Audio Amp Crossover Distortion?

Jim Thompson · Jan 14, 2012

On Fri, 13 Jan 2012 19:53:58 -0500, Bitrex
<bitrex@de.lete.earthlink.net> wrote:

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.

George Herold · Jan 14, 2012

On Jan 13, 7:05 pm, Jim Thompson <To-Email-Use-The-Envelope-I...@On-My-
Web-Site.com> wrote:

On Fri, 13 Jan 2012 15:36:20 -0800 (PST), George Herold

gher...@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

Woah... Some reading material! great.

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.
Yeah I've done plenty of class A.... brute force.

Add more voltage and resistance and I can drive that coil faster.

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.

Dang, I've only done one current mirror... doing circuits out of AoE.
just a few transitors, stuck into white proto board.

That's OK I'll never run out of circuits to try, or novels to read.

Now I've got some nice hearing aid app note to read... Grin

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 -

Phil Allison · Jan 14, 2012

"Kaz Kylheku"
Phil Allison

** 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,

** Like hell - that has a CCS as half the output stage.

The OP's schem is like a donkey with a dog's head.

.... Phil

Bill Bowden · Jan 15, 2012

On Jan 13, 4:03 pm, George Herold <gher...@teachspin.com> wrote:

On Jan 13, 12:16 pm, Phil Hobbs

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

Cheers

Phil Hobbs

Grin... maybe a good heater then.

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

I only made one mistake. That was the time I thought I made a mistake.

-Bill

Jamie · Jan 15, 2012

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.
I would love nothing more than to view that jpg however, It seems that

site is so loaded with Flash content and scam ads that It just wants to
cover all of my screen with pop up forms all over the place.

You see, I need to click on the actual image to see it properly
because it is not sized correctly for view and they know this. You click
on it, which normally brings up the image in fall details but, it also
starts a whole crap load of other scams, ads and forms to pop up all over.

These free sites in my opinion, are worthless if you really want some
one to see the content. They are just lures to get more people to see
their useless ads, take advantage of poeple and in many cases makes
your PC useless when you're trying to shut down the forms as they keep
starting as they attempt to install shopping tool bars and all the other
crap.

Just my opinion. These Free sites are nothing but bone yard traps.

You know, most providers of services (ISP)'s provide their customers
with a personal webpage or webspace of more than enough with a clean
slab to start with.

Jamie

Jim Thompson · Jan 15, 2012

On Wed, 11 Jan 2012 20:14:05 -0800 (PST), Bill Bowden
<bperryb@bowdenshobbycircuits.info> wrote:

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?

Version 4
SHEET 1 880 1108
WIRE -128 80 -128 48
WIRE -128 80 -352 80
WIRE 80 80 -128 80
WIRE 208 80 80 80
WIRE -352 96 -352 80
WIRE 80 128 80 80
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WIRE -416 208 -432 208
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WIRE -144 208 -352 208
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WIRE 80 224 80 208
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WINDOW 39 0 0 Left 0
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SYMATTR Value 8
SYMBOL pnp 144 272 M180
SYMATTR InstName Q1
SYMATTR Value 2N2905A
SYMBOL npn 144 368 R0
SYMATTR InstName Q2
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SYMATTR Value 8
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WINDOW 3 32 32 VTop 0
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WINDOW 39 0 0 Left 0
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SYMATTR Value SINE(0 .25 1000)
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SYMATTR Value .2
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WINDOW 0 -37 42 Left 0
WINDOW 3 -35 76 Left 0
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SYMATTR Value 2k
SYMBOL Opamps\\UniversalOpamp2 -80 320 R0
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SYMBOL res 192 64 R0
SYMATTR InstName R12
SYMATTR Value .2
TEXT -504 600 Left 0 !.tran 0 100m 0 startup

Jamie · Jan 15, 2012

Bill Bowden wrote:

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?

