distortion with Class B (with NFB) vs Class AB

May 23, 2014

I was shocked to see such low distortion figures on this Class B audio amplifier:

http://www.redcircuits.com/Page164.htm

Is negative feedback sufficient to eliminate crossover distortion in Class B?

George Herold · May 23, 2014

On Friday, May 23, 2014 12:31:59 PM UTC-4, mrda...@gmail.com wrote:

I was shocked to see such low distortion figures on this Class B audio amplifier:

http://www.redcircuits.com/Page164.htm

Is negative feedback sufficient to eliminate crossover distortion in Class B?

If you are talking about the first circuit on that page,
then I'm not sure I'd call it class B, there is a path
from the opamp output to the speaker.
(I also thought it should have a bit of resistance in there,
opamp to speaker, but I don't know... JL has posted circuits like that.)

George H.

May 23, 2014

On Friday, May 23, 2014 11:08:14 AM UTC-7, George Herold wrote:

On Friday, May 23, 2014 12:31:59 PM UTC-4, mrda...@gmail.com wrote:

I was shocked to see such low distortion figures on this Class B audio amplifier:

http://www.redcircuits.com/Page164.htm

Is negative feedback sufficient to eliminate crossover distortion in Class B?

If you are talking about the first circuit on that page,

then I'm not sure I'd call it class B, there is a path

from the opamp output to the speaker.

(I also thought it should have a bit of resistance in there,

opamp to speaker, but I don't know... JL has posted circuits like that.)

George H.

Yep, the first circuit. Sure there's a path from opamp pin 6 (output) to the speaker, but the heavy lifting is done by Q1 and Q2, right?

Michael

May 23, 2014

On Friday, May 23, 2014 11:08:14 AM UTC-7, George Herold wrote:

On Friday, May 23, 2014 12:31:59 PM UTC-4, mrda...@gmail.com wrote:

I was shocked to see such low distortion figures on this Class B audio amplifier:

http://www.redcircuits.com/Page164.htm

Is negative feedback sufficient to eliminate crossover distortion in Class B?

If you are talking about the first circuit on that page,

then I'm not sure I'd call it class B, there is a path

from the opamp output to the speaker.

(I also thought it should have a bit of resistance in there,

opamp to speaker, but I don't know... JL has posted circuits like that.)

George H.

On second thought, you raise a good point... shouldn't the output from the opamp drive the bases of the transistors somehow?

May 23, 2014

On Friday, May 23, 2014 12:33:52 PM UTC-7, Jim Thompson wrote:

On Fri, 23 May 2014 11:46:25 -0700, Jim Thompson

To-Email-Use-The-Envelope-Icon@On-My-Web-Site.com> wrote:

On Fri, 23 May 2014 11:08:14 -0700 (PDT), George Herold

gherold@teachspin.com> wrote:

On Friday, May 23, 2014 12:31:59 PM UTC-4, mrda...@gmail.com wrote:

I was shocked to see such low distortion figures on this Class B audio amplifier:

http://www.redcircuits.com/Page164.htm

Is negative feedback sufficient to eliminate crossover distortion in Class B?

If you are talking about the first circuit on that page,

then I'm not sure I'd call it class B, there is a path

from the opamp output to the speaker.

(I also thought it should have a bit of resistance in there,

opamp to speaker, but I don't know... JL has posted circuits like that.)

George H.

Yep. It's really not quite class-B.

This scheme was first done in the mid '60's in the Motorola MC1524.

I used it in the power supply regulator for the Hughes TOW missile

somewhere around 1970-73.

The THD specs are not particularly surprising. What you have to watch

out for is TIM (transient intermodulation) distortion... particularly

to those of us who played clarinet in orchestra, sitting in front of

the oboes and French horns, TIM glares at you when playing a recording

of a Mozart woodwind ensemble.

...Jim Thompson

Correction, it wasn't the MC1524 as I thought. Finally found a

datasheet for the MC1524... it was a classic architecture, implemented

as a hybrid in a TO-5 package, with three chips, two P-type substrate,

one as N-type.

I haven't found what number the rail-driven amplifier was yet. I

loaned out my ancient data book and it never returned :-(

...Jim Thompson

Huh. Not quite Class B... does this scheme have a name? B+ would be neat, haha...

