Summing Output of Mic Preamp

[RodC]

Ok I have lurked here long enough, I decided to post a message. I tried the search function and didn't turn anything. I got my asbestos undies on so....

I have been recording using a PC for a while now, I have a drum setup I like but our new drummer has 2 bass drums. (We have been using a single bass drum with a dbl pedal)

Can I sum the output of my mic preamp, to combine the two bass drum mics, with a simple Y cable?

I have an 8 channel SM Pro 8 for the drum mics.

BTW have you seen their latest model with the combo TRS/XLR inputs and TRS or XLR outputs?

Phase reverse on all channels and Optional ADAT Lightpipe output option

No I don't work for them LOL

http://www.musiciansfriend.com/srs7/g=h ... id/240160/

[brianroth]

Typically no, a straight y-cord cannot be used to combine signal outputs. What happens is that each preamp's output sees the other as a VERY low impedance load. However, you could wire some 1000 (1K) resistors in series with pins 2 and 3 from each XLR and then "Y" the downstream sides of the series resistors. That will isolate each preamp from the other.

Note: the actual value of the resistors isn't critical. I used 1K Ohm because that is a very standard value and will result in minimal loading of the preamp's output. You could used lower values, say 470 Ohms.

Bri

[RodC]

Ok sounds easy, but why resisters in series with both 2 and 3? Wouldn't placing a single resister inline with 2 or 3 affect the overall impedance just the same?

[RodC]

Thanks for your help guys, if your interested here are a couple of things I ran across:

http://www.forsselltech.com/summing%20buss.htm

http://www.forsselltech.com/summing_buss_schematics.htm

There is also some good info here:

http://www.prodigy-pro.com/forum/viewto ... +pro+8+mod

[brianroth]

It looks like you already found the answer!

If your preamps have transformer coupled outputs and you're driving an unbalanced input, you can get away with resistors in just the "hot" lead.

However, all bets are off for transformerless line outputs since there is no consistent way to know how the "low" side is driven.

My double resistor suggestion was based on the assumption you wanted to keep the balanced line properly balanced! <g>

IOW, what you do to pin 2 you also do to pin 3.

Bri

[vvv]

I would consider buying a cheap small mixer, for the flexibility in level adjustment, if nothing else.

[RodC]

Thanks for the replies.. About the mixer, I would like to find a mixer with 8 Mics in, but most if the smaller units I have found only have 2 buses. I would like to maintain 4 cannels at least for my drums.

I'm still looking. A lot of the lower priced mixers only have 2 or 4 Mic inputs, I would like to find a small one just for drums.

And it would be nice if it fit in a single rack space