Audio Amp Crossover Distortion?

[George Herold]

On Jan 12, 7:27 pm, Jim Thompson <To-Email-Use-The-Envelope-I...@On-My-
Web-Site.com> wrote:

On Thu, 12 Jan 2012 08:45:44 -0800 (PST), George Herold





gher...@teachspin.com> wrote:
On Jan 11, 11:55 pm, "Phil Allison" <phi...@tpg.com.au> wrote:
"Bill Bowden"

I see excessive crossover distortion with this audio amp not shown
with LTspice. It simulates ok, but the wired circuit produces about a
50uS dead time step as the signal crosses the mid point. I tried
increasing the bias with no help. Both inputs to the op-amp look good
with no distortion. Any idea what is going on?

** You need to post a schematic  -  dickhead.

Totally  SMARTARSE of you to post only a Spice list on SEB.

...  Phil

I was going to say it's a push-pull.... but it's flipped about.

Here's a pic
http://imageshack.us/photo/my-images/708/crossover.jpg/

Does this output have a name?

George H.

Unstable ?

What's the 10k to the noninverting input about? There's an inversion
somehwere else in the circuit?

Bill, Since it's a single sided power supply a class A would be
easy... And less parts.

George H.

                                        ...Jim Thompson
--
| James E.Thompson, CTO                            |    mens     |
| Analog Innovations, Inc.                         |     et      |
| Analog/Mixed-Signal ASIC's and Discrete Systems  |    manus    |
| Phoenix, Arizona  85048    Skype: Contacts Only  |             |
| Voice480)460-2350  Fax: Available upon request |  Brass Rat  |
| E-mail Icon athttp://www.analog-innovations.com|    1962     |

I love to cook with wine.     Sometimes I even put it in the food.- Hide quoted text -

- Show quoted text -

 

[George Herold]

On Jan 12, 6:09 pm, "Phil Allison" <phi...@tpg.com.au> wrote:

"George Herold"

I was going to say it's a push-pull.... but it's flipped about.

Here's a pichttp://imageshack.us/photo/my-images/708/crossover.jpg/

** Than schem looks horribly familiar, maybe from the same idiot OP before.

It's the sort of thing you find repeated on many hobby sites that cannot
possibly work.

As drawn, it only works if the output transistors are biased for class A
operation  PLUS it cannot possibly drive an 8 ohm load. 50 ohms might be
about the limit.

The twin rail splitters are an abortion.

Bias and load driving ability depend on the + DC rail voltage, which is not
shown.

...  Phil

Yeah why not push-pull? Or if you want to do class A, use one pass
element.

George H.

 

[Phil Allison]

"George Herold"
"Phil Allison"
"George Herold"

I was going to say it's a push-pull.... but it's flipped about.

Here's a pichttp://imageshack.us/photo/my-images/708/crossover.jpg/

** Than schem looks horribly familiar, maybe from the same idiot OP
before.

It's the sort of thing you find repeated on many hobby sites that cannot
possibly work.

As drawn, it only works if the output transistors are biased for class A
operation PLUS it cannot possibly drive an 8 ohm load. 50 ohms might be
about the limit.

The twin rail splitters are an abortion.

Bias and load driving ability depend on the + DC rail voltage, which is
not
shown.

Yeah why not push-pull? Or if you want to do class A, use one pass
element.


** FFS - class A push-pull output stages are very common and technically
elegant.

You know any electronics at all ?




.... Phil

 

[Phil Allison]

"George Herold"


What's the 10k to the noninverting input about? There's an inversion
somehwere else in the circuit?


** FFS - the common emitter output stage inverts the signal.


You asleep ?

 

[Phil Allison]

"Bill Bowden= Imbecile "

A class A circuit wastes too much power.

** Strange how you chose to use one then.


The idea was to get the
highest output voltage with minimum battery drain.


** The schem is 100% fucked.


The output is common collector


** It's common emitter actually.


The 120 ohm resistors are actually a combination of thermistors
and resistors to solve the thermal stability problem.

** Which is impossible that way.

The schem is 100% fucked - it cannot work.



..... Phil

 

[Phil Allison]

"Bill Bowden"
"Phil Allison"

"Bill Bowden= Imbecile "

A class A circuit wastes too much power.