May 23, 2014

On Friday, May 23, 2014 11:08:14 AM UTC-7, George Herold wrote:

On Friday, May 23, 2014 12:31:59 PM UTC-4, mrda...@gmail.com wrote:

I was shocked to see such low distortion figures on this Class B audio amplifier:

http://www.redcircuits.com/Page164.htm

Is negative feedback sufficient to eliminate crossover distortion in Class B?

If you are talking about the first circuit on that page,

then I'm not sure I'd call it class B, there is a path

from the opamp output to the speaker.

(I also thought it should have a bit of resistance in there,

opamp to speaker, but I don't know... JL has posted circuits like that.)

George H.

Here's a different one. Is this more accurately Class B with NFB?

http://www.allaboutcircuits.com/vol_6/chpt_6/10.html

Thanks,

Michael

Jim Thompson · May 24, 2014

On Fri, 23 May 2014 11:08:14 -0700 (PDT), George Herold
<gherold@teachspin.com> wrote:

On Friday, May 23, 2014 12:31:59 PM UTC-4, mrda...@gmail.com wrote:
I was shocked to see such low distortion figures on this Class B audio amplifier:

http://www.redcircuits.com/Page164.htm

Is negative feedback sufficient to eliminate crossover distortion in Class B?

If you are talking about the first circuit on that page,
then I'm not sure I'd call it class B, there is a path
from the opamp output to the speaker.
(I also thought it should have a bit of resistance in there,
opamp to speaker, but I don't know... JL has posted circuits like that.)

George H.

Yep. It's really not quite class-B.

This scheme was first done in the mid '60's in the Motorola MC1524.

I used it in the power supply regulator for the Hughes TOW missile
somewhere around 1970-73.

The THD specs are not particularly surprising. What you have to watch
out for is TIM (transient intermodulation) distortion... particularly
to those of us who played clarinet in orchestra, sitting in front of
the oboes and French horns, TIM glares at you when playing a recording
of a Mozart woodwind ensemble.

...Jim Thompson
--
| James E.Thompson | mens |
| Analog Innovations | et |
| Analog/Mixed-Signal ASIC's and Discrete Systems | manus |
| San Tan Valley, AZ 85142 Skype: Contacts Only | |
| Voice

Jim Thompson · May 24, 2014

On Fri, 23 May 2014 11:23:53 -0700 (PDT), mrdarrett@gmail.com wrote:

On Friday, May 23, 2014 11:08:14 AM UTC-7, George Herold wrote:
On Friday, May 23, 2014 12:31:59 PM UTC-4, mrda...@gmail.com wrote:

I was shocked to see such low distortion figures on this Class B audio amplifier:

http://www.redcircuits.com/Page164.htm

Is negative feedback sufficient to eliminate crossover distortion in Class B?

If you are talking about the first circuit on that page,

then I'm not sure I'd call it class B, there is a path

from the opamp output to the speaker.

(I also thought it should have a bit of resistance in there,

opamp to speaker, but I don't know... JL has posted circuits like that.)

George H.

On second thought, you raise a good point... shouldn't the output from the opamp drive the bases of the transistors somehow?

Nope. What happens is the OpAmp _tries_ to drive the speaker, with
the result that the current in the OpAmp power lead increases driving
the appropriate bipolar device. You want to choose the B-E resistors
such that the bipolar devices conduct before the OpAmp current limits,
but not so large that you have rail-to-rail conduction thru the
bipolar's.

...Jim Thompson
--
| James E.Thompson | mens |
| Analog Innovations | et |
| Analog/Mixed-Signal ASIC's and Discrete Systems | manus |
| San Tan Valley, AZ 85142 Skype: Contacts Only | |
| Voice

May 24, 2014

On Friday, May 23, 2014 4:14:34 PM UTC-7, John Larkin wrote:

....

If you are talking about the first circuit on that page,

then I'm not sure I'd call it class B, there is a path

from the opamp output to the speaker.

(I also thought it should have a bit of resistance in there,

opamp to speaker, but I don't know... JL has posted circuits like that.)

It's a boosted opamp, not really "class B". Voltage regulators, like

LM7805s and such, are sometimes "helped out" by a parallel PNP,

similar idea.

George H.

Here's a different one. Is this more accurately Class B with NFB?

http://www.allaboutcircuits.com/vol_6/chpt_6/10.html

Thanks,

Michael

The rightmost 0.22 uF cap allows the opamp to drive the load some

directly at higher frequencies. A resistor there makes more sense.

