Wiring of a transformer "Color" box w/ bypass 4PDT

[timpratt]

Howdy all,

I'm a bit of an electronics novice, but I read a lot, like to get my hands dirty, and learn.

As such, I have four pairs of line transformers (UTC A-20, Triad HS-66, Stancor WF-30, etc) that I am wanting to wire up in a racked box to use for both tracking and mixing. The idea is not a new one, and has been talked about a great deal since the old "Using Transformers: To Transform Audio" article back in 2010 ( http://tapeop.com/tutorials/76/transformers/ ).

My idea for this project build is something along the lines of this:

http://www.preservationsound.com/?p=5782

My project differs slightly. Instead of using the same style 4PDT as is used in the above article, I am using a bank of eight of the old 70s/80s schadow 4PDT push on/off switches (similar to this: http://www.talonix.com/images/switch/SWPB0034.jpg).

Planing on wiring all the transformer inputs/outputs to 1/4" TRS-F jacks on the back of a 1U or 2U project box, and then patch that in to my patchbay. I am also planning to use a pair of TC Electronic Level Pilots for volume input/output.

The goal of this is to use as inserts for "color" for use during tracking as well as mixing, comping vocals, or making stems... lots of uses I could see. Here is one example I would likely be using it for as well:

Multi-track mix out from DAW
------ IN TO------
16ch DAC
------ IN TO ------
Folcrom 16x2 Summing
------ IN TO ------
Mic Pre
------ IN TO ------
Mix Comp
------ IN TO ------
TC Electronic Level Pilot #1 (input)
------ IN TO ------
Transformer Color Box
------ IN TO ------
TC Electronic Level Pilot #2 (output)
------IN TO ------
2ch ADC back into DAW


I have talked with other engineers that have done something like this, and have read a great deal online from various articles I could fine. I have two main questions:

1) How do I wire up each of the Schadow 4PDT bypass switches? From my testing with a voltmeter, they are setup as four groups of three prongs. The left and right sides are independent of each other, but if you push the switch in, then each of the four groups switches from connecting the center of the three pins from B to A (if that makes sense to you)... like this:


(THE BELOW TEXT MAY NOT VIEW CORRECTLY. DIAGRAM SHOULD LOOK LIKE THIS POST IN THE MIDDLE OF THE PAGE http://www.diystompboxes.com/smfforum/i ... ic=70353.0 )


B | | B

Group #1 | | Group #3

A | | A

B | | B

Group #2 | | Group #4

A | | A


A = button not pushed in (bypass transformer)
B = button pushed in (signal routing through x-frmr)



I am still trying to figure out how to properly use this switch, coming in from a TRS jack... maybe like this? Where do the ground wires connect?



Send to X-frmr (+) in? | | Return from X-frmr (+) out?

Tip (+) input? | | Tip (+) output?

Connect straight through? | -> |

Send to X-frmr (-) in? | | Return from X-frmr (-) out?

Ring (-) input? | | Ring (-) output?

Connect straight through? | -> |



2) That was a very long description. If you're still with me, thanks. My second question, is that I've read that when wiring up a transformer color box such as this, a lot of people keep mentioning the use of different resistors attached to the actual transformers themselves, I believe they are wired to the connect wires (+ & -) of both the ins and outs of the transformers. The original Tape Op article (remember this from earlier? http://tapeop.com/tutorials/76/transformers/) does not mention the user wiring up any resistors when he used just XLR cables to do this same thing. Do I need to use any resistors in this design? If so, where in the circuit are they used, what values, and why? Again, I'm a pretty big newb when it comes to how resistors work exactly, especially in an application such as this.

Thanks in advance to any and all that chime in on this. I'll post some pics as the project progresses, and also post my listening test results.

[timpratt]

Anyone?

[floid]

That looks right - each column of lugs is two spdt switches lined up one after the other, yes? So you've got the rear bank switching tips between tx & bypass, front bank switching rings.

Ground can be as simple as a wire from sleeve to sleeve, with tx ground tied to the input sleeve so you can wire a ground lift switch on the output if you need it. I'd first keep each channel's ground separate (no star ground/ chassis ground) since it probably just invites ground loops between this box and your other gear.

Research slug resistor, you're basically providing the tx a set load regardless of what's going on in the rest of the signal path.