Audio Power Amplifiers

These power amplifiers are under Technical Information because they are not standard products. HOWEVER, all of these designs are available custom built. If you are interested, please ask for a free quotation.

These amps are all available for real time listening comparison using
our Audio Control Center. If you are in the area, please contact us
to arrange a time to come by and listen.

If you a planning to build any of these amplifiers yourself, please note that all this data is believed to be correct but it is furnished as "information only" and neither the author nor TDL Technology, Inc. assumes any liability for its use (or misuse!).

  1. "Build the CF-MOSFET Audio Power Amplifier" by G. Randy Slone, Nuts & Volts Magazine, Feb-Mar 2003. We have made the circuit board smaller so two of them and their common power supply fit in a rack-mount case 5-1/4" high by 10 inches deep (Sescom 3RU10). Click here to download a copy of the zip file with the smaller circuit board layout and revised parts list. We have built the low-power (100 w RMS per channel) version of this amp and it sounds wonderful! (Mr. Slone is not affiliated in any way with TDL. This file is posted here as "information only".)

  2. National Semiconductor makes a 11-pin integrated circuit, the LM3876, which is an audio power amplifier. It needs only a few external components and is rated at 56 watts (typical) output into 8 ohms with low distortion. I built a stereo amp using a pair of these chips and the performance is quite good. Both channels are on a small, single-sided circuit board. The file LM3876.ZIP contains circuit diagrams, parts list, and construction notes in pdf format as well as color photos as jpg files. The circuit board layout is included as a CIRCAD file and you can download the free DOS version of CIRCAD from the Holophase web site to print it.

  3. Not too long ago I was given a free, non-working Luxman L-80V audio amplifier. I checked the power transformer and found it OK so I decided to rebuild just the two-channel power amplifier portion in another enclosure. This amp is rated at 50 watts per channel and uses a basic design with a two-transistor emitter follower (EF) output stage. The file L-80V.ZIP contains the circuit board layout (as a CIRCAD file), circuit diagrams, a parts list with construction notes and parts sources as Adobe pdf files and an internal photo as a jpg file. It's probably not worth it to build this amp from "scratch" but perhaps you can find one that's not working or maybe you'll find this design info interesting.

  4. Dr. Marshall Leach, a professor at the Georgia Institute of Technology has long been interested in audio power amps with low transient intermodulation distortion (TIM). His first article on this subject: "Build A Low TIM Amplifier" was published in the February 1976 issue of Audio magazine. I've had a copy of it in my files these many years because it's an excellent tutorial on TIM and the amp design methodology to minimize it. I have recently scanned the article and you can download an Adobe pdf copy by clicking here. (The size is about 900 kB.) I never got around to building this amp.

    A couple of years later (I'm not sure of the date), he sent info on version 2 to everyone on this mailing list. (I had bought circuit boards for version 1 but never used them.) I didn't get around to building this one either!

    A couple of years ago I finally decided the time had come to build the current version, whatever it was. So I checked his web site at and found a lot of documentation on version 4.5 which I downloaded. I have built this version and it sounds very musical. (I'm working on an article on measuring TIM distortion.) I built this amp exactly as described in the documentation. In fact, I scanned the circuit board layout and then imported the bitmap file into CIRCAD and did an overlay. You can download the circuit board file and a photo of the inside of the amp by clicking here. If I were going to build another one, I would make some mechanical changes and put Molex headers on the circuit board. It's something of a nightmare to get all the flying leads from the output transistors and heat sensing diodes (all on their heatsinks) soldered to the circuit boards. Version 4.5 is still current as of the end of May, 2004. Happy building!

  5. Jeff Macaulay wrote an article: "Hybrid Audio Amplifier" that was published in the March 2004 issue of Electronics World magazine (UK). It uses only two transistors, two VFETS and one vacuum tube per channel and is rated at 80 watts RMS into 8 ohms. I was intrigued by its simplicity so I built one. The performance is excellent so I'm posting the details. The file contains a scan of the article in Adobe pdf format as well as my circuit board layout, parts list, interior photo and a few details the author left out that I discovered during construction and setup. As usual, I built this amp in a rack mount enclosure from SESCOM.

  6. If TDL were going to build an audio power amp as a product, this could be the one. It's a hybrid design described by Marco Ferretti in the February 2001 issue ofAudioXpress magazine. For those who like the sound of a tube amp, this one has the best of both worlds: a tube input stage and a solid-state output which does nothing more than deliver current to the speakers. The file contains my circuit board layouts, interior photo, and three pages of notes. As usual, I built this amp in a rack mount enclosure from SESCOM.

    This note was added on 3 September 2004. I have been listening to this amp quite a bit; mostly classical and jazz. Now that the vacuum tubes have aged some, this is one sweet sounding amp. It's a bit of a hassel to build (see the notes) but I think you will be impressed with its performance.

    Novrmber 2009 -- I added a scan of the audioXpress article to the file. The article is eleven pages so the file is now rather large (24.8 MB) but most people now have a high-speed internet connrction so download time won't be too long.

  7. Added 19 Jan 2005
    I needed a utility amp primarily for testing and listening to new subwoofer designs so I built a new version of the LM3876 amplifier. I added front panel switches to turn the mute on and off, front panel meters to monitor the power out and front panel gain controls. This design is completely described in . (Size is about 327 kB.) The zip file contains the circuit board layout; parts list, construction notes and circuit diagrams as Abobe pdf files and jpg photos of the front and rear panels and an internal view. That is, everything you need to build one.

  8. Added 31 May 2005
    The March 2005 issue of AudioXpress magazine contains an article, "A Minimalist Amplifier Design" by Larry Lisle. Each channel contains just three components: an input transformer, a vacuum tube and an output transformer. I have built this amplifier using an all battery power supply and then an all mains operated supply. You may find the results interesting! The file contains 22 pages of notes, circuit diagrams, circuit board layouts, photos and performance graphs in Adobe pdf and jpg format. The file size is about 563 kB.

  9. Added 5 June 2006
    The April 2006 issue of AudioXpress magazine contains an article, "A Solid-State Single-Ended Power Amp" by Ed Simon. This is another minimalist design with just five transistors per channel and two of them are current sources. I have built this amp twice: first as described by Mr. Simon and then in a modified form so that it would fit into a rack mount enclosure. This is a class A design so it runs somewhat warm but it sounds great! The file contains my notes, circuit diagrams, circuit board layout, photos and a SPICE model with the needed library files. The file size is about 460 kB.

  10. Added 11 December 2008

    I found this class A design by Bruce Heran on the web (address in the text) and was intrigured by its premium performance with so few parts! I built one and it sounds excellent. So I'm posting info about my version here and it includes a SPICE model for those who want to look at design variations the easy way. Please also take a look at Bruce's original article on what he calls the ODDWATT-225. (I kept the name the same.) The file contains my notes, circuit diagrams, circuit board layouts, parts list, photos and the SPICE model. The file size is about 1.1 MB.

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