The gain control is insane. So is the transistor biasing. It's

impressive how many really, really bad audio circuits there are

around. And there is a positive correlation between circuit badness

and web page pontification.

--

John Larkin Highland Technology, Inc

Dang. What's a beginner to do, then? I'd like to make a 12-volt wall-wart-powered class B, or AB, or boosted-opamp thingie, and would like to know *why* it works, too (so that kind of defeats the purpose of chipamps).

Any suggestions?

Thanks!

Michael

Jim Thompson · May 24, 2014

On Fri, 23 May 2014 11:46:25 -0700, Jim Thompson
<To-Email-Use-The-Envelope-Icon@On-My-Web-Site.com> wrote:

On Fri, 23 May 2014 11:08:14 -0700 (PDT), George Herold
gherold@teachspin.com> wrote:

On Friday, May 23, 2014 12:31:59 PM UTC-4, mrda...@gmail.com wrote:
I was shocked to see such low distortion figures on this Class B audio amplifier:

http://www.redcircuits.com/Page164.htm

Is negative feedback sufficient to eliminate crossover distortion in Class B?

If you are talking about the first circuit on that page,
then I'm not sure I'd call it class B, there is a path
from the opamp output to the speaker.
(I also thought it should have a bit of resistance in there,
opamp to speaker, but I don't know... JL has posted circuits like that.)

George H.

Yep. It's really not quite class-B.

This scheme was first done in the mid '60's in the Motorola MC1524.

I used it in the power supply regulator for the Hughes TOW missile
somewhere around 1970-73.

The THD specs are not particularly surprising. What you have to watch
out for is TIM (transient intermodulation) distortion... particularly
to those of us who played clarinet in orchestra, sitting in front of
the oboes and French horns, TIM glares at you when playing a recording
of a Mozart woodwind ensemble.

...Jim Thompson

Correction, it wasn't the MC1524 as I thought. Finally found a
datasheet for the MC1524... it was a classic architecture, implemented
as a hybrid in a TO-5 package, with three chips, two P-type substrate,
one as N-type.

I haven't found what number the rail-driven amplifier was yet. I
loaned out my ancient data book and it never returned :-(

...Jim Thompson
--
| James E.Thompson | mens |
| Analog Innovations | et |
| Analog/Mixed-Signal ASIC's and Discrete Systems | manus |
| San Tan Valley, AZ 85142 Skype: Contacts Only | |
| Voice

Jim Thompson · May 24, 2014

On Fri, 23 May 2014 13:21:55 -0700 (PDT), mrdarrett@gmail.com wrote:

On Friday, May 23, 2014 12:33:52 PM UTC-7, Jim Thompson wrote:
On Fri, 23 May 2014 11:46:25 -0700, Jim Thompson

To-Email-Use-The-Envelope-Icon@On-My-Web-Site.com> wrote:

On Fri, 23 May 2014 11:08:14 -0700 (PDT), George Herold

gherold@teachspin.com> wrote:

On Friday, May 23, 2014 12:31:59 PM UTC-4, mrda...@gmail.com wrote:

I was shocked to see such low distortion figures on this Class B audio amplifier:

http://www.redcircuits.com/Page164.htm

Is negative feedback sufficient to eliminate crossover distortion in Class B?

If you are talking about the first circuit on that page,

then I'm not sure I'd call it class B, there is a path

from the opamp output to the speaker.

(I also thought it should have a bit of resistance in there,

opamp to speaker, but I don't know... JL has posted circuits like that.)

George H.

Yep. It's really not quite class-B.

This scheme was first done in the mid '60's in the Motorola MC1524.

I used it in the power supply regulator for the Hughes TOW missile

somewhere around 1970-73.

The THD specs are not particularly surprising. What you have to watch

out for is TIM (transient intermodulation) distortion... particularly

to those of us who played clarinet in orchestra, sitting in front of

the oboes and French horns, TIM glares at you when playing a recording

of a Mozart woodwind ensemble.

...Jim Thompson

Correction, it wasn't the MC1524 as I thought. Finally found a

datasheet for the MC1524... it was a classic architecture, implemented

as a hybrid in a TO-5 package, with three chips, two P-type substrate,

one as N-type.

I haven't found what number the rail-driven amplifier was yet. I

loaned out my ancient data book and it never returned :-(

...Jim Thompson

Huh. Not quite Class B... does this scheme have a name? B+ would be neat, haha...

