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[ted nightshade]

Hi,

I have these 5 to 1 unbalanced tube mixers (Manley Purist Mixers)I want to use to decode mid/side recordings. You use two of the things for stereo- one for L, one for R.

There are no polarity switches, and each input has it's own input grid, for what it's worth.

Everything in the whole picture is unbalanced.

It's all very straightforward except of course I need to flip the polarity to one input for the -side part.

I'm thinking:
One y-cord from the mid track to an input on each mixer. So far so good.

One y-cord from the side track to an input on the L mixer, the other output of the y-cord to an input on the R mixer. Only, the output of the y-cord to the input of the R mixer needs the polarity flipped, for -side. Can this be done as easily as rewiring that end of the y-cable to flip the polarity? Or is that liable to cause a problem?

Thanks... hope this is fully intelligible...

[John Klett]

You can't do a simple Y cord and flip phase so that one unbalanced input gets a signal in phase and the other unbalanced input gets in reversed phase because the Y cable will bring the common ground side of one input to the signal side of the other input and short out the signal all together.  

In order to get your Phase + and phase minus signals you need to have an active circuit front that does the phase inversion or a transformer with a split secondary or three windings.  If you want to stay with tooobes you can do this with a phase splitter...  you can read about these at the follwoing links and maybe talk to Hutch at Manley about the possibility of jamming one of these into your mixer.  It looked to me like there was a lot of room in that box and maybe you can grab plate and filament supplies for the spitter from the supply in the mixer...  who knows...


http://www.eecs.umich.edu/~mmccorq/tubes/introduction/introd uction.html

http://hhscott.com/cc/phase_inverter_tubes.htm

http://www.dogstar.dantimax.dk/tubestuf/paraph.htm

have funn

[ted nightshade]

Alright, looks like I got my homework cut out for me again! Thanks much for the links, and saving me one failed experiment.

[Gunnar Hellqvist]

Ted,
   this is is a bit off what I really know. But it might be that the input signal goes through a transformer inside the tube mixer box. In that case you could open up the box and reverse either the inputs or the outputs of the transformer. This would give you a permanently "inverse" channel, which might be what you want.

[ted nightshade]

Gunnar Hellqvist wrote on Sat, 15 May 2004 01:52

Ted,    this is is a bit off what I really know. But it might be that the input signal goes through a transformer inside the tube mixer box. In that case you could open up the box and reverse either the inputs or the outputs of the transformer. This would give you a permanently "inverse" channel, which might be what you want.

Thanks, Gunnar, but it's a transformerless type.

Whatever I do to the -S input, I will want to do to the +S input too (but not flipping the polarity), to keep things in balanced... Can't decide if I want to make it a permanent part of the box, or have a separate polarity flip box just for m/s occasions. I have 5 inputs, and 4 tracks, so I could spare a channel for something dedicated.

This one's on the back burner for now, but I will be getting back into this one soon.

[Buzz]

Just use a direct box and an inverted xlr cable !!!!  

Later
Buzz

[Geoff Doane]

What is the source of the "side" track.  If it's balanced, you may be able to run pin 2 to the left mixer, and pin 3 to the right, and get the phase inversion that way.  If it's a floating balanced output, you might need to add a couple resistors from pins 2 and 3 to ground to create a pseudo center tap.

What are these mixers, BTW.  5 grids in one tube, or 5 tubes?

Geoff Doane

[ted nightshade]

cbc6403 wrote on Wed, 09 June 2004 09:01

What is the source of the "side" track.  If it's balanced, you may be able to run pin 2 to the left mixer, and pin 3 to the right, and get the phase inversion that way.  If it's a floating balanced output, you might need to add a couple resistors from pins 2 and 3 to ground to create a pseudo center tap. What are these mixers, BTW.  5 grids in one tube, or 5 tubes? Geoff Doane

Unbalanced out of the mic pre, so far...

There are 3 12AU7's and a 6414 in each mixer... each channel and the monitor send get half a 12AU7. Each channel has it's own input grid, whatever that means...