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ESP is pleased to announce that certain project PCBs will be made available as completely built and tested modules.  You need only add a power supply, and the necessary hardware to have a complete working system.  The initial choice is rather limited (1 module only to start with), but like the PCB offerings, this will grow based on demand.  Additional modules may be added in the future that are not available as projects.

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 the heatsink and power supply.

M27A - 100 Watt Power Amplifier

This is a slightly modified version of the P27A Power Amplifier Module.  The power amplifier as described is not limited in any way to guitar use.  In fact, its performance is as good or better than a great many hi-fi power amplifiers, including those at many times the price.  It has excellent bandwidth, and a respectable slew rate (more than sufficient for the highest quality audio).

Distortion is extremely low, and it is unlikely that very many amplifers will better it in this respect.  Noise is also very low, even though no great pains were taken to minimise the noise level.

In short, this is an excellent amplifier - and despite the qualms one may have about the use of relatively inexpensive power transistors, there is no major parameter that suffers as a result.  This amplifier is ideally suited for guitar, bass guitar, low power subwoofers or the low frequency end of a biamped system.  Full range operation is still very good, but is not in the same class as the P3A (for example).

The ability to use the amplifier as a conventional (low output impedance, or constant voltage mode) amp is augmented by the on-board circuitry to enable high impedance (constant current mode), which is ideal for use with guitar and bass, and in many cases this can be used to advantage with hi-fi as well.

Purchase Details
Order CodeM27A
Size115 x 65 mm
Packed Weight250 grams (approx.)
PriceSee Price List

Please Note:  Send an e-mail to ESP prior to ordering, as these units will not be stocked in large numbers and supply may be delayed.

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.

Absolute Maximum Ratings ( Note 1)

1   Absolute ratings refer to values that, if exceeded, will damage or destroy the module.  These ratings must not be exceeded.

2.   The short circuit protection is not designed to withstand a continuous short at any power level.

(A short circuit is defined for the purposes of this specification as a load impedance of approx. 0.2 ohm (allowing for typical lead resistance) and the protection circuit is designed to protect against momentary overloads only.)

The following specifications were determined using a loaded supply voltage of +/-35V, from a 160VA transformer and 4,700µF filter capacitors.  "Music power" is somewhat higher, with typical output of 120W / 65W (4 ohms / 8 ohms respectively) for 5 ms burst signals.  This is a fairly meaningless quantity, and should be ignored.

Output Power (Continuous RMS)100W (4 ohms - typical)
60W (8 ohms - typical)
Frequency Response *14 Hz - 100 kHz -1 dB @ 1W
14 Hz - 25 kHz -1 dB @ 50W 8 ohms
Noise (measured at output)< 2 mV with 600 ohm source impedance
< 0.5 mV input shorted (-66 dBu)
S/N Ratio (Ref. 50 W / 8 ohms) > 80 dB
Output offset voltage < 40 mV DC
Slew Rate 10 V/us
THD+noise (at 50W/8 ohms) **< 0.04% @ 1 kHz and 10 kHz
< 0.06% @ 100 Hz
Voltage Gain (any impedance) 23 (27 dB) - Constant Voltage
Voltage Gain (8 ohms) 64 (36 dB) - Constant Current
Voltage gain (4 ohms) 38 (32 dB) - Constant Current
Output Impedance < 0.01 ohm @ 1 kHz - Constant Voltage
> 20 ohms - Constant Current
Damping Factor> 160 at 8 Ohms - Constant Voltage
< 0.4  -  Constant Current
Quiescent Current25mA @ 25°C ambient after 10 minutes
Typical Performance Specifications

What You Get
The amplifier module is supplied as a single channel, fully built and tested unit, with steel pressure bars as shown, Sil-Pad (or equivalent) transistor washers, 3mm mounting screws and full documentation for mounting the unit on a heatsink and connecting power, inputs and outputs.

All resistors are 1/2 Watt metal film for lowest noise or 5W wirewound where needed.  Electrolytic capacitors are 105°C rated.  The unit is supplied with 2 spare fuses, although it is extremely unlikely that they will be needed.

What You Need
You will need to provide power (+/-35V @ 1.7A continuous), which means a transformer, bridge rectifiers and filter capacitors.  Full details of power supply requirements and wiring are provided with the module.  You will also need speaker connectors, input connectors, and optionally a volume control.

You will also require a suitable case (a 2RU rack mount case is ideal) and a heatsink rated at 1°C/W or better for each module.  A flat surface of 120 x 70 mm (approx) is needed to mount the PCB.  A heatsink with an integral shelf of 25mm or more may be used if desired.

Supply Specification (Suggested for one amplifier, e.g. guitar amp or monoblock hi-fi)
DescriptionTypical Requirement
Transformer25-0-25 V AC @ 3A (150VA) toroidal
Rectifier35A 200V chassis mount bridge
Filter Capacitors2 x 4,700µF 50V - 105°C electrolytic (minimum)
Mains Fuse2A/4A slow blow (230/110V respectively)

Limited Warranty

The supplied amplifier module is warranted to be free of manufacturing defects or other faults in materials or workmanship, including damage sustained in transit from ESP to the purchaser.  Limitations on this warranty are based on the fact that ESP has no control over the final disposition of the unit, or that it has been correctly wired and mounted, and operated in accordance with the supplied instructions.  Units that have been used in excess of any absolute maximum parameter (as detailed above) or have been incorrectly wired (for example reverse polarity) or inadequately mounted to the heatsink are not covered by this warranty.

If used completely within the ratings, the module is covered by a 12 month repair or replacement warranty, provided that it is returned properly packed, and intact and unmodified in any way.  ESP reserves the right to deny warranty claims if it is determined that the fault was caused by excess voltage, tampering of any kind, PCB or component physical damage (other than damage in transit from ESP to the purchaser), prolonged short circuit operation or incorrect mounting to the heatsink.  It is worth noting that these will be the primary causes of failure.

A repair service is available for units that have been damaged, but it is at the discretion of ESP as to repair an existing unit or replace it completely (depending on the damage sustained).

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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 09 Feb 2002