Preamplifier for the
World's Smallest Fully Self-Contained 20 Watt Class AB Power Amplifier


7" x 6" x 1 1/2"

In seeking a preamp for the world's smallest 20 watt amplifier, I benchmarked a variety of different approaches.  I ended up using a kit I built for my headphone amplifier.  For a variety of reasons, it wasn't suitable for that use.  However, when I coupled it to my tiny amp on the bench, the results were very surprising.

I have matched this preamp and amp with my retrofitted FLAC based iPod, the best personal music player ever.

This stereo preamplifier makes use of the Philips TDA1524A. It provides up to 20dB of voltage gain for both channels, +/-15dB of bass and treble control, left/right channel balance and selectable loudness contour.

Preamplifier Features

  • Pilot Light
  • On-Off Volume
  • Bass
  • Treble
  • Balance
  • Loudness in/out
  • Select inputs A, B, C

Back

  • 1/8" stereo output to Power Amplifier
  • 1/8" Inputs A, B, C
  • Switched Outlet limited to 4 amps for Power Amplifier
  • 117 volt power, no wall wart.

Specs:

  • Frequency Response (-1dB): 10 - 50 000Hz
  • Input Voltage / Gain: 300mV / Gain = 20dB
  • 3Vrms / Gain = 0dB
  • Output Voltage: 3Vrms
  • Input Impedance: 10k Ohm
  • Output Impedance: 300 Ohm
  • Bass boost/cut: 15dB at 50 Hz
  • Treble boost/cut: 15dB at 15 kHz

 

This is a single IC preamplifier which uses the TDA1524A chip.  It was built from a kit I got while experimenting and designing my headphone amplifier.  The power supply is integrated into the preamp and the yellow square capacitor is line filtering.  This preamp is equipped with a fused switched outlet. 


K100 kit


K100

 

Bass Boost

 


Preamp paired with its tiny power amp.

The final results when hooked to my FE-103 Radio Shack 40-1197 speakers is...very clean.  The soft singing female jazz vocal and accompaniment is stunning for such a small system.  There is something to be said for two devices with a very minimum of parts.  Also, having the total sound come through only one driver is ... well very clear, accurate and pleasing. 

You're not going to blow anyone away with this system, nor are you likely to win over any esoteric hifi nuts.  However, the above can be achieved for less than a hundred dollars.  I did spend a about $20 more for the extra parts and metal boxes.