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good books on amplifier construction

Discussion in 'General Electronics' started by pil, Apr 10, 2004.

  1. pil

    pil Guest

    I am interested in buying the following books:


    PRACTICAL AUDIO AMPLIFIER CIRCUIT PROJECTS
    Author : Andrew Singmin



    HIGH-POWER AUDIO AMPLIFIER CONSTRUCTION MANUAL: 50 TO 500 WATTS FOR
    THE AUDIO PERFECTIONIST
    Author : G. Randy Slone; Randy Slone; Slone



    Any comments on these books?

    Which books would you recommend for a third year EE student who is very much
    into amplifiers and sound? I am looking for a book which actually have
    circuits that I can construct.

    Thanks

    Johan Wagener
     
  2. Joerg

    Joerg Guest

    Johan, I don't know these or many other audio books. Just one hint: Nowadays I
    would certainly try to learn about class D audio amps, the digital kind. That
    seems to be where technology goes.

    Regards, Joerg.
     
  3. Unfortunately there do not appear to be any texts that cover class D audio;
    all that exists, as far as I've been able to determine anyway, is
    manufacturer application notes.
     
  4. Johan, since you're an EE student you may have access to a university
    library, which means you may be able to take a look at those and other books
    for free. Take advantage of that resource if you have it!!

    I have the Slone book. It does have plenty of projects that you can
    actually construct; and the philosophy of the book seems sensible and
    realistic. I have not personally tried building the projects, so I can't
    comment on whether there are technical errors - but that is something you
    always want to watch out for when building projects out of a book or web
    site. Never assume a schematic is perfect; always check to see if what
    you're about to build makes sense. Component values may be wrong by orders
    of magnitude, parts may be underspecified (e.g., resistor power rating not
    specified), wires may be incorrectly joined or not joined.

    Douglas Self's "Audio Power Amplifier Design Handbook" is a very good
    resource if you're trying to learn about audio. It does contain working
    circuits, but it's not really a project book; however, it will definitely
    help you understand the reasoning behind the circuits you're building. I'd
    recommend it.

    In modern commercial audio power amplifiers, quite a lot of the circuitry
    has to do with protection rather than amplification: protecting the speakers
    against DC faults, protecting the output transistors against overheating,
    and so forth. Unfortunately, many project books and web site projects don't
    include the protection circuitry. (Slone's book is an exception: it does
    discuss protection circuits at some length.) If you find an older (1970's)
    commercial power amp it will often not have any protection circuitry, or at
    least not much more than a temperature switch on the heat sink and a fuse on
    the speaker output. Those older circuits will amplify just fine, and sound
    fine, but they are not as reliable as the more modern amps are; you're more
    likely to accidentally fry your amp, the speakers, or both.
     
  5. Joerg

    Joerg Guest

    Yes, Walter, unfortunately it takes a long time until new stuff makes it into
    university teaching and books. But I bet Winfield Hill will pick up class D in
    future editions of "The Art of Electronics" which I consider a "must have" for
    any serious EE.

    Manufacturers do a good job though for someone who likes to remain on the
    cutting edge. A class D example for starters:

    http://www.irf.com/product-info/audio/classdtutorial.pdf

    After that it's on to app notes and schematics. For my career I have learned
    more from those than text books and university combined. Plus lots of hands-on
    work.

    Regards, Joerg.
     
  6. pil

    pil Guest


    Good thing you mentioned that. I always wanted to know this: What is the
    difference between digital and analog?

    How can a digital signal be amplified???
    How can a one become a louder one?
    And most important to me: How can you drive a speaker with a digital
    signal???

    As far as I am concerned every "digital" hi-fi must still have an analog
    amplifier somewhere in its design. The amplified speakers (which they claim
    to be digital speakers) has a DAC and a normal analog amplifier right?


    I would greatly appreaciate answer on this
     
  7. Ian Bell

    Ian Bell Guest

    pil wrote:
    snip
    Anything by Douglas Self. Find him here
    http://www.dself.dsl.pipex.com/ampins/ampins.htm

    Ian
     
  8. No. Digital audio (class D) treats the speaker current like the
    output of a switching regulated supply that has AC capability. There
    is nothing but two levels coming out of the speaker terminals, except
    for the effect of filtering components.

    A good intro to this kind of amplifier is the datasheet for one of the
    integrated versions.

    http://focus.ti.com/lit/ds/symlink/tpa3001d1.pdf
     
  9. Karl Uppiano

    Karl Uppiano Guest

    It's debatable whether class "D" is really digital. While it's true that
    internally, the signal is switched, it isn't a digital signal. It's pulse
    width modulation. The pulse width is continuously variable, making it an
    analog quantity.

