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Understanding Input Sensitivity Specs

mattkhan

Distinguished Member
I have a power amp that has some confusing (to me) specs for input sensitivity. I'm trying to unwind this to determine whether I am driving it to the full potential or not.

It quotes

Input Sensitivity @ 8ohm = 3.61 V
Input Sensitivity @ 4ohm = 3.40 V
Input Sensitivity @ 2ohm = 3.17 V

It also has a switch on the back with 3 settings;

1Vrms
+32dB
+26dB

which are described in the manual as

When the gain switch is on 1Vrms, the input sensitivity of the amplifier 1Vrms.
When it is on 32dB, the amplification gain range is within 32dB.
When it is on 26dB, the amplification gain range is within 26dB.

My amplifier 101 course (i.e. google) has yielded a couple of references that have given me sufficient knowledge to get some of the numbers to agree but I'm now confused as to what it all means o_O

The amp in question is a Focux D6, the manual for which can be found here

My workings so far go as follows

Vout = √(P x R) = √(1100*4) = 66.33V
Vin = 3.4V
Voltage Gain (Av) = 20 * Log (Vout/Vin) = 20 Log(66.33/3.4) = 25.8

This basically lines up with the stated specs of +26dB gain (in fact the same calc for 8ohm is almost dead on 26dB)

My Q concerns that 1Vrms setting.... is the sensitivity reduced so it magically delivers +36dB gain or that it pegs the max output at about 1/3 power (1V in x 26dB = 20V out)?

If we assume that my preout can deliver sufficient voltage to fully drive it then which setting would you choose and why? I think I have gathered that the higher gain settings are noiser but I don't understand why this would be so.
 

sammy the squid

Distinguished Member
I have a power amp that has some confusing (to me) specs for input sensitivity. I'm trying to unwind this to determine whether I am driving it to the full potential or not.

It quotes

Input Sensitivity @ 8ohm = 3.61 V
Input Sensitivity @ 4ohm = 3.40 V
Input Sensitivity @ 2ohm = 3.17 V

It also has a switch on the back with 3 settings;

1Vrms
+32dB
+26dB

which are described in the manual as

When the gain switch is on 1Vrms, the input sensitivity of the amplifier 1Vrms.
When it is on 32dB, the amplification gain range is within 32dB.
When it is on 26dB, the amplification gain range is within 26dB.

My amplifier 101 course (i.e. google) has yielded a couple of references that have given me sufficient knowledge to get some of the numbers to agree but I'm now confused as to what it all means o_O

The amp in question is a Focux D6, the manual for which can be found here

My workings so far go as follows

Vout = √(P x R) = √(1100*4) = 66.33V
Vin = 3.4V
Voltage Gain (Av) = 20 * Log (Vout/Vin) = 20 Log(66.33/3.4) = 25.8

This basically lines up with the stated specs of +26dB gain (in fact the same calc for 8ohm is almost dead on 26dB)

My Q concerns that 1Vrms setting.... is the sensitivity reduced so it magically delivers +36dB gain or that it pegs the max output at about 1/3 power (1V in x 26dB = 20V out)?

If we assume that my preout can deliver sufficient voltage to fully drive it then which setting would you choose and why? I think I have gathered that the higher gain settings are noiser but I don't understand why this would be so.

I'd like to help you Matt, but it's a bit much for a Sunday evening this:eek::zonked:!
 

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