** Strange how you chose to use one then.

The idea was to get the
highest output voltage with minimum battery drain.

** The schem is 100% fucked.

The output is common collector

** It's common emitter actually.

The 120 ohm resistors are actually a combination of thermistors
and resistors to solve the thermal stability problem.

** Which is impossible that way.

The schem is 100% fucked - it cannot work.

So, why does it work in LTspice?


** The components are all idealised so impossible things happen in
simulations.

FFS - find another schem cos that one is NO FUCKING GOOD.

And learn some damn electronics too.



..... Phil

 

[George Herold]

On Jan 12, 9:30 pm, Jim Thompson <To-Email-Use-The-Envelope-I...@On-My-
Web-Site.com> wrote:

On Thu, 12 Jan 2012 18:12:59 -0800 (PST), George Herold





gher...@teachspin.com> wrote:
On Jan 12, 7:27 pm, Jim Thompson <To-Email-Use-The-Envelope-I...@On-My-
Web-Site.com> wrote:
On Thu, 12 Jan 2012 08:45:44 -0800 (PST), George Herold

gher...@teachspin.com> wrote:
On Jan 11, 11:55 pm, "Phil Allison" <phi...@tpg.com.au> wrote:
"Bill Bowden"

I see excessive crossover distortion with this audio amp not shown
with LTspice. It simulates ok, but the wired circuit produces about a
50uS dead time step as the signal crosses the mid point. I tried
increasing the bias with no help. Both inputs to the op-amp look good
with no distortion. Any idea what is going on?

** You need to post a schematic  -  dickhead.

Totally  SMARTARSE of you to post only a Spice list on SEB.

...  Phil

I was going to say it's a push-pull.... but it's flipped about.

Here's a pic
http://imageshack.us/photo/my-images/708/crossover.jpg/

Does this output have a name?

George H.

Unstable ?

What's the 10k to the noninverting input about?  There's an inversion
somehwere else in the circuit?

Bill, Since it's a single sided power supply a class A would be
easy... And less parts.

George H.

I like "sliding" class-A... 1/2 the normal standby power.

Hmm, never heard of sliding class-A, a JT invention?

So I'll guess some outer control loop that senses the voltage and
adjusts the bias. A second pass element?

But it's gotta be fast. Is it load specific?

George H.

                                        ...Jim Thompson
--
| James E.Thompson, CTO                            |    mens     |
| Analog Innovations, Inc.                         |     et      |
| Analog/Mixed-Signal ASIC's and Discrete Systems  |    manus    |
| Phoenix, Arizona  85048    Skype: Contacts Only  |             |
| Voice480)460-2350  Fax: Available upon request |  Brass Rat  |
| E-mail Icon athttp://www.analog-innovations.com|    1962     |

I love to cook with wine.     Sometimes I even put it in the food.- Hide quoted text -

- Show quoted text -

 

[Bill Bowden]

On Jan 12, 6:12 pm, George Herold <gher...@teachspin.com> wrote:

On Jan 12, 7:27 pm, Jim Thompson <To-Email-Use-The-Envelope-I...@On-My-



Web-Site.com> wrote:
On Thu, 12 Jan 2012 08:45:44 -0800 (PST), George Herold


gher...@teachspin.com> wrote:
On Jan 11, 11:55 pm, "Phil Allison" <phi...@tpg.com.au> wrote:
"Bill Bowden"

I see excessive crossover distortion with this audio amp not shown
with LTspice. It simulates ok, but the wired circuit produces about a
50uS dead time step as the signal crosses the mid point. I tried
increasing the bias with no help. Both inputs to the op-amp look good
with no distortion. Any idea what is going on?

** You need to post a schematic  -  dickhead.

Totally  SMARTARSE of you to post only a Spice list on SEB.

...  Phil

I was going to say it's a push-pull.... but it's flipped about.

Here's a pic
http://imageshack.us/photo/my-images/708/crossover.jpg/

Does this output have a name?

George H.

Unstable ?

 What's the 10k to the noninverting input about?  There's an inversion
somehwere else in the circuit?

Bill, Since it's a single sided power supply a class A would be
easy... And less parts.

George H.

A class A circuit wastes too much power. The idea was to get the
highest output voltage with minimum battery drain.