Version 4
SHEET 1 880 1108
WIRE -128 80 -128 48
WIRE -128 80 -352 80
WIRE 80 80 -128 80
WIRE 208 80 80 80
WIRE -352 96 -352 80
WIRE 80 128 80 80
WIRE 208 176 208 160
WIRE -416 208 -432 208
WIRE -352 208 -352 176
WIRE -144 208 -352 208
WIRE -512 224 -512 208
WIRE 80 224 80 208
WIRE 144 224 80 224
WIRE 80 240 80 224
WIRE -352 256 -352 208
WIRE -144 304 -144 208
WIRE -112 304 -144 304
WIRE 80 320 -48 320
WIRE 208 320 208 272
WIRE 320 320 208 320
WIRE 336 320 320 320
WIRE 432 320 400 320
WIRE -112 336 -144 336
WIRE 80 336 80 320
WIRE -208 352 -208 336
WIRE 208 368 208 320
WIRE -80 384 -80 352
WIRE 144 416 80 416
WIRE -480 432 -480 416
WIRE 80 432 80 416
WIRE -208 448 -208 432
WIRE -144 448 -144 336
WIRE -144 448 -208 448
WIRE -96 448 -144 448
WIRE 16 448 -16 448
WIRE -208 464 -208 448
WIRE -480 528 -480 512
WIRE 80 544 80 512
WIRE -208 560 -208 544
WIRE 16 608 16 448
WIRE 320 608 320 320
WIRE 320 608 16 608
FLAG -80 288 +V
FLAG -480 416 +V
FLAG -480 528 0
FLAG -80 384 0
FLAG 432 400 0
FLAG -512 224 0
FLAG -352 336 0
FLAG 208 544 0
FLAG -208 336 +V
FLAG 80 544 0
FLAG -208 560 0
FLAG -128 48 +V
SYMBOL voltage -480 416 R0
WINDOW 123 0 0 Left 0
WINDOW 39 0 0 Left 0
WINDOW 0 44 23 Left 0
WINDOW 3 51 56 Left 0
SYMATTR InstName V1
SYMATTR Value 8
SYMBOL pnp 144 272 M180
SYMATTR InstName Q1
SYMATTR Value 2N2905A
SYMBOL npn 144 368 R0
SYMATTR InstName Q2
SYMATTR Value 2N2219A
SYMBOL res 64 112 R0
SYMATTR InstName R1
SYMATTR Value 120
SYMBOL res 64 224 R0
SYMATTR InstName R2
SYMATTR Value 560
SYMBOL res 64 320 R0
SYMATTR InstName R3
SYMATTR Value 560
SYMBOL res 64 416 R0
SYMATTR InstName R4
SYMATTR Value 120
SYMBOL res 416 304 R0
SYMATTR InstName R5
SYMATTR Value 8
SYMBOL cap 400 304 R90
WINDOW 0 0 32 VBottom 0
WINDOW 3 32 32 VTop 0
SYMATTR InstName C2
SYMATTR Value 470ľ
SYMBOL voltage -416 208 R90
WINDOW 0 -32 56 VBottom 0
WINDOW 3 57 63 VTop 0
WINDOW 123 0 0 Left 0
WINDOW 39 0 0 Left 0
SYMATTR InstName V2
SYMATTR Value SINE(0 .25 1000)
SYMBOL res 0 432 R90
WINDOW 0 0 56 VBottom 0
WINDOW 3 32 56 VTop 0
SYMATTR InstName R6
SYMATTR Value 10k
SYMBOL res -368 240 R0
WINDOW 0 54 44 Left 0
WINDOW 3 52 76 Left 0
SYMATTR InstName R9
SYMATTR Value 20k
SYMBOL cap -352 192 R90
WINDOW 0 0 32 VBottom 0
WINDOW 3 32 32 VTop 0
SYMATTR InstName C4
SYMATTR Value 1ľ
SYMBOL res -224 336 R0
WINDOW 0 -38 44 Left 0
WINDOW 3 -38 74 Left 0
SYMATTR InstName R7
SYMATTR Value 2k
SYMBOL res -368 80 R0
WINDOW 0 50 43 Left 0
WINDOW 3 49 76 Left 0
SYMATTR InstName R10
SYMATTR Value 20k
SYMBOL res 192 448 R0
SYMATTR InstName R11
SYMATTR Value .2
SYMBOL res -224 448 R0
WINDOW 0 -37 42 Left 0
WINDOW 3 -35 76 Left 0
SYMATTR InstName R8
SYMATTR Value 2k
SYMBOL Opamps\\UniversalOpamp2 -80 320 R0
SYMATTR InstName U2
SYMBOL res 192 64 R0
SYMATTR InstName R12
SYMATTR Value .2
TEXT -504 600 Left 0 !.tran 0 100m 0 startup
I don 't understand why you don't see it in the sim?

I see all kinds of problems there.

THe outputs are current modes and the beta on the outputs are most
likely are not going to match well.

On top of that, LTspice shows the upper output (PNP) going into
discontinue state at the cross over. This is going to give you a period
of what I call a flat liner and 99% sure this is where your cross over
error is coming from.

Plot the current on R12.

Jamie

George Herold · Jan 16, 2012

On Jan 15, 2:17 pm, Jamie
<jamie_ka1lpa_not_valid_after_ka1l...@charter.net> wrote:

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.

I would love nothing more than to view that jpg however, It seems that
site is so loaded with Flash content and scam ads that It just wants to
cover all of my screen with pop up forms all over the place.

You see, I need to click on the actual image to see it properly
because it is not sized correctly for view and they know this. You click
on it, which normally brings up the image in fall details but, it also
starts a whole crap load of other scams, ads and forms to pop up all over..

These free sites in my opinion, are worthless if you really want some
one to see the content. They are just lures to get more people to see
their useless ads, take advantage of poeple and in many cases makes
your PC useless when you're trying to shut down the forms as they keep
starting as they attempt to install shopping tool bars and all the other
crap.

Just my opinion. These Free sites are nothing but bone yard traps.

