questions on Class B audio amplifier

[John Fields]

On Wed, 22 Oct 2008 08:03:54 +0100, Eeyore
<rabbitsfriendsandrelations@hotmail.com> wrote:

mrdarrett@gmail.com wrote:

I took a look at this:
http://openbookproject.net//electricCircuits/Exper/EXP_6.html#xtocid24829

It's a total heap of garbage. It's almost beyond a joke. If the rest of the
site is like that then try to forget anything you 'learnt' there.

---
My, my...

A blanket condemnation, but nothing to back it up with?

How typical of you!


JF

 

[Phil Allison]

"John Fields"

Eeyore

For God's sake get yourself a good book on electronics and stop buggering
about
with websites written by intellectual cripples.

---
You have a web site?
---

** Try:

http://www.grahamstevenson.co.uk/

Was available up until a few days ago.

But since the pommy puke has been issuing all kinda legalistic sounding
threats against ALL his imaginary on line enemies - the gutless pommy
poonce musta pulled it.

Besides revealing his residential address - it had nothing whatever to
say.

Just like the man himself.




...... Phil

 

[John Fields]

On Wed, 22 Oct 2008 13:49:28 +1100, "Phil Allison"
<philallison@tpg.com.au> wrote:

"John Fields"

I took a look at this:

http://openbookproject.net//electricCircuits/Exper/EXP_6.html#xtocid24829

It appears that this unit's max continuous power output on +/-12VDC at
4 ohms is 18W, if I calculated that right...

---
You calculated it right, but the TL082 isn't a rail-to-rail output
opamp, so the output into the emitter follower pair would be
considerably less than 12V resulting in, consequently, less than 18
watts CW into the four ohm load.
---


** Lets see what it *really* is then:

From the data on the TL082, with +/-12 volt rails and say 500 ohms load, the
available output swing is +/- 7 volts.

Equates to 14mA peak.

From the data on the TIP41, Hfe = 50typ at Ic=1A & Vce= 4 volts.

50 times 15 = 700mA.

700 mA into 4 ohms = 2.8 volts peak.

Or 1 watt, rms continuos.

Long, long way from 18 .........

---
Yup.

Nicely done. Thanks!
JF

 

[John Larkin]

On Wed, 22 Oct 2008 01:09:17 +0100, Eeyore
<rabbitsfriendsandrelations@hotmail.com> wrote:

mrdarrett@gmail.com wrote:

I took a look at this:
http://openbookproject.net//electricCircuits/Exper/EXP_6.html#xtocid24829

It appears that this unit's max continuous power output on +/-12VDC at
4 ohms is 18W, if I calculated that right...

I wanted to build it, but I realized that increasing the voltage much
beyond +/- 12V would exceed the TL082 op amp's maximum voltage spec.

Why do you waste your time like this ?

Please become an adult.

Graham

Sure, there's only one way to build an amp, has been for 30 or 40
years, and nobody should dare do anything different.

John

 

[John Larkin]

On Tue, 21 Oct 2008 16:13:57 -0700 (PDT), mrdarrett@gmail.com wrote:

I took a look at this:
http://openbookproject.net//electricCircuits/Exper/EXP_6.html#xtocid24829

It appears that this unit's max continuous power output on +/-12VDC at
4 ohms is 18W, if I calculated that right...

I wanted to build it, but I realized that increasing the voltage much
beyond +/- 12V would exceed the TL082 op amp's maximum voltage spec.

If I used a couple of higher-voltage TLE2141Cs, good to +/- 22V, would
this give a max continuous output power of 60W?

Since this is class B, and not Class AB... does the first op amp in
the schematic above do a good job of removing the "dead time" between
crossover? THD < 1%?

Pure class B will have some crossover distortion, because the opamps
can't slew through the deadband infinitely fast.

Replacing the right-most 0.22 uF cap with a resistor *can* kill the
crossover distortion.

Does this Class B amp waste less power than Class AB (since only one
transistor is on at a time)?

Yes.

I'm guessing that all the "junk" (input stage, VAS) between the line
input and output transistors on a typical power amplifier schematic
serves pretty much the same purpose of the two op amps here...?

Yes, but uses a lot more parts. Some people like that.

John

 

[Kevin Aylward]

John Fields wrote:

On Wed, 22 Oct 2008 08:03:54 +0100, Eeyore
rabbitsfriendsandrelations@hotmail.com> wrote:



mrdarrett@gmail.com wrote:

I took a look at this:
http://openbookproject.net//electricCircuits/Exper/EXP_6.html#xtocid24829

It's a total heap of garbage. It's almost beyond a joke. If the rest
of the site is like that then try to forget anything you 'learnt'
there.

---
My, my...

A blanket condemnation, but nothing to back it up with?

For starters, the pot can be set to infinite gain, making the amp output go
to the rail and take out the speaker due to amp offsets. There is no current
limiting, hence will blow up pretty much as soon as wiring it up to a
speaker is attempted.

The schematic is truly a non starter.

Kevin Aylward

www.kevinaylward.co.uk

 

[Kevin Aylward]

Eeyore wrote:

Tim Wescott wrote:

Yes, but a typical power amp sounds better....

And Universities are turning out kids even stupider than this !

Graham

Shirley you mean knowledge challenged?

