Input Selector

alterboy07

Member
2019-12-17 7:06 pm
Hello Everybody!

I am new to the forum. I actually joined since I was looking for help for a project of mine.
I wanted to build a small Audio Input selector to use with my JBL L305s. I want to be able to connect my Audio Interface and my Turntable's pre amp to the Monitors. In my head it sounds like a simple project, but since I have no experience in Electronics I decided to ask here.
So, 2 stereo Inputs(T(R)S) and 1 stereo output. If there is a variant of a non powered one that would be great. Otherwise, an On/Off switch would be great.

I am very thankful for your help in advance :)
 
Does your phonopre have an output level control at all? Otherwise you may be better off with a little compact mixer with at least one pair of balanced inputs from one of the usual suspects (Behringer, Mackie, whatever - my Mackie 402VLZ4 features the desired power switch and wasn't that much used).

Switching between two balanced stereo sources passively requires at least a 4PDT switch, or even a 6PDT if you want to be switching the shield connection as well. Internal wiring would be unshielded twisted pair in the former case and shielded twisted pair in the latter.
 
Thank you for your Answer!
Yes, I already have a volume control for the Turntable :)
Buying a small mixer is a great Idea, but I was thinking to build it myself. So, I could do it passively. That is great, since I won't need any power cables and power switches :)
Would you recommend switching the shield connection? I would like to give it a go!

Thanks again!
 

Galu

Member
2018-04-17 6:50 pm
For stereo switching you need a 4 Pole Double Throw (4PDT) switch.

One stereo input goes to the top row of four terminals and the other to the bottom row.

The output is taken from the middle row.

Signal and shield connections will be switched.
 

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Galu

Member
2018-04-17 6:50 pm
@ alterboy07

I did not initially catch on fully to your requirements - sgrossklass understood them better than I!

Are we talking?

2 x 1/4" TRS input sockets (L&R channels) for the interface.
2 x 1/4" TS input sockets (L&R channels) for the turntable.
2 x 1/4" TRS output sockets (L&R channels) for the output to the monitors.
 
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Thank you for the explanation! I am starting to understand :)
I am using balanced cables with my monitors and interface and simple rca to TS for the turntable. So all of the 6 ports (2x2 Inputs and 1x2 output) should be TRS compatible. Should I use the 4pdt?

It's not complicated... a DPDT switch will give you two inputs. If you need more just expand it to a Dual Pole rotary switch with the number of stops you need.

For stereo, you would use 4PDT for wired as twice what's in the thumbnail. For more than two inputs you would need a 4 pole rotary switch with the required number of stops.

The switch itself won't be all that expensive. It's the box and connectors that will get pricey.
Construction is easy... it's just a wiring job, inside the box.

This would be Soooo much simpler if you were using RCA interconnects.
 

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@ alterboy07

I did not initially catch on fully to your requirements - sgrossklass understood them better than I!

Are we talking?

2 x 1/4" TRS input sockets (L&R channels) for the interface.
2 x 1/4" TS input sockets (L&R channels) for the turntable.
2 x 1/4" TRS output sockets (L&R channels) for the output to the monitors.

Yes, exactly! :)
Sorry for my lack of knowledge... But that is exactly what I need :)
 
A 4PDT is insufficient - you're going to need a rotary switch as Douglas has indicated.

You'll need to learn how rotary switches work before you can figure out how to use one for your application.

Here's the tutorial! http://info.ee.surrey.ac.uk/Teaching/Labs/docs/RotarySwitchHowTo.pdf

Actually, with two stereo inputs and one stereo output a 4PDT switch would be perfectly adequate... It's balanced so it would simply be two of my DPDT examples for stereo.
 
It would still be balanced. Presumably the monitor speakers are balanced inputs so youd have to convert the turntable from singled ended to the balanced input.

The switch has 3 input pins per selection and 3 output pins. So on the turntable input pins youd need to connect the ground with cold input.

Youd have extra selection inputs for expansion.

I think it's a nifty solution tbh.