Audio Projects

This is an example of the XFMR-TAP Lib component in Micro Cap. It is not reversible, but can be re-written and used as an Output Transformer for a Class tube (or valve, if you will) A/B audio amplifier.

Backwards Output Transformer Model

First we’ll write the correct circuit.

The reversed XFMR-TAP model

.SUBCKT XFMR-TAP 1 2 3 4 5 PARAMS: RATIO=.069

*RATIO is the ratio of the output voltage across each tap V(3,4) or V(4,5)

*divided by the input voltage V(1,2). The voltage gain across each tap is

*RATIO and the gain across both taps is 2*RATIO. (The Turns Ratio N)


E1 7 8 5 4 {RATIO}
F1 5 4 VM1 {RATIO}
RP1 5 4 214
RP2 3 4 214
RS 6 2 .410
VM1 7 6
E2 9 1 3 4 {RATIO}
F2 3 4 VM2 {RATIO}
VM2 9 8
E3 2 1 7 9 {UNO}

.ENDS XFMR-TAP

This method is a bit abstract and is not bidirectional like a real transformer. The model above worked, but only when built from the ground up with Voltage Controlled Current Sources (VCIS) and fixed gain E sources without using the XFMR-TAP model or even the XFMR model from whence the -TAP model is derived. there are fixed Rp and Rs resistors in these models which makes them nearly impossible to work with other than the two configurations shown.

A better way is to build a model from discrete ideal inductors, capacitors and resistors using the inductive coupling core primitive.