Wiring an autoformer for RCA+XLR in/out?

[andyjevans]

I have a pair of autoformers for a tube stage or possibly stand-alone passive pre which I haven't wired up yet,
but I'd like to do so. Wiring for RCA inputs and outputs looks straightforward. But how do you wire in the added option of XLR in and out?

I always assumed that you put the variable resistor or I guess autoformer between pins 2 and 3. So I'm at a bit of a loss to see how you combine
phono and xlr inputs and outputs.

Can anybody clarify with a wiring diagram?

 

[JMFahey]

XLR in principlen implies floating / not directly referenced to ground.

Not sure how an *auto* transformer might achieve that.

 

[audiowize]

If you want to do this, set the autoformers aside and switch to TVCs.

 

[andyjevans]

If you want to do this, set the autoformers aside and switch to TVCs.

OK, how would you wire up a TVC for both RCA and XLR?

 

[audiowize]

OK, how would you wire up a TVC for both RCA and XLR?

A TVC input is balanced unless you provide an unbalanced earth reference on your own. For XLR input, pins 2 and 3 go to the input side of the TVC. The RCA jacks connect similarly, and you have the option of providing a DPDT switch to enable or disable the galvanic isolation of the TVC. To maintain the balanced input, you'll want to use a 4 pole switch to let you switch hot/ground on the RCA jacks and +ve and -ve on the XLRs as a function of the input switching.

The output side is a little simpler, as you can have a toggle switch that either earths one of the ends of the secondary winding to allow for unbalanced outputs or floats the winding for balanced output.

 

[andyjevans]

Thanks, that's helpful.

 

[andyjevans]

how to build a pre using S&B TX-102 transformers

Wiring diagrams post 57. Excellent thread about building a TVC. The S&B TX102 was popular at the time of the thread and Thorsten Loach has good input as usual.

 

[RLRB]

tx102 as autoformer

Hello
i cant see the schematics.
The question is: do i have to use primary and secondary? in this case ++ goes to 0.
or do i have to use only primary? in this case + goes to 0 i understand
or do i have to use primary and secondary in paralell?
which of three conections has 6db gain?
thanks

 

[RLRB]

A TVC input is balanced unless you provide an unbalanced earth reference on your own. For XLR input, pins 2 and 3 go to the input side of the TVC. The RCA jacks connect similarly, and you have the option of providing a DPDT switch to enable or disable the galvanic isolation of the TVC. To maintain the balanced input, you'll want to use a 4 pole switch to let you switch hot/ground on the RCA jacks and +ve and -ve on the XLRs as a function of the input switching.

The output side is a little simpler, as you can have a toggle switch that either earths one of the ends of the secondary winding to allow for unbalanced outputs or floats the winding for balanced output.

you say i can i use the tx102 as autoformer in balanced? with primary and seconday in paralell? if you can make a schema

thanks

 

[audiowize]

This image gives you instructions on how to hook up the primary windings in series or parallel. We'll assume you are using these in unity mode.

For SE input, RCA shell goes to - and RCA center pin to ++. You would have a switch to connect - to output cold (which is the circuit audio ground), which you may or may not need.

For XLR input, pin 2 goes to ++, pin 3 goes to -, and pin 1 to chassis.

 

[daanve]

TVC balanced input

Maybe this helps:

 

[RLRB]

Hello. I have mk3 trafos. I Can use rca and xlr but is not balanced because I have mine wired as auto former. But I think I only use the secondary. In this case has 6db gain?

 

[audiowize]

If you want balanced inputs, you should use them as TVCs and not wire them as autoformers. You should also not use one secondary. They either go in series or in parallel.