Topic: Soundboard attenuator DIY?

[Nick_Riviera]

I've got a Roland R-07 and an upcoming show I'm considering trying to get a soundboard from. It has a mic in port and you can turn the power off and run powered mics, but from what I've read (on the R07 review threads here) I'd need an attenuator to patch in a SBD.

I'm very much a DIY sort of person, so I'm wondering how exactly I can make one, and how much troubleshooting might be involved - is it plug and play, or would I have to mess with the sensitivity and give the sound guys a reason to dislike me?

Apart from that, I've been really happy with the R07 so far. Very compact and some great features. My only wish might've been an xlr connection over the 3.5mm.

[goodcooker]

Here's a pad diagram that can be built into the shell of an XLR connector. I made some years ago. You can fit the necessary resistors inside the shell of the XLR. It's just an Lpad type of voltage divider across pins 2 and 3.

[Sebastian]

Here's a pad diagram that can be built into the shell of an XLR connector. I made some years ago. You can fit the necessary resistors inside the shell of the XLR. It's just an Lpad type of voltage divider across pins 2 and 3.

This method only works with a balanced signal. While this is obviously the case with most SBD feeds these days, there have been occasions in the past in which I have been given an unbalanced signal from the board when all balanced outputs were already taken. Therefore I'd suggest a slightly different approach that also works with a single-ended signal.

A single 4.7kΩ resistor (which is a standard value) in series with the non-inverting signal (pin 2 of the XLR input) will form a simple resistive divider with your R07's input impedence (4.5kΩ). This roughly divides the voltage in half, giving you a -6dB attenuation. Use a 15kΩ resistor instead for -12dB or 47kΩ for -21dB. You can leave pin 3 of the XLR input floating because your R07's input is single-ended anyway. And you'd only need one resistor instead of three.

[checht]

Here's a pad diagram that can be built into the shell of an XLR connector. I made some years ago. You can fit the necessary resistors inside the shell of the XLR. It's just an Lpad type of voltage divider across pins 2 and 3.

This method only works with a balanced signal. While this is obviously the case with most SBD feeds these days, there have been occasions in the past in which I have been given an unbalanced signal from the board when all balanced outputs were already taken. Therefore I'd suggest a slightly different approach that also works with a single-ended signal.

A single 4.7kΩ resistor (which is a standard value) in series with the non-inverting signal (pin 2 of the XLR input) will form a simple resistive divider with your R07's input impedence (4.5kΩ). This roughly divides the voltage in half, giving you a -6dB attenuation. Use a 15kΩ resistor instead for -12dB or 47kΩ for -21dB. You can leave pin 3 of the XLR input floating because your R07's input is single-ended anyway. And you'd only need one resistor instead of three.

Great point, in the past, I was given rca outs b/c nothing else was available.
This design also has the virtue of being simple enough to fit into rca connector, which is what I've done.

[Nick_Riviera]

Thanks so much to everyone here! I'll investigate these options more. Might have to pick up another Roland or another recorder - I'd hate to put all my eggs in this basket to find out I flubbed this up (I won't get a chance to try it out or troubleshoot much ahead of time).

As far as plugging into the soundboard, which xlr connector should I be looking at?  Can't say I've ever spent much time looking at one before. I would probably wire it directly through a 3.5mm to plug into the R07.

[checht]

Yup, a Y cable with 2 - xlr female plugs to a 1/9" trs will do it.

If you always/only run a little recorder, you can build the attenuation into the xlrs.
I usually run a MixPre 6 that can take pro line in so doesn't need attenuation, so I have a Y cable plus a 1/*" female to 1/8" male attenuating cable to add inline for going to a Sony A10.

[Nick_Riviera]

Yup, a Y cable with 2 - xlr female plugs to a 1/9" trs will do it.

If you always/only run a little recorder, you can build the attenuation into the xlrs.
I usually run a MixPre 6 that can take pro line in so doesn't need attenuation, so I have a Y cable plus a 1/*" female to 1/8" male attenuating cable to add inline for going to a Sony A10.

I might need to research this a bit more - I had assumed I'd just need a single xlr. How would the wiring for a y cable work? Grd-grd, then... ?

I'll look up available xlr connectors and post back later, just to be sure I'm on the right page. Edit: something like this? Or should it be mini-xlr?

https://www.mouser.com/ProductDetail/Amphenol-Audio/AC3F-AU?qs=Lbk6Md3wKLuE7GFTJvXnsw%3D%3D

This sounds simple enough; I'd probably shoot for the 12db attenuation to be on the safe side. With the BT connection I could scale up the sensitivity pretty quickly if necessary.

[Sebastian]

I'll look up available xlr connectors and post back later, just to be sure I'm on the right page. Edit: something like this? Or should it be mini-xlr?

https://www.mouser.com/ProductDetail/Amphenol-Audio/AC3F-AU?qs=Lbk6Md3wKLuE7GFTJvXnsw%3D%3D

Yeah, that'll work. But I personally would always go for connectors by Neutrik. They are really sturdy and easy to assemble. The one by Amphenol feels a little cheap.

This one, the NC3FX, is a de-facto industry standard:
https://mou.sr/3TLHbmn

The NC3FX-BAG is the black version of that. Or get the NC3FXX line if you want a little more modern looking connectors.

Here are some assembly instructions:
https://www.neutrik.com/media/8050/download/xlr-xx-series.pdf?v=1

[Nick_Riviera]

I'll look up available xlr connectors and post back later, just to be sure I'm on the right page. Edit: something like this? Or should it be mini-xlr?

https://www.mouser.com/ProductDetail/Amphenol-Audio/AC3F-AU?qs=Lbk6Md3wKLuE7GFTJvXnsw%3D%3D

Yeah, that'll work. But I personally would always go for connectors by Neutrik. They are really sturdy and easy to assemble. The one by Amphenol feels a little cheap.