    The amplifier you referenced is a pulse width modulator. The input is
    analog, and the output is analog. Noise and distortion are not particularly
    outstanding, either. It's primary claim to fame is extremely high
    efficiency, approaching 90%. It might be acceptable for battery-powered
    equipment or automotive audio. Conventional class A-B linear amplifiers are
    still preferable for high fidelity.

    Here's a web site that has some great practical designs and discussions:
    http://sound.westhost.com/index2.html
     
  10. Active8

    Active8 Guest

    Since the OP sorta hints at sound quality...

    I was recently poking around for info on the distortion
    characteristics of tube amps and found this interesting tidbit at
    www.audioasylum.com:

    "One of the clearest indicators of the musical value of tube audio
    gear is the fact that there are more manufacturers of high end tube
    stereo equipment now than at any point in history! Many of the new
    components are expensive, ranging in price from about $800 to a
    staggering $180,000US for the most exotic modern tube amplifiers.
    Some of the better-known brands are Conrad-Johnson, Audio Research,
    VTL, Cary, Jadis, and Sonic Frontiers, just to name a few."

    Maybe a thorough google for amp schematics would reveal designs from
    some of these mfgs. I didn't have much trouble turning up schems of
    guitar amps, both tube and solid state.

    Also, in a very recent thread which pointed to a page on the largest
    listening room in the world - the one with the huge 8x18" subwoofer
    - I found some pages on preamplifiers with NO feedback. There's a
    tube version and FET version of one that I looked at briefly. The
    page mentioned that the distortion of FET preamps is more tubelike.

    http://www.royaldevice.com/ampli.htm

    Somewhere it read something about tubes being even harmonic
    producers. Other info I turned up, however, indicates that tubes
    aren't purely even harmonic producers when overdriven, rather they
    produce a more significant amount of 2nd harmonic which colors the
    sound in a more bearable way. Tube, bipolar :() and IC amps were
    tested and the harmonic content bargraphed.

    Gotta admit, my mother's ancient tube phonograph with the IIRC oval
    speakers sounded pretty good.
     
  11. Active8

    Active8 Guest

    But it's taken around 20 years for it to take off if you can
    actually say it's taken off - perhaps from the perspective of
    integration it has/is. If I dug deep enough, I could probably lay
    hands on an old audio review on one of the first class D systems. It
    had a 100 kHz switching supply (possibly one per channel) and though
    I can't remember the PWM period, it basically applied the signal and
    a sawtooth wave to a compparator and used the output to switch the
    MOSFETs. LC pi or L LP filter on the output.

    SOS, different day ;)
     
  12. Active8

    Active8 Guest

    ^^^^^^^^^ correction. triangle.
     
  13. Joerg

    Joerg Guest

    Tubes do sound nice, Mike. The first amp I ever built was with color TV tubes
    because they were cheap. The big ones of the 6KD6 kind and plenty of them. One
    little "Aaaaah" into the mike stalled a 1 1/2. kilowatt gas generator... Then I made
    a gorilla size amp with two QB5/1750 which aren't well known here in the US. They
    are the size of a 1/2 gallon milk jug and can take 500W of plate dissipation. Each.

    The last restoration project contained a couple 6J6's. Those little tubes fill the
    whole living room with sound. It's amazing.

    Regards, Joerg.
     
  14. Joerg

    Joerg Guest

    Wow, Mike, I didn't know the technique was this old. But sometimes it takes a long
    time. Like spread spectrum which I believe was invented by an Austrian actress but
    took about 20 years to get going. Now it is everywhere.

    With class D it takes some company to get enough engineers behind it and I bet they
    could make a stellar product. Question is whether the market is there or whether
    people think that what they got now is good enough.

    Regards, Joerg.
     
  15. Active8

    Active8 Guest

    impressive. one little rut in the earth stalled a 1 ton Ford (fix or
    repair daily) truck today.
    Wow, big.
    I haven't seen any tube equip in many years, but that's a good idea
    using TV tubes. I'll have to keep my eyes peeled for old tube
    sets... do my own subjective listening test and heat some air space
    at the same time. Good winter project.
     
  16. Active8

    Active8 Guest

    Amazing, Juerg. I didn't expect that tidbit to come out in this
    thread. It was Heddy Lemar. She was married to cockbreath's minister
    of munitions before she came to the US. She and her producer worked
    out a system to foil the jammers they used on the U-boats to jam our
    torpedo sonar. It frequency hopped the sonar signal according to
    holes punched in a roll of paper like those used on player pianos.

