#### djtetei

##### Audiophyte

**Behringer KM750 specifications state a voltage gain of 32dB.**However, if we do the math, the published voltage gain value doesn't add up.

The specifications states that the KM 750 delivers 200 watts into 8 ohms with an input sensitivity of 0.775 Volts.

Output voltage formula: sqrt (power x impedance)

Output voltage calculated: sqrt (200 x 8) = 40V

Voltage gain (amplification factor): output voltage / input voltage = Av (amplification factor)

Voltage gain (amplification factor) calculated: 40 V / 0.775 V = 51.62

Voltage gain (dB) formula: 20log(Av)

**Voltage gain (dB) calculated: 20log(51.61) = 34.25 dB**

The calculated voltage gain is 2 dB higher than the specified voltage gain.

The only scenario the specified voltage gain is 32 dB is if the input sensitivity is, in fact, 1 Volt.

**Furthermore, if we take the officially specified input sensitivity (0.775 V) and voltage gain (32 dBU) and do the math, we arrive at a different result for the output power of 119 watts, which is less than the officially specified power into 8 ohm load.**

So, the following question arises: when input sensitivity of 0.775 V is selected, the maximum input voltage required for maximum rated power is 0.775 V (0 dBU) or 1 V (+2 dBU)?

So, the following question arises: when input sensitivity of 0.775 V is selected, the maximum input voltage required for maximum rated power is 0.775 V (0 dBU) or 1 V (+2 dBU)?

The following scenario applies to Behringer KM 1700, also.

Update:

On 29.06.2022, MusicTribe Customer Solutions Specialist Mr Kyle Johnson replied to my support ticket, and his answer is as follows:

*"The 200W is the peak power not the RMS, the calculation should based on the RMS 130W for KM750 and 310W for KM1700. Also, the peak power is actually about 210W."*This is important information and should definitely be included in the product's user manual.

Starting from this, suppose we now have a peak power of 210W into 8 ohm load.

Calculate the peak voltage: SQRT(210*8)=40.987 Vpeak

Calculate the RMS voltage: 40.987*0.707=28.977 Vrms

**Calculate power (RMS): SQR(28.977)/8=104.95 W**

Calculate amplification factor (X) for 0.775 input sensitivity: 28.977/0.775=37.389

**Calculate dB voltage gain: 20*LOG(37.389)=31.454 dB**

As you can see, the statement about 130 W RMS doesn't hold up.

**Amplifier power is calculated, not measured.**

A Voltmeter measures voltage in volts. An Ammeter measures current in amperes. An Ohmmeter measures resistance in ohms. Any two of these measurements will allow calculation of amplifier power (in watts).

**Anyway, as a conclusion, it seems that if you want to match your speakers RMS / continous power rating with a Behringer amplifier power rating, you should expect half of the declared power ratings**.

Therefore, the calculated parameters for Behringer KM 750 and Behringer KM 1700, based on published specifications are as follows:

**Behringer KM 750:**

Peak Power / channel @ 8 ohm: 200 W

Peak voltage: SQRT(200X8)=40 V

RMS voltage: 40X(1/SQRT(2))=28.284 V

**Average continous power @ 8 ohm**: SQR(28.284)/8=

**100 W**

RMS current: 100/28.284=3.535 A

Peak Power / channel @ 4 ohm: 400 W

Peak voltage: SQRT(400X4)=40 V

RMS voltage: 40X(1/SQRT(2))=28.284 V

**Average continous power @ 4 ohm**: SQR(28.284)/4=

**200 W**

RMS current: 200/28.284=7.071 A

Amplification factor for 0.775 V input sensitivity: 28.284/0.775=36.519

Voltage gain for 0.775 V input sensitivity: 20XLOG(36.519)=31.250 dB

Amplification factor for 1.4 V input sensitivity: 28.284/1.4=20.203

Voltage gain for 1.4 V input sensitivity: 20XLOG(20.203)=26.108 dB

**Behringer KM 1700:**

Peak Power / channel @ 8 ohm: 500 W

Peak voltage: SQRT(500X8)=63.245 V

RMS voltage: 63.245X(1/SQRT(2))=44.721 V

**Average continous power @ 8 ohm**: SQR(44.721)/8=

**250 W**

RMS current: 250/44.721=5.590 A

Peak Power / channel @ 4 ohm: 800 W

Peak voltage: SQRT(800X4)=56.568 V

RMS voltage: 56.568X(1/SQRT(2))=40 V

**Average continous power @ 4 ohm**: SQR(40)/4=

**400 W**

RMS current: 400/40=10 A

Amplification factor for 0.775 V input sensitivity: 44.721/0.775=57.742

Voltage gain for 0.775 V input sensitivity: 20XLOG(36.519)=35.229 dB

Amplification factor for 1.4 V input sensitivity: 44.721/1.4=31.943

Voltage gain for 1.4 V input sensitivity: 20XLOG(31.943)=30.087 dB

Feel free to express opinions and share your experiences with Behringer KM 750 and KM 1700 amplifiers.

Last edited: Jul 5, 2022