Unbalanced pre out to balanced amp in

Is 'across' meant in-series or in-parallel?

By 'across' , I mean in parallel with the output.

If the input of the xformer is supposed to be 20K and the output 600ohms, then the xformer will express 20K to the input if there is a 600 ohm resistance across the secondary.

Its the same idea that you see in a conventional tube amplifier: if the tubes are supposed to have a 3000 ohm load, that will only be the case if the output (8 ohm tap for example) is loaded at 8 ohms.

You'll notice that in the test circuits that produced the graphs on the first page, that there is indeed a 600 ohm resistor (or a pair of 300 ohm units) loading the output of the transformer.

thx,
that's what I mean and sometimes use to half the resistance.

Ralph, I think Bob raises a valid concern. This is basically a 1:1 transformer, not a transformer with a significant step-down ratio (which would obviously be inappropriate for a line-level interface).

So while adding a 600 ohm resistor to the secondary would make the transformer perform better, it would very conceivably cause problems relative to the output stage of the preamp (or source component, if that is what it is used with). If the output impedance of the preamp or source component is a significant fraction of 600 ohms, and is not perfectly constant as a function of frequency, then a frequency response irregularity would be introduced. And, depending on its specific design, the output stage might be unhappy providing the current that a 600 ohm load would draw, as well.

Or are we missing something?

Regards,
-- Al

The specs call for a source impedance maximum of 2Kohms. There are a lot of preamps that can do that, although some of them may have trouble making bass.

IMO/IME, you are better off with a step-down transformer, maybe 10K to 600 ohms. You loose some voltage gain, but a wider range of sources can drive it.

At the input of the amp could be another transformer that is 600 to 10K... then there would be no loss in gain. The bigger the step down/step up, the more transformer artifacts are introduced. That is one of the reasons I prefer to direct-couple :)