Building a class A audio amplifier - no audio out

On May 11, 1:32=A0pm, Eeyore <rabbitsfriendsandrelati...@hotmail.com>
wrote:
> mrdarr...@gmail.com wrote:
> > "pimpom" <pim...@invalid.invalid> wrote:
> > > mrdarr...@gmail.com wrote:
>
> > > > Ah. =A0I'd neglected to say that a 1W amp would be fine for learnin=
g
> > > > purposes.
>
> > > > If I just wanted power I'd go for an LM3886 or just buy an Onkyo
> > > > system. =A0I'd like to understand how the amps work.
>
> > > > Any comments on this circuit as a beginner project?
> > > >http://www.redcircuits.com/Page33.htm
>
> > > Looks ok to me. You have to pay heed to the instructions, especially =
about
> > > adjusting the quiescent (no-signal) current.
>
> > > I'd recommend mounting the two output transistors Q3 and Q4 on a smal=
l
> > > heatsink, making sure that they are electrically isolated from each o=
ther
> > > and from ground and other components. The two transistors can theoret=
ically
> > > dissipate nearly 1W each with a 4-ohm load. That may seem small, but =
it's
> > > enough to get a bare TO220 transistor quite hot.
>
> > > One 0.47-ohm 1/2-watt resistor in series with the emitter of each out=
put
> > > transistor will aid stability.
>
> > > Q2 dissipates about 0.25W which will also cause the small transistor =
to run
> > > quite hot to the touch. I suggest using a BD135-16 or a BD137-16
>
> You'll have trouble getting any BD135 or 137 IME these days at least at a=
 sensible
> price. They're 30 year old devices in an little used package these days.


30 cents is unreasonable to you?  Available at mouser.com


> Half the trouble is the most half-assed DIY websites use exclusively obso=
lete
> parts. Thinks 2N2222 for example. Metal can, expensive and outperformed n=
ow by a
> 2c TO-92 device.


I bought a mixed bag of NPNs at the local Radio Shack, and they were
all plastic TO-92s, not metal cans.

BC337s are 6 cents at mouser... what TO-92 NPNs go for 2 cents?


> > > instead of
> > > the BC337. Choosing a sub-type with the -16 suffix ensures that it wi=
ll have
> > > about the same gain level as the BC337.
>
> Hahahahaha ! Just try getting suffixed types. LMAO.
>
> > Ah, thank you very much. =A0I'll heatsink the transistors, and thanks
> > for the tip about emitter resistors.
>
> Sinclair ( of Sir Clive Sinclair fame ) made audio modules for DIYers in =
the 70's.
> Their Z30 and Z50 power amps neglected to use emitter resistors and subse=
quently
> failed regularly.


Thanks for the warning.

> I even wrote to the company pointing out the design error. FINALLY after =
God knows
> how many returns they found PCB space to fit some. Problem fixed.
>
> What you need to understand is WHY they were important. That comment is t=
o you Mr
> Darrett or you'll never be a designer.


Exactly.  The "why" is what makes for slow going... else I'd just buy
an Onkyo or an LM3886, as I mentioned earlier.


>
> Graham


Michael

mrdarrett@gmail.com wrote:

> Been there, borrowed Self's book from the library, still a bit over my
> head.

Buy this. It's ANCIENT and refers to a lot of obsolete op-amps which with
intelligence you can substitute with better modern parts but it covers some good
ground like noise calculations for example. It helps you get the feel.

I have an original print copy of course. Finally it''s been reprinted.

http://www.amazon.com/National-Semiconductor-Audio-Radio-Handbook/dp/1882580354

TI have some super and huge IC mainly handbooks too that you should have. I'll
need to recheck their filenames.

Graham

On May 11, 1:44=A0pm, Eeyore <rabbitsfriendsandrelati...@hotmail.com>
wrote:

....

