Sum stereo to mono with switch

Lameller · May 23, 2019, 05:54:28 AM

Hi

I would like some help building the following little switch setup.

I have two instrument level inputs (from two guitar pickups) that I would like to switch between having them as seperate signals in stereo and a summed mono signal.

For the summing of the signals I have learned that a resistor on each signal before they are summed would do the trick (with about a 6dB loss in signal).

But what kind of switch should I use and how should it be wired in order for it to achieve what I am trying to do?

Below are two small sketches showing what I imagine in terms of audio flow.

Any help would be greatly appreciated.

Best

Lameller

rankot · May 23, 2019, 06:38:17 AM

I did it this way in my output selector, which also includes stereo to mono switch (must be 4PDT).

Volume pot is stereo, but it can be omitted or separated, if you want.

Lameller · May 23, 2019, 06:43:52 AM

Perfect! Thankyou vey much!

Lameller · May 23, 2019, 06:50:46 AM

Oh wait, I was actually looking to do this in a passive box. I admit to being a complete noob in terms of diagrams, but it looks as if the sketch requires 12V. Is that correct?

Best Lameller

antonis · May 23, 2019, 06:51:16 AM

Didn't have a DPDT switch pic handy, so ignore 3rd column..

Lameller · May 23, 2019, 07:02:12 AM

Again perfect! Thankyou SO much for all your speedy help

lukeferg · May 23, 2019, 07:52:24 AM

Quote from: antonis on May 23, 2019, 06:51:16 AM
Didn't have a DPDT switch pic handy, so ignore 3rd column..

Wouldn't it be better to have the resistors coming off lugs 3 and 6 and then tied together for mono. That way, when they are seperate stereo outs the resistors are out of the path.
Or do you want the 6db loss when they are in stereo?

Lameller · May 23, 2019, 08:38:15 AM

Good point. I guess actually a permanent 6db loss would be the best for my purposes.

I have a guitar pickup that is split into two separate humbuckers (one under E and A and one under the other four strings). When using the stereo outputs, the output from the E and A string pickup goes through an octave pedal.

So when I flick the switch I cancel out the octave signal and only send a straight mono signal to the output. So it behaves as a regular guitar basically.

So in short, all the signals should have the same amount of output.

Best Lameller

davent · May 23, 2019, 01:39:32 PM

I used this in a hifi preamp.

dave

PRR · May 23, 2019, 07:48:24 PM

No reason to get more complicated than this. 68K is what Fender always used to mix two instruments; will work as well for two pickups on one instrument.

Lameller · May 24, 2019, 04:10:30 AM

And the switch should be wired like one of the other suggestions?

Best Lameller

Lameller · May 26, 2019, 09:56:40 AM

Wired it up last night like the first sketch. Sure enough the signals are summed, but when i switch to the summing position, output 2 starts buzzing.

So I did sketch no.2. Shouldn't some part of the switch be connected to ground like volume pots etc. are?

Any thougts on sketch no.2 before I fire up the soldering iron again?

Best

Lameller

PRR · May 26, 2019, 09:39:34 PM

> Any thougts on sketch no.2

It is always mono.

{EDIT} Image removed --- brain fart, would not work.

Lameller · May 27, 2019, 01:58:32 AM

Hi PRR.

Thankyou for the reply. I'm not sure I understand. I have the grounds from both pickups combined and soldered directly to the output stereo jack. Is that the wrong way to go about it?

Hope that makes sense?

Best

Lameller

Lameller · May 27, 2019, 05:47:32 PM

Quote from: PRR on May 26, 2019, 09:39:34 PM
> Any thougts on sketch no.2

It is always mono.

{EDIT} Image removed --- brain fart, would not work.

Fair enough

No matter how I wire up the switch I end up with a nice summed signal on output 1 and a lot of hum on the other output. I can't seem to kill output 2. which is what I need when output 1 has the summed signal.

PRR · May 27, 2019, 05:55:52 PM

> when i switch to the summing position, output 2 starts buzzing.

You need to ground the idle #2 Out when in mono-to-1.

*Somebody* check me here. For some reason I am posting bogus plans.

Lameller · May 27, 2019, 06:00:55 PM

PRR - you are such a great help

I will try and decipher your sketch. Am I correct in assuming that you are showing a DPDT switch? I realize that this is an electronic diagram but I might have of trouble translating it into what goes where - but I will give it a go for sure

Lameller · May 27, 2019, 06:19:53 PM

I think I got it now. Sorry about the danish sketch... I believe my problem was that I was grounding the switch wrong. Will try this out and get back.

Again, thanks to everyone helping out!

Lameller · May 28, 2019, 06:29:50 AM

So for the internet archives the sketch in the previous post worked

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Sum stereo to mono with switch