Impedance switch kit resistor question w/S.E.X. 2.1

[physicsmajor]

I have a S.E.X. version 2.1 and am installing the impedance switch kit. The cans I plan to use are HE-500s.

Earlier in this thread from 2012, there is discussion of 120 ohm resistors, and removing these when using low-impedance, low-sensitivity headphones like my orthodynamics. I assume these 120 ohm resistors were connected from signal to ground, perhaps at the headphone jack as in the stock Crack kit. My plan was to omit these.

However, my S.E.X. 2.1 manual has no mention of any resistors at the switching jack, nor is there a single 120 ohm resistor anywhere in the kit. Perhaps these were eliminated in version 2.1?

That isn't the main question, though. No resistors are removed from the circuit when the Impedance Switch kit is installed. Despite this, from what I can understand of the impedance switch kit and what it replaced, the two 60 ohm resistors in series effectively reintroduce this for each channel!

Thus, the real question: Is it safe and correct to just jumper across the positions for these two 1/4 watt resistors to maintain the stock gain of the 2.1 kit? Or am I missing something obvious here?

[Paul Birkeland]

However, my S.E.X. 2.1 manual has no mention of any resistors at the switching jack, nor is there a single 120 ohm resistor anywhere in the kit. Perhaps these were eliminated in version 2.1?

This is the essence of what you're noticing.  The resistors on the impedance switch boards serve a different function, I would not eliminate them (if you replace them with wire jumpers, you'll get no output).  All they are doing is providing a solid and very well balanced ground reference. 

[Doc B.]

The 120s were in series with the output in order to bring the output level of headphones of different impedances closer together at a given level setting. The 60s in the switch kit create a balanced output to a virtual ground reference created by floating the existing ground connection at the cold end of the output transformer secondary and the running one resistor from that cold end to ground and the other resistor from the hot end to ground.

[physicsmajor]

Thanks experts, as always quick and definitive!