Marc Girard
Well-known member
Hello all,
I'm trying to build myself a small passive summer for my Apogee AD-8000. I've got the DAC-8 card, which have 8 balanced outputs at +4dBm. My needs are simple: I want 4 stereo pairs going to two. The panning and the rest will be taken care of in the box... I'm gonna be amplifiying the result with a Buzz Audio MA-2.2 or a Neve 1272.
Now, I've searched this forum inside out, I didn't want to post yet another tread about this. I tried to figure it out by myself: I just couldn't, too complicated for my little brain. Then, I looked at NewYorkDave's schematics for building your own passive mixer.
The formula says:
R = ( N-1 ) / ( N+1 ) * Z
Now, I've read that the Folcrom's outputs have an impedance of 150 ohms. I'm guessing that's what most mic preamps like to "see".
So, let's do the math:
R = ( 4-1 ) / ( 4+1 ) * 150 = 90 ohms.
Now, I'm balanced, so resistors of 45 ohms would be needed... Damn, we're talking about 5Ks and 10Ks all over the place here, my 45 ohms looks awfully small as a R value. I'm missing the point.
Now, some details and findings:
My Buzz Audio preamp mic inputs impedance can be switched 1.2k ohms or 3k ohms. I don't know much about my Neve 1272 but I think I've read somewhere that's it's 300 ohms, I might be completely wrong. Output of the Folcrom passive mixer is 150 ohms. I tried to find anything about the Apogee DAC-8 output card, nothing... It's line level, +4 and balanced...
Now, I assume it can't be that complicated. I'm tempted to simply put 5K ohm resistors like most designs use.
If you can figure this out better than me, I'd be GREATLY thankful.
I'm trying to build myself a small passive summer for my Apogee AD-8000. I've got the DAC-8 card, which have 8 balanced outputs at +4dBm. My needs are simple: I want 4 stereo pairs going to two. The panning and the rest will be taken care of in the box... I'm gonna be amplifiying the result with a Buzz Audio MA-2.2 or a Neve 1272.
Now, I've searched this forum inside out, I didn't want to post yet another tread about this. I tried to figure it out by myself: I just couldn't, too complicated for my little brain. Then, I looked at NewYorkDave's schematics for building your own passive mixer.
The formula says:
R = ( N-1 ) / ( N+1 ) * Z
Now, I've read that the Folcrom's outputs have an impedance of 150 ohms. I'm guessing that's what most mic preamps like to "see".
So, let's do the math:
R = ( 4-1 ) / ( 4+1 ) * 150 = 90 ohms.
Now, I'm balanced, so resistors of 45 ohms would be needed... Damn, we're talking about 5Ks and 10Ks all over the place here, my 45 ohms looks awfully small as a R value. I'm missing the point.
Now, some details and findings:
My Buzz Audio preamp mic inputs impedance can be switched 1.2k ohms or 3k ohms. I don't know much about my Neve 1272 but I think I've read somewhere that's it's 300 ohms, I might be completely wrong. Output of the Folcrom passive mixer is 150 ohms. I tried to find anything about the Apogee DAC-8 output card, nothing... It's line level, +4 and balanced...
Now, I assume it can't be that complicated. I'm tempted to simply put 5K ohm resistors like most designs use.
If you can figure this out better than me, I'd be GREATLY thankful.
(Doorman). Thanks again!