The output is common collector with a phase inversion between the op-
amp and output, so the feedback connects to the (+) input for a gain
of 11. The 120 ohm resistors are actually a combination of thermistors
and resistors to solve the thermal stability problem.
But as Tim said, the problem is probably slew rate. What op-amp would
you recommend?

-Bill

 

[Bill Bowden]

On Jan 12, 7:12 pm, "Phil Allison" <phi...@tpg.com.au> wrote:

"Bill Bowden=  Imbecile "

A class A circuit wastes too much power.

** Strange how you chose to use one then.

The idea was to get the
highest output voltage with minimum battery drain.

** The schem is 100% fucked.

The output is common collector

** It's common emitter actually.

The 120 ohm resistors are actually a combination of thermistors
and resistors to solve the thermal stability problem.

** Which is impossible that way.

 The schem is 100% fucked -  it cannot work.

....  Phil

So, why does it work in LTspice? Or did you even try it?

-Bill

 

[George Herold]

On Jan 12, 10:07 pm, Bill Bowden <bper...@bowdenshobbycircuits.info>
wrote:

On Jan 12, 6:12 pm, George Herold <gher...@teachspin.com> wrote:





On Jan 12, 7:27 pm, Jim Thompson <To-Email-Use-The-Envelope-I...@On-My-

Web-Site.com> wrote:
On Thu, 12 Jan 2012 08:45:44 -0800 (PST), George Herold

gher...@teachspin.com> wrote:
On Jan 11, 11:55 pm, "Phil Allison" <phi...@tpg.com.au> wrote:
"Bill Bowden"

I see excessive crossover distortion with this audio amp not shown
with LTspice. It simulates ok, but the wired circuit produces about a
50uS dead time step as the signal crosses the mid point. I tried
increasing the bias with no help. Both inputs to the op-amp look good
with no distortion. Any idea what is going on?

** You need to post a schematic  -  dickhead.

Totally  SMARTARSE of you to post only a Spice list on SEB.

...  Phil

I was going to say it's a push-pull.... but it's flipped about.

Here's a pic
http://imageshack.us/photo/my-images/708/crossover.jpg/

Does this output have a name?

George H.

Unstable ?

 What's the 10k to the noninverting input about?  There's an inversion
somehwere else in the circuit?

Bill, Since it's a single sided power supply a class A would be
easy... And less parts.

George H.

A class A circuit wastes too much power. The idea was to get the
highest output voltage with minimum battery drain.

The output is common collector with a phase inversion between the op-
amp and output, so the feedback connects to the (+) input for a gain
of 11. The 120 ohm resistors are actually a combination of thermistors
and resistors to solve the thermal stability problem.
But as Tim said, the problem is probably slew rate. What op-amp would
you recommend?

-Bill- Hide quoted text -

- Show quoted text -

I'm not that current on the latest opamps. But I use a lot of
OPA134's (mostly dual 2134's) 20V/us slew rate. But a 'tad' more
expensive than a LM358.

What about a standard push-pull to save power.... or class D? (I never
done a class D thing.)

George H.

 

[Phil Hobbs]

On 01/12/2012 11:45 AM, George Herold wrote:

On Jan 11, 11:55 pm, "Phil Allison"<phi...@tpg.com.au> wrote:
"Bill Bowden"

I see excessive crossover distortion with this audio amp not shown
with LTspice. It simulates ok, but the wired circuit produces about a
50uS dead time step as the signal crosses the mid point. I tried
increasing the bias with no help. Both inputs to the op-amp look good
with no distortion. Any idea what is going on?

** You need to post a schematic - dickhead.

Totally SMARTARSE of you to post only a Spice list on SEB.

... Phil

I was going to say it's a push-pull.... but it's flipped about.

Here's a pic
http://imageshack.us/photo/my-images/708/crossover.jpg/

Does this output have a name?

George H.

You could call it "Output stage that oscillates fiercely with no load,
and melts transistors rapidly"

Cheers

Phil Hobbs

--
Dr Philip C D Hobbs
Principal Consultant
ElectroOptical Innovations LLC
Optics, Electro-optics, Photonics, Analog Electronics

160 North State Road #203
Briarcliff Manor NY 10510
845-480-2058

hobbs at electrooptical dot net
http://electrooptical.net

 

[Kaz Kylheku]

On 2012-01-12, George Herold <gherold@teachspin.com> wrote:

I was going to say it's a push-pull.... but it's flipped about.

