Stereo balanced to dual mono balanced

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JW

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Jun 8, 2005
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Location
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Does this look right? I'm trying to make a sum to mono switch, maintaining the balanced signal, but ending up with dual mono balanced.

There's this Rane document: http://www.rane.com/note109.html

But it's stereo balanced to single mono balanced, not dual mono.

 

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Simply eliminate or do not use the second output; it will be mono. If it seems to be loading the circuit, that is feeding the network ; try raising the value of the resistors to 2.4k-4.7k.
 
Thanks Bill,

This is for going into a Crown monitor amp. Both it's channels are balanced. So how would I feed two balanced mono inputs? Just feed both pin 2's in parallel from the junction where the two 475 ohm resistors connect? And then the same for both pin 3's?

 
Okay

Maybe I'm not explaining enough to get many responses.

I'm trying to wire a sum to mono switch right before my speaker amp, so that instead of two balanced channels of stereo mix, I get two balanced channels of a collapsed to mono mix.

The input to my amp is 20K
 
I would use Figure 3 from the Rane notes

n109fig3.gif


and just y-cable the summed output to both of your amps input.
 
JW said:
Okay

Maybe I'm not explaining enough to get many responses.

I'm trying to wire a sum to mono switch right before my speaker amp, so that instead of two balanced channels of stereo mix, I get two balanced channels of a collapsed to mono mix.

The input to my amp is 20K
If I understand correctly, you still want your monitors working. The problem with your passive system is that connecting it to unbalanced inputs will unbalance the signal to your monitor amp. It may or may not be an issue.
Note that, with the values shown, that will introduce a certain amount of cross-feed, resulting in about -30dB x-talk. Again, it may or may not be an issue.
If I were you, I would consider an active solution; a basic diff amp and a summer (3 opamps in total) would provide a perfect working solution. It could easily be breadboarded.
 
I could breadboard something for sure, but I can't dream what this differential circuit would be.

As for the un balanced issue. It isn't. My monitor amp's inputs are balanced (or unbalanced if I wish, but the point is to keep them balanced)
 
JW said:
I could breadboard something for sure, but I can't dream what this differential circuit would be.
Google differential amp, or look there https://groupdiy.com/index.php?topic=65116.msg825138#msg825138 On sheet 1/4, the circuit around 1/2U1, with 4 resistors and 4 caps, that's a balanced input stage, that converts a balanced input in an unbalanced signal, without altering the balanced signal. It is not the utmost solution; for that, check http://www.thatcorp.com/datashts/THAT_1200-Series_Datasheet.pdf Fig 10 is what you want to build.

As for the un balanced issue. It isn't. My monitor amp's inputs are balanced (or unbalanced if I wish, but the point is to keep them balanced)
OK, my bad. However, there's so many things can happen when connecting things together, the advantages of active  are unbeatable.
 
Thanks Abbey,

I have all the parts on hand for a passive summer like the RANE document, so I'm gonna try it passively first. But I'll make a note of the THAT corp document.

As for a Y cable, like this?

 

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Oh, right.

Embarrassing.

I was trying to imagine a Y cable feeding two balanced inputs from 1 balanced output and confused myself more than usual.

So, the second to last schemo is essentially what Silent Arts is talking about in regards to a Y cable.
I'm using 50 ohm outs>20K inputs with this mono summer inbetween.
 
Okay,

Clearly when I implement the switch, I'm winding up with both hots and both colds in continuity with each other when it is in normal (stereo) position.

 

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The answer?

Bringing me back to almost exactly like the first schematic I posted. Now I'm actually using 1.2K resistors instead of 475R and 22K instead of 20K.

This works pretty well, but I'd like slightly less attenuation when switched to mono if possible. Is that a matter of dropping the resistance of the 1.2K resistors?

And, do I need the 20K resistor at this point?
 

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JW said:
Okay,

Clearly when I implement the switch, I'm winding up with both hots and both colds in continuity with each other when it is in normal (stereo) position.
  Looking at this, I understand that you want to make a stereo/mono switch for your monitors. This is not what your original post suggested. I thought you wanted to create two additional mono feeds for a different amp/speaker.
The answer is much simpler.
 

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Thanks very much Abbey for the help.

I suppose I'm exposing myself as extremely dense here.

But I don't see a situation in your drawing where the signal is not being forced through the two resistors. Which side is input?
 
> Which side is input?

The side which is not being shorted-together to make Mono.
 
abbey road d enfer said:
  Looking at this, I understand that you want to make a stereo/mono switch for your monitors. This is not what your original post suggested. I thought you wanted to create two additional mono feeds for a different amp/speaker.
The answer is much simpler.

Hi there,

What resistor values would you use if I were to put this in a simple DIY passive monitor controller connecting a 50Ω output to 10kΩ inputs (speakers)

Sincerely,
Sam
 

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