True Bypass Pedal Popping with LED

[Shawk]

Hi.

I couldn't find the specific answer on this in the archives so I thought I would post this.

I built a dual loop true bypass pedal with leds. The led circuit is wired with the negative leads to ground and they are each broken with one side of  each of the 3PDT switches.

The leds I'm using have a operating voltage of 2V and a maximum current of 20mA. I am using a 2.2K resistor on each negative leg of the leds.

With 9v DC power connected to the unit, I get pops when turning the loops on and off.

When the power is disconnected, switching is quiet.

I've read about using capacitors, and larger current limiting resistors to reduce or eliminate popping but which exactly should I use?

If I were to use maybe, super bright leds with high current limiting resistors, does anyone have the Mouser part numbers?

And if I were to use capacitors, what size do I need and where does the leads go?

Thanks

[Mike Burgundy]

so aside from the LED-and-resistor pairs there's no electronics in there, right?
Then using caps (for blocking DC) is useless - there's nothing to block.
ry using a larger resistor on your LED: this popped up a while ago on the BBS. The sudden current draw can produce pops.
Also pulldown resistors (just one from the loop to ground, 1M or something) might work but if you can get away with not using them I'd leave them out.

[Shawk]

Thanks for your reply.

No, there are not other electronics in the box and I do not have any pulldown resistors in there.

I tried a 4.3K resistor in there and seems that just seems to make the leds less bright. (obviously)

If it doesn't pop at all when the DC is unplugged, there has to be a fix to make the leds work without popping. Or, greatly minimize it at least.

Would a super bright led and maybe a 22K resistor help any?

ANY ideas would be greatly appreciated.

[Kleber AG]

Try a 100uF cap across the "+" and "-" terminals of your loop box, this cap would buffer the sudden need for voltage when you do switch loops...
errr... don't forget to put the cap well oriented/polarised (+ and -)
Try it, let us know if it works
There is a discussion involving "pops" the last days where they talk about these caps....

Hope it solves your "pop" problems
Kleber AG

[Shawk]

Ok, I lifted the DC ground from circuit ground and found no difference in the pops.

Now, by having the DC ground seperate from the circuit ground, I tried these things:

Tried the cap. 100uF 35v Sprague. Did nothing. I am assuming that the short leg of the cap and the black stripe on that side is negative right?

Put a 1M ohm resistor between the signal output and chassis ground. This helped a lot on reducing the pops.

Put a 1M ohm resistor between the + and - terminals at the DC jack and this helped even more but will this hurt anything?

[Skreddy]

Use the brightest LEDs you can afford.  Bright red, for example, will be plenty bright if you use an 8.2k current-limiting resistor.  Bright blue, in my experience, requires a smaller resistor to be as bright as the red, like maybe half.

R.G. has written about the fact that if you're using a stereo jack on the input side to complete the ground for the power, then you risk generating noise if the contacts are dirty or oxidized.  He suggests moving the stereo jack to the output side.

I've also heard people say that it helps to break your LED resistors into a pair,  one on the negative and one on the positive side, to boost the efficiency of the 100uf power-supply decoupling (LED buffer) cap.

I've seen a schematic by a studio audio wizard who suggests using a true switching jack to turn power on and off instead of the cheap 'cheat' that we pedalbuilders have adopted with the stereo jack.

I'm not sure how you're wiring everything together, because I've made several Dual Loops without any pops, and I've never had to add caps or resistors or separate the signal from the power grounds to help in that regard.   I do place my current-limiting resistors on the + side of the LED and just make/break ground with the switch.

All you're doing with the 1M across the power rails is draining current (short circuit).  

Correct on the cap orientation.

The 1M resistor from signal out to ground just provides a drain to the input cap of the next device in line.   What is next, by the way?  Amp?

You're going to have to go into more detail about the specifics of how you wired this thing, because if you have truly isolated the LED's ground from the signal grounds, there couldn't possibly be any pops.  But I doubt that everything is really separate.  Are you using a stereo input jack to switch the power ground, for example?  Do you have all the signal grounds hard wired, or are you expecting them to make ground through the chassis?  Etc...

[toneman]

Hi Shawk,

U wrote---
"I built a dual loop true bypass pedal with leds.
The led circuit is wired with the negative leads to ground and they are each broken with one side of each of the 3PDT switches."

then, U wrote---
"The leds I'm using have a operating voltage of 2V and a maximum current of 20mA.
I am using a 2.2K resistor on each negative leg of the leds."
also--
"With 9v DC power connected to the unit,
I get pops when turning the loops on and off."

:?  i just havent got the hang of "quotes"   :?

So, if I understand U correctly,
U have an "unpowered "  dual-loop.
Help me out...by "dual-loop" do U mean an A/B box?
or, do U mean a "dual" A/B box?
So the only thing U use the 9V pwr 4 is for the LEDs(?)
U say *without* 9V applied(LEDs not working) U have no pops(?)
Don't see how U can get pops unless U are generating
"inductive kick" at turnon/turnoff(?)  
With a LEDs 20ma, don't C how....
My first suspect is gnds not correct.
R U switching the gnds on/off when U do the A/B?
Got a schemo?
What about a jpg of your actual wiring...?
Please excuse my density.....  :?
I have my lightpen ready to probe your circuit
stayunpopped
tone

[Skreddy]

I assume he means the same basic idea as this Dual Loop...



Let me show you how I wire mine (using switching jacks for the loop ins and outs so it's a bypass when nothing's plugged in)...

[Shawk]

Sorry for the confusion.


I wanted to see what the pops did with the negative and postive voltages for the leds by wiring directly to the DC jack and not using chassis ground to run the negative voltage through.

No difference.

I do not use the stereo jacks as I am using DC jack. The next device in line is the amp.