Here's a pic
http://imageshack.us/photo/my-images/708/crossover.jpg/

This circuit is very poorly designed.

I wouldn't even punch this circuit into a machine to simulate it, it is
obviously so bad.

One thing that stands out right away is that it runs off a single supply and
generates reference voltages using unbypassed voltage dividers, which is
a naive practice that begs for oscillation.

The flipped-about push-pull arrangement seems not to be operating
the transistors near cutoff like a conventional push-pull design,
which is the main idea behind class AB.

I haven't done the calculations, but at a glance, I can tell this thing will
have a lot of current flowing through the transistors at quiescence.

I wouldn't even bother thinking about cross-over distortion. That can't be a
factor here, because it doesn't look like the transistors are not going to be
cut off simultaneously.

For instance if we look at Q2, you have half the supply voltage
dropping through a 560/120 divider providing the base bias. This is likely
enough to turn on the transistor, given enough supply voltage and the same
thing is happening in the upper half, which is a PNP mirror-image. Resistor R11
provides only very modest feedback to limit the current because it is small.

Let's assume a supply of 12, so the midpoint is 6V. 120/560 * 6 gives us
1.3V. This is way above VBE so transistor will turn on. We can estimate
maximum collector current using (1.3V - 0.7V)/0.2 Ohms = 3A (!). There isn't
nearly enough current-limiting by the tiny emitter resistors.

 

[David Eather]

On Sat, 14 Jan 2012 03:16:30 +1000, Phil Hobbs
<pcdhSpamMeSenseless@electrooptical.net> wrote:

On 01/12/2012 11:45 AM, George Herold wrote:
On Jan 11, 11:55 pm, "Phil Allison"<phi...@tpg.com.au> wrote:
"Bill Bowden"

I see excessive crossover distortion with this audio amp not shown
with LTspice. It simulates ok, but the wired circuit produces about a
50uS dead time step as the signal crosses the mid point. I tried
increasing the bias with no help. Both inputs to the op-amp look good
with no distortion. Any idea what is going on?

** You need to post a schematic - dickhead.

Totally SMARTARSE of you to post only a Spice list on SEB.

... Phil

I was going to say it's a push-pull.... but it's flipped about.

Here's a pic
http://imageshack.us/photo/my-images/708/crossover.jpg/

Does this output have a name?

George H.

You could call it "Output stage that oscillates fiercely with no load,
and melts transistors rapidly"

Cheers

Phil Hobbs

OSOF or OSOF-MT ?

 

[Jim Thompson]

On Fri, 13 Jan 2012 15:36:20 -0800 (PST), George Herold
<gherold@teachspin.com> wrote:

On Jan 12, 9:47 pm, George Herold <gher...@teachspin.com> wrote:
On Jan 12, 9:30 pm, Jim Thompson <To-Email-Use-The-Envelope-I...@On-My-





Web-Site.com> wrote:
On Thu, 12 Jan 2012 18:12:59 -0800 (PST), George Herold

gher...@teachspin.com> wrote:
On Jan 12, 7:27 pm, Jim Thompson <To-Email-Use-The-Envelope-I...@On-My-
Web-Site.com> wrote:
On Thu, 12 Jan 2012 08:45:44 -0800 (PST), George Herold

gher...@teachspin.com> wrote:
On Jan 11, 11:55 pm, "Phil Allison" <phi...@tpg.com.au> wrote:
"Bill Bowden"

I see excessive crossover distortion with this audio amp not shown
with LTspice. It simulates ok, but the wired circuit produces about a
50uS dead time step as the signal crosses the mid point. I tried
increasing the bias with no help. Both inputs to the op-amp look good
with no distortion. Any idea what is going on?

** You need to post a schematic  -  dickhead.

Totally  SMARTARSE of you to post only a Spice list on SEB.

...  Phil

I was going to say it's a push-pull.... but it's flipped about.

Here's a pic
http://imageshack.us/photo/my-images/708/crossover.jpg/

Does this output have a name?

George H.

Unstable ?

What's the 10k to the noninverting input about?  There's an inversion
somehwere else in the circuit?

