DPDT to Switch between Mono/Stereo

[thehallofshields]

I'd like to use a DPDT switch to give me the option keep two signal paths independent, or combine them.

Basically:

2 Input Jacks
2 Output Jacks
1 DPDT Switch

I can't figure out how to wire the DPDT to merge the signal the output jacks without obvious 'feedback loop' problems.
It seems like I'm going to need to use a pair of Diodes, but I could use some advice in that dept. too.

Help?

[Jazz P Bass]

Summing Network

I have attached a "summing" pdf file from Rane.
Pretty much covers it.

[Jazz P Bass]

Summing Network With Switch & Jacks

Here is a sketch of what I believe you are talking about.
Pay attention to the fact that they specify "stereo jacks". Tip, Ring, Sleeve.
By using the "ring" as a secondary ground, you insure a positive connection to ground.
The switch is double pole, single throw.
On/ Off. Two sides.

[Enzo]

Um...

First thought: diodes??

How did you decide on the DPDT switch without having a circuit in mind?

Just to be sure, you want the options to be two independent through signals? or two signals combined into mono but still feeding both outputs? And not A or B or Both all ending up in one output?

If you want two through signals to be mono'd, then you have the classic stereo to mono.

Jazz, I don;t follow your summing box. Oh wait, I see what you did. They use TRS jacks at the Rane example so a balanced line can be plugged into it. You used them.

[Jazz P Bass]

Thanks for the clarification on Rane's print.
I was not thinking "balanced" input.
You are correct.
I do like the spring loaded "ring" being grounded when a 1/4" mono cord is plugged in.
A good positive connection.

[thehallofshields]

Thanks for the quick responses, you guys are awesome.

I'm building a pedal-board and am simply trying to give myself a bit of versatility. The first stage of the board is a Phantom Power box and I'm going to try to integrate the summing box schematic into the enclosure. What I don't understand is why the resistors are ring signal path. In my particular setup, the rings on the input side are already in use.

Also, can you guys throw some resistor values at me so that I can use this with standard electric guitar impedance?

[Jazz P Bass]

Look again.
The ring is grounded.
The resistors are on the Tip.
You can erase every ring connection on the drawing if you want to.
The 10K has to go to ground then.

[Enzo]

perhaps he is referring to the input jack on the FX units, those are often wired for the ring to complete the battery circuit, hence the ring is "in use." That shouldn;t matter in this AB box, but that might be what he is thinking.

[thehallofshields]

Look again.
The ring is grounded.
The resistors are on the Tip.
The 10K has to go to ground then.

My mistake. I always associate the longer arm with the tip connection. BTW: much thanks for the PDF's, I really appreciate the help.

1. It appears that the 10k resistor to ground is in parallel with both outputs. When the switch is switched on; should I expect both outputs to act equally. If so; would I run into the Y-Splitter problems (as described in the "Why not Wye" .pfd) if I have both summed outputs in use at the same time?

2. What does that 10k output resistor actually do? Dump voltage spikes to ground?

3. Should the Input Resistors just be simple Impedance Bridging Values? 1MOhm for Electric Guitar?

4. Would it be possible to rig this with a DPDT switch? The schematic calls for a DPST switch, but I don't have any on hand and it would be nice to not have to order new parts.

[thehallofshields]

perhaps he is referring to the input jack on the FX units, those are often wired for the ring to complete the battery circuit, hence the ring is "in use."

Sorry for not clarifying, I always try to make posts simple and generalized so others can use the information. I'd like this "Summer" to share enclosure space with a phantom power system that shoots DC power up the Right Channel of a stereo cable.

[Enzo]

OK, that is very different from what I assumed. That would be a nonconventional wiring scheme, and as such you really ought to point it out. I appreciate that you are trying to think of the others reading the thread. I make such an effort myself.

The 10k is there to complete the voltage divider so the two 470 ohm resistors can work as summers instead of disappear.

[thehallofshields]

Thanks for all the info. I'm about to start building this, but I never got a response regarding the input resistor values.

Do I really want to use 470Ohm resistors? That seems like a number for a low-impedance microphone or something. If this has, say, two electric guitars running straight into it wouldn't I want resistors more in the range or 1megohm?

[Jazz P Bass]

The circuit is a summing /voltage divider.
100 mv guitar signal in will result in a 96mv signal out.
Voltage Divider Calculator