> > > I'd have known that was crap by my mid
> > > teens. It's about as simple as it gets. I was building stuff more com=
plex at
> > > age 12.
>
> > Ah, good for you. =A0I wasted my teen years teaching myself C
> > programming, assembly language programming, and modifying Michael
> > Abrash's VGA Mode X graphics routines. =A0Then Windows 95 came out and
> > made my experience worthless. =A0Eh. =A0That's life.
>
> I was offered a job programming in C back around 1984. I took one look at=
 the
> bizarre syntax and ran away. My career would have been surely very differ=
ent and
> probably wealthier had I taken the offer but I might have missed a lot of
> interesting challenges.


How could you be offered a job in C programming if you didn't know C
programming?  (thoroughly confused)  That would never fly over here.

On that note... I took a biochemistry lab class where I had to
calculate the A, C, G and T fractions from DNA analysis of a
bacterium.  It involved *a lot* of punching numbers into a
calculator.  I thought, "screw this" and wrote a Pascal program to do
it.  I turned in the source code with my lab report.  The grader wrote
"Mabey (sic) you're in the wrong major" on the top of my report.
Mabey he was right.  ;D

....

> BUT ! Before anything else. Do you know how to bias a single transistor s=
mall
> signal amplifier. Don't touch anything else until you've mastered that to=
gether
> with all its variants and effects.


Nope.  Will start there.  Thanks.


> Even better ... start with an emitter follower and ask yourself why they'=
re used
> and then do the same with the complementary version ( may not be instinct=
ively
> obvious but every audio power amp of any note uses one ).


You mean a Sziklai?
http://en.wikipedia.org/wiki/Sziklai_pair

I noticed that a lot of power amps use the Sziklai pair vs. the
Darlington.  Is the Sziklai demonstrably superior?


> Actually, I nearly forgot. UK magazine Wireless World had a 3 or so part =
monthly
> article on discrete design by a practical college lecturer as opposed to =
an Ivory
> Towers University type. I learnt more from that, faster than anything els=
e. I must
> see if I still have it. It dropped all the ultra-theoretical bunk and got=
 on with
> how to make circuits that work and why.
>
> Graham

On May 11, 1:53=A0pm, Eeyore <rabbitsfriendsandrelati...@hotmail.com>
wrote:
> mrdarr...@gmail.com wrote:
> > Been there, borrowed Self's book from the library, still a bit over my
> > head.
>
> Buy this. It's ANCIENT and refers to a lot of obsolete op-amps which with
> intelligence you can substitute with better modern parts but it covers so=
me good
> ground like noise calculations for example. It helps you get the feel.
>
> I have an original print copy of course. Finally it''s been reprinted.
>
> http://www.amazon.com/National-Semiconductor-Audio-Radio-Handbook/dp/...
>
> TI have some super and huge IC mainly handbooks too that you should have.=
 I'll
> need to recheck their filenames.
>
> Graham


Ah, thanks.  You know, the title sounds similar to some texts my dad
has.  I'll have to examine his library.

Michael

On Mon, 11 May 2009 19:57:07 +0100, Eeyore
<rabbitsfriendsandrelations@hotmail.com> wrote:

>mrdarrett@gmail.com wrote:
>
>> Ah.  I'd neglected to say that a 1W amp would be fine for learning
>> purposes.
>
>First you need to learn how discrete circuits work and how to measure / troubleshoot
>them.

I agree.  As you point out elsewhere, things have moved from learning
these details to using functional blocks created by others who know.
That's too bad in some ways.  In others, it means more people can have
at it without having to spend so much time informing themselves well
and fully, I suppose.

I'm just a hobbyist and in no way do I imagine I understand all of the
important details.  But I've cobbled together my own designs for a few
usably working audio amplifier circuits, when I was much younger.  And
at least for me, learning things in discrete steps helped a lot.  At
some point, it's time to figure out how to combine functions a bit.
But to start out, separating them seems to help.  For me, it did.

