IC Amplifier for LF

Andre' Kesteloot akestelo@bellatlantic.net
Thu, 08 Jul 1999 23:23:28 -0400

Hello Tacoistas,

Those of you who attended the AMRAD meeting this Thursday 8 July saw the little
amplifier assembled by Dave Borden K8MMO.

This little amplifier would be ideal to get you started on 136 KHz.  It easily
puts out 20 watts, which, as you remember, is the maximum power allocated to our
German brethren on LF. And German hams are making lots of QSOs with 20 watts.

This is a 24 watt mono audio amplifier kit, sporting the LM1875 IC.   Well
designed, the kit comprises a good quality printed circuit board, and all the
parts required to make it work. You need to add only a large heat sink.

The LM1875 is fool proof, in that it has a built-in temperature limiting
circuit, is short-circuit proof, (is even rumored to lower your cholesterol
level), etc.

I tested it extensively at 136 kHz, and had no problem getting more than 20
watts RMS (sine wave output) into a 4 ohm resistive load, with 48 volts Vcc.   I
am not too sure about their claim of only -3 DB at 250 kHZ, but it certainly
operates very well at 136 kHz.

The kit, marketed by Maplin of England, is known as the Maplin LU96 kit, and is
available for about $30 US  from


Welcome to Quality Kits
Price: $50.23 CDN
This low distortion, high quality audio amplifier kit, based on the LM1875,
is capable of delivering 25W into 4 ohm to 8 ohm loads and can be operated
from split or single rail supplies.  It also features short circuit and thermal
This amplifier is an ideal building block project for use in many audio

 Supply Voltage       60V (+/-30V) max.
 Supply Current       70 ma (typical), POUT 0W
 Output Power POUT      25W, THD = 1%
 Load Impedance       4 ohm to 8 ohm
 THD       (f = 1 kHz) 0.022%
 POUT = 20W, 4 ohm load    (f = 20 kHz) 0.07%
 Full Power Bandwidth     DC to 250 kHz (-3dB)
 Open Loop Gain (DC)     90 dB
 Slew Rate           8 V/us

Andre' N4ICK