When we designed our limited run Smack headphone amp kit we developed a neat little pair of PC boards that mount under the output transformers. The boards contain slide switches that allow one to easily switch the output impedance of the output transformer without having to desolder and reconnect any wires.
The form factor of the S.E.X. 2.1 and Stereomour output transformers are the same as the Smack output transformers, so we thought it would be cool to offer the same switching arrangement as an option for those kits.
In a Stereomour kit it allows one to switch from 2,4,8,and 16 ohms output impedance. In the SEX kit with an OT-2 it allows one to switch from 4,8,16 and 32 ohms, and with the optional OT-3 transformer the choices are 16,32,64 and 128 ohms, like Smack.
To switch the impedance one simply unplugs the amplifier, lifts out the chassis plate and flips it over, and then throws the switches to the proper configuration for the output impedance desired.
Balanced speaker connection? Yeah. Sounds weird, huh. We began playing with this concept about a year ago and for some odd reason we got tighter, more dynamic bass when we wired the output transformers to operate with the center tap of the secondary grounded rather than grounding one end of the winding. We won't offer any theories, and if you think we're nuts you can run your speakers balanced or unbalanced by throwing a switch on the PC board.
Unfortunately balanced operation won't work with the TRS headphone jack on the S.E.X. kit because a TRS jack uses a common ground between the two channels. But it will work on both the S.E.X. 2.1 and Stereomour speaker outputs. The kit comes with two PC boards, six switches, standoffs, mounting hardware, resistors for both Stereomour and S.E.X. 2.1and a manual on CD.