Stereo link and M/S en-/decode in a stereo EQ

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Tritalos

Member
Joined
May 30, 2017
Messages
13
Hi everybody,

I'm mostly new in this whole DIY-thing and I am playing around with the thought of a stereo m/s-switchable version of the old Neumann W492 EQ.

My first idea about integrating the stereo link feature was to equip the left side set of controlls with double-pots, wo I can switch the right side to it. Has anybody already done that and can tell me if it'll work or if there's another (better) workaround?

My thought of implementing the M/S matrix was simply "dunno".
And again: Has anybody already done that and can tell me his experiences? Any schematics?

Thanks for your time.

Tritalos
 
There are a number of DIY MS encode/decode options out there, which allow any equipment to be used in that mode. 
 
Most of these EQs already use dual section pots. So you would need quad section pots to make stereo. If you can find them, then it's fairly straight forward making a stereo. But it is problematic to make it switchable because you would either have to run those relatively high Z low level signals over long cables from one side to the other or just make one side a dual circuit and then switch circuits.
 
emrr said:
There are a number of DIY MS encode/decode options out there, which allow any equipment to be used in that mode.
I will keep on looking out for these, thanks.
 
squarewave said:
Most of these EQs already use dual section pots. So you would need quad section pots to make stereo. If you can find them, then it's fairly straight forward making a stereo. But it is problematic to make it switchable because you would either have to run those relatively high Z low level signals over long cables from one side to the other or just make one side a dual circuit and then switch circuits.
I planned on using already designed boards, so a dual circuit is barely an option.
The design of this EQ uses four one section pots an for dual section, so going for dual and quad would be possible, but still got these long cable issues. Is there another way or is it just the better choice to step back from it and focus on the MS matrix?
I mean, it will hardly lose any L/R-balance in MS mode.
 
Does anyone know What will happen if you use a mixer just as a kind of decoder with a stereo signal? IE mono center +3db, L panned left, Right panned right and inverted????

Taking down the mono gives more side etc......

Sorry to derail but, it made me remember I wanted to get some input on this too.....

 
One option:

http://www.ka-electronics.com/kaelectronics/MS_Matrix/MS_Matrix.htm
 
emrr said:
One option:

http://www.ka-electronics.com/kaelectronics/MS_Matrix/MS_Matrix.htm
Thank you, that seems to be an easy option.
In my case it would be enough to get the matrix part after the input of the EQ with a switch to bypass the circuit, right?
 
Tritalos said:
a stereo m/s-switchable version of the old Neumann W492 EQ
The last thing you want when you work in M/S mode is common controls. Quite often the idea is applying EQ to one of the components only, M or S, not both or two different EQ's, for example boosting the low-mids in M for increased punch, and boosting the high-mids in S to increase the "spaciousness".
 
abbey road d enfer said:
The last thing you want when you work in M/S mode is common controls.
Exactly.

Another reason to go MS is because no two pots behave exactly the same -- unless matched meticulously. So you now want to match quad pots? Forget it.

Build a  dedicated MS  thingy (Sahib or Kirkwood or transformers) and insert your EQ. Then adjust M and S by ear, not eye.
 
abbey road d enfer said:
The last thing you want when you work in M/S mode is common controls. Quite often the idea is applying EQ to one of the components only, M or S, not both or two different EQ's, for example boosting the low-mids in M for increased punch, and boosting the high-mids in S to increase the "spaciousness".
I think I didn't get you right.  Why shouldn't I want to apply different EQ settings on mid and side?
 
Script said:
Exactly.

Another reason to go MS is because no two pots behave exactly the same -- unless matched meticulously. So you now want to match quad pots? Forget it.

Build a  dedicated MS  thingy (Sahib or Kirkwood or transformers) and insert your EQ. Then adjust M and S by ear, not eye.
But I don't need quad pots. My current plan is, to build a dual mono EQ, one channel left, one channel right and have an MS switch on it, so the left channel processes the mid and the right channel processes the side signal.
The EQ schematics don't need to be changed.

Supplement:
Did I mention, the stereo link think is just written off? Forgot that, sorry.
 
sahib said:
Perhaps you may consider our module.

https://groupdiy.com/index.php?topic=62527.0
Looks like this is a cool thing, but for I already have a not fully filled 500 series rack and I would have to go with the TAC rack, that's right now not an option.
Thanks anyway
 
Tritalos said:
Looks like this is a cool thing, but for I already have a not fully filled 500 series rack and I would have to go with the TAC rack, that's right now not an option.
Thanks anyway

You do not have to buy a TAC rack. However, you will require insert points in your rack. These are pin 7 and 9 on the card edge connector. Naturally these two ports are unbalanced. If you do not mind unbalanced operation  then all you will need to do is to open up two holes, install two jacks and wire them onto pin 7 and 9. For ESD protection I have an ESD/EMI card that installs onto the MID-SIDE ONE main board. These protect the inputs (to a degree).

If you want balanced operation then we have INSERT ONE which plugs directly into the MID-SIDE ONE. It has the ESD/EMI protection already built in.  https://groupdiy.com/index.php?topic=65067.msg824491#msg824491

You can of course build your own insert points too if you want to go down that route. Jeff (CAPI) offers blank 500 metalwork with edge connector adapter card. Build two balanced to unbalanced and unbalanced to balanced buffers and you are done. In fact I am currently helping out to a forum member on this. I have designed a simple opamp-buffer and the PCB. It is attached. You can configure it to balanced to unbalanced and unbalanced to balanced.You do not have to buy the PCB from me. The circuit is there.  You may even have opamps in your junk box that you can use.  I have laid it out in a way that you can build it on a  perfo board with all of the connections on one edge. You have a choice of using straight or right angle 0.1" header to solder it onto a main perfo board . You can then incorporate the input protection if you want to (highly advisable).
 

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Tritalos said:
I think I didn't get you right.  Why shouldn't I want to apply different EQ settings on mid and side?
Then, why would you work in M/S mode? If you want to apply the same processing to both sides, better stay in L/R mode. I think I gave you earlier an example of what applying different EQ's on M and S could do; please do re-read.
 
scott2000 said:
Does anyone know What will happen if you use a mixer just as a kind of decoder with a stereo signal? IE mono center +3db, L panned left, Right panned right and inverted????
You need three channels to code or decode M/S.
One that sends L in equal parts to L & R, the second sends R to L, the third sends R out-of-phase to R.
Now L becomes M and R becomes S. Indeed, proper calibration of the channels must be thorough, in particular, the channel that sends L to center must compensate the pan-pot loss.
 
Tritalos said:
I think I didn't get you right.  Why shouldn't I want to apply different EQ settings on mid and side?
To better answer your question, look at the difference between what is in the M output and S output... M is primary direct signals, while S is often room ambience.

For one example EQ'ing S can alter the apparent brightness or darkness of the acoustic space.

This is subtle stuff..

JR

 
abbey road d enfer said:
Then, why would you work in M/S mode? If you want to apply the same processing to both sides, better stay in L/R mode. I think I gave you earlier an example of what applying different EQ's on M and S could do; please do re-read.
Okay, well I DID get you wrong (no native speaker).
Processing mid and side differently is exactly what I want to be able with this unit.

My naive thought was kind of like that:
9iKz3cMGm971Wuxbth6_YxCay_olGdpXJdki9CccYII

So talking about the Kirkwood Circuit, would it be enough to take it from "B" to "G", when I still use the original input and output section of the eq?
 

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