You know, most providers of services (ISP)'s provide their customers
with a personal webpage or webspace of more than enough with a clean
slab to start with.

Jamie- Hide quoted text -

- Show quoted text -

Yeah sorry, It seems to have gotten much worse.

Got a better image hosting site? I tries this tinyurl one. But it
wanted me to enter
a security code for each image.

I suppose I could try and set up a web page.... Yola?

George H.

Kaz Kylheku · Jan 16, 2012

On 2012-01-15, Jamie <jamie_ka1lpa_not_valid_after_ka1lpa_@charter.net> wrote:

http://imageshack.us/photo/my-images/708/crossover.jpg/

Does this output have a name?

George H.
I would love nothing more than to view that jpg however, It seems that
site is so loaded with Flash content and scam ads that It just wants to
cover all of my screen with pop up forms all over the place.

I didn't notice.

Ah that's right, I run the NoScript blocker available for Firefox. NoScript
identifies all the sites which, for the given page, are being used as sources
of JavaScript code. You can individually add them to the good list.

These free sites in my opinion, are worthless if you really want some
one to see the content. They are just lures to get more people to see
their useless ads, take advantage of poeple and in many cases makes

What ads? Adblock! I absolutely do not see a single ad or popup on this site.
Just text, a few buttons like "Sign Up" (That one is scripted: clicking on
it works) and the image.

Your fault for not getting a clue about what browsers can do for you.

Bill Bowden · Jan 16, 2012

On Jan 15, 11:40 am, Jamie

<jamie_ka1lpa_not_valid_after_ka1l...@charter.net> wrote:

I don 't understand why you don't see it in the sim?

I see all kinds of problems there.

THe outputs are current modes and the beta on the outputs are
most
likely are not going to match well.

On top of that, LTspice shows the upper output (PNP) going into
discontinue state at the cross over. This is going to give you a
period
of what I call a flat liner and 99% sure this is where your cross
over
error is coming from.

Plot the current on R12.

Jamie

Yes, I did view the current through R12 which looks normal. The thing
operates class AB, so only one transistor is on at a time, so a 50%
discontinuous current is normal. I did improve the distortion using a
1458 op-amp in place of the 358. Looks much better now. The problem
now is I only get 1.5 volts peak into 8 ohms with an 8 volt supply and
I was trying for 3 volts or more. The HFE figure for the 2N2219A is
minimum 40 at 500mA or 7.5mA at 300mA. The 120 ohm resistor draws .
7/120 = about 6 mA so the op-amp must deliver 13.5 mA and the spec
sheet says only 10 mA short circuit. So, apparently, it needs higher
gain transistors or an op-amp with lower output impedance, or both.
Any ideas?

-Bill

Jamie · Jan 16, 2012

George Herold wrote:

On Jan 15, 2:17 pm, Jamie
jamie_ka1lpa_not_valid_after_ka1l...@charter.net> wrote:

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.

I would love nothing more than to view that jpg however, It seems that
site is so loaded with Flash content and scam ads that It just wants to
cover all of my screen with pop up forms all over the place.

You see, I need to click on the actual image to see it properly
because it is not sized correctly for view and they know this. You click
on it, which normally brings up the image in fall details but, it also
starts a whole crap load of other scams, ads and forms to pop up all over.

These free sites in my opinion, are worthless if you really want some
one to see the content. They are just lures to get more people to see
their useless ads, take advantage of poeple and in many cases makes
your PC useless when you're trying to shut down the forms as they keep
starting as they attempt to install shopping tool bars and all the other
crap.

Just my opinion. These Free sites are nothing but bone yard traps.

You know, most providers of services (ISP)'s provide their customers
with a personal webpage or webspace of more than enough with a clean
slab to start with.

Jamie- Hide quoted text -

- Show quoted text -

Yeah sorry, It seems to have gotten much worse.

Got a better image hosting site? I tries this tinyurl one. But it
wanted me to enter
a security code for each image.

I suppose I could try and set up a web page.... Yola?

George H.
Your best bet would be to take advantage of your ISP service, that is,

if you're using a private one instead of those free Email or economical
services.

I know times are tough and all the starving chiefs out there are
trying their best to profit off the innocent indians. We wouldn't want
them to be reminded of what it is like to actually to do something for
that money.

As far as image hosting sites, I am sure you can find another that
isn't so overwhelmed with useless garbage.

Your provider should be giving you a small chunk of personal web
space. It's an easy thing to do. You simply navigate your browser using
the copy and paste to your page or use a FTP program. Then you provide
the link to your site plus the name of the image you put there.

By the looks of your address, it looks like you should be able to get
one that provides you a clean page, not one that is a child form of a
business page, which is just as bad!

Myself, I have the option of 5 E-mails, each one around 100megs of
space the last time I checked. It's been a while.

Jamie

Jamie · Jan 16, 2012

Bill Bowden wrote:

On Jan 15, 11:40 am, Jamie

jamie_ka1lpa_not_valid_after_ka1l...@charter.net> wrote:

I don 't understand why you don't see it in the sim?

