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!).
"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".)
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.
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.
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
http://users.ece.gatech.edu/~mleach/lowtim/ 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
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
macaulay.zip 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.
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
ferretti.zip 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
Novrmber 2009 -- I added a scan of the audioXpress article to
the ferretti.zip 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.
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 slm3876.zip
. (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.
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 lisle.zip 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.
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 simon.zip 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.
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 odd225.zip 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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