LED just as much?  Obviously C1 can't be on the grounded side of the LED because by that point the current has already passed through the LED, but I don't see a reason why the resistors can't move around.

Also with the capacitor where it is wouldn't it already theoretically be charged when the switch is thrown, rendering its placement useless?  Or is that not how it works?

That's much better.  Thanks again for your patience.

--Wes

[PRR]

> reword my questions with appropriate labels:

{sigh} Either way, I think I already answered at least half your questions. Re-Think your questions.

> Is R2 really all that necessary here?

You propose this?



This is essentially the "normal" way. Several-K resistor to +9V. The +9V typically has a bypass cap on it.

[beatnik]

Hi everybody,

thanks a lot for all the useful comments, links and theory explaination, there is a lot to learn.

Anyway, I disconnected the LED from the bypass circuit, but the pedal still pops, so I guess the problem is not the LED.

I am stuck with it, don't know what is happening. I hope you could find a solution, because I actually don't have a clue. I've tried replacing switch, jacks, checking all the onboard components and solderings, potentiometers wiring, etc..

Looks like there is some kind of popping ghost inside this pedal!!

[beatnik]

bump

[Gurner]

Unless I'm missing it, your schematic shows how your circuit is glued together, but not how tyour bypass switch with all its associated contacts are wired...and how that actual switch then connects into the circuit.

there's heaps you can do to get to the bottom of the problem, but without the full complete picture of *everything* and how it all interconnects, it's surely going to be painful.