Conventional power amplifiers serving audio signal requirements are typically concerned with 20kHz bandwidth. However, since the LX711 and LX721 signal processing modules cover the much wider bandwidth of 200kHz, the need for a wide band power amplifier suitable for reference measurements is desireable.

Many loudspeaker measurements also involve very low frequencies, and for this reason a power amplifier with response down to DC is also ideal. This enables ultra low frequency measurements to be performed with zero phase shift.

High quality true impedance measurements require that a loudspeaker be driven under voltage source conditions, rather than current source conditions. The LX741 provides both voltage and current monitor outputs which enable true impedance to be obtained by merely dividing the signal data. Acoustic SPL data can also be measured at the same time.

Features
• 20W/4 - 10W/8 Output Power
• Very Wide Bandwidth DC - 200kHz
• Very Low Output Distortion
• Very Low Output Impedance
• BNC Voltage Monitor Output
• BNC Current Monitor Output
• True Voltage Source Impedance
• Simultaneous SPL & Impedance
• Balanced/Unbalanced XLR Input
• Selectable Gain: 0dB,+10dB,+20dB
• Floating Isolated Common
• High Frequency Output Stage
• Auto Bias Output Stage
• Dynamic Bias Output Stage
• Temperature Overload Protection
• Short Circuit Current Protection

Typical audio power amplifiers employ power output transistors which have gain bandwidth products of 20-60MHz. While this generally meets the needs of amplifiers handling frequencies to 20kHz, a 200kHz amplifier places an order of magnitude higher demands on the output stage.

The LX741 features an output stage created from a large array of small signal transistors, with gain bandwidth products of 650MHz. This enables very low stored charge in the LX741 output stage to handle 200kHz signals as easily as conventional amplifiesr handle 20kHz signals.

To reduce high frequency distortion further, the LX741 output stage also features auto bias and dynamic bias circuitry. Conventional amplifiers generally operate in a manner where current through one side of the output stage is entirely shut off during high current in the other side. This produces a substantial discontinuity that becomes difficult to correct at higher frequencies where less loop gain is available. The LX741 maintains bias current in both halfs of the output stage during all signal transitions providing a much more linear power voltage follower.

The output stage also features custom SMT heatsink convection cooling, current limiting, and temperature sensing for enhanced overload protection. Amplifier current is not returned to the LX700 common.