Stereo To mono

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Stereo To mono

Postby lukatosh » 29 Dec 2016, 23:54

Hello guys,

My name is Lucas and I'm writing you from Chile. So ... Excuse my english.

Well, I would like to make a box that offers the option to give a mono out from a stereo signal at the input.

The stereo signal at the input comes from the last pedal of my set-up, an eventide time factor that sometimes i use in stereo.

To achieve this, i took the GGG simple guitar mixer circuit. With a 3PDT i would like to select betwen stereo (stereo in - stereo out, just routing) or mono out (Left in and Rignt In mixed).

The third row of the 3pdt will be used for led indicators: Mono or stereo.

Also, i would like to use this as a standar routing box. Sometimes I use the mono out of the eventide or other effect. For that, i added a switched input jack for the R-In. If the jack is unplugged, the right signal that goes into the mixer is muted (grounded). Then... the output will be only the L/mono input.

This goes like this, to match the "mono led".

The other way is seting the 3pdt to stereo mode (just routing) and then just use the L/mono-in and L/mono-out, but the "stereo led" will be on.

i'm planning to put thi on the breadboard probably the next week, but before that i would like to ask you for maybe some correctios or improvements to the proposed idea (Noise performance - Should add a Pf capacitor on the feedback loop of first op amp?, maybe use NE5532, What about impedances?)

Hope you can help me, here is the design.


Image



Thanks in advance, best regards... happy new year! [smilie=drink.gif]
lukatosh
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Re: Stereo To mono

Postby lukatosh » 06 Feb 2017, 23:48

any thoughts?

Thanks!
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Re: Stereo To mono

Postby phatt » 07 Feb 2017, 12:12

Hi luka,
If I'm reading this right and all you want to do is stereo to mono,,, then you just need a switch to bridge the two channels.
There is no need to over think this and it would need no power unless you want a led indicator.
All you need is 2 in's and 2 out's and a switch to bridge the 2 hot lines. When the 2 hots are bridged both outputs are then mono so either output can be used for mono.
Phil.
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Re: Stereo To mono

Postby grrrunge » 07 Feb 2017, 19:47

phatt wrote:Hi luka,
If I'm reading this right and all you want to do is stereo to mono,,, then you just need a switch to bridge the two channels.
There is no need to over think this and it would need no power unless you want a led indicator.
All you need is 2 in's and 2 out's and a switch to bridge the 2 hot lines. When the 2 hots are bridged both outputs are then mono so either output can be used for mono.
Phil.


I don't really know how to feel about this suggestion :scratch: It might work, and it might not hurt the Timefactor's outputs, but here's my thoughts on the matter:

By bridging the two output channels, you're effectively using the output impedances of the output amplifiers as a voltage divider between the two output voltages. Hence - in the ideal case where the two input impedances are equal - the output at the junction becomes the average of the two signals, which isn't equal to the sum.

If you then connect the bridged outputs to the input of an amp or another pedal, either output amplifier is looking into a low impedance (the other amplifiers output impedance) paralleled with a high impedance (pedal/amp input impedance), and as such the signal amplitude is reduced significantly due to the resulting voltage division.

On top of the two statements above, it's worth considering that if the op-amps driving the output are not protected from current running back into the output stage, you will have signals with an amplitude of a few volts inducing currents through the very small output impedances of the op-amps, trying to draw several amperes ( try 1V/0.1Ω, and you'll see what i mean ;) ) thus frying the output amplifiers on a rather expensive piece of equipment.

Lukatosh: Is there a reason why you're not simply using output 1 on the timefactor, which gives you a summed mono signal, when there's nothing connected to output 2?
A true believer in the magic of Sherwood Forest Pedal Pirates
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Re: Stereo To mono

Postby phatt » 08 Feb 2017, 01:15

Unlikely but possible, Frankly I doubt the designer would be that stupid but
2 x 100~500R series resistors between input sockets and switch will solve that if it's a concern. :thumbsup

There is always a tiny loss in the process, never been an issue for those that understand you just make it up down the line.
Phil.
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