stereo to mono

[Fredrik]

Whats the best way of doing a stereo to mono switch? I have looked around a bit and it seems that summing L,R thru resistors into an opamp is the way to handle this. I assume that if dual mono is needed one would deal with that by splitting the signal into two opamps like in a distribution amp, correct?

I have been thinking about a mono switch that also lets you choose L,R or sum. Would that be as simple as putting a switch on the feeds to the suming opamp, perhaps with a different resistor value aswell to makeup for the change in resistance?

Also, on some stereo inputs left is marked (mono) so that if a jack is inserted only in left it´s paralelled to both left and right. How is this usually acheived? Would it be possible to get this behaviour in a patchbay?

 

[CJ]

Do you have any Hybrid UTC's laying around?

 

[Fredrik]

Hey CJ, no unfortunately I dont have any. What would you suggest if I did? Is it worth trying to get some for this purpose?

 

[radiance]

[quote author="Fredrik"]Whats the best way of doing a stereo to mono switch? I have looked around a bit and it seems that summing L,R thru resistors into an opamp is the way to handle this. I assume that if dual mono is needed one would deal with that by splitting the signal into two opamps like in a distribution amp, correct?[/quote]

Yes

[quote author="Fredrik"]I have been thinking about a mono switch that also lets you choose L,R or sum. Would that be as simple as putting a switch on the feeds to the suming opamp, perhaps with a different resistor value aswell to makeup for the change in resistance? [/quote]

No need for a different value resistor if you use virtual ground summing (- input from opamp for summing, + input tied to ground). And yes, switch on the feeds will work AFAIK

[quote author="Fredrik"]Also, on some stereo inputs left is marked (mono) so that if a jack is inserted only in left it´s paralelled to both left and right. How is this usually acheived? Would it be possible to get this behaviour in a patchbay?[/quote]

Don't quite get your question ...

 

[ioaudio]

[quote author="radiance"]
[quote author="Fredrik"]Also, on some stereo inputs left is marked (mono) so that if a jack is inserted only in left it´s paralelled to both left and right. How is this usually acheived? Would it be possible to get this behaviour in a patchbay?[/quote]

Don't quite get your question ...[/quote]

some stereo inputs with two TRS jacks, if you connect the left(mono) jack only and leave the right unconnected, the signal goes to both sides L+R.
it´s quite simple: the jacks have a switch which sense if there´s something plugged into. so the left signal´s tip goes to the right signal´s tip until something is plugged into the right jack which breaks this connection.

 

[radiance]

[quote author="ioaudio"][quote author="radiance"]
[quote author="Fredrik"]Also, on some stereo inputs left is marked (mono) so that if a jack is inserted only in left it´s paralelled to both left and right. How is this usually acheived? Would it be possible to get this behaviour in a patchbay?[/quote]

Don't quite get your question ...[/quote]

some stereo inputs with two TRS jacks, if you connect the left(mono) jack only and leave the right unconnected, the signal goes to both sides L+R.
it´s quite simple: the jacks have a switch which sense if there´s something plugged into. so the left signal´s tip goes to the right signal´s tip until something is plugged into the right jack which breaks this connection.[/quote]

Yes, I think you answered your own question right? The switches in the jack chassis parts take care of the mono to stereo thing. However, I don't think this is done with opamps. Just two resistors one feeding the left and one feeding the right bus. Stereo to mono switch with opamps gives less (none) crosstalk between busses but seems a bit overkill to have on all inputs.
I should only use it on th monitor section.

 

[Fredrik]

Thanks for the input guys. I have though of using this in a small utility mixer for some samplers, daw, and turntable. The idea is that everything should be able to record any source instantly without any patching. The mono switch is for the turntable input.

The idea of using patchbay jacks to split a signal to dual mono is for a insert return.


[quote author="radiance"]
No need for a different value resistor if you use virtual ground summing (- input from opamp for summing, + input tied to ground). And yes, switch on the feeds will work AFAIK
[/quote]

Radiance, I had a look at your mixer in progress and the mono circuit you have used. Are you saying that disabeling one of the feeds to the sum amp would not change the gain? Wouldn´t doing so change the resistance going in from 5k (as a result of 2 paralell 10k resistors) to 10k and thus the amplification to unity since the feedback loop is also 10k?

P.S I might use your solution if it´s ok for you? :green:

 

[CJ]

Darn, I saw the perfect Rat Shack box on evil bay, a stereo to, mono junction box, you plug all your inputs into the back, there are a couple of knobs on the front, one to select the source, the other to change from mono to stereo, anyway, I will keep look if this is what you are after.

 

[radiance]

[quote author="Fredrik"]
Radiance, I had a look at your mixer in progress and the mono circuit you have used. Are you saying that disabeling one of the feeds to the sum amp would not change the gain? Wouldn´t doing so change the resistance going in from 5k (as a result of 2 paralell 10k resistors) to 10k and thus the amplification to unity since the feedback loop is also 10k?[/quote]

Just short one 10K resistor to ground.


[quote author="Fredrik"]P.S I might use your solution if it´s ok for you? :green:[/quote]

It's not my design but sure, go ahead...