    That's about all that was said about it in the chapter on the
    history of SS in "The Spread Spectrum Handbook" - McGraw Hill.

    I don't remember if/how the concept was used.
     
  17. I built a Class D amplifier as my EE systems lab project in 1988. I was
    inspired by a 1978 paper by Slobodan Cuk (no, I didn't use his topology).
    So the idea (and working examples) has been around at least 26 years, but
    boy o boy, has the hardware ever got better since then. I was using these
    DS0026 driver chips for the output stage that would let out all their magic
    smoke if you looked at them funny. Nowadays, the MOSFET drivers, power
    MOSFETs, and some great PWM modulators are off the shlef items.
     
  18. Joerg

    Joerg Guest

    Mike, it has gotten hard to find tubes these days. Some of the large TV set tubes had
    sometimes been designed into ham radio gear (the xmit final amp stage) so they are still
    available at those stores. However, prices are climbing. Personally I always liked the
    6146B better, especially the version with the graphite plate. Not quite as powerful as
    the TV tubes but very tough.

    Ain't nothing like the glow of tubes. Somehow that gives me a different perspective of
    radio when I fire up one of the old tube sets. My wife made me part with some of them but
    I kept the oldest ones. It is amazing what sound they produce from one little audio amp
    tube of just a few watts capability. Even on AM where most of these "modern" receivers
    sound terrible.

    Regards, Joerg.
     
  19. Joerg

    Joerg Guest

    Mike, I believe it was never used during WW II. But she didn't invent it alone. It was a
    typical engineer's approach at some kind of dinner where she and George Antheil probably
    drew it up on a napkin. The puzzler here is neither was an engineer. Hedy was an actress
    and George a composer.

    IEEE awarded them the honors for it recently but as far as I know Hedy Lamarr passed away
    in 2000. Also, since the electronics weren't there at the time to develop something for
    communications the patent lapsed and they didn't make any money. But I guess in show biz
    the more famous people make enough money anyways.

    Regards, Joerg.
     
  20. Ben Bradley

    Ben Bradley Guest

    In
    alt.electronics,sci.electronics,sci.electronics.basics,sci.electronics.design,

    The Class D amps are certainly making many inroads in many consumer
    products, but how fast it replaces analog power amplifiers remains to
    be seen. For stereos sold at Wal-Mart, the transition may already be
    100 percent, but I doubt you could find a 'Class D' amp in high-end
    audio stores, or if so, that it sounds as good as any analog amplifier
    in the store. Analog amps in that area (admittedly not a large
    consumer market) will surely be around for a long time, unless Class D
    amps show substantially more improvement over current state of the
    art.

    For the Original Poster, Douglas Self is one writer/designer of
    audio power amps, and here's the relevant part of his site:

    http://www.dself.dsl.pipex.com/ampins/ampins.htm

    For some really interesting schematics and discussions, click on Power
    Amplifier Design, then Distortion in Power Amplifiers. Read the text
    while all the figures and plots load. I found the rest of his site
    interesting as well. I recall reading amazon.com reviews of his book,
    and the opinions were varied - some really liked him, but some
    suggested books by other authors instead.

    There are large numbers of hifi audio power amplifier schematics
    and discussions on the Web. For some gurus and their musings and
    schematics, google for Marshall Leach, Nelson Pass and Borbely.
    That (punse-width modulation) is the traditional Class D approach.
    Some "Class D" amps work just like sigma-delta modulators in A/D
    converters. The output is either a 1 or a 0, and the time is also
    quantized: the output only changes states at specific times, at the
    sample rate, which is very much higher than the audio range, usually
    around 2 MHz. These have advantages over straight PWM, but with an odd
    disadvantage that there can be significant delays (as in a few
    milliseconds) between input and output.
    This is still very true, OTOH there are amps designed for
    "home-theatre" applications using Class D amps (for small size and low
    heat - compare the heat output of six 25-watt Class B amps vs. Class
    D).
    TI's Class D audio amps claim less than 0.1 percent distortion,
    which is allededlly 'fairly good' but the spectrum of the distortion
    products can cause a harsher sound than an analog amp (especially a
    tube amp) with the same or even a much higher distorion figure. These
    Class D chips can be regarded as the 'dumbing down' of audio much the
    same way as lossy psychoacoustic compression such as MP3.
    TI has been notable in promoting their Class D chips for use in
    home theatre '5.1' multichannel audio amplifiers. These are either a
    significant advance in audio, or an abomination to sound reproduction,
    depending on how good your hearing is.
     
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