Mid Side M-S Matrix Construction Information

[mediatechnology]

You could also use a 2 pole unity gain Sallen Key HP filter in the Side path.


Unity Gain Sallen Key Filters courtesy of Rod Elliot.

http://sound.westhost.com/articles/acti ... ers.htm#s3

[fuccimain]

I saw that design, I also saw this 1st order design. I'd like to be able to have say 4 or 5 selectable frequencies, and with the 2 order one that may be too complex if I have to change more than 1 component etc, with 1st order I believe it's just changing the shunt resistor, I believe.

http://www.electronics-tutorials.ws/fil ... ter_6.html

[mediatechnology]

I'd like to be able to have say 4 or 5 selectable frequencies, and with the 2 order one that may be too complex if I have to change more than 1 component etc, with 1st order I believe it's just changing the shunt resistor, I believe.

Correct. Make sure one resistor is always in circuit to provide a bias current path. I honestly think for a LF mono crossover single order would be best. A low bias op amp (LME49860 or Bifet) would allow a relatively high shunt R value and allow the use of film caps.

We had a thread in the design forum where the poster was using a mult-order in the Side path but that was for warp reduction for disc playback transfer. The reasoning was that HP filtering side would allow it to have a very high cutoff without sonic consequences while having a relatively low cutoff for the Mono component. It would be unlikely the disc recording would have much LF side information in the original master but it would seem the opportunity for warping to create side information on playback would be fairly high.

I have an article somewhere regarding introducing a LF mono crossover point to optimize ear bud listening.

[fuccimain]

Think I'm working out that design with a 10uf series and for 20hz cutoff a 795k shunt. Haven't figured which opamp yet but I'll look into the one you suggested I should add a 2nd resistor to the design for bias? And subtract that resistance from what I get for a given frequency then, correct?

And for the 5532 gain adjustments, what value pots should I order?

Grazie!

[fuccimain]

The bias resistor should be a shunt correct?

[mediatechnology]

Think I'm working out that design with a 10uf series and for 20hz cutoff a 795k shunt.

I think you mean 796 Ohms for a 20 Hz cutoff.

However I'd use a film cap to lower distortion.
0.47uF for 20 Hz is about 17K Ohms minus a little change.
18K/0.47uF is 18.8 Hz and probably close enough.
The bias resistor would be a shunt from the + input to ground.
If you're not switching the HP filter out (and thus not opening the filter shunt R) you don't need an added bias resistor to ground.
If you do switch out the filter something higher than 18K, maybe 100K would be a good choice.
If you put a 22K in parallel with 100K you'd wind up with about 18K so you could simply open the 22K to shift the filter from 20Hz to 3.4Hz.

[fuccimain]

Heya. I wanted to reply to this sooner but I ended up in the hospital for a coupe days and haven't had the chance to work this out further. I really appreciate all the info in the last post, but before I dive into it, I wanted to see how I was getting a shunt resistor value well above what you said I should be getting for 20hz, so I redid the math and I'm still getting 796k. I must be doing something terribly wrong so I've attached a pic of my calculations....

If I could be clued into my folly in this I'd really appreciate it, then I'll try to figure out switching to .47uf with maybe 4 fixed frequency selections.

Thanks again.

[fuccimain]

.although at .47uf at 20hz I did get 16.93k, which I believe is correct. You said 17k minus some change so Im Assuming I got it correct. Curious why my other numbers were so off..

[mediatechnology]

10 uF is 10^-6

Your calculations are for 10 nF which is 10^-9.

This is a good calculator site
http://www.muzique.com/schem/filter.htm

[fuccimain]

, oh, yeah I was originally calculating for 10nf, as I was using the example on the page where the circuit came from. .. So I had it right for 10nf