It's sorta class-AB, _except_ that the loop gain jumps up when the
bipolar's come active... which means you have to compensate the loop
based on that extra gain and lose effective feedback when only the
OpAmp is active. It's probably something I should analyze in
detail... for amusement-sake ;-)

...Jim Thompson
--
| James E.Thompson | mens |
| Analog Innovations | et |
| Analog/Mixed-Signal ASIC's and Discrete Systems | manus |
| San Tan Valley, AZ 85142 Skype: Contacts Only | |
| Voice

Jim Thompson · May 24, 2014

On Fri, 23 May 2014 13:40:39 -0700 (PDT), mrdarrett@gmail.com wrote:

On Friday, May 23, 2014 11:08:14 AM UTC-7, George Herold wrote:
On Friday, May 23, 2014 12:31:59 PM UTC-4, mrda...@gmail.com wrote:

I was shocked to see such low distortion figures on this Class B audio amplifier:

http://www.redcircuits.com/Page164.htm

Is negative feedback sufficient to eliminate crossover distortion in Class B?

If you are talking about the first circuit on that page,

then I'm not sure I'd call it class B, there is a path

from the opamp output to the speaker.

(I also thought it should have a bit of resistance in there,

opamp to speaker, but I don't know... JL has posted circuits like that.)

George H.

Here's a different one. Is this more accurately Class B with NFB?

http://www.allaboutcircuits.com/vol_6/chpt_6/10.html

Thanks,

Michael

John Larkin · May 24, 2014

On Fri, 23 May 2014 13:40:39 -0700 (PDT), mrdarrett@gmail.com wrote:

On Friday, May 23, 2014 11:08:14 AM UTC-7, George Herold wrote:
On Friday, May 23, 2014 12:31:59 PM UTC-4, mrda...@gmail.com wrote:

I was shocked to see such low distortion figures on this Class B audio amplifier:

http://www.redcircuits.com/Page164.htm

Is negative feedback sufficient to eliminate crossover distortion in Class B?

If you are talking about the first circuit on that page,

then I'm not sure I'd call it class B, there is a path

from the opamp output to the speaker.

(I also thought it should have a bit of resistance in there,

opamp to speaker, but I don't know... JL has posted circuits like that.)

It's a boosted opamp, not really "class B". Voltage regulators, like
LM7805s and such, are sometimes "helped out" by a parallel PNP,
similar idea.

George H.

Here's a different one. Is this more accurately Class B with NFB?

http://www.allaboutcircuits.com/vol_6/chpt_6/10.html

Thanks,

Michael

The rightmost 0.22 uF cap allows the opamp to drive the load some
directly at higher frequencies. A resistor there makes more sense.

The gain control is insane. So is the transistor biasing. It's
impressive how many really, really bad audio circuits there are
around. And there is a positive correlation between circuit badness
and web page pontification.

--

John Larkin Highland Technology, Inc

jlarkin att highlandtechnology dott com
http://www.highlandtechnology.com

May 24, 2014

On Friday, May 23, 2014 5:42:26 PM UTC-7, Jim Thompson wrote:

On Fri, 23 May 2014 16:22:22 -0700 (PDT), mrdarrett@gmail.com wrote:

On Friday, May 23, 2014 4:14:34 PM UTC-7, John Larkin wrote:

...

If you are talking about the first circuit on that page,

then I'm not sure I'd call it class B, there is a path

from the opamp output to the speaker.

(I also thought it should have a bit of resistance in there,

opamp to speaker, but I don't know... JL has posted circuits like that.)

It's a boosted opamp, not really "class B". Voltage regulators, like

LM7805s and such, are sometimes "helped out" by a parallel PNP,

similar idea.

George H.

Here's a different one. Is this more accurately Class B with NFB?

http://www.allaboutcircuits.com/vol_6/chpt_6/10.html

Thanks,

Michael

The rightmost 0.22 uF cap allows the opamp to drive the load some

directly at higher frequencies. A resistor there makes more sense.

The gain control is insane. So is the transistor biasing. It's

impressive how many really, really bad audio circuits there are

around. And there is a positive correlation between circuit badness

and web page pontification.

--

John Larkin Highland Technology, Inc

Dang. What's a beginner to do, then? I'd like to make a 12-volt wall-wart-powered class B, or AB, or boosted-opamp thingie, and would like to know *why* it works, too (so that kind of defeats the purpose of chipamps).