Bill, Since it's a single sided power supply a class A would be
easy... And less parts.

George H.

I like "sliding" class-A... 1/2 the normal standby power.

Hmm, never heard of sliding class-A, a JT invention?

So I'll guess some outer control loop that senses the voltage and
adjusts the bias.  A second pass element?

But it's gotta be fast.  Is it load specific?

George H.

OK that was a silly idea. (Two pass elements is not going to save any
power.)

(It isn't any fun to google before posting... :^)
So a sliding class A is also called class H? A variable (switch mode)
power supply rail run a volt or two above the linear pass element.

That's a pretty cool!

So how fast can you oscillate a SMPS and how fast can you swing it's
output voltage?

George H.


[snip]

Google or Wiki are not always reliable sources of information.

Check out...

http://www.analog-innovations.com/SED/HearingAidSlidingClassA.pdf

as one way I've done it.

Normal class-A has one active signal device loaded with resistance or
a fixed current mirror of value I. Say your supplies are +V and -V,
load to ground. So the peak power that can be driven into the load is
I*V. Quiescent power 2*I*V.

Now imagine a current mirror load whose value decreases when the
active signal device increases its current (and vice versa). Say the
quiescent condition is the same as above. But now you can drive peak
power of 2*I*V, twice what the normal class-A can do.

...Jim Thompson
--
| James E.Thompson, CTO | mens |
| Analog Innovations, Inc. | et |
| Analog/Mixed-Signal ASIC's and Discrete Systems | manus |
| Phoenix, Arizona 85048 Skype: Contacts Only | |
| Voice480)460-2350 Fax: Available upon request | Brass Rat |
| E-mail Icon at http://www.analog-innovations.com | 1962 |

I love to cook with wine. Sometimes I even put it in the food.

 

[Jim Thompson]

On Fri, 13 Jan 2012 23:54:46 +0000 (UTC), Kaz Kylheku
<kaz@kylheku.com> wrote:

On 2012-01-13, Phil Allison <phil_a@tpg.com.au> wrote:
** FFS - class A push-pull output stages are very common and technically
elegant.

Indeed, that looks like what the circuit is shooting for.

I found a this schematic which has a similar configuration of transistors
as the OP's circuit, also single supply, but seems better:

http://www.circuitstoday.com/wp-content/uploads/2011/03/class-A-headphone-amplifier-circuit.png

Here, a pair of diodes and resistor R5 are used to set up the collector current
through the transistors, instead of a resistive voltage divider bias. Since
diodes are used, there is independence from fluctuations in the rails. R5 at
39 ohms is much larger than the 0.2 ohm emitter resistors in the circuit
discussed in this thread, so the quiescent current is kept to about 18 mA.
(Approximation: 1.4V diode stack minus 0.7 forward voltage, divided by 39
ohms).

The OP's circuit could be improved by adopting some of these ideas, and also
with the addition of some bypass caps on those voltage dividers around the op
amp.

While you are amusing yourself, what is it that determines the output
Q-point... quiescent voltage at the + node of C3 ?

...Jim Thompson
--
| James E.Thompson, CTO | mens |
| Analog Innovations, Inc. | et |
| Analog/Mixed-Signal ASIC's and Discrete Systems | manus |
| Phoenix, Arizona 85048 Skype: Contacts Only | |
| Voice480)460-2350 Fax: Available upon request | Brass Rat |
| E-mail Icon at http://www.analog-innovations.com | 1962 |

I love to cook with wine. Sometimes I even put it in the food.

 

[George Herold]

On Jan 12, 9:47 pm, George Herold <gher...@teachspin.com> wrote:

On Jan 12, 9:30 pm, Jim Thompson <To-Email-Use-The-Envelope-I...@On-My-





Web-Site.com> wrote:
On Thu, 12 Jan 2012 18:12:59 -0800 (PST), George Herold

gher...@teachspin.com> wrote:
On Jan 12, 7:27 pm, Jim Thompson <To-Email-Use-The-Envelope-I...@On-My-
Web-Site.com> wrote:
On Thu, 12 Jan 2012 08:45:44 -0800 (PST), George Herold

gher...@teachspin.com> wrote:
On Jan 11, 11:55 pm, "Phil Allison" <phi...@tpg.com.au> wrote:
"Bill Bowden"

I see excessive crossover distortion with this audio amp not shown
with LTspice. It simulates ok, but the wired circuit produces about a
50uS dead time step as the signal crosses the mid point. I tried
increasing the bias with no help. Both inputs to the op-amp look good
with no distortion. Any idea what is going on?