I basically it wired like your Skreddy but:

No stereo jacks, no batteries.

Two switches instead of one. These are the blue 3PDT's from Small Bear.

Negative DC  to chassis ground, negative side of led has 2.2K resistor and is connected directly to the middle pole on one side of the 3PDT switch and broken. (on/off)

Postive side of leds has no resistor and both leds are wired directly to the positive side of the DC jack.

The voltage and mA current I described in my first post was from the manufacturer's spec sheet. No actual readings has been taken.

Some other things to note:

The jacks are all Switchcraft.

Led legs has heat-shrink tubing on them.

Anymore ideas?

Thanks

[toneman]

AMZ has a really good explanation of TrueByPass here:
http://www.muzique.com/lab/true_bypass.htm
and here:
http://www.muzique.com/lab/truebypass.htm

GEOFX's explanation is a little more complex here:
http://www.geofex.com/Article_Folders/bypass/bypass.htm

There is no need 4 the 3rd part of a 3PDT switch, the part
that switches the LED on/off,  to B tied to signal gnd.
The LED part of the sw can B completely isolated.
Just an LED and resistor connected thru the sw to the Batt.
Hope this gets it 4 U...
T

[mrsage]

I assume he means the same basic idea as this Dual Loop...

Interesting...So does that just switch from Loop A to Loop B? Or is there an option to bypass both entirely? Can you turn them both on at once?

[Skreddy]

Yes. No. And No.  Of course each effect in each loop can be turned on/off too, so it doesn't really need all those other options, IMO.  It's intended for effects that you never use at the same time, like Fuzzface on one hand and compression and chorus on the other.
It'sa lika DEES.

It's rather obvious if you think about it; a schematic is virtually unnecessary.

[Shawk]

I am still currently messing with this pedal.

I have noticed that for some reason, putting a higher value resistor on the negative resistor legs doesn't do any good at reducing the pops. I tried 20.2 (18K in series with 2.2K).

Again, all grounds are common including the DC power ground. DC ground is connected to the chassis ground, LED negative leads are connected to ground but broken on/off with the 3PDT switch. Positive leads are connected directly back to the DC jack's postive terminals.

Plug in the power to the LEDs, pops. Unplug the power to the LEDs, no pops.

My pedal is wired similiar to Skreddy's unit exept that I use two switches instead of one.

The LED is broken with one side of the 3PDT switch. Chassis ground on middle terminal, negative LED leg to the adjacent terminal for "On".

My unit works great and is dead quiet without the leds. Again I say, without LEDs.

The only thing I did to actually reduce the pops when I was experimenting was when I put a Sprague Radial Lead 100uF Cap in series from - DC terminal to chassis ground. This also dropped the illumination of the LED's considerably. I took the resistors off the LED legs and it still wasn't bright enough. No pops though.

These LED's I am using are the Mouser # 35CA007 & 35CA008 LEDs.

Adapter that I am using at home to test is rated at 9V 800mA output.

Seems like I tried everything. Anyone else got any ideas?

How about some sort of optical type switching that would allow only a trace of voltage through the 3PDT switch and control the higher voltage on the LED circuit? This way it would keep high voltages away from the switch.

[Gilles C]

Did you try isolating the DC ground from the Audio Ground?

That's what I did in this A/B+Loop Box to make sure there would be no connection between the LED circuit and the audio circuit.

http://www.finitesite.com/gtechblues/Files/SWschem2.gif

Gilles

[Shawk]

Did you try isolating the DC ground from the Audio Ground?

Yes. Still popped. I think the 3PDT switch is the culprit but I tried several. The off varying degrees of popping. Needs the lowest voltage/current possible while still having enough to light an LED.

I don't think that having the grounds seperate is a good idea anyway because the audio wires inside the enclosure are not shielded. May experience hum in some setups.

[Gilles C]

Ok, I used shielded wires in mine, so I suppose it helped in my case.


Today, I received a few 3PDT switches I ordered from Aron. I want to experiment a little circuit to see if it would help to get rid of pop-ups.

So I will build a new Switchbox with this kind of circuit for the LED.



The parts values in the schematic are just a starting point. I'll adjust them depending on the result.

Gilles C

[Nick123]

What about low current  LED's?
I  allways  use  R=8k2  with  red  LED  ( around  0.9mA )
because  2mA  is  max  current.
As  far  as  I  remember  someone  suggested  that  use  of  
low  current  LED's  could  reduce  pops.

[Shawk]

I have a variety of super bright and low current LEDs coming from Mouser that I am going to try.

I have some higher value resisitors coming too.

One question though, what are you guys using to house the LEDs in? The ones I were buying, already had a bezel with it.

And Toneman, I got your PM but I have no way to scan or draw the unit to send to you. Sorry.

[gtech]

For a while, I just pushed the LED through a hole just tight enough to hold it tight.

But for the last high current LEDs that I bought, I asked the dealer for the correct bezels for those LEDs.

After seeing the look they give, I decided to use them again.  

Gilles

[Shawk]

Ok, so I got the other LEDs in and I noticed that to drastically reduce the pop where I can live with it, I had to use a 25v 33uF Sprague Can Capacitor in series with the negative LED leads and use a super bright, low current led.

This does not get rid of the pop but greatly reduces it.

There are no resistors on the LEDs now. Resistors just do not work at removing pop in the unit. I used all the way up to 18K and found no difference in the pop. All this did was reduce brightness.

MAX forward voltage for the particular LEDs is 1.8V and I am reading 1.6 volts on the positive side using the capacitor.

My questions are:

Is it ok to use the capacitor?

What kind of problems would I run into in the future if any?

What are the chances of the cap going bad and shorting out and delivering the full 9v to the LEDs and frying them?