Any suggestions?

Thanks!

Michael

Ohm's and Kirchhoff's Laws never fail you.

(Kirchhoff's Law is particularly applicable to circuit analysis... I

call it, "What gozinta must gozouta" ;-)

Norton and Thevenin too, I bet. The stuff that made me hate electronics after taking the electronics class at Davis. Took me a long time to like electronics again after that.

Michael

May 24, 2014

On Friday, May 23, 2014 8:31:04 PM UTC-7, John Larkin wrote:

On Fri, 23 May 2014 16:22:22 -0700 (PDT), mrdarrett@gmail.com wrote:

On Friday, May 23, 2014 4:14:34 PM UTC-7, John Larkin wrote:

...

If you are talking about the first circuit on that page,

then I'm not sure I'd call it class B, there is a path

from the opamp output to the speaker.

(I also thought it should have a bit of resistance in there,

opamp to speaker, but I don't know... JL has posted circuits like that.)

It's a boosted opamp, not really "class B". Voltage regulators, like

LM7805s and such, are sometimes "helped out" by a parallel PNP,

similar idea.

George H.

Here's a different one. Is this more accurately Class B with NFB?

http://www.allaboutcircuits.com/vol_6/chpt_6/10.html

Thanks,

Michael

The rightmost 0.22 uF cap allows the opamp to drive the load some

directly at higher frequencies. A resistor there makes more sense.

The gain control is insane. So is the transistor biasing. It's

impressive how many really, really bad audio circuits there are

around. And there is a positive correlation between circuit badness

and web page pontification.

--

John Larkin Highland Technology, Inc

Dang. What's a beginner to do, then? I'd like to make a 12-volt wall-wart-powered class B, or AB, or boosted-opamp thingie, and would like to know *why* it works, too (so that kind of defeats the purpose of chipamps).

Any suggestions?

Thanks!

Michael

Look for some of the older literature, like the GE Transistor manuals and the

National Linear Applications books. They were into discrete transistor design.

Start with a simple 1-transistor class A amp and understand its bias and gain.

Horowitz and Hill, The Art of Electronics, is a good book to have around.

Chapters 1 and 2 start with electrical basics and make it up to bipolar

transistor amps.

Build this and listen to it. It's a real class B amp.

https://dl.dropboxusercontent.com/u/53724080/Circuits/Amps/Class_B_Amp.JPG

Then try things to make it less horrible.

An oscilloscope is worth having here. Like a Rigol or something.

--

John Larkin Highland Technology Inc

www.highlandtechnology.com jlarkin at highlandtechnology dot com

Precision electronic instrumentation

Ok, I think I'll go ahead and grab Horowitz and Hill then.

Ooh, thanks! TIP31A and its PNP spouse are OK for output transistors?

Much appreciated!

Michael

Phil Allison · May 24, 2014

<mrdarrett@gmail.com>

I was shocked to see such low distortion figures on this Class B audio
amplifier:

http://www.redcircuits.com/Page164.htm

Is negative feedback sufficient to eliminate crossover distortion in Class
B?

** Only zero bias class B designs have incurable crossover notches and that
schem is something different - class AB with a twist if you like. The 5534
drives the speaker direct and the current in its supply rails bring the two
boosters on as needed.

Bias current in the boosters is not defined - it depends on the 5543's
supply current and that varies from sample to sample and brand to brand. It
also very much depends on the Hfe and temperature of the boosters - they
will need a decent size heatsink to prevent thermal runaway.

Seeing as the collectors are linked, the boosters can be bolted to the same
heatsink with no insulators ( just a smear of silicone grease) - but the
heatsink cannot be grounded.

The THD figures are indeed very low and that is mainly down to the
exceptional performance of the 5534.

..... Phil

Jim Thompson · May 24, 2014

On Fri, 23 May 2014 16:22:22 -0700 (PDT), mrdarrett@gmail.com wrote:

On Friday, May 23, 2014 4:14:34 PM UTC-7, John Larkin wrote:

...

If you are talking about the first circuit on that page,

then I'm not sure I'd call it class B, there is a path

from the opamp output to the speaker.

(I also thought it should have a bit of resistance in there,

opamp to speaker, but I don't know... JL has posted circuits like that.)

It's a boosted opamp, not really "class B". Voltage regulators, like

LM7805s and such, are sometimes "helped out" by a parallel PNP,

similar idea.