Part of this will be learning about conditioning the input source
appropriately and well.  Degenerative voltage amplifiers aren't that
hard to understand and design and may be a good place to actually
start.  In that regard, the student manual for the Art of Electronics
is important -- the book doesn't cover the details well enough on its
own -- if that book is to be used.  The student manual includes a
"compute this first, then that second, then..." approach.  Very easy
to follow.  (Then include bootstrapping of the input from the BJT
emitter as a 'next thing' to gather well.)  As you also point out in
another post, emitter followers for output.

Although some of these functions can be combined in a given design, I
don't think I could have handled it when I was going through this.  It
was the fact that they could be taken in steps that allowed me to
succeed, as much as I did.  So I recommend taking this in parts.

I started out trying my hand at understanding the basic degenerative
BJT amplifier, then gaining a foothold on the bootstrap to stiffen the
input a bit.  I used a well designed power supply, a well designed
signal generator, and a well designed oscilloscope as tools --
designed by professionals while learning about simply voltage
amplification.  (It's remarkable to me how complicated it all seemed
at first and how so much simpler it seems in after-thought, looking in
hindsight.)  It was after that when I began worrying about how to work
with various input sources worked; sometimes their own supplies and in
all cases some kind of matching to avoid distortion or avoidable loss
of signal.  I actually built my own carbon granule microphone, in
fact.  Most of my experience was with dynamic microphones, but later
this included electret.  Then I worked on outputs (mostly just the
typical 4-8 ohm speaker, but also various kinds of headphones.)  One
such I also built by hand, winding wire, using fixed magnets, and
using tiny metal plates as diaphrams.)

It was fun but took a lot of time.  I made stuff that didn't work
well, too.

>You'll have fun finding a book that'll teach that. My first came from 1969 (
>Mullard ) followed by an RCA handbook and a full blown theory book my Dad
>bought me and people were already well into ICs by the mid 70s.

I learned this stuff in the late '60s and early 70's, when I had the
time as a kid and young adult, too.

Jon

stratus46@yahoo.com wrote:

> Well then perhaps this 'golden oldie' might be of interest.
> 
> http://www.swtpc.com/mholley/PopularElectronics/Dec1967/PE_Dec1967.htm
> 
> G²

I remember building that !  If it didn't get lost when we moved it will
still be kicking around in a box in the garage !  I might even still
have the original magazine.

Just Lurking  :-)

-- 
Best Regards:
                     Baron.

Eeyore wrote:
> 
> mrdarrett@gmail.com wrote:
> 
> > "pimpom" <pim...@invalid.invalid> wrote:
> > > mrdarr...@gmail.com wrote:
> > >
> > > > Ah.  I'd neglected to say that a 1W amp would be fine for learning
> > > > purposes.
> > >
> > > > If I just wanted power I'd go for an LM3886 or just buy an Onkyo
> > > > system.  I'd like to understand how the amps work.
> > >
> > > > Any comments on this circuit as a beginner project?
> > > >http://www.redcircuits.com/Page33.htm
> > >
> > > Looks ok to me. You have to pay heed to the instructions, especially about
> > > adjusting the quiescent (no-signal) current.
> > >
> > > I'd recommend mounting the two output transistors Q3 and Q4 on a small
> > > heatsink, making sure that they are electrically isolated from each other
> > > and from ground and other components. The two transistors can theoretically
> > > dissipate nearly 1W each with a 4-ohm load. That may seem small, but it's
> > > enough to get a bare TO220 transistor quite hot.
> > >
> > > One 0.47-ohm 1/2-watt resistor in series with the emitter of each output
> > > transistor will aid stability.
> > >
> > > Q2 dissipates about 0.25W which will also cause the small transistor to run
> > > quite hot to the touch. I suggest using a BD135-16 or a BD137-16
> 
> You'll have trouble getting any BD135 or 137 IME these days at least at a sensible
> price. They're 30 year old devices in an little used package these days.
> 
> Half the trouble is the most half-assed DIY websites use exclusively obsolete
> parts. Thinks 2N2222 for example. Metal can, expensive and outperformed now by a
> 2c TO-92 device.

