Yes, that one I understand!

OK so if you looks at the schematic in post #419 you will see there is a string of series resistors from the input to 0V. If you add those all up (because they are in series) you get about 27K. If you recall from earlier I said the EQ is designed to be driven from a source impedance of 2K5 so we add a 2K4 resistor in series with the input (I will explain why later) so this gives us a total of 29K4. The transformer we know prefers a load of 10K so we need to work out what resistor to put in parallel with 29K4 so that together they make 10K. The answer is 15K (to make the numbers easy call 29K4 as 30K. So 30 x 15 is 450 and 450 divided by 30 + 15 is 450/45 which is 10K).

So now the transformer is happy but what about the 2K4 source impedance for the EQ. Transformers do what they say on the tin - they transformer voltages, currents and impedances. They have no intrinsic impedance of their own. So, although the Jensen transformer is labelled 10K:10K that only means that, due to the practical limitations of making real world transformers, it works best at that impedance over the audio band. However, you will probably drive it from an interface of some sort which will have a relatively low output impedance - maybe 100 to 200 ohms or maybe even less.. The transformer will transformer this so the source impedance of the secondary will appear to be that of the interface i.e 100 ohms or so. But we want the EQ to be fed from about 2K5 which is why we added a series resistor of 2K4.

In practice it is even more complicated than this because the transformer is not perfect and it windings will also have resistance and in a 10K:10K transformer these often amount to a few thousand ohms. So if we connected the EQ to this transformer we probably do not need the 2K4 series resistor. This means our original calculation for the parallel resistor is wrong; it really needs to be about 16K but 15K is close enough.

Bottom line, stick a 15K across the transformer secondary and feed it straight into the EQ.

As you can see, audio design is not a trivial exercise.

Cheers

Ian