George H.

Here's a different one. Is this more accurately Class B with NFB?

http://www.allaboutcircuits.com/vol_6/chpt_6/10.html

Thanks,

Michael

The rightmost 0.22 uF cap allows the opamp to drive the load some

directly at higher frequencies. A resistor there makes more sense.

The gain control is insane. So is the transistor biasing. It's

impressive how many really, really bad audio circuits there are

around. And there is a positive correlation between circuit badness

and web page pontification.

--

John Larkin Highland Technology, Inc

Dang. What's a beginner to do, then? I'd like to make a 12-volt wall-wart-powered class B, or AB, or boosted-opamp thingie, and would like to know *why* it works, too (so that kind of defeats the purpose of chipamps).

Any suggestions?

Thanks!

Michael

John Larkin · May 24, 2014

On Fri, 23 May 2014 20:34:00 -0700 (PDT), mrdarrett@gmail.com wrote:

On Friday, May 23, 2014 8:31:04 PM UTC-7, John Larkin wrote:
On Fri, 23 May 2014 16:22:22 -0700 (PDT), mrdarrett@gmail.com wrote:

On Friday, May 23, 2014 4:14:34 PM UTC-7, John Larkin wrote:

...

If you are talking about the first circuit on that page,

then I'm not sure I'd call it class B, there is a path

from the opamp output to the speaker.

(I also thought it should have a bit of resistance in there,

opamp to speaker, but I don't know... JL has posted circuits like that.)

It's a boosted opamp, not really "class B". Voltage regulators, like

LM7805s and such, are sometimes "helped out" by a parallel PNP,

similar idea.

George H.

Here's a different one. Is this more accurately Class B with NFB?

http://www.allaboutcircuits.com/vol_6/chpt_6/10.html

Thanks,

Michael

The rightmost 0.22 uF cap allows the opamp to drive the load some

directly at higher frequencies. A resistor there makes more sense.

The gain control is insane. So is the transistor biasing. It's

impressive how many really, really bad audio circuits there are

around. And there is a positive correlation between circuit badness

and web page pontification.

--

John Larkin Highland Technology, Inc

Dang. What's a beginner to do, then? I'd like to make a 12-volt wall-wart-powered class B, or AB, or boosted-opamp thingie, and would like to know *why* it works, too (so that kind of defeats the purpose of chipamps).

Any suggestions?

Thanks!

Michael

Look for some of the older literature, like the GE Transistor manuals and the

National Linear Applications books. They were into discrete transistor design.

Start with a simple 1-transistor class A amp and understand its bias and gain.

Horowitz and Hill, The Art of Electronics, is a good book to have around.

Chapters 1 and 2 start with electrical basics and make it up to bipolar

transistor amps.

Build this and listen to it. It's a real class B amp.

https://dl.dropboxusercontent.com/u/53724080/Circuits/Amps/Class_B_Amp.JPG

Then try things to make it less horrible.

An oscilloscope is worth having here. Like a Rigol or something.

--

John Larkin Highland Technology Inc

www.highlandtechnology.com jlarkin at highlandtechnology dot com

Precision electronic instrumentation

Ok, I think I'll go ahead and grab Horowitz and Hill then.

There should be lots of used ones around, 2nd edition.

Ooh, thanks! TIP31A and its PNP spouse are OK for output transistors?

Much appreciated!

Michael

Sure. You'll understand what crossover distortion is really about.

--

John Larkin Highland Technology Inc
www.highlandtechnology.com jlarkin at highlandtechnology dot com

Precision electronic instrumentation

John Larkin · May 24, 2014

On Fri, 23 May 2014 16:22:22 -0700 (PDT), mrdarrett@gmail.com wrote:

On Friday, May 23, 2014 4:14:34 PM UTC-7, John Larkin wrote:

...

If you are talking about the first circuit on that page,

then I'm not sure I'd call it class B, there is a path

from the opamp output to the speaker.

(I also thought it should have a bit of resistance in there,

opamp to speaker, but I don't know... JL has posted circuits like that.)

It's a boosted opamp, not really "class B". Voltage regulators, like

LM7805s and such, are sometimes "helped out" by a parallel PNP,

similar idea.

George H.

Here's a different one. Is this more accurately Class B with NFB?

http://www.allaboutcircuits.com/vol_6/chpt_6/10.html

Thanks,

Michael

The rightmost 0.22 uF cap allows the opamp to drive the load some

directly at higher frequencies. A resistor there makes more sense.

