Compact Power Amplifier LPC1

The Amplifier LPC1 presented here combines some properties like high output power, high sound quality and compact housing in brick-form.

The harmonic distortion, typically 0.1 % in most class D amplifiers, is eliminated here with some patented circuits. Distortion is very low (<< 0.003 %@ 1kHz) at average listening levels (0-400W) which makes this amplifier sound better than a good class AB amplifier. Crossover distortion at zero-crossings like in class AB doesn't occur at all.

The remaining distortion components are low order harmonics increasing gradually with output level like in loudspeakers and most ears.

The main application of the amplifier module is construction inside loudspeaker cabinets or with 2 or more modules and a supply-unit inside a 19"-rack as a PA-amplifier, in which active fan-cooling is not possible.

More Voltage
In most class-D Amplifiers, the voltages are limited by the driver-IC at 80 or 100 V. A patented driver circuit with galvanic isolation in this amplifier makes higher supply- and output-voltages possible, at which high power can be generated without the need for a bridge or unpractical low impedance's. This amplifier can work with a supply voltage of typically 160 VDC, limited only by the N-channel mosfet's. The maximum output voltage is 70 V peak.

Less Distortion
The 1st most common distortion mechanism in class D amplifiers is the dead time between the off-switching of one mosfet and the on-switching of the other. In this short period both mosfet's are in off-state and the output is floating. The momentary voltage in this period is strongly dependent on load current and thus non-linear, generating a kind of crossover distortion at higher current-levels.

In the patented driver circuit, this dead time is much shorter and matched accurately to the transition time of the output, eliminating this dead-time-distortion distortion.

The 2nd distortion mechanism is supply-line pollution, generating intermodulation of the output signal. With a patented PWM-generator this distortion is eliminated completely by compensating the modulation from the supply-voltage.

Power
Unlike most class-D amplifiers, the amplifier module described here is just half of a bridge, with one output-node connected to ground. Output-voltage and Power can be doubled with 2 modules in bridge-mode. The 2 outputs should be connected in anti-series, and the 2 inputs should be connected in parallel and in anti-phase. This way the output power can be doubled at twice the impedance.

Easy Cooling
The small heat sink integrated in the brick housing provides enough cooling in free air at short peak power or 300 W continuous power. More passive cooling for 1,2 kW continuous is possible by mounting the module to an external heat sink or housing. Two sides of the module are made flat for mounting easily at bigger surfaces. For use inside closed loudspeaker-cabinets a fan is not possible and not needed.

LPC1 Module with cover removed, last version.

Specifications:

Output Power :
( driven at 1kHz sine, <0.1%THD, supply voltage 2*80V)
per module:

4 Ohms: 600 Watts RMS
2 Ohms: 1100 Watts RMS
1 Ohms: 1800 Watts Peak

per 2 modules, bridged:

8 Ohms: 1200 Watts RMS
4 Ohms: 2200 Watts RMS
2 Ohms: 3600 Watts Peak

Slew rate: 16 V/ microsec per module

Frequency Response :
+/- 0.1 dB, 20 Hz -20 kHz at 2 Ohms
+/- 1.2 dB, 10 Hz -20 kHz at 1 or 4 Ohms
+/- 3 dB, 1 Hz - 40 kHz at 2 Ohms

Overshoot squarewave: 10 % (2 Ohm).

Total Harmonic Distortion (THD) :
< 0.03 %, -70 dB , 1000W, 2 Ohms, 1 kHz
<0.01 %, -80 dB , 700 W in 2 Ohms or 500W in 4 Ohms, 1 kHz
<0.003 %, -90 dB , 400 W in 2 or 4 Ohms, 1 kHz

Output Noise : 0.15 mV RMS, -110 dB referenced to full output (20Hz-20kHz, unweighted)

Switching Frequency (250 kHz) at output : <50 mV RMS

Damping Factor : >150 (4 Ohms, 2 Hz- 500 Hz)

Input Sensitivity : 0.75 Volt RMS or 1.07 V peak for full output (1 kW in 2 Ohm)

Voltage Gain : 60 X (35 dB)

Input Impedance : 2 * 220 kOhms, balanced

Load Protection : Fuseless short-circuit protection, clip limiting, current limiting at 60A.

Cooling : Passive free-air at average signal < full power -6 dB,
With external heat sink at full power continuous.

Size : 200 mm W x 50 mm H x 100 mm D

Power Efficiency : 93% (2 Ohms) to 95% (4 Ohms), at half to full power.

Supply requirements :
Main supply voltage : 2* 40- 80V DC, depending on power.
(Peak output voltage = 0,83 … 0,87 * supply voltage)
Idle-current: supply voltage/ 1,2 kOhm (60-70 mA at 2*80V)
Max current: 28 Amps peak, 14 Amps average, (2*80V, 1kW sine)

2nd supply (driverstage): voltage: 2* 12 V DC
current: 250 mA, +12V,
50 mA, -12V