-20db pad for WSW preamp - in and out

[dukeofearl]

I've read the various threads about pads - and a few websites including the uneeda.com one. I understand it a little better now and that the input impedance of the amp and output impedance of the mic interact and that would effect what the resistor values should be. I'm still not clear what you do if you have microphones of varying impedance.  I guess you have to deal with the impedance changing slightly which is fine with me.

I'm trying to make a -20db pad switch for a WSW (or studio technik) silicon 811-403 mic-pre. It was racked by TAB funkenwerk a long time ago when they were in seattle. It has phantom and polarity switches. I'm surprised there was no pad added because it is super hot and impossible to record drums without some kind of pad. I have one I've been plugging in but would like to make switches so it's easy to check the different sounds.

I'd like to make external pad switches for input and output. It sounds great when driven hard, that's why I'd like one on the output too.

On the input it has an impedance switch. From the manual it looks like 180, 600 and 1900. The manual says 30 ohms output impedance, but there is a note that says output is 600 ohms.

I've seen these resistor values for a -20 db U-pad: 620, 620 and 169. Also 680, 680 and 150. It doesn't have to be exactly -20, but somewhere around there, higher is better than lower. Any suggestions? Would this also work on the output?

Thanks!

 

[PRR]

"Usually" the mike wants to see well over 1K, and the mike amp wants to see a couple hundred Ohms.

So a 20dB (10:1) mike pad starts like a U pad with two 1K and one 220r.

For simplicity, to get more dB trim the 220r down to 150r or 100r. This will be a fine fit in any situation where you need a pad.

For less dB, take the 220r up to 270r or 330r, then start reducing both 1Ks. But past about 680r both places starts to load mikes. (The values you cite seem to be for true 600 Ohm both ways circuits, which most mike inputs are not.)

> says 30 ohms output impedance, but there is a note that says output is 600 ohms.

It is a ~~30 Ohm source intended to drive >600r loads.

As your loads are probably 10K, this is trivial. The 1K-220r-1K U-pad will do. The 220r may be trimmed almost any way you want to get the dB you need. 1K-10K-1K is hardly-any, and will work fine. 1K-10r-1K reduces Line to near Mike.

 

[Whoops]

Great post PRR

Thanks