I see all kinds of problems there.

THe outputs are current modes and the beta on the outputs are
most
likely are not going to match well.

On top of that, LTspice shows the upper output (PNP) going into
discontinue state at the cross over. This is going to give you a
period
of what I call a flat liner and 99% sure this is where your cross
over
error is coming from.

Plot the current on R12.

Jamie

Yes, I did view the current through R12 which looks normal. The thing
operates class AB, so only one transistor is on at a time, so a 50%
discontinuous current is normal. I did improve the distortion using a
1458 op-amp in place of the 358. Looks much better now. The problem
now is I only get 1.5 volts peak into 8 ohms with an 8 volt supply and
I was trying for 3 volts or more. The HFE figure for the 2N2219A is
minimum 40 at 500mA or 7.5mA at 300mA. The 120 ohm resistor draws .
7/120 = about 6 mA so the op-amp must deliver 13.5 mA and the spec
sheet says only 10 mA short circuit. So, apparently, it needs higher
gain transistors or an op-amp with lower output impedance, or both.
Any ideas?

-Bill

That op-amp does not pull the reals, the 358 will do that effect on the
load side and there by give you more v to bias the transistors.

I don't think you have a current demand problem, you may have a rail
to rail problem how ever.

The 1458, as old as it is, still has a lot of usages. The las time I
looked, that op-amp (dual) only provides ~ Vcc-1.5 and Vee-1.5. Here you
have lost 3 volts to start with. This now gives you 5 volts to play with.

Of course, you really don't want to saturate the amp, so lets assume
you have only 4.5V to work with..

split that in half, since you looks apparrent you are operating in
Class A state on the output side of the op-amp and you get ~ 2.25 volts
Peak to play with.

Now., let us not forget, the minimum required for each of those
transistors to start working. ~ 0.7 and then times this by 2 and you get
1.4. Remove that value off the top and you are now getting closer to
where the problem is.

That configuration you're using in the first place is fighting against
you. As one side is conducting the other side is still conducting, just
about all the way through. This is going to remove a good chunk of your
output.

Have you considered a config like the following or something in this line?

8Volts-----------------------------+
+ |
|
|
+
|<
+-----------------+|
___ | |\
+--+|___|-+----------------++ |
| | | +
+ | | |
|| | |\+ | | 1Ku
-||+--++-------------+|-\ | | ||
|| | >+-------+----------+---+||+-----+
+-+-|+/ | || |
4Volts |/+ | +
| | |
| | .-.
| | | |
+ + | |8
| |/ '-'
+-----------------+| |
|> GND
+
|
|
===
GND

Jamie

Jim Thompson · Jan 16, 2012

On Mon, 16 Jan 2012 09:34:51 -0500, Jamie
<jamie_ka1lpa_not_valid_after_ka1lpa_@charter.net> wrote:

Bill Bowden wrote:

On Jan 15, 11:40 am, Jamie

jamie_ka1lpa_not_valid_after_ka1l...@charter.net> wrote:

I don 't understand why you don't see it in the sim?

I see all kinds of problems there.

THe outputs are current modes and the beta on the outputs are
most
likely are not going to match well.

On top of that, LTspice shows the upper output (PNP) going into
discontinue state at the cross over. This is going to give you a
period
of what I call a flat liner and 99% sure this is where your cross
over
error is coming from.

Plot the current on R12.

Jamie

Yes, I did view the current through R12 which looks normal. The thing
operates class AB, so only one transistor is on at a time, so a 50%
discontinuous current is normal. I did improve the distortion using a
1458 op-amp in place of the 358. Looks much better now. The problem
now is I only get 1.5 volts peak into 8 ohms with an 8 volt supply and
I was trying for 3 volts or more. The HFE figure for the 2N2219A is
minimum 40 at 500mA or 7.5mA at 300mA. The 120 ohm resistor draws .
7/120 = about 6 mA so the op-amp must deliver 13.5 mA and the spec
sheet says only 10 mA short circuit. So, apparently, it needs higher
gain transistors or an op-amp with lower output impedance, or both.
Any ideas?

-Bill

That op-amp does not pull the reals, the 358 will do that effect on the
load side and there by give you more v to bias the transistors.

I don't think you have a current demand problem, you may have a rail
to rail problem how ever.

The 1458, as old as it is, still has a lot of usages. The las time I
looked, that op-amp (dual) only provides ~ Vcc-1.5 and Vee-1.5. Here you
have lost 3 volts to start with. This now gives you 5 volts to play with.

Of course, you really don't want to saturate the amp, so lets assume
you have only 4.5V to work with..

split that in half, since you looks apparrent you are operating in
Class A state on the output side of the op-amp and you get ~ 2.25 volts
Peak to play with.

Now., let us not forget, the minimum required for each of those
transistors to start working. ~ 0.7 and then times this by 2 and you get
1.4. Remove that value off the top and you are now getting closer to
where the problem is.

