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AMZ Mini-Booster mu-amp

AMZ Mini-booster schematic
Points A & B on the schematic are merely for mods and future expansion


PC Boards are now available for purchase. Make your own minibooster & modify it with a tone control or other variations!

The AMZ Projects Newsletter contains further information on mini-booster circuit variations.

Pre-assembled mini-booster modules are now available for purchase. Just wire it into a box of your choice!


History of the Mini-Booster

Here is a scan of the shop-worn cover of my Radio Shack reprint of a National Semiconductor databook. It was published in February 1973 and I bought it in 1976 (for $1.60) when I was working in electronics repair. In this book is the applications note AN-32 which contains the cookbook circuit for the jfet mu-amp circuit, which is the basis for the mini-booster. This connection has always been acknowledged on my site and in the material I have published about the circuit. Anyone who has my CD can verify the long standing acknowledgement by looking at the article published there.

Even though I had the databook in 1976, I did not make the first pedal using this jfet circuit until 1980. I made one and loved the sound and then had to make a second one when a keyboard-player friend, who had a Mini-Moog, tried it and wanted one to fatten the sound of the oscillators on the synth. I'm positive about the time frame of this because of the date when that player was in my band. Note that it got the name "Mini-Booster" because of the connection with the Mini-Moog at the time. I also made the first dual mini-booster not long after that to add even more harmonics and fat sounds.

Before the Internet was available to the general public, there were independently operated bulletin boards that you dialed up, and then several commercial online services, including GEnie, Compuserve, Prodigy, and later, America Online. I have been members of all of those at one time or another, but was very active in the GEnie network in the late 1980s and early 90s.

Which brings me to schematics and DIY effects. A number of my pedal designs, including the Son of Screamer, Fuxx Face, Mini-Booster and others, existed long before the Internet was commercialized and I posted them to several bulletin boards and on commercial services. There was an active music forum on GEnie that was hosted by Craig Anderton and my designs were available there for free download to users. The forum was quite active and users could communicate with each other privately via an internal message system much like email. (Remember this is in the late 1980s and many of my circuits including the Mini-Booster were available online pre-Internet.)

In 1995, my site went live on the Internet and became the second guitar effects and schematics site to be available! The first site was called the Leperís Abode and it has since disappeared, leaving my web site as the longest continuously available DIY guitar effects site on the Net.

When I posted the original Mini-Booster schematic on my web site, I also linked to the appnote AN-32 which was available at the time on National Semiconductor's web site that was at (anyone remember that?). They then bought the domain name and began transferring all of the info over to that site and much of it (including AN-32) became unavailable for a while.

I have provided my design free of charge for DiY enthusiasts to build and play. Hundreds of people have built the mini-booster and enjoyed its sound. I have also provided hours of free support to hobbyists when they had trouble getting the circuit to work properly.

I encourage everyone who enjoys the guitar to build one and listen to the pleasant changes it can make to your tone. It is easy to construct on perfboard or use a pcb, which I find a bit easier.

The mini-booster was derived from the application note - that has always been acknowledged - but the original is just that... an appnote with a basic building block circuit. I took that basic building block and developed it into a working circuit that has had numerous application in effects and produces some of the best guitar tones available. Note that not a single component in the mini-booster is the same as the appnote.  

Click here to download the complete AN-32 appnote which contains numerous interesting jfet circuits. If you are still reading at this point you might be interested in knowing that the National Semiconductor circuit is a jfet derivative of an expired patent of a vacuum tube circuit for a "Series balanced Amplifier", US Patent 2,310,342 issued Feb. 1943 though the patent circuit is more like a basic SRPP and not the mu-amp. Click here to get a pdf copy of this vacuum tube circuit patent.

Build a mini-booster for great phat boosted sound. The pc boards that I offer are sent with a sheet of instructions and link to a special web page with further help and modifications.

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