amp sensitivity switch?

[monekh]

just setting up our system for the first time with the driverack and macrotech amps (running two T60s and two Otop 12s)

the driverack is asking what sensitivity each amp is set at.
I've opened up the P.I.P. compartment and found the switch - 0.775V, 1.4V, or 26 dB - but have no idea what I should be setting each amp to, or what factors determine appropriate sensitivity. haven't managed to find much useful information elsewhere, so thought I'd come ask you trusty folk! any advice / explanations much appreciated.

cheers

[dswpro]

From a Macrotech manual:

The Input Sensitivity Switch is located inside the back of
the amplifier (Figure 5.1). It is set at the factory to 0.775
volt for rated output into 8 ohms. It can also be switched
to a sensitivity of 1.4 volts, or a fixed voltage gain of 26
dB (4.8 volts for rated output).

What this switch does is adjust the amplifier input to match the equipment you intend to drive the amp with.
You do not need to change it from the default setting, just let the drive rack know how it is set.

If you look up Line Level on Wikipedia there is a section which states:

A line level describes a line's nominal signal level as a ratio, expressed in decibels, against a standard reference voltage. The nominal level and the reference voltage against which it is expressed depend on the line level being used. While the nominal levels themselves vary, only two reference voltages are common: decibel volts (dBV) for consumer applications, and decibels unloaded (dBu) for professional applications.

The reference voltage for the decibel volt (0 dBV) is 1 VRMS.[1] The reference voltage for the decibel unloaded (0 dBu) is the AC voltage required to produce 1 mW of power across a 600 Ω load (approximately 0.7746 VRMS).[2] This awkward unit is a holdover from the early telephone standards, which used 600 Ω sources and loads, and measured dBm dissipated in them. Modern audio equipment does not use 600 Ω matched loads, hence the use of "dBm unloaded" = dBu.

The most common nominal level for consumer audio equipment is −10 dBV, and the most common nominal level for professional equipment is +4 dBu (by convention, decibel values are written with an explicit sign symbol).

Your Drive Rack wants to know what your amp is set to so it can adjust its output voltage to match your amp expectations. If incorrectly matched, the drive rack may not deliver enough voltage to get your amp to deliver what you want to send to your speakers, or worse yet, cause your amp to deliver more voltage than you expect. A proper match will also ensure the Drive Rack output meters mean something relevant to your amplifier/speaker combination. Ideally your drive rack meters should show you how close you are to your amp output limit.

You should not rely on this alone to protect your speakers, however, and should set your drive rack limiters while measuring your unloaded amp so as not exceed the maximum voltage recommended for your speaker drivers.