Questions about the SEX 2.1

[Todd R]

Got the new amp going yesterday.

Does this amp run hotter than the usual BH amp? I touched the transformer and it was much hotter than other amps I've built (or did I wire something wrong?)

This amp has too much gain.
I had a pair of 120ohm resistors left over and even though they are shown in the schematic, the instructions never tell you how to put them in.

I'm sure they belong on the headphone jack, and assume the wire from the output transformer would be connected to the terminal that feeds the speaker outputs. From there you would connect the resistor from that terminal to the terminal that feeds the headphones, but I don't know which is which on this jack.
Could someone fill me in please?

[Grainger49]

Todd,

This question comes up every so often.  Paul designs the transformers with high temperature in mind.  They do run hotter than some other power transformers, but that is part of the design.  The fuse should blow if you are drawing too much power. 

Can you keep your hand on the transformer for a few seconds?  I think that was a measure used before.

[Todd R]

Can someone tell me why the drain wire isn't connected between terminals 22 & 23 like it is on the other channel between 12 & 13?

[Paul Joppa]

Can someone tell me why the drain wire isn't connected between terminals 22 & 23 like it is on the other channel between 12 & 13?

Yes, the signal ground is connected to chassis ground at only one point. This eliminates the possibility of a ground loop - a closed loop of conductors. In the presence of a magnetic field such as that from the power transformer, that field would induce a current, and the current would generate a voltage across the small resistance of the conductors - and the voltage would get amplified, resulting in hum.

[Todd R]

I see. That makes sense.
It just kinda threw me since all the other BH kits i've built were pretty symmetrical.
It IS very quiet, big improvement over previous headphone amps.