# Optimal Linear Stereo Matrix for three Speakers

#### Mashie Saldana

Joined Feb 12, 2016
9
When you consider that humans can barely detect a difference of 3db and that represents a 50% change in power, you have to realize 0.1% precision isn't necessary. Personally, I'd settle for 1% and still get called dirty names by a, "real" engineer.
Fair point, any suggestions that makes my life easier are welcome.

I have been looking at powering options and would prefer to drive this using a DC power brick as I rather not mess with transformers fed from 240V. How much of a pain would it be to get +/-12v to the opamps that way? After all everything seems to be powered from +5v DC nowadays, however Google isn't very helpful in finding good examples to copy.

#### #12

Joined Nov 30, 2010
18,190
Hard to believe, but I can find 5% resistors at 9 cents and 1% resistors at 7 cents!
As for bricks? Two isolated 12 volt bricks with one connected 'backwards' will get you +/- 12v or +/- 15V
Digital stuff is going from 5 volts down, but audio work still requires a good fat split 12 or split 15 power supply. It's caused by that peak to average ratio of 10 to one in the voltage department and trying to work pretty far above the noise floor.

#### #12

Joined Nov 30, 2010
18,190
db=20log v2/v1
0.1 = 20 log v2/v1
0.005 = log v2/v1
1.01158 = v2/v1
Therefore, an accuracy of 0.1 db requires 1% resistors.

#### AnalogKid

Joined Aug 1, 2013
8,314
Interesting part. Great price, especially for lambda.
For low noise performance the datasheet recommends input and output filters. Note the restriction on total output capacitance.
I understand the simplicity and appeal, but I still recommend linear supplies.

ak

#### Mashie Saldana

Joined Feb 12, 2016
9
Interesting part. Great price, especially for lambda.
For low noise performance the datasheet recommends input and output filters. Note the restriction on total output capacitance.
I understand the simplicity and appeal, but I still recommend linear supplies.

ak
How do I calculate the capacitance it needs to be able to drive?

#### AnalogKid

Joined Aug 1, 2013
8,314