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PostPosted: 03 Nov 2015, 08:37 

Joined: 03 Oct 2012, 12:34
Posts: 5
Location: padova, Italy
Hi everybody,
I'm quite new to the world of electronics and I'd like to build a simple audio circuit which would also suit my needs in live applications, especially when input channels on mixers are limited.
What I want to do is a balanced XLR stereo to mono summing box, which I can use, for example, for keyboards.
In addition, I'd like to add a phase switch on one of the two inputs (DPDT switch?) and a PAD on just one input aswell.
This way I could use it as a snare top/bottom combiner (using two mics), with the pad used to tame the bottom snare.
I'll start off saying I have quite few understandings of the huge world of electronics, after searching the web I have a rough idea of how to start but i still have some doubts.
I think it would be good to start with this circuit
placing the phase switch just before the points where the two sources join.
Regarding the pad switch, should I integrate a H PAD?
I found a calculator
from my poor understanding, I suppose that the summed input and output resistors on the PAD channel should match the values of the ones on the unaffected channel (correct me if I'm wrong) .
But what about the behaviour of that bridge power load resistance once the Pad kicks in? Will it affect the channel input impedance, hence the two inputs have now different impedances? Or is that negligible?
Will keeping its value as low as possible minimize its effect (again, if this is really something undesirable)?

Sorry for asking a lot of questions, but as I said I'm quite new and inexpert and I don't know directly any electronics expert :)
Thanks a lot to anyone who will respond and will give me an help about this.

PostPosted: 04 Nov 2015, 11:04 
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Joined: 04 Jun 2008, 20:59
Posts: 4326
Location: Arizona, USA
Hi, A tad bit out of my usual areas..but I would consider either an assembled matcher or getting the matcher transformers from EDCOR to do this diy. My sense is that using transformers will do a few things that the resistive one can not. First you can arrange it for electrical isolation of the two inputs as well as the output. It would be able to ground lift each from each other. Second you can flip the phase of either input or even the output if desired. Third it would have lower signal loss. Just some thoughts.

Good listening

Some of my DIY Tube Amplifier Projects:

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