The gain control is insane. So is the transistor biasing. It's

impressive how many really, really bad audio circuits there are

around. And there is a positive correlation between circuit badness

and web page pontification.

--

John Larkin Highland Technology, Inc

Dang. What's a beginner to do, then? I'd like to make a 12-volt wall-wart-powered class B, or AB, or boosted-opamp thingie, and would like to know *why* it works, too (so that kind of defeats the purpose of chipamps).

Any suggestions?

Thanks!

Michael

Look for some of the older literature, like the GE Transistor manuals and the
National Linear Applications books. They were into discrete transistor design.

Start with a simple 1-transistor class A amp and understand its bias and gain.

Horowitz and Hill, The Art of Electronics, is a good book to have around.
Chapters 1 and 2 start with electrical basics and make it up to bipolar
transistor amps.

Build this and listen to it. It's a real class B amp.

https://dl.dropboxusercontent.com/u/53724080/Circuits/Amps/Class_B_Amp.JPG

Then try things to make it less horrible.

An oscilloscope is worth having here. Like a Rigol or something.

--

John Larkin Highland Technology Inc
www.highlandtechnology.com jlarkin at highlandtechnology dot com

Precision electronic instrumentation

May 24, 2014

On Saturday, May 24, 2014 8:04:38 AM UTC-7, Jim Thompson wrote:

On Fri, 23 May 2014 21:31:22 -0700, John Larkin

jjlarkin@highNOTlandTHIStechnologyPART.com> wrote:

On Fri, 23 May 2014 20:34:00 -0700 (PDT), mrdarrett@gmail.com wrote:

On Friday, May 23, 2014 8:31:04 PM UTC-7, John Larkin wrote:

On Fri, 23 May 2014 16:22:22 -0700 (PDT), mrdarrett@gmail.com wrote:

On Friday, May 23, 2014 4:14:34 PM UTC-7, John Larkin wrote:

...

If you are talking about the first circuit on that page,

then I'm not sure I'd call it class B, there is a path

from the opamp output to the speaker.

(I also thought it should have a bit of resistance in there,

opamp to speaker, but I don't know... JL has posted circuits like that.)

It's a boosted opamp, not really "class B". Voltage regulators, like

LM7805s and such, are sometimes "helped out" by a parallel PNP,

similar idea.

George H.

Here's a different one. Is this more accurately Class B with NFB?

http://www.allaboutcircuits.com/vol_6/chpt_6/10.html

Thanks,

Michael

The rightmost 0.22 uF cap allows the opamp to drive the load some

directly at higher frequencies. A resistor there makes more sense.

The gain control is insane. So is the transistor biasing. It's

impressive how many really, really bad audio circuits there are

around. And there is a positive correlation between circuit badness

and web page pontification.

--

John Larkin Highland Technology, Inc

Dang. What's a beginner to do, then? I'd like to make a 12-volt wall-wart-powered class B, or AB, or boosted-opamp thingie, and would like to know *why* it works, too (so that kind of defeats the purpose of chipamps).

Any suggestions?

Thanks!

Michael

Look for some of the older literature, like the GE Transistor manuals and the

National Linear Applications books. They were into discrete transistor design.

Start with a simple 1-transistor class A amp and understand its bias and gain.

Horowitz and Hill, The Art of Electronics, is a good book to have around.

Chapters 1 and 2 start with electrical basics and make it up to bipolar

transistor amps.

Build this and listen to it. It's a real class B amp.

https://dl.dropboxusercontent.com/u/53724080/Circuits/Amps/Class_B_Amp.JPG

Then try things to make it less horrible.

An oscilloscope is worth having here. Like a Rigol or something.

--

John Larkin Highland Technology Inc

www.highlandtechnology.com jlarkin at highlandtechnology dot com

Precision electronic instrumentation

Ok, I think I'll go ahead and grab Horowitz and Hill then.

There should be lots of used ones around, 2nd edition.

Ooh, thanks! TIP31A and its PNP spouse are OK for output transistors?

Much appreciated!

Michael

Sure. You'll understand what crossover distortion is really about.

Then take the feedback from the actual output, rather than from the

OpAmp.

I had a feeling that was part of my "homework" to make it "less horrible."

Michael

distortion with Class B (with NFB) vs Class AB

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