I have an audio transformer (SP-66) with a 1:1 ratio and centre taps on the primary and secondary windings.
Tests: When I input a 6.5 kHz 8 Vpp sinusoid on the primary (pins 1 & 3), I observe an 8 Vpp sinusoid on the secondary (pins 4 & 6). (1:1 ratio).
Input on pins 1 & 2, I observe a 16 Vpp sinusoid on pins 4 & 6. (1:2 ratio).
Input on pins 1 & 3, I observe a 4 Vpp sinusoid on pins 4 & 5. (2:1 ratio).
My pcb is already soldered with the sp-66, and I need to double the output voltage. I tried shorting pins 2 and 3 together on the primary to achieve a 1:2 winding ratio. Instead, I still observe 8 Vpp, a 1:1 ratio.
Question: Why does shorting the centre tap on the primary to pin 1 or 3 still result in a 1:1 ratio on the secondary?