So, you bought a Zoom R16 (or R24 for that matter) and you're happy as a pig in a ditch 'cause now you can record your band playing live. Well, yes, and no. If you want to run a whole bunch of mic cables and hang mics in front of everything on stage you can do that just fine. But wait, you say in your happy delirium, we already mic everything on stage so I can just run the sound board direct outs to the R16 line ins since the Zoom website says the R16 can handle line or mic level input. Wrong bassoon breath! The Zoom R16 (and R24) can handle consumer level line input. What's that? That would be the ever popular -10dBV. For an explanation, see here. What happens when you run +4dBu professional level line output into the Zoom R16 which is expecting -10dBV input? It overdrives the input. In many cases, even when you have the gain knob set to the absolute minimum. So, what's the solution? You could kindly ask your sound engineer (if you have one) to please set the input levels for each stage mic really low. I'm sure he (or she) won't kill you more than once. Another solution is to go out and buy eight, 40dB or 50dB L-pad attenuators. The cheapest I could find came in at seventeen dollars US (of course your mileage may vary). The cheapest solution is to make your own 40dB or 50dB L-pads. There are plenty of places on the web that have the instructions.
Since I have two R16s that I link
together, and my band has 13 separate inputs, either mic or
line, I decided that I would build my own L-pads. So,
having made this momentous decision I had to think up a simple
way to do this without going broke. Most examples show
single L-pads built into XLR tubes. Since the tubes cost
almost as much as the pre-built attenuators this didn't seem
like a great idea. I did find one example where they said
you could just put the L-pad in a small, metal project
box. Still too expensive. How about eight L-pads in
a single, large metal project box? That should work.
A plastic project box would be even better (read cheaper) but
might be vulnerable to noise from external sources. Since
I used to build
my own guitars from scratch (pre-Katrina, which took all
my tools) I had some copper foil shielding tape laying around
that I didn't need. Aha, I can use a plastic box and
shield it with copper foil tape (actually, the metal tape that
is used on air conditioning ducts works just as well).
So, what do I need? Sixteen 1/4"
jacks (GLS Audio 1/4" Jacks Female TS
Mono Panel Mount Jack - 20 PACK, twenty dollars, or a
buck apiece, from Amazon). Some wire (I had some scraps
that I could use). A plastic project box large enough to
accommodate sixteen 1/4" jacks and some wire and resistors
(Hammond 1591ESBK ABS Project Box, 7.5" x 4.3" x 2.2", Black, about ten bucks at
Amazon). A good soldering iron and some solder (most
people have these). Shielding tape (free since I already
had it). Oh, I almost forgot, sixteen resistors (about 14
cents apiece from DigiKey).
After reading a bunch of things on the good old interwebs about
overdriving R16s I decided that I would make 50dB L-pads using
the following circuit:
+Line level input ---------- R1 ----------+--+ Mic level output
+------- R2 -----+
Ground (input) ----------+-------------------- Ground (output)
R1 = 33K ohms
R2 = 100 ohms
That probably looks familiar
if you looked at the links in the first paragraph ;-) I
used 1%, 100 ohm metal film axial resistors for R2 and 5%, 33K
ohm metal film axial resistors for R1. The power level
doesn't matter much but mine were 1/4 watt for R2 (DigiKey part
number S100CACT-ND) and 1/2 watt for R1 (DigiKey part number
CF12JT33K0CT-ND). So, money out of pocket so far is about
thirty-five bucks for a single box (seventy bucks for me since I
was making two boxes).
Important note - I am not an electronics
wizard (I'm a programmer).
Warning - the following is not pretty ;-)