That configuration you're using in the first place is fighting against
you. As one side is conducting the other side is still conducting, just
about all the way through. This is going to remove a good chunk of your
output.

Have you considered a config like the following or something in this line?

8Volts-----------------------------+
+ |
|
|
+
|
+-----------------+|
___ | |\
+--+|___|-+----------------++ |
| | | +
+ | | |
|| | |\+ | | 1Ku
-||+--++-------------+|-\ | | ||
|| | >+-------+----------+---+||+-----+
+-+-|+/ | || |
4Volts |/+ | +
| | |
| | .-.
| | | |
+ + | |8
| |/ '-'
+-----------------+| |
|> GND
+
|
|
===
GND

Jamie

krw@att.bizzzzzzzzzzzz · Jan 16, 2012

On Mon, 16 Jan 2012 17:54:45 +0000 (UTC), Kaz Kylheku <kaz@kylheku.com> wrote:

On 2012-01-16, George Herold <gherold@teachspin.com> wrote:
I suppose I could try and set up a web page.... Yola?

A circuit image should compress extremely well because it contains pixels of a
few colors, and most of them are white. Therefore you should be able to post
it right to the newsgroup, uuencoded into a single article.

(Yes, I can hear it now: ``gasp, a binary to a discussion group?'')

Well, if it is small and on-topic, what is the harm?

The "harm" is that it sets a bad precedent. It won't propagate anyway, so
there is little point.

The benefit is that is that the picture permanently stays with the discussion.

These URL's people post will be long gone, making much of the archived
discussion junk.

Kaz Kylheku · Jan 16, 2012

On 2012-01-16, George Herold <gherold@teachspin.com> wrote:

I suppose I could try and set up a web page.... Yola?

A circuit image should compress extremely well because it contains pixels of a
few colors, and most of them are white. Therefore you should be able to post
it right to the newsgroup, uuencoded into a single article.

(Yes, I can hear it now: ``gasp, a binary to a discussion group?'')

Well, if it is small and on-topic, what is the harm?

The benefit is that is that the picture permanently stays with the discussion.

These URL's people post will be long gone, making much of the archived
discussion junk.

fungus · Jan 16, 2012

On Jan 16, 6:54 pm, Kaz Kylheku <k...@kylheku.com> wrote:

A circuit image should compress extremely well because it contains pixels of a
few colors, and most of them are white. Therefore you should be able to post
it right to the newsgroup, uuencoded into a single article.

If you choose the right image format and do
everything 100% correctly, sure.

Well, if it is small and on-topic, what is the harm?

It sets a precedent. Before you know it people
are posting 75MB uncompressed TIFF files
and ISPs are banning the newsgroup.

Instead of educating the posters after-the-fact
why don't we educate the readers beforehand?

I didn't see any adverts or popups on that site
and neither did some other readers. It's all
down to using setting up your web browser
properly.

Jamie · Jan 17, 2012

Jim Thompson wrote:

On Mon, 16 Jan 2012 09:34:51 -0500, Jamie
jamie_ka1lpa_not_valid_after_ka1lpa_@charter.net> wrote:

Bill Bowden wrote:

On Jan 15, 11:40 am, Jamie

jamie_ka1lpa_not_valid_after_ka1l...@charter.net> wrote:

I don 't understand why you don't see it in the sim?

I see all kinds of problems there.

THe outputs are current modes and the beta on the outputs are
most
likely are not going to match well.

On top of that, LTspice shows the upper output (PNP) going into
discontinue state at the cross over. This is going to give you a
period
of what I call a flat liner and 99% sure this is where your cross
over
error is coming from.

Plot the current on R12.

Jamie

Yes, I did view the current through R12 which looks normal. The thing
operates class AB, so only one transistor is on at a time, so a 50%
discontinuous current is normal. I did improve the distortion using a
1458 op-amp in place of the 358. Looks much better now. The problem
now is I only get 1.5 volts peak into 8 ohms with an 8 volt supply and
I was trying for 3 volts or more. The HFE figure for the 2N2219A is
minimum 40 at 500mA or 7.5mA at 300mA. The 120 ohm resistor draws .
7/120 = about 6 mA so the op-amp must deliver 13.5 mA and the spec
sheet says only 10 mA short circuit. So, apparently, it needs higher
gain transistors or an op-amp with lower output impedance, or both.
Any ideas?

-Bill

That op-amp does not pull the reals, the 358 will do that effect on the
load side and there by give you more v to bias the transistors.

I don't think you have a current demand problem, you may have a rail
to rail problem how ever.

The 1458, as old as it is, still has a lot of usages. The las time I
looked, that op-amp (dual) only provides ~ Vcc-1.5 and Vee-1.5. Here you
have lost 3 volts to start with. This now gives you 5 volts to play with.

Of course, you really don't want to saturate the amp, so lets assume
you have only 4.5V to work with..

split that in half, since you looks apparrent you are operating in
Class A state on the output side of the op-amp and you get ~ 2.25 volts
Peak to play with.

