Parallelling XLR inputs

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Quayhog

Well-known member
Joined
Oct 11, 2014
Messages
135
Location
Bay Area California
Is there anything I need to worry about while hooking up two tube mixers into a tube PA amp?
I have a pair of Altec 1968a power amps for my studio PA amps.  I now have a pair of Altec 1967a mixers and a pair of Grommes G5M mixers in my rack.  I'm getting ready to make some input and output pigtails.  Polarity, hum, ?

I'd like to be able to plug one of each mixer into an  Altec amp.  This is for amplifying my bluegrass band so we can use mics, ease our discomfort about using microphones etc.  during practice situation. 

I use Electro Voice 1x12 floor monitors for speakers.

Jonathan Horne
 
I see Altec 1568 and 1567a  but not 1968-67a.  If it is the 1567a then,you would run the output of mixer 2 into input 5 Hi level in of mixer 1 .    It would then be a sub master for mixer 2.  If you parallel both mixers together you need some kind of passive or active mix network to combine with out having the mixers cross feed into the outputs of one another from the common connection.  This would create a distortion of the output to the power amp.    New York Dave posted a passive mix network that might work for this somewhere on the GroupDIY forum.  It will attenuate the signal so you need to make sure there is enough drive to the power amp with the insertion loss  If you combine at the outputs of each mixer. 
 
I was being dyslexic. The mixer is a 1567a the amp is also an Altec 1568a.

So you're saying is plug one mixers' output into a channel of the other mixer.  Then use one mixers entire output into the Altec head.  It makes sense to do it that way. 
In my opinion the Grommes is a better mixer than the Altec.  I feel lucky to have both.
Jonathan Horne
 
Yes one into the others line input.  Grommes G5M has input 6 as line in so use that as an input.  4 mixers mean a long chain but a lot of inputs.  Its cool that you use tube mixers for everything.  What do you use for speakers.  La Scalla's would be nice with that combo.   

I use to be the live recording engineer on Etown.  We always multi mic everything.  But Nick,  the shows host and producer wanted to use 1 mic and everybody mixed around that 1 mic like the Bill Monroe days of Blue grass.  His band was Hot Rise.  When they broke up he and Helen started Etown.  Great bluegrass bands on that show as well as every other kind of music. 
 
For the band room and tape playback I use Electro Voice FM12-2 speakers.  When I run signal through the house stereo I use an Ampex stereo preamp and a 807 stereo amp.  Otherwise I have a pair of Altec 1568a amps.

All this stuff is pretty much hard wired into my rack.  I've just acquired a pair of Grommes G77 amps and another G5 ( as yet to be delivered). The G77 is a strange and undocumented amp that has a pair of 6GT5 tubes and the front end is the same as four channels of the G5 mixer.  All of these are in the reliability check and repair queue.
 
The G-77 noted in my previous post is now documented.  I found the schematic and the four page manual.  I've attached it here.  I hope it shows up.
 

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