Building a class A audio amplifier - no audio out

Tim Wescott wrote:

> Eeyore wrote:
> > mrdarrett@gmail.com wrote:
> >
> >> I tried to build this Class A amplifier circuit as a learning
> >> experience:
> >> http://www.techlib.com/electronics/audioamps.html#class-a
> >
> > Why why why ?
> >
> > It puts DC through the speaker is is horribly badly biased. It's a JOKE.
>
> And how is a beginner supposed to know?

He's not that much of a beginner. I'd have known that was crap by my mid
teens. It's about as simple as it gets. I was building stuff more complex at
age 12.


> Do you have any suggestions for a site to look at, or a book?

Application notes are good, as long as you can find one that covers the
subject. Discrete design is rare these days and apart from the experts, the
standard of it seems to be going downhill fast as people aren't taught
'circuits' and it just becomes 'building blocks'.

A decent audio site is here.
http://www.dself.dsl.pipex.com/ampins/ampins.htm

Graham

mrdarrett@gmail.com wrote:

> On May 11, 8:16 am, stratu...@yahoo.com wrote:
> >  On May 11, 7:32 am, Tim Wescott <t...@seemywebsite.com> wrote: > Eeyore wrote:
> >
> >  > > Why why why ?
> >  >
> >  > > It puts DC through the speaker is is horribly badly biased. It's
> >  > > a JOKE.
> >  >
> >  > And how is a beginner supposed to know?
> >  >
> >  > Do you have any suggestions for a site to look at, or a book?
> >
> > Lots of good stuff here
> >
> > http://sound.westhost.com/

Another decent one.


> Ah, thank you for the reply.
>
> One thing I noticed is, the larger amps on westhost.com (10W+) need
> split power supplies (+/-).  I'd like to start with something needing
> just 0V-6V or 0V-12V.

Then you'll *need* capacitor coupling which is generally considered a 'bad thing' (
for 101 reasons ). All top-notch audio uses split supplies.

Graham

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. 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.

Graham

On May 11, 11:50=A0am, Eeyore <rabbitsfriendsandrelati...@hotmail.com>
wrote:
> Tim Wescott wrote:
> > Eeyore wrote:
> > > mrdarr...@gmail.com wrote:
>
> > >> I tried to build this Class A amplifier circuit as a learning
> > >> experience:
> > >>http://www.techlib.com/electronics/audioamps.html#class-a
>
> > > Why why why ?
>
> > > It puts DC through the speaker is is horribly badly biased. It's a JO=
KE.
>
> > And how is a beginner supposed to know?
>
> He's not that much of a beginner.


He's not?  :D  You might be surprised.  My background is in chemistry,
not electronics.


> I'd have known that was crap by my mid
> teens. It's about as simple as it gets. I was building stuff more complex=
 at
> age 12.


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.

For some odd reason, electronics seem much harder to me than
chemistry... I wonder why... but I enjoy exercising the old brain
cells.


> > Do you have any suggestions for a site to look at, or a book?
>
> Application notes are good, as long as you can find one that covers the
> subject. Discrete design is rare these days and apart from the experts, t=
he
> standard of it seems to be going downhill fast as people aren't taught
> 'circuits' and it just becomes 'building blocks'.
>
> A decent audio site is here.http://www.dself.dsl.pipex.com/ampins/ampins.=
htm
>
> Graham


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

I found this interesting, though.
http://www.st-andrews.ac.uk/~www_pa/Scots_Guide/audio/part1/page3.html

Thanks,

Michael

mrdarrett@gmail.com wrote:

> Any comments on this circuit as a beginner project?
> http://www.redcircuits.com/Page33.htm

Grossly obsolescent design.

I'm actually having some trouble figuring some aspects of it's operation. It's a bit
oddball.

Learn how low level preamps work first, then tack on emitter followers to see how power
amps work.

