HELP! Trying to make a XLRtoXLR/PHONE A/B switching pedal

[sleejay80]

Hi.  I'm trying to make a XLRtoXLR/PHONE A/B switching pedal.
Similar to this Radial offering,
http://www.radialeng.com/hotshotabo.php
but with one of the output as a phone jack.

IN will be a vocal mic, OUT-A will go to PA Mixer for much of the time, but in some occasions I will step on this pedal to route my vocals into my guitar looper(phone jack), to make vocal loops.

I am a novice at electronics, but I have built a guitar true bypass looper before.  I was wondering if I could use that knowledge and a 3PDT switch for this as well.

I have drawn a diagram of what I thought up, but I am practically clueless, so if this is just out of whack, would someone please write me a diagram, or link me to one?

If I'm on the right track, here are 3 questions that are floating in my head.

I would really appreciate it if you guys can lead me on this project.  Thanks!



Questions:

[1] Where should I connect #3, when going out to OUT-B? (marked by pink question mark)

[2] OUT-A 2&3 and OUT-B TIP are not grounded when disconnected.  Is that alright, because for a true bypass looper for guitar pedals, everything needed to be grounded when disconnected.  (I've read somewhere it IS alright in case of dynamic non-phantom-powered mics, little pop noise)

[3] Will the IN > OUT-A to Mixer signal still be balanced?

[vigilante397]

First of all, welcome to the forum

Second of all:

[1] If you're using a mono jack for the looper it should be bridged to the tip of the jack. If you're using stereo that would go to the ring connector.

[2] That should be fine, though in some circuits not grounding the input can result in noise leakage (bleeding through).

[3] Yes.

[sleejay80]

Thanks for your insight.  Follow up questions:

[1] If you're using a mono jack for the looper it should be bridged to the tip of the jack. If you're using stereo that would go to the ring connector.

So both HOT and COLD from the MIC, BOTH go to the OUT-B tip, am I correct?

[2] That should be fine, though in some circuits not grounding the input can result in noise leakage (bleeding through).

Hold on, let me take back what I've said, I think I need to ground the OUT-B tip, at least, because I just imagined plugging in a mic into the looper (Boss RC-20XL) while it's on, and it would make a VERY loud popping noise.  I would be doing the same thing here essentially, so I think I need to ground the OUT-B tip.  How could that be possible, do I need a 4PDT switch?

[sleejay80]

Now how about this?

I've changed the switch to a 4PDT, and

1) Connected the IN#3 to OUT-B TIP, as advised by vigilante397.
2) Grounded OUT-B TIP when disconnected to IN.

Any additional advices appreciated!

[vigilante397]

Follow up questions:

So both HOT and COLD from the MIC, BOTH go to the OUT-B tip, am I correct?

That's correct. You're taking a stereo (XLR) source and feeding it to a mono (TS) jack. That means bridging the left and right (that's what the L and R in XLR stand for) into the tip of the 1/4" jack.

Now how about this?

Looks great If you have a 4PDT on hand I can't see any reason this wouldn't work.

Granted this whole thing is kind of ignoring impedance, but pretending that isn't an issue (which in many cases it isn't) this should be perfect for what you're doing.

[Fender3D]

XLR carries a balanced 2 phases signal, where pin 2 is positive phase and pin 3 is negative (the opposite in USA), pin 1 is GND, usually connected to mic enclosure, not to audio signal path.
Then, if you connect pin 2 and pin 3, you'll sum 2 opposite phase of the same signal, result: no signal anymore...

You should connect one of the pins to GND if you need signal at unbalanced jack output.

In this case you'll realize that if you use an european mic AND shorting pin 2 to GND you might have no or low signal at jack out, the same with a Shure mic and shorting pin 3 to GND.

If you'll use this A/B pedal always with the same mic. you can just check what's the better connection and use it that way, otherwise you should use a differential amp or an audio transformer to convert balanced signal to unbalanced.

Obviously you should take care if any phantom power supply....

[sleejay80]

You should connect one of the pins to GND if you need signal at unbalanced jack output.

