Noob summing question

guitarguy12387 · 20th December 2009, 03:03 AM

Hey everyone. I simply want to sum a balanced stereo signal to balanced mono. Not sure how best to go about it! Any tips? Thanks!

gfiandy · 22nd December 2009, 11:28 PM

I would treat the two signals completely seperately and buid two summing amplifers using an opamp to sum the signals at the virtual earth. Then the two ouputs of the opamps become your positive and negative outputs.

To do this configure the opamp in inverting mode and the gain is then equal to Rf / Rin so if you make Rin 2 x Rf you will get a gaiin of 0.5 on each input.

You need to be sure you have enough head room in the power supply and input to the next stage, or you could configure the summing stage to have a gain of 0.5 to ensure that you don't clip.

Regards,
Andrew

guitarguy12387 · 23rd December 2009, 01:39 AM

Hey thanks for the reply!

Well that would work... but i'm trying to do it purely passively. But i don't want to overload my soundcard either so i'm not sure the best way to go about it.

godfrey · 23rd December 2009, 03:05 AM

How about just blending with resistors?
Simple is good!

Key · 23rd December 2009, 04:40 AM

Y cable. No I'm not joking and yes I have tested this. Probably depends on how you are bridging the impedance but on my particular balanced system just soldering the cables together gave me the best results with the least passive loss, THD etc......

20th December 2009, 03:03 AM	#1
guitarguy12387 diyAudio Member Join Date: Mar 2008	Noob summing question Hey everyone. I simply want to sum a balanced stereo signal to balanced mono. Not sure how best to go about it! Any tips? Thanks!

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22nd December 2009, 11:28 PM	#2
gfiandy Audio Engineer diyAudio Member Join Date: Jul 2003 Location: Cambridge UK	I would treat the two signals completely seperately and buid two summing amplifers using an opamp to sum the signals at the virtual earth. Then the two ouputs of the opamps become your positive and negative outputs. To do this configure the opamp in inverting mode and the gain is then equal to Rf / Rin so if you make Rin 2 x Rf you will get a gaiin of 0.5 on each input. You need to be sure you have enough head room in the power supply and input to the next stage, or you could configure the summing stage to have a gain of 0.5 to ensure that you don't clip. Regards, Andrew

23rd December 2009, 01:39 AM	#3
guitarguy12387 diyAudio Member Join Date: Mar 2008	Hey thanks for the reply! Well that would work... but i'm trying to do it purely passively. But i don't want to overload my soundcard either so i'm not sure the best way to go about it.

23rd December 2009, 04:40 AM	#5
Key diyAudio Member Join Date: Jan 2009	Y cable. No I'm not joking and yes I have tested this. Probably depends on how you are bridging the impedance but on my particular balanced system just soldering the cables together gave me the best results with the least passive loss, THD etc......