Now., let us not forget, the minimum required for each of those
transistors to start working. ~ 0.7 and then times this by 2 and you get
1.4. Remove that value off the top and you are now getting closer to
where the problem is.

That configuration you're using in the first place is fighting against
you. As one side is conducting the other side is still conducting, just
about all the way through. This is going to remove a good chunk of your
output.

Have you considered a config like the following or something in this line?

8Volts-----------------------------+
+ |
|
|
+
|
+-----------------+|
___ | |\
+--+|___|-+----------------++ |
| | | +
+ | | |
|| | |\+ | | 1Ku
-||+--++-------------+|-\ | | ||
|| | >+-------+----------+---+||+-----+
+-+-|+/ | || |
4Volts |/+ | +
| | |
| | .-.
| | | |
+ + | |8
| |/ '-'
+-----------------+| |
|> GND
+
|
|
===
GND

Jamie

What sets the quiescent current thru the PNP-NPN path?

...Jim Thompson

The quiescent I of the op-amp and load.

In Ltspice it was ~ 70 ma with that basic circuit in both
the PNP and NPN. I was using 700..800 ma trannies.

Putting an R between Vcc and B of the PNP will drop that down
a bit and bring it closer to being symmetrical. Also, you can
use a R on the op output to the collector bridge to lower the
Quies.

I Didn't save the spice I used but I am sure I can put it together
again and post it if you wish, I just used what was in the stock lib.

Jamie

Jim Thompson · Jan 17, 2012

On Mon, 16 Jan 2012 19:07:38 -0500, Jamie
<jamie_ka1lpa_not_valid_after_ka1lpa_@charter.net> wrote:

Jim Thompson wrote:

On Mon, 16 Jan 2012 09:34:51 -0500, Jamie
jamie_ka1lpa_not_valid_after_ka1lpa_@charter.net> wrote:

Bill Bowden wrote:

On Jan 15, 11:40 am, Jamie

jamie_ka1lpa_not_valid_after_ka1l...@charter.net> wrote:

I don 't understand why you don't see it in the sim?

I see all kinds of problems there.

THe outputs are current modes and the beta on the outputs are
most
likely are not going to match well.

On top of that, LTspice shows the upper output (PNP) going into
discontinue state at the cross over. This is going to give you a
period
of what I call a flat liner and 99% sure this is where your cross
over
error is coming from.

Plot the current on R12.

Jamie

Yes, I did view the current through R12 which looks normal. The thing
operates class AB, so only one transistor is on at a time, so a 50%
discontinuous current is normal. I did improve the distortion using a
1458 op-amp in place of the 358. Looks much better now. The problem
now is I only get 1.5 volts peak into 8 ohms with an 8 volt supply and
I was trying for 3 volts or more. The HFE figure for the 2N2219A is
minimum 40 at 500mA or 7.5mA at 300mA. The 120 ohm resistor draws .
7/120 = about 6 mA so the op-amp must deliver 13.5 mA and the spec
sheet says only 10 mA short circuit. So, apparently, it needs higher
gain transistors or an op-amp with lower output impedance, or both.
Any ideas?

-Bill

That op-amp does not pull the reals, the 358 will do that effect on the
load side and there by give you more v to bias the transistors.

I don't think you have a current demand problem, you may have a rail
to rail problem how ever.

The 1458, as old as it is, still has a lot of usages. The las time I
looked, that op-amp (dual) only provides ~ Vcc-1.5 and Vee-1.5. Here you
have lost 3 volts to start with. This now gives you 5 volts to play with.

Of course, you really don't want to saturate the amp, so lets assume
you have only 4.5V to work with..

split that in half, since you looks apparrent you are operating in
Class A state on the output side of the op-amp and you get ~ 2.25 volts
Peak to play with.

Now., let us not forget, the minimum required for each of those
transistors to start working. ~ 0.7 and then times this by 2 and you get
1.4. Remove that value off the top and you are now getting closer to
where the problem is.

That configuration you're using in the first place is fighting against
you. As one side is conducting the other side is still conducting, just
about all the way through. This is going to remove a good chunk of your
output.

Have you considered a config like the following or something in this line?

8Volts-----------------------------+
+ |
|
|
+
|
+-----------------+|
___ | |\
+--+|___|-+----------------++ |
| | | +
+ | | |
|| | |\+ | | 1Ku
-||+--++-------------+|-\ | | ||
|| | >+-------+----------+---+||+-----+
+-+-|+/ | || |
4Volts |/+ | +
| | |
| | .-.
| | | |
+ + | |8
| |/ '-'
+-----------------+| |
|> GND
+
|
|
===
GND

Jamie

What sets the quiescent current thru the PNP-NPN path?

...Jim Thompson

The quiescent I of the op-amp and load.

In Ltspice it was ~ 70 ma with that basic circuit in both
the PNP and NPN. I was using 700..800 ma trannies.

