Line input vs. line output transformers

What is the difference between line input and line output transformers?

As I see it, they handle same voltages. There is always low impedance at input, and high at output. So, why are they listed separately?

What if I put transformer between two line stages, say between compressor and eq. Or PC card output and mixer line input. Or mixer output and PC card input.... Then transformer becomes both output of previous stage, and input to another stage. Can I use for this either line input or line output model?

thnx

The difference is the coil resistance: for output transformers we're needing lower resistance of the secondary.

Regards Andreas

Also:

For input transformers, we have unpredictable (and possibly high'ish) source impedance. This means that we need quite a lot of inductance to be sure to transfer low-end even at higher source impedance. One exception is e.g. the Pultec filter circuit, which depends on such a low source impedance anyway, that an output transformer can/needs-to be used here (which we do in the G-Pultec)

For output transformers, we know for-sure the source impedance - and we can often make this very-low - so much less inductance is needed as safety margin.

The higher needed inductance is what makes input transformers more expensive than output ditto.

Jakob E.

And: line input transformers need high CMRR, i.e. a Faraday shield. Output transformers usually don't. Check an002.pdf.

Samuel

If I put line transformer externally inbetween two line units, like between DAW outputs and mixer (both balanced), which transformer to use? Input or output?

Is it that if I put it near the DAW outputs, with cable loading transformer then I use output transformer? And if I put it near input of mixer, I use input transformer?

Does it matter at all in such case?

[quote author="gnd"]If I put line transformer externally inbetween two line units, like between DAW outputs and mixer (both balanced), which transformer to use? Input or output? [/quote]

You're needing a transformer with minimum damping and Z in = Z out.

Andreas

[quote author="AndreasS"][quote author="gnd"]If I put line transformer externally inbetween two line units, like between DAW outputs and mixer (both balanced), which transformer to use? Input or output? [/quote]

You're needing a transformer with minimum damping and Z in = Z out.

Andreas[/quote]

Damping is voltage loss? Like 1dB in case of LL1593?
And and Z in = Z out is that static resistance? Like 20ohm in case of LL1593?

When you are putting out signal over a line involving long distances what you need is a full power transfer as well as voltage. Therefore in such applications the source is commonly loaded with 1:1 600 ohm output transformer. At this stage you are not concerned with CMRR (as the common noise will be picked up along the line) and the transformer does not need to have faraday shielding.

But when you are receiving a signal from a long line, then you want a full voltage transfer with attention to CMRR. So you use 1:1 10K line input transformer which has faraday shielding etc. (as Samuel pointed out).

However, above is a rule of thumb. Depending on your application you may use transformers with different turn ratios.


In your application which appears to be a relatively short connection between two equipment, normally there is no need to use a transformer as both the source and the load are at line level and balanced, and the balanced input stage of the load will handle the common noise.

However, if you really want to couple them with a transformer then the concern will be at the receiving end of the signal, hence the use of 1:1 10K line input transformer (such as Jensen JT-11P series) will be appropriate and the transformer should be placed near the load.


Cemal

I was just minding why output transformers were usually bigger in size than inputs transformers?

saint gillis said:

I was just minding why output transformers were usually bigger in size than inputs transformers?

Click to expand...

Its about power... Transformers are magnetic circuits that convert voltage signals to a magnetic flux for conversion back to voltage in secondaries.

Input transformers are very lightly loaded so transfer minimal power.  Output transformers are designed to drive lower impedance loads so must handle larger power and higher magnetic flux.

The larger size of output transformers is that simple.

JR