out of phase mono switch

[peat]

Hey!

Quick question. It's late and I can't picture this in my head.

I've got a monitor controller with a bunch of 4PDT switches on it.
What would the schematic for an out of phase mono switch look like with this switch.

Any help would be great!

 

[abbey road d enfer]

Hey!

Quick question. It's late and I can't picture this in my head.

I've got a monitor controller with a bunch of 4PDT switches on it.
What would the schematic for an out of phase mono switch look like with this switch.

Any help would be great!

Impossible to answer! It depends on the rest of the schemo. How can we reverse phase if the signal is unbalanced? (Cue: it would take an active stage). How can we mix L&R?

 

[peat]

hi,

the signal is balanced, stereo.

I understand to get out of phase mono you want to invert the polarity of one channel and then add them together.
So L+ gets added to R-
and L- gets added to R+

I just can't picture how to do this with a 4PDT switch

 

[abbey road d enfer]

hi,

the signal is balanced, stereo.

I understand to get out of phase mono you want to invert the polarity of one channel and then add them together.

That's the difficult part. Although it is possible to do that passively with floating signals (i.e. not referenced to ground), I doubt it would work with most of the outputs delivered by electronically balanced equipment ( and surely not AT ALL with unbalanced signals). So you have to EITHER add an active mixing stage AND reverse polarity of one of the signals, OR add transformers in the signal path, which would simultaneously reverse the polarity of one of the signals AND mix them.

I just can't picture how to do this with a 4PDT switch

A switch, however sophisticated, is not enough to do what you want.

 

[peat]

what about two switches

First one inverts polarity of the right channel.

The next switch just adds L+ to R+ and L- to R-

 

[Sammas]

Rob Squire @ Pro Harmonic wrote an article about doing what you want - http://www.proharmonic.com/articles/AT78_OTB.pdf


You need a 4p3t switch though. You could remove the plain of "mono" poles and just wire the stereo & Left and out of phase right mono'ed signals I suppose.

 

[abbey road d enfer]

what about two switches

First one inverts polarity of the right channel.

That is the easy part.

The next switch just adds L+ to R+ and L- to R-

I just wrote that a simple switch alone cannot do that. When you solve the problem of how to sum signals, the switchiing arrangement becomes a minor question.

 

[peat]

ok, I'll try something out and see how it goes.

I've already got one 4PDT switch that is performing the mono correctly, I'll see what happens when I invert the right channel before it.

The mono switch has the input coming to the poles, one throw just goes through as per normal, on the other throw I've got a link between the two +'s and the two -'s

 

[abbey road d enfer]

ok, I'll try something out and see how it goes.

I've already got one 4PDT switch that is performing the mono correctly, I'll see what happens when I invert the right channel before it.

The mono switch has the input coming to the poles, one throw just goes through as per normal, on the other throw I've got a link between the two +'s and the two -'s

Straight paralleling is a very crude way of mono-ing signals, but it works somewhat because the difference between L&R is generally small, so the resulting currents do not create absurd distortions. But when summing out-of-phase signals, the sources see each other as a short-circuit, so you end up with a very distorted mono signal.
And as I mentioned earlier, this won't work with unbalanced signals.

 

[peat]

So i've got this working by having one switch which swaps pins 2 and 3 on the L channel.
This then feeds another switch which connects L+ to R+ and L- to R-

Flicking the second switch is a normal mono, flicking both switches gives me out of phase mono (sides)

Seems to work perfectly to me.

I would imagine that putting transformers or an active stage in your monitoring path would be much more crude than this.

Do you have any information of how basic mono'ing of signals works in commercially available monitor controllers or console monitor sections?

 

[abbey road d enfer]

So i've got this working by having one switch which swaps pins 2 and 3 on the L channel.

As I said before, it works somewhat. There are many limitations, though. You may not have encountered them, but they exist. In particular, someone with different equipment may find that some functionality doesn't work for them.

This then feeds another switch which connects L+ to R+ and L- to R-

Flicking the second switch is a normal mono, flicking both switches gives me out of phase mono (sides)

Seems to work perfectly to me.

Are you doing that pre or post volume control?

I would imagine that putting transformers or an active stage in your monitoring path would be much more crude than this.

In what respect would it be more crude? An active inverter stage paired with an active mixer cannot be qualified of crude. Transformer secondaries connected in series cannot be qualified of crude. Connecting two active balanced outputs in parallels IS crude, more so if they are in reverse polarity. Think about putting to car batteries in parallels, no big deal but still any differences in charge status will result in one of the batteries sucking the other. Now put them in opposite polarity. Indeed, you would achieve your goal of summing them out-of-phase. Would it be representative of anything useful? I won't influence you with my answer.

Do you have any information of how basic mono'ing of signals works in commercially available monitor controllers or console monitor sections?

I have more than basic information. That's all in my previous posts. Passive monitor controllers rely on a number of prerequisite such as floating-balanced low-impedance outputs, balanced inputs; some of their functionalities do not work in the absence of one of these prerequisite.
Well-designed active controllers are similar to those built in mixers. 99% ot the times, all external signals are debalanced and buffered so mono'ing is just a matter of shorting two medium-impedance lines together, out-of-phase involves an active inverting stage, dimming and muting are done via basic DP1T switches, the volume control being buffered before being sent to a balanced line driver that allows driving long cables without HF loss.
Just look at the schemo of any decent Soundcaft mixer (6000, TS24), DDA, SSL, Studer, Harrison, they all do it the same.