** You need to post a schematic  -  dickhead.

Totally  SMARTARSE of you to post only a Spice list on SEB.

...  Phil

I was going to say it's a push-pull.... but it's flipped about.

Here's a pic
http://imageshack.us/photo/my-images/708/crossover.jpg/

Does this output have a name?

George H.

Unstable ?

What's the 10k to the noninverting input about?  There's an inversion
somehwere else in the circuit?

Bill, Since it's a single sided power supply a class A would be
easy... And less parts.

George H.

I like "sliding" class-A... 1/2 the normal standby power.

Hmm, never heard of sliding class-A, a JT invention?

So I'll guess some outer control loop that senses the voltage and
adjusts the bias.  A second pass element?

But it's gotta be fast.  Is it load specific?

George H.

OK that was a silly idea. (Two pass elements is not going to save any
power.)

(It isn't any fun to google before posting... :^)
So a sliding class A is also called class H? A variable (switch mode)
power supply rail run a volt or two above the linear pass element.

That's a pretty cool!

So how fast can you oscillate a SMPS and how fast can you swing it's
output voltage?

George H.

                                        ...Jim Thompson
--
| James E.Thompson, CTO                            |    mens     |
| Analog Innovations, Inc.                         |     et      |
| Analog/Mixed-Signal ASIC's and Discrete Systems  |    manus    |
| Phoenix, Arizona  85048    Skype: Contacts Only  |             |
| Voice480)460-2350  Fax: Available upon request |  Brass Rat  |
| E-mail Icon athttp://www.analog-innovations.com|   1962     |

I love to cook with wine.     Sometimes I even put it in the food.- Hide quoted text -

- Show quoted text -- Hide quoted text -

- Show quoted text -- Hide quoted text -

- Show quoted text -

 

[Bill Bowden]

On Jan 13, 10:28 am, Kaz Kylheku <k...@kylheku.com> wrote:

On 2012-01-12, George Herold <gher...@teachspin.com> wrote:

I was going to say it's a push-pull.... but it's flipped about.

Here's a pic
http://imageshack.us/photo/my-images/708/crossover.jpg/

This circuit is very poorly designed.

I wouldn't even punch this circuit into a machine to simulate it, it is
obviously so bad.

One thing that stands out right away is that it runs off a single supply and
generates reference voltages using unbypassed voltage dividers, which is
a naive practice that begs for oscillation.

The gain is set with the two 2K resistors and the 10K for a gain of
11. Bypass caps would upset the gain figure.

The flipped-about push-pull arrangement seems not to be operating
the transistors near cutoff like a conventional push-pull design,
which is the main idea behind class AB.

I haven't done the calculations, but at a glance, I can tell this thing will
have a lot of current flowing through the transistors at quiescence.

I wouldn't even bother thinking about cross-over distortion. That can't be a
factor here, because it doesn't look like the transistors are not going to be
cut off simultaneously.

There is cross-over distortion which doesn't seem to be related to the
bias current since I ran the supply voltage up to increase the bias
current with no effect on distortion.

For instance if we look at Q2, you have half the supply voltage
dropping through a 560/120 divider providing the base bias. This is likely
enough to turn on the transistor, given enough supply voltage and the same
thing is happening in the upper half, which is a PNP mirror-image. Resistor R11
provides only very modest feedback to limit the current because it is small.

Let's assume a supply of 12, so the midpoint is 6V. 120/560 * 6 gives us
1.3V. This is way above VBE so transistor will turn on. We can estimate
maximum collector current using (1.3V - 0.7V)/0.2 Ohms = 3A (!). There isn't
nearly enough current-limiting by the tiny emitter resistors.

The tiny resistors are only there to measure the bias current. Thermal
stability is another problem.

-Bill

 

[Bitrex]

On 1/13/2012 7:13 PM, Jim Thompson wrote:

On Fri, 13 Jan 2012 23:54:46 +0000 (UTC), Kaz Kylheku
kaz@kylheku.com> wrote:

On 2012-01-13, Phil Allison <phil_a@tpg.com.au> wrote:
** FFS - class A push-pull output stages are very common and technically
elegant.