You're right, Shure's site (I'm using a BETA58A) says "When an XLR to 1/4" cable is used pin 2 of the XLR is tied to the tip of the 1/4" and pins 3 & 1 of the XLR are connected to the sleeve of the 1/4"." http://shure.custhelp.com/app/answers/detail/a_id/60/kw/sm58%20wiring/session/L3RpbWUvMTQwNzAzNjk4MS9zaWQvMiozZUxULWw%3D

Obviously you should take care if any phantom power supply....

I won't be.

Follow-up question, my last concern:

Is there some way to minimize the pop noise, when connecting to OUT-A?
I presume there will be some, maybe loud in some cases, just like when plugging/unplugging XLRs when the mixer is on.
Or will there be...?

Similar product by Radial, "Hot Shot ABO", I assume is designed in a similar way, since the manual PDF specifically says it is prone to popping when using phantom power.
"Phantom power could cause loud transients in your sound system when the ABo & ABi are switched."
http://www.radialeng.com/pdfs/manual-hotshot-abi-abo.pdf

But I assume the pop is minimal/non-existant for non-powered dynamic mics like the Shure BETA58A I will be using?
Could that be possible?



This question still unanswered, but here's my updated revision 3:

[PRR]

[sleejay80]

Wow.  Thanks for this.
You've reversed it to a 3PDT switch and added a "resistor"? (You can see how clueless I am)
What was the purpose of this revision?

And, will it ease the popping issue? (If not, what can I do to minimize the pop noise?)

[vigilante397]

Adding a resistor into the circuit is called the pull-down resistor. Literally its sole purpose is to get rid of the pop of engaging the switch.

[sleejay80]

Adding a resistor into the circuit is called the pull-down resistor. Literally its sole purpose is to get rid of the pop of engaging the switch.

OK, so by doing that, I don't need to ground the OUT-B tip anymore?  That would be great.

I assume this won't be a "true-bypass" signal path anymore though, right?
(Not that it matters, just for the sake of learning)

What are the pro/cons of adding a pull-down resistor, vs making it true bypass?

[vigilante397]

Nope, this is still true bypass. Adding a buffer is what makes it no longer true bypass, and I personally don't see any reason to do that in this case.

[Fender3D]

and I personally don't see any reason to do that in this case.

Channel high gain aside...   

[vigilante397]

Channel high gain aside...   

Realistically though, what's a little extra gain between friends? 

[danmill]

Total newbie here. I solder my own leads etc and that's about it
I'm Looking at making one of these but with an XLR out. Can anyone help me with that diagram and include how to wire in the LED
Thanks

[escapeplan]

If you want to do both as xlr, you'd just have the bottom row of lugs on the switch hooked up to the same number xlr pins on the new jack as the top (so left to pin 2, center to lug 3, and sleeve is still common to all). You can still incorporate a pull down resistor off of hot if you like.

Sent from my SCH-I535 using Tapatalk

[danmill]

Cheers. I thought it'd be that simple. Not quite sure hoe to add and wire the LED though. I know you have to add a resistor which can change depending on LED and battery/power combo right?

[MaxPower]

 http://www.ohmslawcalculator.com/led-resistor-calculator

Or do a search for "led resistor calculator" for more options.

Or use Ohm's Law to figure out the size of the resistor needed to limit the current to a safe level. Check the data sheet for the led to get the voltage drop and the operating current limits.

[bluebunny]

...what MaxPower said: learn Ohm's law and how that relates to what the LED can take.

But note that the many LED resistor calculators out there will simply give you the minimum resistance needed to avoid zorching your LED.  You can typically increase that value by an order of magnitude (or more, depending on the LED).  Know what the minimum is, but then try out some other values to give you a level that is visible but doesn't blind you (you could use a trimmer for this exercise).  This approach will also reduce the current draw of your pedal - the LED can often take more than your stomp circuit!

[danmill]

Got all the gear, ready to go. Anyone able to help with how to secure the XLR plugs in to a Die cast Aluminium case?
Screws (specific) or pop rivets or something else? Gaffa? LOL
Cheers