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Designing an output pad for the A12

PostPosted: Fri Apr 16, 2010 10:43 am
by RalphNicastro
I have been thinking about designing an output pad for the A12, as I love the sound but it is a little hot on drums. I would like to design an output pad to take off 12db. I found a website with an explanation but I have a few questions. Would I need to use 1/4watt resistors or 1/2watt resistors? What is the output impedance of the A12?
Thanks for your help!

PostPosted: Mon Apr 19, 2010 6:19 am
by tpryan
Use a string of three 1/4W resistors, 220-150-220. Apply the signal across the whole string and take the -12dB signal across the 150 ohm resistor. Remove the jumper on the board at R38 - otherwise the module will be driving a 300 ohm load instead of a 600 ohm load.

PostPosted: Fri Apr 23, 2010 1:16 pm
by Randyman...
I built some -6dB pads that worked well with Tim's input - but I also think I liked the ability to drive the outputs even harder with a -12 or -14dB pad. You should dig the sound IMO - Everyone always says "The sound of Rock Drums is API driven hard" - and padding the A12 into an A/D gets a good deal of that sound IMO. You will even get some light limiting (clipping) on the hard hits! I generally pad the Kick, Snare, and Overhead outputs into the A/D...

:cool:

PostPosted: Mon May 03, 2010 7:44 am
by RalphNicastro
ok so you are suggesting a U pad design? If that is the case, the other set of numbers I found were 5k, 3.6k, and 5k for 12db reduction. What is the difference between these two sets of numbers?

PostPosted: Mon May 03, 2010 9:07 am
by tpryan
What is the difference between these two sets of numbers?


Assuming 0 ohms source impedance and very large load impedance:

220+150+220 = 590 ohms input Z, 150 ohms output Z
5K+3K6+5K = 13K6 ohms input Z, 3K6 ohms output Z

20*log(150/590) = -11.9 dB
20*log(3K6/13K6) = -11.5 dB

PostPosted: Mon May 03, 2010 1:49 pm
by RalphNicastro
Your numbers make much more sense, I will go with those. I plan to use DPDT mini toggle switches on a blank rack panel to switch them in and out as needed. Are there any other things I should do other then remove the jumpers?