Putting an R between Vcc and B of the PNP will drop that down
a bit and bring it closer to being symmetrical. Also, you can
use a R on the op output to the collector bridge to lower the
Quies.

I Didn't save the spice I used but I am sure I can put it together
again and post it if you wish, I just used what was in the stock lib.

Jamie

Try it in the real world. Have lots of spare transistors on hand

Jamie · Jan 17, 2012

Jim Thompson wrote:

On Mon, 16 Jan 2012 19:07:38 -0500, Jamie
jamie_ka1lpa_not_valid_after_ka1lpa_@charter.net> wrote:

Jim Thompson wrote:

On Mon, 16 Jan 2012 09:34:51 -0500, Jamie
jamie_ka1lpa_not_valid_after_ka1lpa_@charter.net> wrote:

Bill Bowden wrote:

On Jan 15, 11:40 am, Jamie

jamie_ka1lpa_not_valid_after_ka1l...@charter.net> wrote:

I don 't understand why you don't see it in the sim?

I see all kinds of problems there.

THe outputs are current modes and the beta on the outputs are

most

likely are not going to match well.

On top of that, LTspice shows the upper output (PNP) going into
discontinue state at the cross over. This is going to give you a

period

of what I call a flat liner and 99% sure this is where your cross

over

error is coming from.

Plot the current on R12.

Jamie

Yes, I did view the current through R12 which looks normal. The thing
operates class AB, so only one transistor is on at a time, so a 50%
discontinuous current is normal. I did improve the distortion using a
1458 op-amp in place of the 358. Looks much better now. The problem
now is I only get 1.5 volts peak into 8 ohms with an 8 volt supply and
I was trying for 3 volts or more. The HFE figure for the 2N2219A is
minimum 40 at 500mA or 7.5mA at 300mA. The 120 ohm resistor draws .
7/120 = about 6 mA so the op-amp must deliver 13.5 mA and the spec
sheet says only 10 mA short circuit. So, apparently, it needs higher
gain transistors or an op-amp with lower output impedance, or both.
Any ideas?

-Bill

That op-amp does not pull the reals, the 358 will do that effect on the
load side and there by give you more v to bias the transistors.

I don't think you have a current demand problem, you may have a rail
to rail problem how ever.

The 1458, as old as it is, still has a lot of usages. The las time I
looked, that op-amp (dual) only provides ~ Vcc-1.5 and Vee-1.5. Here you
have lost 3 volts to start with. This now gives you 5 volts to play with.

Of course, you really don't want to saturate the amp, so lets assume
you have only 4.5V to work with..

split that in half, since you looks apparrent you are operating in
Class A state on the output side of the op-amp and you get ~ 2.25 volts
Peak to play with.

Now., let us not forget, the minimum required for each of those
transistors to start working. ~ 0.7 and then times this by 2 and you get
1.4. Remove that value off the top and you are now getting closer to
where the problem is.

That configuration you're using in the first place is fighting against
you. As one side is conducting the other side is still conducting, just
about all the way through. This is going to remove a good chunk of your
output.

Have you considered a config like the following or something in this line?

8Volts-----------------------------+
+ |
|
|
+
|
+-----------------+|
___ | |\
+--+|___|-+----------------++ |
| | | +
+ | | |
|| | |\+ | | 1Ku
-||+--++-------------+|-\ | | ||
|| | >+-------+----------+---+||+-----+
+-+-|+/ | || |
4Volts |/+ | +
| | |
| | .-.
| | | |
+ + | |8
| |/ '-'
+-----------------+| |
|> GND
+
|
|
===
GND

Jamie

What sets the quiescent current thru the PNP-NPN path?

...Jim Thompson

The quiescent I of the op-amp and load.

In Ltspice it was ~ 70 ma with that basic circuit in both
the PNP and NPN. I was using 700..800 ma trannies.

Putting an R between Vcc and B of the PNP will drop that down
a bit and bring it closer to being symmetrical. Also, you can
use a R on the op output to the collector bridge to lower the
Quies.

I Didn't save the spice I used but I am sure I can put it together
again and post it if you wish, I just used what was in the stock lib.

Jamie

Try it in the real world. Have lots of spare transistors on hand

...Jim Thompson

Actually Jim, I have done that in real world cases. Which is why I
suggested it.. It does work when you use the correct set of components
and is a basic of many designs that i've seen over the years. A very
particle way to having current outputs

Old time 741 with Emitter outputs and related type power amp Ic's
work very nicely with a config like that. Of course in many cases, you
need to tailor the bias a little with some bypass R's on the Rail to the
base of each side if the Qu current is too high.

I had a load of LM380's years ago that I put to some good use making
little half bridge servos with a circuit of that type.

The only problem with that design is, if the driving op-amp happens
to circuit for some reason. It will take out the outputs. A current
limiting R on the op-amp output to the collector node is a good
practice, something I did not use here in this example. And don't forget
the bypass bias R's incase the QU Is too high in the chip that is used.