Indeed, that looks like what the circuit is shooting for.

I found a this schematic which has a similar configuration of transistors
as the OP's circuit, also single supply, but seems better:

http://www.circuitstoday.com/wp-content/uploads/2011/03/class-A-headphone-amplifier-circuit.png

Here, a pair of diodes and resistor R5 are used to set up the collector current
through the transistors, instead of a resistive voltage divider bias. Since
diodes are used, there is independence from fluctuations in the rails. R5 at
39 ohms is much larger than the 0.2 ohm emitter resistors in the circuit
discussed in this thread, so the quiescent current is kept to about 18 mA.
(Approximation: 1.4V diode stack minus 0.7 forward voltage, divided by 39
ohms).

The OP's circuit could be improved by adopting some of these ideas, and also
with the addition of some bypass caps on those voltage dividers around the op
amp.

While you are amusing yourself, what is it that determines the output
Q-point... quiescent voltage at the + node of C3 ?

...Jim Thompson

Looks like R3 should go to the output node. It doesn't make any sense
being where it is now. Then DC feedback would make the output sit at
about 5 volts, which would be about right for a symmetric swing given
the compliance of the upper current source. I also don't know why R3 is
connected where it is, it would make more sense connected to the top of
R1. I think you'd then have a pretty conventional, but workable amplifier.

 

[Kaz Kylheku]

On 2012-01-13, Phil Allison <phil_a@tpg.com.au> wrote:

** FFS - class A push-pull output stages are very common and technically
elegant.

Indeed, that looks like what the circuit is shooting for.

I found a this schematic which has a similar configuration of transistors
as the OP's circuit, also single supply, but seems better:

http://www.circuitstoday.com/wp-content/uploads/2011/03/class-A-headphone-amplifier-circuit.png

Here, a pair of diodes and resistor R5 are used to set up the collector current
through the transistors, instead of a resistive voltage divider bias. Since
diodes are used, there is independence from fluctuations in the rails. R5 at
39 ohms is much larger than the 0.2 ohm emitter resistors in the circuit
discussed in this thread, so the quiescent current is kept to about 18 mA.
(Approximation: 1.4V diode stack minus 0.7 forward voltage, divided by 39
ohms).

The OP's circuit could be improved by adopting some of these ideas, and also
with the addition of some bypass caps on those voltage dividers around the op
amp.

 

[George Herold]

On Jan 13, 12:16 pm, Phil Hobbs
<pcdhSpamMeSensel...@electrooptical.net> wrote:

On 01/12/2012 11:45 AM, George Herold wrote:





On Jan 11, 11:55 pm, "Phil Allison"<phi...@tpg.com.au>  wrote:
"Bill Bowden"

I see excessive crossover distortion with this audio amp not shown
with LTspice. It simulates ok, but the wired circuit produces about a
50uS dead time step as the signal crosses the mid point. I tried
increasing the bias with no help. Both inputs to the op-amp look good
with no distortion. Any idea what is going on?

** You need to post a schematic  -  dickhead.

Totally  SMARTARSE of you to post only a Spice list on SEB.

...  Phil

I was going to say it's a push-pull.... but it's flipped about.

Here's a pic
http://imageshack.us/photo/my-images/708/crossover.jpg/

Does this output have a name?

George H.

You could call it "Output stage that oscillates fiercely with no load,
and melts transistors rapidly"

Cheers

Phil Hobbs

--
Dr Philip C D Hobbs
Principal Consultant
ElectroOptical Innovations LLC
Optics, Electro-optics, Photonics, Analog Electronics

160 North State Road #203
Briarcliff Manor NY 10510
845-480-2058

hobbs at electrooptical dot nethttp://electrooptical.net- Hide quoted text -

- Show quoted text -

Grin... maybe a good heater then.

Bill, I hope you'll take this as good natured kidding. We all make
mistakes.

(I can only learn by making mistakes, so the faster I make 'em the
more I know.)

When I've got something new to design, I like to think of a bunch of
ways to solve the problem. Then if you try a hair-brained one and it
fails, you've got something to fall back on.

George H.