synthetic

Passive Attenuator/Downmix Question
« on: February 23, 2006, 12:45:32 AM »
I want to build a passive downmixer and attenuator for a Super Audio CD player. I want the Center channel reduced by -3dB and sent to the left and right speakers. (No center in this listening system.) I also want a stereo attenuator for the surround channels.



All of the signals are unbalanced -10 level. Can someone help me with the values for R1 and R2? My electronic textbooks are buried somewhere. Thanks for your help.


NewYorkDave

Passive Attenuator/Downmix Question
« Reply #1 on: February 23, 2006, 10:58:56 AM »
The image isn't showing up.

kruz

Passive Attenuator/Downmix Question
« Reply #2 on: February 23, 2006, 11:07:46 AM »
i can see the image with no problemo :roll:

NewYorkDave

Passive Attenuator/Downmix Question
« Reply #3 on: February 23, 2006, 11:17:51 AM »
Maybe it's blocked by my employer's sysadmins. They've been going nuts with blocking sites lately, some of them for no apparent reason.

Could you email it to electronic_dave

at

ya

hoo

dotkom

or post it on twin-X, perhaps?

kruz

Passive Attenuator/Downmix Question
« Reply #4 on: February 23, 2006, 11:24:03 AM »
sent!

NewYorkDave

Passive Attenuator/Downmix Question
« Reply #5 on: February 24, 2006, 03:46:23 PM »
Thanks for emailing the image.

There's a problem with the center channel mixing circuit as you've drawn it. The amount of center channel attenuation is overly dependent on the source impedance of L and R. And, with the resistors chosen to give 3dB attenuation of the center channel working against the source impedances of L and R, the loading on L and R will be excessive.

The circuit below will mix in the center channel with the center down by about 3dB relative to left or right, while maintaining source and load impedances that should work reasonably well with typical "consumer" equipment.



Problem is, it reduces your overall signal level by one half. But that's the name of the game with passive mixing! Most CD players have fairly hot outputs, though.

the amount of crosstalk between L and R will depend on the source impedances of L, C and R. If it's excessive, then the 3.3K and 2.2K resistors can be increased in value--as long as you maintain the same ratio between them. The price will be increased insertion loss, and also a higher source impedance driving the cable to your amplifier. In any case, the mixing network should be located close to your amplifier, connected with a reasonably short cable if possible.

synthetic

Passive Attenuator/Downmix Question
« Reply #6 on: February 27, 2006, 12:59:16 PM »
Thanks for your help. I'm off to buy some protoboard.
 :guinness:  :guinness:

synthetic

Passive Attenuator/Downmix Question
« Reply #7 on: February 27, 2006, 01:00:06 PM »
Is it OK if I fax this to my manufacturer in China?  :wink:  :green:


 

Related Topics

  Subject / Started by Replies Last post
1 Replies
2573 Views
Last post October 26, 2005, 02:46:40 AM
by gyraf
0 Replies
2042 Views
Last post August 07, 2007, 01:55:15 PM
by undertone
14 Replies
3700 Views
Last post April 23, 2008, 06:33:49 PM
by clintrubber
12 Replies
5421 Views
Last post June 23, 2016, 07:48:34 PM
by clintrubber