Soundboard attenuator DIY?

[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.