Graham

On May 11, 8:30=A0am, mrdarr...@gmail.com wrote:
> On May 11, 8:16=A0am, stratu...@yahoo.com wrote:
<snip>
 > > Lots of good stuff here
 >
 > >http://sound.westhost.com/
 >
 > > G=B2
 >
 > Ah, thank you for the reply.
 >
 > One thing I noticed is, the larger amps on westhost.com (10W+) need
 > split power supplies (+/-). =A0I'd like to start with something
needing
 > just 0V-6V or 0V-12V.
 >
 > Thanks again,
 >
 > Michael

Well then perhaps this 'golden oldie' might be of interest.

http://www.swtpc.com/mholley/PopularElectronics/Dec1967/PE_Dec1967.htm

G=B2

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.


> > 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.

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

mrdarrett@gmail.com wrote:

> Eeyore <rabbitsfriendsandrelati...@hotmail.com> wrote:
> > Tim Wescott wrote:
> > > Eeyore wrote:
> > > > mrdarr...@gmail.com wrote:
> >
> > > >> I tried to build this Class A amplifier circuit as a learning
> > > >> experience:
> > > >>http://www.techlib.com/electronics/audioamps.html#class-a
> >
> > > > Why why why ?
> >
> > > > It puts DC through the speaker is is horribly badly biased. It's a JOKE.
> >
> > > And how is a beginner supposed to know?
> >
> > He's not that much of a beginner.
>
> He's not?  :D  You might be surprised.  My background is in chemistry,
> not electronics.

Well, you post often enough here and usually get good info. Just on that basis I'd
hope you'd picked something up.


> > I'd have known that was crap by my mid
> > teens. It's about as simple as it gets. I was building stuff more complex at
> > age 12.
>
> 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.

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 different and
probably wealthier had I taken the offer but I might have missed a lot of
interesting challenges.


> For some odd reason, electronics seem much harder to me than
> chemistry... I wonder why... but I enjoy exercising the old brain
> cells.
>
> > > Do you have any suggestions for a site to look at, or a book?
> >
> > Application notes are good, as long as you can find one that covers the
> > subject. Discrete design is rare these days and apart from the experts, the
> > standard of it seems to be going downhill fast as people aren't taught
> > 'circuits' and it just becomes 'building blocks'.
> >
> > A decent audio site is here.http://www.dself.dsl.pipex.com/ampins/ampins.htm
>
> Been there, borrowed Self's book from the library, still a bit over my
> head.
>
> I found this interesting, though.
> http://www.st-andrews.ac.uk/~www_pa/Scots_Guide/audio/part1/page3.html

First look seems promising.

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

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 instinctively
obvious but every audio power amp of any note uses one ).

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 else. 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

mrdarrett@gmail.com wrote:

> I found this interesting, though.
> http://www.st-andrews.ac.uk/~www_pa/Scots_Guide/audio/part1/page3.html

Ah, it's maintained by Jim Lesurf. That explains why it's good.

Graaham

On May 11, 1:31=A0pm, stratu...@yahoo.com wrote:
> On May 11, 8:30=A0am, mrdarr...@gmail.com wrote:> On May 11, 8:16=A0am, s=
tratu...@yahoo.com wrote:
>
> <snip>
> =A0> > Lots of good stuff here
> =A0>
> =A0> >http://sound.westhost.com/
> =A0>
> =A0> > G=B2
> =A0>
> =A0> Ah, thank you for the reply.
> =A0>
> =A0> One thing I noticed is, the larger amps on westhost.com (10W+) need
> =A0> split power supplies (+/-). =A0I'd like to start with something
> needing
> =A0> just 0V-6V or 0V-12V.
> =A0>
> =A0> Thanks again,
> =A0>
> =A0> Michael
>
> Well then perhaps this 'golden oldie' might be of interest.
>
> http://www.swtpc.com/mholley/PopularElectronics/Dec1967/PE_Dec1967.htm
>
> G=B2


Thanks a bunch!

Michael