This one, the NC3FX, is a de-facto industry standard:
https://mou.sr/3TLHbmn

The NC3FX-BAG is the black version of that. Or get the NC3FXX line if you want a little more modern looking connectors.

Here are some assembly instructions:
https://www.neutrik.com/media/8050/download/xlr-xx-series.pdf?v=1

Fantastic, so maybe simpler than I thought.

Just one connector I'd need, correct? It would carry both channels?

Thank you for digging all of this up, most of the searching I did led me to overly technical, old web pages without any helpful links to parts like you've provided.

[Sebastian]

Fantastic, so maybe simpler than I thought.

Just one connector I'd need, correct? It would carry both channels?

Thank you for digging all of this up, most of the searching I did led me to overly technical, old web pages without any helpful links to parts like you've provided.

No, one connector per channel.

[checht]

Fantastic, so maybe simpler than I thought.

Just one connector I'd need, correct? It would carry both channels?

Thank you for digging all of this up, most of the searching I did led me to overly technical, old web pages without any helpful links to parts like you've provided.

No, one connector per channel.

Thus the Y cable...

[Nick_Riviera]

No, one connector per channel.

Thus the Y cable...

Ah - I think I see now, from Sebastian's initial post.  I was using tapatalk and the images weren't showing up, but now that I'm on my PC I see it.  P1+P1 = Grd (sleeve); P2a = R (Ring); P2b = L (Tip).  P3a and P3b both dead end.  Super simple!  Thank you both so much! I'll gather parts and then do a quick build post in a week or two

[checht]

Here's my latest version:

[Nick_Riviera]

Here's my latest version:

Nice.  I was thinking I'd have about 6" from the XLRs leading to about 4" on the TRS for my cabling

What db reduction are you using, or which have you found to be best? 

[checht]

I went with 12db attenuation, as the recorders used have low noise floors.

[Nick_Riviera]

I went with 12db attenuation, as the recorders used have low noise floors.

Based on some comments in the R-07 review thread, I might try for -15db (unless your -12db has worked fine for an R-07 - I saw some comments from you in the thread).

For others stumbling on this post and wanting to know the math like me, it's dB = 20log(R2/(R1+R2), where R1 = in line resistor value and R2 = input impedance of the recorder.  For a ~15dB attenuation, I would need 22kΩ resistors.

[checht]

Based on some comments in the R-07 review thread, I might try for -15db (unless your -12db has worked fine for an R-07 - I saw some comments from you in the thread).

Yup, always was enough attenuation for the r-07,

[Sebastian]

I went with 12db attenuation, as the recorders used have low noise floors.

Based on some comments in the R-07 review thread, I might try for -15db (unless your -12db has worked fine for an R-07 - I saw some comments from you in the thread).

For others stumbling on this post and wanting to know the math like me, it's dB = 20log(R2/(R1+R2), where R1 = in line resistor value and R2 = input impedance of the recorder.  For a ~15dB attenuation, I would need 22kΩ resistors.

Yeah, -12dB should be plenty. Always keep in mind this is a logarithmic scale. So -6dB equals a gain factor of 0.5 and -12dB equals a gain factor of 0.25. That means at -12dB, your attenuated signal is only 0.25 times as "loud" as your input signal.

[Nick_Riviera]

Thank you again, everyone!  I finished this project today, and am waiting on a pair of RCA connectors so I can have a couple of options.

Supplies:
1) Mogami 2330 cable I had laying around from another project (https://www.markertek.com/product/2330/mogami-w2330-miniature-unbalanced-microphone-cable-black-per-foot) - maybe $10 shipped for this project?
2) Multi-pack of resistors from Amazon (https://www.amazon.com/dp/B09PLNPX3P) - $15 shipped
3) A 3.5mm TRS Monster cable (https://www.amazon.com/dp/B015RA5P0C) - $11 shipped
4) Shrink wrap as needed
5a) A pair of Neutrik XLR connectors (https://www.mouser.com/ProductDetail/568-NC3FXX-B) - $16ish shipped; I bought a set of red and white boots which added a few dollars to the order
5b) A pair of Neutric RCA connectors (https://www.performanceaudio.com/products/neutrik-nf2c-b-2-profi-professional-rca-plugs-pair) - $25 shipped

First step - cutting the mogami cables to about 5", then trimming the ends to expose the wire:


Second step - soldering the resistors and bundling it up with about 6" of the 3.5mm cable, then testing continuity to ensure good ground to ground to sheath, and comparable resistance to either channel.


Last step - soldering to the Neutrik connector and assembling it, easy peasy.


The Neutriks are pretty bulky, with a significant metal component, so these would likely set off a metal detector. 

[Sebastian]

Looks great! The only thing I don't understand is why you ordered the resistors for $15 from Amazon when you could have added literally hundreds of them to your Mouser order for a few dollars.

And yes, the XLR connectors will probably set off a metal detector. But when you're getting a soundboard patch, that usually isn't a problem.

[Nick_Riviera]

Looks great! The only thing I don't understand is why you ordered the resistors for $15 from Amazon when you could have added literally hundreds of them to your Mouser order for a few dollars.

And yes, the XLR connectors will probably set off a metal detector. But when you're getting a soundboard patch, that usually isn't a problem.

I agree they're a bit overpriced on Amazon, and that I am not very good at searching Mouser's catalog, but there were a few reasons that boiled down to convenience.  Amazon does have hundred packs for $6ish, but I don't need a hundred of this specific flavor of resistor, so I bought a kit with a wide selection (20 each) to cover any future projects.  They come in nice little organizers, too.