   Idiot!  The PN2222 is the same die in a TO-92 package, and the
MMBT2222 is the same die in a SOT-23 package it isn't obsolete, just
repackaged for modern designs.  2N2222 is considered the generic name
for the family, since it was first.  Both the 2N2222 & the 2N32222A are
in stock at Digikey, which means the metal cased TO-18 package isn't
obsolete for all designs.

> 
> > > instead of
> > > the BC337. Choosing a sub-type with the -16 suffix ensures that it will have
> > > about the same gain level as the BC337.
> 
> Hahahahaha ! Just try getting suffixed types. LMAO.
> 
> > Ah, thank you very much.  I'll heatsink the transistors, and thanks
> > for the tip about emitter resistors.
> 
> Sinclair ( of Sir Clive Sinclair fame ) made audio modules for DIYers in the 70's.
> Their Z30 and Z50 power amps neglected to use emitter resistors and subsequently
> failed regularly.


   Typical British design quality.


> I even wrote to the company pointing out the design error. FINALLY after God knows
> how many returns they found PCB space to fit some. Problem fixed.
> 
> What you need to understand is WHY they were important. That comment is to you Mr
> Darrett or you'll never be a designer.
> 
> Graham


-- 
Service to my country? Been there, Done that, and I've got my DD214 to
prove it.
Member of DAV #85.

Michael A. Terrell
Central Florida

http://www.flickr.com/photos/materrell/

On Mon, 11 May 2009 12:01:07 -0700, mrdarrett wrote:

> Ah, good for you.  I wasted my teen years teaching myself C
> programming, assembly language programming, and modifying Michael
> Abrash's VGA Mode X graphics routines.  Then Windows 95 came out and
> made my experience worthless.  Eh.  That's life.

C programming is still very useful. Apart from C itself, C++,
Objective-C, Java and C# are all heavily based upon it.

Assembler isn't so useful in application programming, but
it's still useful if you're programming microcontrollers, or writing
system code (OS kernels, compilers, interpreters), or performance-critical
applications (e.g. games). Although most of the above is written in C
or C++ rather than assembler, being able to mentally translate into
assembler will result in much better code than that written by someone who
only understands the language as a theoretical abstraction.

On Mon, 11 May 2009 13:31:51 -0700 (PDT), stratus46@yahoo.com wrote:

>Well then perhaps this 'golden oldie' might be of interest.
>
>http://www.swtpc.com/mholley/PopularElectronics/Dec1967/PE_Dec1967.htm

I remember it!  There was a follow-up article with another version, as
I recall.

Jon

> On May 11, 1:44&#4294967295;pm, Eeyore <rabbitsfriendsandrelati...@hotmail.com>
> wrote:

>> I was offered a job programming in C back around 1984. I took one look
>> at the bizarre syntax and ran away.

That "bizarre" syntax is pretty much the industry standard nowadays. C++,
C#, Java, and JavaScript all look very similar. Any deviation from C
syntax (e.g. Python) is considered bizarre.

On Mon, 11 May 2009 13:57:28 -0700, mrdarrett wrote:

> How could you be offered a job in C programming if you didn't know C
> programming?  (thoroughly confused)  That would never fly over here.

In 1984, C was still a fairly uncommon language. It wouldn't be
unreasonable to prefer someone with a reasonable amount of overall
programming experience (particularly if it's experience in the relevant
domain) who would need to learn C over someone with less overall
experience (or less relevant experience) with some C. Learning a new
language is easier than learning programming.

Of course, that doesn't hold if hiring is done by HR types with no
knowledge of the field (and no willingness to consult). A classic example
was when Java took off, companies were advertising for programmers with 2
or 3 years' Java experience when Java's existence had been public
knowledge for less than a year.