Add A/B Selectable Input to DIY Gear - 2-Pole or 3-Pole?

Hello,

Simple question - If I wanted to add a second input to any of my DIY gear (like a compressor where input "A" = Mic Pre for tracking, input "B" = DAW DAC return for post processing) - is it as simple as adding a descent DPDT switch to the +/- legs of each XLR Input?  Should the shields be switched with a 3-pole switch - or can they remain tied together w/o any ill effects and a 2-pole switch?

Also - What might be a good switch for something like this?  I'm thinking Rotary "Break Before Make" - but the ones I've found @ mouser seem to be overly expensive (over $10/ea and I'll need 8 of them!).  Just a simple double pole (or triple pole if shields are needed) 2-way rotary switch that won't break the bank - not even too picky on size, but a 1/4" shaft is preferred.  I'll keep the shields intact through their length with a small un-shielded area at the switch itself (no more than 1/2").  This is mainly for a DIY-Racked 2-1176 (plan on using the unused "comp/bypass" opening), TG, D-LA2A, and eventually Dan's 2-1176 (for reference).

Thanks for clarification and switch suggestions! 

Happy New Year to all!  Have a few drinks for me while I'm at work 8)

I would go with relays to keep the signal path short.

2 pole should be fine. the grounds can stay connected

Or use a patchbay....

Thanks for your reply!

If I can keep the wires practically the same length (might be adding 6" vs XLR direct to input Attenuator) - and if I don't want to mess with the extra power and complexity of adding relays - is there anything inherently bad about using a double pole switch?  Chances are the wires would be longer with relays as I'd have to find a place to mount them cleanly, then have more power wires crossing the chassis, etc.  I'm looking at a "point to point" wiring scenario regardless - the more simplistic the better IMO...

Any good suggestions on a descent rotary switch that won't break the bank?  I was hoping to find something respectable for $5/ea or so.

PS - Patch Bay - I'd love to get one at some point - but my current work space isn't setup for one - and I kind of like having direct XLR > XLR connections from Mics > Pres > Comps > ADC (no longer than needed and with as few termination points as possible).  I have plenty of spare DAC outputs in my system - so feeding the compressor's second input from the PC is far easier in my odd setup (use the same ADC input from the Comp regardless).  All it takes is a recall on the DAW and the twist of a switch on the Comp - no re-patching...

Thanks, and I hope your 2011 is off to a good start!  I'm stuck at work 


8)

This may be ok for your application:

http://www.mouser.com/catalog/specsheets/CK1461-6.35X17.5MM-RND-SHAFT-Lorlin-datasheet-160877.pdf

haven't used these specifically, but it looks like the CK1591 or 1592 could work. Build 8 of these into a 2U box along with the jacks and it would mean you only have to build one unit to control 8 ch of switching, versus having to rebuild all of your back panels. If you use a shallow chassis, it shouldn't add much wire length, and whatever it does add will be balanced, and isolated in its own case, far away from transformers and power, so added noise should be less of a concern. Extra cost in XLR jacks and a chassis, but it will save time, and save you from drilling already-completed work. Your input switching also becomes accessible from the front of your rack, so no fooling around behind your gear every time you want to switch an input. Also note that 4 pole 2 pos toggles seem to turn up at surplus / mom-and-pop electronics stores pretty regularly, are usually dirt cheap ($2 per) and could be used for this too, allowing you to not tie all grounds. No idea if those are shorting or not though.

Those look to be in my price range.  I guess the 4-Pole 3 Pos or the 3-Pole 4 pos would work - both the same price (I'm assuming I can limit the rotary action to 2 positions with "Stop Pins" - similar to the switches on my Seventh Circle Preamps?).  I might use the 4-Pole as a ganged stereo/2CH input selector on one or two of my units (save front panel real estate).  The Mom & Pop Surplus Stores is also a FANTASTIC resource - I'll begin scouring and see what comes up.

I will be adding these to the existing chassis with front-mounted switches as I'm tight on rackspace (I'm also combining two separate Hairball 1176's into a single 2-1176 just to save space!)  - and an external chassis would also mean a $ Chassis, plus tons more XLR Cables AND XLR connectors (versus adding a single XLR input and a patch cable from DAC to that extra input).  I have a stepped drill bit on the way for the XLR holes - and at least one of my 2-1176's will have an extra pre-drilled front-panel opening that will be perfect place for this switch (versus the un-used 1/4" I've seen others slap in this hole ) - and I'm sure I can shoe-horn them in the other chassis (minus the SB4000 - It's already jam packed!).  Rack Space really is a precious commodity for me.

On the 1176 especially, the XLR Input goes straight to the front panel attenuator - so adding the switch to the front panel (switch will then feed attenuator) will literally add only a few inches of wire (maybe 6" max).  I'm not too concerned about that - and like you mentioned it will be balanced and shielded.  The D-LA2A, TG, and SA3A I'm not sure about yet as I'm still waiting to get all of my parts in before I can dig in on those projects (I'll look at the schematics later and see if there might be any compromises with these other units).

Thanks for the switch recommendations and other valuable input.  Any further suggestions are welcomed.

Rock on  8)