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A
Variable Width Circuit for The Precision MS Matrix

Our build thread for DIY projects,
including the MS Mid Side Matrix.

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6 posts • Page 1 of
1

A

by
mediatechnology
» Fri Oct 07, 2011 2:53 pm

I was contacted today by
someone wanting to build the MS matrix. They had the simple question: "How do I
add a width control?"

The obvious answer of course is to vary the
ratio of mid to side between the encoder and decoder. If there's already a
processor in that insert just use it's gain trim.

But
what if I just want to hook up a pot to the board for a Width Control?
Where?

Turns out it's pretty easy. I'll draw a schematic and post
it. For now let's use the original block diagram.

To make the board into a variable width circuit do
the following:

Use the decoder as
your encoder. The Left and Right Inputs are at "E." The PC board point
marked "GL" (G Left) becomes "GM" or G Mid. "GR" becomes "GS" or G
Side.

Add a two section 10K linear pot
at insert point "G." Wire the pot so that at CW rotation mid is at full,
side attenuated. Full CW rotation is zero width (Mono), full CCW is full
Side.

Take the output of the "Encoder,"
which is Mid and Side and feed that into the "Decoder" inputs at point "A."
Why the encoder/decoder role change? Because U9 is there to provide a
buffer for the pot.

The Width-controlled
Left and Right outputs are now taken from point "D."

MS
with variable width added.

Here's a short demo of the variable width
control:

http://www.ka-electronics.com/content/MS_Width_Demo_Train_Meet_Virginia_Live.mp3
(3.5 MB)

http://www.waveulator.com/
http://www.ka-electronics.com/
http://www.linkedin.com/in/waynekirkwood
“Logic
will get you from A to B. Imagination will take you everywhere.”

mediatechnology

Posts: 1777

Joined: Sat Aug 11, 2007 2:34 pm

Location: Oak Cliff, Texas

Website

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Re:
A Variable Width Circuit for The Precision MS Matrix

by
mediatechnology
» Sat Jul 07, 2012 7:18 am

This
picture shows how easy it is to provide variable width for the MS
Matrix.

MS
Matrix With Variable Width Control

(I don't normally build finished
projects with solid telephone wire. But, this is
science.)

Some
notes:

Insert "GL" is Mid Level
Insert "GR" is Side
Level

The pot for Mid/Side ratio is a 10K dual linear cross wired so that
as one increases level the other decreases.
The pot should have a linear
taper to provide, at mid-point, -6dB attenuation.
(As shown, full Side is at
full clockwise "CW" rotation.)

Because the roles of the encoder and
decoder are reversed, the PCB silkscreen requires redefinition.

This is how the
encode inputs and outputs map:

Left In > PCB Mid
In
Right In > PCB Side In

Mid Out > PCB Left Out
Side Out
> PCB Right Out

The two jumpers looping across the top of the PCB are
the Mid/Side Process Insert.
Variable width with additional processing in
either Mid, Side or both can be inserted here.

The decode inputs and outputs
map:

Mid In > PCB Left In
Side In > PCB Right
In

Left Out > PCB Mid Out
Right Out > PCB Side Out

The
builder may want to change the gain in the 5532 stage from -6dB to 0dB.
There
will be gain changes as width is changed: It's the nature of MS.
There's
always going to be more energy in mono.

http://www.waveulator.com/
http://www.ka-electronics.com/
http://www.linkedin.com/in/waynekirkwood
“Logic
will get you from A to B. Imagination will take you everywhere.”

mediatechnology

Posts: 1777

Joined: Sat Aug 11, 2007 2:34 pm

Location: Oak Cliff, Texas

Website

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Re:
A Variable Width Circuit for The Precision MS Matrix

by
mediatechnology
» Tue Oct 16, 2012 2:08 pm

The builder may want to change the gain in the 5532 stage from -6dB to
0dB.

I did and it works much better now having an
essentially unity gain "encode-decode" gain structure rather than ~ -6-8 dB
loss.

I also strongly recommend raising the input resistors of U9, and
also the feedback, to reduce loading on the pot. (Cfb is also lowered to 10
pF.)
The pot loading (which is in the MS domain) results in an approximately
-0.8dB encode-decode insertion loss.
To provide bypass without level shift,
the value of the bypass resistor is raised to 56K2.
An alternative is to
buffer the pot with an outboard unity gain stage.
In reality the 0.8dB dip in
the middle of rotation (normal stereo) is quite small compared to the level
changes resulting from changes in correlation as the width is varied from mono
to full side.

Mid
Side MS Matrix with Variable Width and Bypass

http://www.waveulator.com/
http://www.ka-electronics.com/
http://www.linkedin.com/in/waynekirkwood
“Logic
will get you from A to B. Imagination will take you everywhere.”

mediatechnology

Posts: 1777

Joined: Sat Aug 11, 2007 2:34 pm

Location: Oak Cliff, Texas

Website

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Re:
A Variable Width Circuit for The Precision MS Matrix

by
Nescafe
» Sun Aug 18, 2013 7:10 am

Hi,
I just think about using MS in Tube comp and also
Pico Compressor (original mono and not finished yet
), using this also as balancing debalancing card, since the compressor itself
have gain, could You tell me what is the difference between using xfader and
using compressor gain output in individual MS channel?

Thank
You

OOT: any information or document to guiding me how to put a
feedback/feed forward mod switch in the Original Pico?

Thank You
again

Nescafe

Posts: 22

Joined: Sat Aug 03, 2013 10:39 am

Location: Jakarta-INDONESIA

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Re:
A Variable Width Circuit for The Precision MS Matrix

by
mediatechnology
» Sun Aug 18, 2013 10:46 am

could You tell me what is the difference between using xfader and using
compressor gain output in individual MS channel?

None
really. Using the comp gain does the same thing.

In terms of switching
the Pico into feed-back mode that would be a question for Roger Foote.

http://www.waveulator.com/
http://www.ka-electronics.com/
http://www.linkedin.com/in/waynekirkwood
“Logic
will get you from A to B. Imagination will take you everywhere.”

mediatechnology

Posts: 1777

Joined: Sat Aug 11, 2007 2:34 pm

Location: Oak Cliff, Texas

Website

Top

Re:
A Variable Width Circuit for The Precision MS Matrix

by
Nescafe
» Sun Aug 18, 2013 3:07 pm

Hi Wayne,

Thank You, so I don't need to mess with
another pot

OK maybe I should make another thread about Pico, I think that I will
put FB mode for the MS mode using Pico.

Nescafe

Posts: 22

Joined: Sat Aug 03, 2013 10:39 am

Location: Jakarta-INDONESIA

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