easy xfmr bal/unbal question

ok that's really basic but I need someone to confirm 

I need an input xfmr for 'balanced to unbalanced' conversion and impedance matching,
so I assume something like 2+2:1 will do. Same for output xfmr but 1:2+2.

Can I just get a 2+2:1+1 input xfmr (or 1+1:2+2 for out xfmr) and connect only one of the two secondaries (or primaries for out xfmr)?

thanks 
w.

You can configure these as 1:1/1:2/1:4 and vice-versa.

You can use split coils to achieve this, or parallel coils in order to alter DC resistance and inductance where necessary.

hi rodabod, thanks for your help but I'm not sure if I'm following... :

I understood your point about 1:1/1:2/1:4 but does this mean that using a 'unbal-to-bal' (or vice-versa) configuration is not possible?
AFAIU these configuration (1:1/1:2/1:4) will solve my impedance matching issue but not the balancing issue?
Am I missing something?
Sorry for my ignorance....

w.

As long as the secondaries are not connected to anything inside the box, only to the output connector, the output shall be balanced.

I see... so my initial though will not work....

thanks

That will work. ARDE was suggesting that if you tied either side of the secondary to ground then it would be forced to unbalanced.

Add a switch to disconnect the ground from input to output in case you ever need it.

rodabod said:

ARDE was suggesting that if you tied either side of the secondary to ground then it would be forced to unbalanced.

Click to expand...

thanks rodabod. is that what you mean? 

I would tie the input pin1 to the case of the box, and then tie pin1 of the output to a switch which can also connect to the case.

You want the case grounded somehow to avoid picking up hum. You don't always want the input ground connected to the output ground (via the case). That allows you to completely isolate the two circuits in the situation of ground-loops.

ok, that's what you mean then 

So regarding the secondaries, all the taps (apart from the one that goes to pin3 ) are connected to the ground.

I would disconnect one side of the "spare" secondary from the other to just leave one side grounded. Otherwise it looks like a shorted coil, and it will look like a short reflected over to the primary. Or just disconnect the whole coil and leave it floating.

Switch looks good.

I'd be tempted to connect the other secondary to an output jack our XLR. Then you have a handy signal splitter and your gadget is twice as useful.

Is the change of signal polarity intentional ? (connecting secondary hot/XLR-pin2 to gnd instead of XLR-pin3 to gnd)

zebra50 said:

I'd be tempted to connect the other secondary to an output jack our XLR. Then you have a handy signal splitter and your gadget is twice as useful.

Click to expand...

very good idea, thanks. I was actually thinking the same by the time you suggested it but wasn't sure. Now I am

Harpo said:

Is the change of signal polarity intentional ? (connecting secondary hot/XLR-pin2 to gnd instead of XLR-pin3 to gnd)

Click to expand...

Thanks Harpo. Well spotted. I've changed it

rodabod said:

I would disconnect one side of the "spare" secondary from the other to just leave one side grounded. Otherwise it looks like a shorted coil, and it will look like a short reflected over to the primary. Or just disconnect the whole coil and leave it floating.

Switch looks good.

Click to expand...

Thanks rodabod. I was actually confused a bit by your previous post

ARDE was suggesting that if you tied either side of the secondary to ground then it would be forced to unbalanced.

Click to expand...

and that's why I ground the secondary.


OK, I've updated the draft with both cases (in and out). This might look funny for some people here but hopefully it will help anyone
who feels as useless as me...  :

anyway, please let me know if you spot anything wrong or something that will improve the design.

thanks again for all your help!
w.

The top diagram shows pin3 connecting to ground. You probably don't want this unless you want that side to be unbalanced and referenced to ground.

rodabod said:

The top diagram shows pin3 connecting to ground. You probably don't want this unless you want that side to be unbalanced and referenced to ground.

Click to expand...

in my case, the secondary will be connected to the actual circuit and the output of the circuit will be connected to the primaries of the output xfmr.
(input xfmr --> circuit --> output xfmr)
So I assume I have to use ground as reference for pin 3....
as usual not 100% sure though 

I'm lost on what you want here. A balancing box, or just general equipment interfacing?


The top drawing would only be correct for debalancing for an unbalanced input to a circuit which requires a source referenced to ground.

yes sorry for the confusion

What I want to do is input "input xfmr --> circuit --> output xfmr".
The only reason I added the XLRs  was to simplify the sketch but it looks like I messed it up  :

Looks ok to me.

Whats the advantage of using only one of the primary/secondary windings, instead of connect them in parallel?

ChrioN said:

Whats the advantage of using only one of the primary/secondary windings, instead of connect them in parallel?

Click to expand...

advantage? I would call it ignorance  ;D

can you elaborate please? what's the advantage of  connecting them in parallel?