I know your an old pro and I am sure you have had your share of
smoking some silicon.

Jamie

Jim Thompson · Jan 17, 2012

On Mon, 16 Jan 2012 19:59:06 -0500, Jamie
<jamie_ka1lpa_not_valid_after_ka1lpa_@charter.net> wrote:

Jim Thompson wrote:

On Mon, 16 Jan 2012 19:07:38 -0500, Jamie
jamie_ka1lpa_not_valid_after_ka1lpa_@charter.net> wrote:

Jim Thompson wrote:

On Mon, 16 Jan 2012 09:34:51 -0500, Jamie
jamie_ka1lpa_not_valid_after_ka1lpa_@charter.net> wrote:

Bill Bowden wrote:

On Jan 15, 11:40 am, Jamie

jamie_ka1lpa_not_valid_after_ka1l...@charter.net> wrote:

I don 't understand why you don't see it in the sim?

I see all kinds of problems there.

THe outputs are current modes and the beta on the outputs are

most

likely are not going to match well.

On top of that, LTspice shows the upper output (PNP) going into
discontinue state at the cross over. This is going to give you a

period

of what I call a flat liner and 99% sure this is where your cross

over

error is coming from.

Plot the current on R12.

Jamie

Yes, I did view the current through R12 which looks normal. The thing
operates class AB, so only one transistor is on at a time, so a 50%
discontinuous current is normal. I did improve the distortion using a
1458 op-amp in place of the 358. Looks much better now. The problem
now is I only get 1.5 volts peak into 8 ohms with an 8 volt supply and
I was trying for 3 volts or more. The HFE figure for the 2N2219A is
minimum 40 at 500mA or 7.5mA at 300mA. The 120 ohm resistor draws .
7/120 = about 6 mA so the op-amp must deliver 13.5 mA and the spec
sheet says only 10 mA short circuit. So, apparently, it needs higher
gain transistors or an op-amp with lower output impedance, or both.
Any ideas?

-Bill

That op-amp does not pull the reals, the 358 will do that effect on the
load side and there by give you more v to bias the transistors.

I don't think you have a current demand problem, you may have a rail
to rail problem how ever.

The 1458, as old as it is, still has a lot of usages. The las time I
looked, that op-amp (dual) only provides ~ Vcc-1.5 and Vee-1.5. Here you
have lost 3 volts to start with. This now gives you 5 volts to play with.

Of course, you really don't want to saturate the amp, so lets assume
you have only 4.5V to work with..

split that in half, since you looks apparrent you are operating in
Class A state on the output side of the op-amp and you get ~ 2.25 volts
Peak to play with.

Now., let us not forget, the minimum required for each of those
transistors to start working. ~ 0.7 and then times this by 2 and you get
1.4. Remove that value off the top and you are now getting closer to
where the problem is.

That configuration you're using in the first place is fighting against
you. As one side is conducting the other side is still conducting, just
about all the way through. This is going to remove a good chunk of your
output.

Have you considered a config like the following or something in this line?

8Volts-----------------------------+
+ |
|
|
+
|
+-----------------+|
___ | |\
+--+|___|-+----------------++ |
| | | +
+ | | |
|| | |\+ | | 1Ku
-||+--++-------------+|-\ | | ||
|| | >+-------+----------+---+||+-----+
+-+-|+/ | || |
4Volts |/+ | +
| | |
| | .-.
| | | |
+ + | |8
| |/ '-'
+-----------------+| |
|> GND
+
|
|
===
GND

Jamie

What sets the quiescent current thru the PNP-NPN path?

...Jim Thompson

The quiescent I of the op-amp and load.

In Ltspice it was ~ 70 ma with that basic circuit in both
the PNP and NPN. I was using 700..800 ma trannies.

Putting an R between Vcc and B of the PNP will drop that down
a bit and bring it closer to being symmetrical. Also, you can
use a R on the op output to the collector bridge to lower the
Quies.

I Didn't save the spice I used but I am sure I can put it together
again and post it if you wish, I just used what was in the stock lib.

Jamie

Try it in the real world. Have lots of spare transistors on hand

...Jim Thompson

Actually Jim, I have done that in real world cases. Which is why I
suggested it.. It does work when you use the correct set of components
and is a basic of many designs that i've seen over the years. A very
particle way to having current outputs

Old time 741 with Emitter outputs and related type power amp Ic's
work very nicely with a config like that. Of course in many cases, you
need to tailor the bias a little with some bypass R's on the Rail to the
base of each side if the Qu current is too high.

I had a load of LM380's years ago that I put to some good use making
little half bridge servos with a circuit of that type.

The only problem with that design is, if the driving op-amp happens
to circuit for some reason. It will take out the outputs. A current
limiting R on the op-amp output to the collector node is a good
practice, something I did not use here in this example. And don't forget
the bypass bias R's incase the QU Is too high in the chip that is used.

I know your an old pro and I am sure you have had your share of
smoking some silicon.

Jamie

Audio Amp Crossover Distortion?

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