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 Elliott Sound Products BP4078 



The BP4078 Class-D power amplifier is now available from ColdAmp. You need only add a power supply, and the necessary hardware (chassis, input and output connectors) to have a complete working system. The module described is not a kit - it has been completely built and tested at full operating levels, and all major specifications are verified for each module. You need to add a basic heatsink and power supply.

ESP no longer supplies these modules, but they may be obtained direct from ColdAmp. Please mention that you found out about the ColdAmp products from the ESP website.

BP4078 - 400 Watt Class-D Power Amplifier

The power amplifier is suitable for powered speakers, subwoofers, or full range high powered amplifier systems. With performance as good or better than a great many conventional hi-fi power amplifiers (including some at many times the price), it has excellent bandwidth, and very low noise and distortion.

This is an excellent amplifier - and despite the qualms one may have about Class-D for full range amplifiers, there is no major parameter that suffers as a result. This amplifier is ideally suited for hi-fi, public address, bass guitar, high power subwoofers or the low frequency end of a very high power biamped system.

Purchase Details

Order CodeNo Longer Available
Size96 (L) x 72 (W) x 39 (H) mm
Packed Weight250 grams (approx.)

Photo of Complete Module


The following specifications are typical, but may vary slightly from one unit to the next.  The major parameters are very well defined, and the variations in practice will be extremely small. These are not guaranteed specifications, as the quality of the power supply will have an influence on noise and power output. All specifications can be reasonably expected to be met if assembled according to the data supplied with the module.

Electrical Specifications

Supply Voltage (+VCC and -VSS to GND) Note 135-65Volts
Modulator optional external supply voltage (+ve and -ve)8-25Volts
MOSFET driver optional external supply voltage (referred to -VSS)15-25Volts
Peak output current Note 2-18-Amps
ON / OFF pin voltage0-12Volts
Minimum load impedance2--Ohms
Operating Temperature--80°C

Audio Performance (Measured at ±60V with 10,000uF filter caps unless noted otherwise)

Output power, 4 Ohms400W0.5% THD, 1kHz Sinewave
Output power, 8 Ohms240W0.5% THD, 1kHz Sinewave
THD (Total Harmonic Distortion + Noise)0.02%100Hz, 1W, 5 Ohms
SNR (Singal to Noise Ratio)<100dBInputs shorted to GND
Bandwidth (-3dB)6 - 50kHz8 Ohm load
Bandwidth (-1dB)17 - 20kHz8 Ohm load
Output Impedance Note 3TBDOhmsTo Be Determined
Output Ripple (at switching frequency)500mV (P-P)Inputs shorted to GND

Additional Parameters (Measured at ±60V with 10,000uF filter caps unless noted otherwise)

Switching frequency270kHz
ON/ OFF threshold voltage2.5VModule deactivated below 2.5V
Efficiency (output stage)93%400W into 4 Ohms
Standby power (shutdown mode)6WMeasured with no input
+VCC current at idle40mAMeasured with no input
-VSS current at idle70mAMeasured with no input
Clip LED output current8mA
Modulator supply current (external)+35/ -20mAPositive and negative supplies
MOSFET driver supply current (external)60mA
Protect mode output voltage12V0V when not activated
CLK output amplitude6V P-PTriange wave


1   Below ±35V, under-voltage protection is activated. Above ±68V, over-voltage protection is activated.
2   Limited by over-current protection. Once tripped, remains activated for approx. 2 seconds.
3   Output impedance is not influenced by overcurrent protection, since no series sense resistor is used in the speaker line.

What You Get
The amplifier module is supplied as a single channel, fully built and tested unit, mounted in an aluminium chassis as shown above. You will need 'Fast-On' (quick connect) crimp terminals - standard 6.32mm (¼ inch) to connect the GND (ground / earth), +VCC, -VSS and SPK (speaker) leads to the module. ESP will supply 4 terminals with each module.

You will also need a 3 pin line socket (2.54mm / 0.1" pitch) for the input header. One of these is supplied with the module. Optionally, you will need additional 2 and 3 pin line sockets for the volume control and remote On/ Off (3 pin), thermistor output, clipping LED output and protect output (2 pin).

What You Need
You will need to provide power (±56V nominal @ 2A continuous is suggested), which means a transformer (300VA for one channel with 4 ohm load, intermittent duty) , bridge rectifiers and filter capacitors. Full details of power supply requirements and wiring are provided with the module. You will also need chassis mounted speaker and input connectors, and optionally a volume control pot.

You will also require a suitable case (a 2RU rack mount case is ideal) and either a heatsink rated at around 2.5°C/W or better for each amp module, or a chassis built using a 2mm aluminium plate for the base - this will be sufficient heatsinking for domestic use.

Supply Specification (Suggested for one amplifier, e.g. subwoofer amp or monoblock hi-fi)

ItemTypical Requirement
Transformer40-0-40V AC @ 3.75A (300VA) toroidal
Rectifier35A 400V chassis mount bridge
Filter Capacitors2 x 10,000uF 75V - 105°C electrolytic
Supply Fuses5A fast blow (each supply, +ve and -ve)
Mains Fuse4A / 8A slow blow (230 / 110V respectively)

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Copyright Notice. This article, including but not limited to all text and diagrams, is the intellectual property of Rod Elliott, and is Copyright © 2002. Reproduction or re-publication by any means whatsoever, whether electronic, mechanical or electro- mechanical, is strictly prohibited under International Copyright laws. The author (Rod Elliott) grants the reader the right to use this information for personal use only, and further allows that one (1) copy may be made for reference while constructing the project. Commercial use is prohibited without express written authorisation from Rod Elliott.
Page Created and Copyright © Rod Elliott 23 Dec 2005