Kevin Aylward

www.kevinaylward.co.uk

 

[John Fields]

On Wed, 22 Oct 2008 19:06:31 GMT, "Kevin Aylward"
<kaExtractThis@kevinaylward.co.uk> wrote:

John Fields wrote:
On Wed, 22 Oct 2008 08:03:54 +0100, Eeyore
rabbitsfriendsandrelations@hotmail.com> wrote:



mrdarrett@gmail.com wrote:

I took a look at this:
http://openbookproject.net//electricCircuits/Exper/EXP_6.html#xtocid24829

It's a total heap of garbage. It's almost beyond a joke. If the rest
of the site is like that then try to forget anything you 'learnt'
there.

---
My, my...

A blanket condemnation, but nothing to back it up with?



For starters, the pot can be set to infinite gain, making the amp output go
to the rail and take out the speaker due to amp offsets. There is no current
limiting, hence will blow up pretty much as soon as wiring it up to a
speaker is attempted.

---
Now, see, that's what _Graham_ should have said.

JF

 

[Rich Grise]

On Tue, 21 Oct 2008 22:04:06 -0500, John Fields wrote:

On Wed, 22 Oct 2008 02:35:37 +0100, Eeyore

Would you two please take your personal piss-fest elsewhere? This is
sci.electronics.basics, where there is no such thing as a dumb quetion;
all newbies are welcome here. Remember, we were all beginners once.

Thanks,
Rich

 

[Rich Grise]

On Wed, 22 Oct 2008 19:06:35 +0000, Kevin Aylward wrote:

Eeyore wrote:
Tim Wescott wrote:

Yes, but a typical power amp sounds better....

And Universities are turning out kids even stupider than this !

Shirley you mean knowledge challenged?

Well, stupid is as stupid does. ;-)

Cheers!
Rich

 

[BobG]

Seems like you could get rid of the 1st amp... it just buffers the 10k
pot. You could make the 2nd amp non inverting and feed the input pot
wiper into the + input.

 

[Phil Allison]

"Kevin Aylward"

For starters, the pot can be set to infinite gain, making the amp output
go to the rail and take out the speaker due to amp offsets. There is no
current limiting,

** Err - not true.

The output current is limited by the Hfe of the TIP41/42s to about 700 - 800
mA peak, since the TL082 has internal limiting at about +/-15mA.

hence will blow up pretty much as soon as wiring it up to a speaker is
attempted

** Not true at all.



...... Phil

 

On Oct 21, 7:49 pm, "Phil Allison" <philalli...@tpg.com.au> wrote:

"John Fields"

I took a look at this:

http://openbookproject.net//electricCircuits/Exper/EXP_6.html#xtocid2...

It appears that this unit's max continuous power output on +/-12VDC at
4 ohms is 18W, if I calculated that right...

---
You calculated it right, but the TL082 isn't a rail-to-rail output
opamp, so the output into the emitter follower pair would be
considerably less than 12V resulting in, consequently, less than 18
watts CW into the four ohm load.
---

** Lets see what it *really* is then:

From the data on the TL082, with +/-12 volt rails and say 500 ohms load, the
available output swing is +/- 7 volts.

Equates to 14mA peak.

From the data on the TIP41, Hfe = 50typ at Ic=1A & Vce= 4 volts.

50 times 15 = 700mA.

700 mA into 4 ohms = 2.8 volts peak.

Or 1 watt, rms continuos.

Long, long way from 18 .........

...... Phil

Gain problem could be fixed with two Sziklai pairs of transistors,
right?

Michael

 

On Oct 22, 8:58 am, John Larkin
<jjlar...@highNOTlandTHIStechnologyPART.com> wrote:

On Tue, 21 Oct 2008 16:13:57 -0700 (PDT), mrdarr...@gmail.com wrote:
I took a look at this:
http://openbookproject.net//electricCircuits/Exper/EXP_6.html#xtocid2...

It appears that this unit's max continuous power output on +/-12VDC at
4 ohms is 18W, if I calculated that right...

I wanted to build it, but I realized that increasing the voltage much
beyond +/- 12V would exceed the TL082 op amp's maximum voltage spec.

If I used a couple of higher-voltage TLE2141Cs, good to +/- 22V, would
this give a max continuous output power of 60W?

Since this is class B, and not Class AB... does the first op amp in
the schematic above do a good job of removing the "dead time" between
crossover? THD < 1%?

Pure class B will have some crossover distortion, because the opamps
can't slew through the deadband infinitely fast.

Replacing the right-most 0.22 uF cap with a resistor *can* kill the
crossover distortion.



Does this Class B amp waste less power than Class AB (since only one
transistor is on at a time)?

Yes.



I'm guessing that all the "junk" (input stage, VAS) between the line
input and output transistors on a typical power amplifier schematic
serves pretty much the same purpose of the two op amps here...?

Yes, but uses a lot more parts. Some people like that.

John

For those who want to impress with More Parts... this Class D chip amp
is for you... page 12 : http://www.zetex.com/3.0/pdf/zxcd1000.pdf

Michael

 

[Phil Allison]

<mrdarrett@gmail.com>

From the data on the TL082, with +/-12 volt rails and say 500 ohms load,
the
available output swing is +/- 7 volts.


Where did you get 500 ohms for load?

** See above.