# good books on amplifier construction

P

#### pil

Jan 1, 1970
0
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

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

J

#### Joerg

Jan 1, 1970
0
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.

W

#### Walter Harley

Jan 1, 1970
0
Joerg said:
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.

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.

W

#### Walter Harley

Jan 1, 1970
0
pil said:
I am interested in buying the following books [...]

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

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
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.

J

#### Joerg

Jan 1, 1970
0
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.

P

#### pil

Jan 1, 1970
0
Joerg said:
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.

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

I

Jan 1, 1970
0
J

#### John Popelish

Jan 1, 1970
0
pil said:
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

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.

K

#### Karl Uppiano

Jan 1, 1970
0
John Popelish said:
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.

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

A

#### Active8

Jan 1, 1970
0
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.

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

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.

A

#### Active8

Jan 1, 1970
0
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.

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

A

#### Active8

Jan 1, 1970
0
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
^^^^^^^^^ correction. triangle.

J

#### Joerg

Jan 1, 1970
0
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.

J

#### Joerg

Jan 1, 1970
0
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.

A

#### Active8

Jan 1, 1970
0
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...

impressive. one little rut in the earth stalled a 1 ton Ford (fix or
repair daily) truck today.
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.

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

Regards, Joerg.

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.

A

#### Active8

Jan 1, 1970
0
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.

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.

R

#### Ralph & Diane Barone

Jan 1, 1970
0
Joerg said:
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.

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.

J

#### Joerg

Jan 1, 1970
0
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.

J

#### Joerg

Jan 1, 1970
0
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.

B

Jan 1, 1970
0
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.
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.

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.
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.

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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