Launched June 20, 2001. last updated 29 April, 2002. (new music links)
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Build the "Li'l 4x4"
A Quest for Hi-Fi Audio from Lo-Fi Parts
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"Li'l 4x4" is a self-contained, 4-stage, 4-watt general-purpose tube amplifier circuit with a wide range of applications. It uses relatively inexpensive parts in an op-amp style topology to give superior performance compared to traditional circuits using such components.

Possible applications include:
  • Super-clean instrument practise amplifier
  • Stage monitor for instruments or vocals
  • Hi-fi "centre-channel" reproduction amp
  • Stereo system (requires 2 units)
  • Bench test amplifier
  • Extension amplifier for shop or den
When used with an efficient speaker system, the "Li'l 4x4's" 4 watts RMS output power is plenty for small rooms. I use mine primarily as an instrument amplifier for electric guitar, giving a clean, rich sound for practise and solo performance purposes.

Some experience with vacuum tubes is recommended, but the project is sufficiently uncomplicated to be suitable as an intermediate project before tackling larger or more complex amplifier designs. The first preamplifier stage may be omitted if instrument-level sensitivity is not required (as for a centre-channel amplifier, etc.)

This article details my quest for the "perfect" low-power instrument amplifier, and includes a side-by-side comparison with an authentic classic design using similar components.

new A new addition (July 2001) is a very simple yet effective compressor option, intended mainly for use with electric guitars.

Demo recording available here

Features:
  • 4 watts RMS power output 
  • Dual Line level (Av=10) input/outputs
  • Instrument level (Av=250) input (optional)
  • 4-stage design 
  • Uses inexpensive tubes and other components 
  • Push-pull design throughout (except for input stage) 
  • Low hum and noise 
  • Low distortion in active region using negative feedback 

Copyright Notice:
All contents of this website, including schematics, text, diagrams and photographs are Copyright ©2001 by Fred Nachbaur, Dogstar Music. All rights reserved. This site may be freely linked, but none of the contents may be posted anywhere else without express permission of the copyright holder.

The information presented here may be used for personal, non-commercial use only. Any commercial applications of this design or any part thereof requires previous licensing arrangements with the author and copyright holder, Fred Nachbaur.

Article Index:

      1: Introduction

      2: How It Works

      3: Benchmarks

      4: Building the Li'l 4x4

      5: Compressor Option

      6: Parts List

Resources:
Following is a listing of available resources for building the "Li'l 4x4". Included are a full-size schematic and off-site parts resources.


Document: Filename:
Full Schematic Diagram (7.5"x10" @ 300 dpi) 4x4large.gif
An excellent site for tubes and related parts Triode Electronics
Good quality transformers Hammond Manufacturing

 
Contact
You may contact me regarding this project at fnachbaur@netscape.net. I'd be happy to hear from you, and any bug reports or suggestions for improvement are always welcome.


To find out what other kinds of trouble I get into, check out my sites listed below:

Free Music Downloads

Back to Tube Projects Main Page
My main Dogstar Music site
Fred's ZX81 retro computer page
My Theremin Exploits
Original music on IUMA.com
... and on Soundclick. Nice bio.
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