Jumper pin on Balanced input

valkyrie

Well-Known Member
Sep 12, 2011
65
10
315
About two months got my first Pass amplifier - X150.5. Very happy and excited about this purchase. So much so that when I set it up, with RCA inputs from my preamp, I did NOT install the jumpers in the balanced inputs.

The sound? Best way I can explain it was that everything sounded like my old Maggie types (20.0) being driven by tube amps. Rather "mushy" and diffuse. But I thought it rather "kool" and felt that I was only hearing the Pass "tube like" sound.

Later I went to balanced cables from my preamp (Kimber Hero).

Does anybody know what gives with the balanced jumper plug when operating the balanced amp with an unbalanced input? Did I do some harm? Because with the balanced input cable I have far more volume (expected) but I also have a much more precise sound.
 

Don C

Well-Known Member
Jul 20, 2013
208
35
333
USA
There is less noise, and better quality sound, with the jumper installed in the balanced input, when using RCA interconnects.

The jumper shorts the balanced input.

Read the MANUAL!

Email Pass Labs service, they will mail them to you for free.
 

valkyrie

Well-Known Member
Sep 12, 2011
65
10
315
Read the manual? You mean RTFM? IS that what you are suggesting?

Please!! I have what is to me a dream purchase and you want me to stop and read the "manual"? Really? Please!!!.

Plus - I am an audiophile - I don't read manuals.

thanks for your input.
 

Cyclotronguy

Well-Known Member
Aug 31, 2012
78
13
313
N. CA
The X150.5 is a fully balanced amp, with two identical gain paths.
One for the standard input (+)
One for the inverted input (-)

The jumper references the inverted input to signal ground when applied between pins 1(ground) and pin 3 (inverted input) on the XLR.

When running single ended without the jumper.... one half the amp is just sitting there doing nothing.

Gain is down by 6dB, noise is up.... there is less voltage swing available at the speaker binding posts. The supersymmetery (tm) topology complicates the story somewhat... but that's the short of it.

All of this does no harm to the amp........ there now we can ignore the manual.

Cyclotronguy
 

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