Line input transformers used as output

[Quayhog]

Is there a reason that you couldn't use a quality line input transformer as an output transformer, or vice versa? An example I've seen is the Altec 15095 which is usually used as an output transformer used as an input.  Google the schematics of Altec 1567a (output) and the Altec 1568a where it is used as an input.

I have a UTC HA-100x which I'm using in a DIY LA-2A, I also have a UTC HA-133 which is classed as a line output.  It has the same, or very similar  specs to the fore mentioned 100x but is hooked up differently.  Is there a reason that they couldn't be used interchangeably?  There isn't much current running through the transformer so wire guage shouldn't be an issue.  Is there a difference in lamination material or count?

I have a large quantity of transformers that I could possibly repurpose as either input or output transformers.  Any comments that would help my general understanding are welcome.  Next up, questions about reflected impedance.

 

[ruffrecords]

The short answer is probably not. In the old days of true 600 ohm inputs you would have had more chance of doing it. However, today's line inputs are expected to be 10K bridging which probably means you cannot use old 600 ohm output transformers as input transformers.

Cheers

Ian

 

[joaquins]

There are certain difference in construction on some high quality transformers (and not so high, but not so often).

For example jensen input transformers have shielding and inter layered windings, while outputs doesn't have shielding and use multifilar winding. May be some exceptions. Also the size of the core, outputs are bigger to be able to drive higher levels at lower impedance while inputs are smaller to reduce losses and distortion from higher impedance sources. 150Ω for a mic at a quite low level, prepared to drive ~2kΩ loads. Up to few hundreds ohms sources prepared to drive bridging loads ~10kΩ at mid level for line level inputs. ~0Ω source at an output stage prepared to drive 600Ω load for an output at high line level.

There are some optimizations that are taken into consideration in the transformers, depending on level and impedance, if those match for you application you will be fine, matching minimum impedance load, maximum impedance source and level within a reasonable margin you won't have any problems, in fact the transformer may be optimized for you application even if the name doesn't say so, that could be the case of the Altec you are saying (I haven't analyze the particular case), high output impedance in a tube output stage, step down for a low line level application to drive 600Ω loads may be a situ able task for a mic input transformer, as long as it can manage the level without saturation. Proper loading will be needed to avoid peaks in the response but that's always the case.

JS