|DO IT YOURSELF PROJECTS
|DIY Op Amps: The How and Why
of building your own op amps. Simple high-performance op amps are easy to make out of as
few as six discrete components whose total cost is less than a dollar. It is the purpose
of this article to show how easy it is.
Balanced Zen Line Stage
( Audio Electronics ): "So is this the anticipated Bride of the Son
of Zen? I suppose it is. It has an identical topology and is perfectly suited for driving
the Son of Zen, but there is much utility to this circuit. It also serves as a nice
balanced-in to unbalanced-out or unbalanced-in to balanced-out converter".
|The Son of ZEN ( Audio
Electronics, 2/97): "Letters suggesting design improvements to the ZEN provide the
direction and the excuse to proceed with the Son of Zen. Son of Zen has been designed
scalable, and can be built with an output from one to fifty watts without any change in
the schematic of the amplifier itself."
|The Bride of ZEN ( The Audio
Amateur, 4/94): "This is the second installment of a trilogy of construction projects
centered around the performance obtainable from absolutely minimalist circuitry. Part one
described the Zen amplifier, a 10 watt single-ended class A power amplifier using a single
MOSFET gain stage. In this piece we will examine its preamplifying mate, also a single
gain stage MOSFET circuit. "
|ZEN Revisited ( The Audio
Amateur, 3/94): Upgrades to the Single-Stage, Single-Ended, Class A Mosfet Amplifier.
|The Pass ZEN Amplifier ( The
Audio Amateur, 2/94): 10 Watts of Single-Stage Single-Ended Class A:
"There are two most essential principles to audio amplifier design. The first
is simplicity. The second is linearity. "
|Build the A75 Power Amplifier - Part 2
( The Audio Amateur, 1/93): THE STORY BEHIND the A75 power amplifier continues. In Part I,
we discussed its origins and direct predecessor, the Pass A40, as well as some general
guidelines to follow before initiating such a project. We covered such topics as MOSFETs
and differential pairs. In this concluding part, we will analyze the amplifier's component
parts in depth, beginning with the source.
|Build the A75 Power Amplifier - Part 1
( The Audio Amateur, 4/92): READERS' REQUESTS FOR more power are reasonable, but not
interesting enough to justify another article. Hanging some output transistors on the
original and beefing up the power supply is best left as an exercise to the reader. While
the A75 delivers more power, particularly into low-impedance loads, that is not the
primary goal of this project. We wish to introduce more advanced concepts in amplifier
design, including balanced inputs, dual differential inputs, true DC response, cascode and
folded cascode operation, tiered and regulated supplies, operation with and without
feedback, and details of designing with the new generation of power MOSFETS.
|Build a MOSFET Citation 12 (
The Audio Amateur, 2/81): In its time the Citation 12 was a truly excellent amplifier,
employing a number of concepts which have only recently become popular: dual split power
supplies, DC output coupling, and no active current limiting. These characteristics
allowed it to sonically outperform the Dynaco 120 which was its popular competitor. It
could drive anything with high reliability, and in the time I spent as a repair technician
I fixed a few Dynaco, Phase Linear, McIntosh, Pioneer, and Sansui amplifiers, but I've
never seen a broken Citation 12.
|The Pass A-40 Power Amplifier ( The
Audio Amateur, 4/1978): Given then that the circuit should be simple, we must find a way
to achieve the exceptional performance as advertised. While we want simple distortion
types, we also want a lot less of them, which brings us to the question: what techniques
will extract maximum performance from a few parts? In this case I have chosen two very
effective approaches: constant current sourcing and class A operation which are combined
in a deceptively simple 40 Watt per channel amplifier.
|Construct A Class-A Amplifier (
Audio, February 1977): In spite of their high cost and low efficiency, class A power
amplifiers have recently been receiving more attention from audiophiles who demand
uncompromising accuracy. Both the price and quality of these amplifiers result from the
operation of their output stages in class A mode, where the amplifying devices are
constantly operated in their linear region, above cutoff and below saturation. Whether
made from tubes or semiconductors, circuits operating in class A mode yield the smoothest
transfer functions and widest bandwidths, hence their near universal application in
preamplifiers and other low power circuitry.
|Super Symmetric Amplification:
U.S. Patent # 5376899 describes a new amplifying circuit topology that takes advantage of
the character of special matched balanced amplifiers that are cross-coupled to provide
cancellation of distortion and noise. The result provides high performance with very
simple linear circuits, better than previous efforts by an order of magnitude. We have
dubbed the approach Super-Symmetry (Su-Sy), an homage to particle physics.
|Single Ended Class A:
Single-Ended Class A amplifiers have certainly hit it big in the four years since we began
testing the first Aleph 0. So is this just another audio fad, or is there something
fundamental about this kind of design, justifying a revival of the old approaches to
|Power Supplies: A Commentary for Consumers:
The entire power circuitry of an amplifier can be seen as a community water
system. The sun, driving the weather cycle, deposits water on the landscape, and it
collects in a lake behind a dam. The community draws water as needed through pipes. In the
winter, the rain collects in the lake, and the water pressure increases as it fills. In
the summer the water level falls, and so does the pressure. When the community draws more
water than usual, the level goes down more, and it often takes more than one season to
build it back up.
|Cascode Amp Design (Audio,
March 1978): Lowering distortion in power circuits without compromising their transient
response remains a primary problem for designers of audio power amplifiers. Until fairly
recently, the favorite technique for removing distortion components in linear amplifiers
was to cascade many gain stages to form a circuit having enormous amounts of gain and then
using negative feedback to control the system and correct for the many errors introduced
by this large number of components.
|Speaker Cables : Science or Snake Oil
( Speaker Builder Magazine, 2/80): Audiophiles recently began
re-examining the performance of every link in the audio playback chain, and before long
their attention turned to the lowly loudspeaker cable. In response to demand, a number of
companies are producing or distributing new and exotic cables claimed to improve audio
power transmission from amplifier to speaker. Pointing to lower resistance and inductance,
proponents of the newer cables insist they sound significantly better ("better than
an expander!"); however, the subject is controversial, and some hi-fi notables claim
performance increase is negligible and the higher capacitance of some new cables can cause
amplifier instability and damage.
|Phase Coherent Crossover Networks
( Speaker Builder Magazine, 2/82): The importance of phase response in the audio chain has
been brought to greater focus recently by equipment claims of phase coherency, (the output
signal has the same phase relationships as the input signal). It is not particularly
obvious that two different frequency components of a signal can go into a device at
precisely the same time and emerge at different times, but it is extremely common.
||Amplifier having an active current source.
||Amplifier with gain stages coupled for differential error
||Efficient high fidelity audio power amplifier.
||Active low frequency acoustic resonance suppressor.
||Opto-isolated bias circuit for operating push-pull
amplifiers in class A and class AB modes.
||Constant voltage - constant current high fidelity amplifier.
||Active bias circuit for operating push-pull amplifiers in
class A mode.
|For complete copies of the patents go to the
Patent & Trademark Office web site or the IBM patent web site.......see our links page.
|Some of the schematics are provided in .PDF
format (Acrobat Reader 3.0) for better down loading and printing. Acrobat Reader is
available FREE directly from Adobe. (www.adobe.com)
for Mosfets and other parts include Digi-Key (http://www.digikey.com)
and Mouser (http://www.mouser.com). Pass Labs does not
provide parts or kits for any of the projects listed below.