1. Home
  2. Hobby Electronics Basics
  3. Audio Amp Crossover Distortion?

Audio Amp Crossover Distortion?

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 470=B5 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 1=B5 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

Reply to
Bill Bowden
Loading thread data ...

"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 - d*****ad.

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

... Phil

Reply to
Phil Allison

open it with ltspice and you can see the schematic

It's not just a netlist.

--
?? 100% natural

--- Posted via news://freenews.netfront.net/ - Complaints to news@netfront.net
Reply to
Jasen Betts

"Jasen Betts = TROLLING PSYCHO PARROT "

** Fuck off to hell !!!

You MORONIC pile of Kiwi sheep shagging shit.

Reply to
Phil Allison

What he posted *is* a schematic.

--
"For a successful technology, reality must take precedence 
over public relations, for nature cannot be fooled."
                                       (Richard Feynman)
Reply to
Fred Abse

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

Here's a pic

formatting link

Does this output have a name?

George H.

Reply to
George Herold

If you look at the opamp output in the simulation you'll see that it has some near-vertical segments at crossover -- this means you're working the amp pretty hard, and it's an opportunity for Bad Things to happen.

Make sure that the slew rate, DC gain, and gain-bandwidth product of your "universal" op-amp matches the data sheet for what you're using. You may want to check the real op-amp's output impedance, if it's even listed. If not, try tossing a 600 ohm resistor in series with your op-amp's output, see what that does.

And take a look at your real op-amp output in your real circuit; see what it's doing.

Beyond that -- I dunno.

--
My liberal friends think I'm a conservative kook.
My conservative friends think I'm a liberal kook.
Why am I not happy that they have found common ground?

Tim Wescott, Communications, Control, Circuits & Software
http://www.wescottdesign.com
Reply to
Tim Wescott

** Fuckwit, pedantic twaddle .
Reply to
Phil Allison

"George Herold"

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

Here's a pic

formatting link

** 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

Reply to
Phil Allison

Unstable ?:-) ...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  |             |
| Voice:(480)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.
Reply to
Jim Thompson

Yes, slew rate may be the problem. I was using a LM358 which may not be the best. I thought anything would work at audio freqs. The book shows 10uS to move 3 volts into 2K with a 15 volt supply. The output impedance also appears high since adding a 560 resistor in series with the output doesn't change things much. The distortion is present at the op-amp output and looks about the same as the main output.

The thing I don't understand is how the feedback signal from the distorted output looks so good at the (+) input to the op-amp. It's a

10K resistor with a distorted waveform on one side and a clean signal on the other.

-Bill

Reply to
Bill Bowden

Time to pretend you live in the same universe as the rest of us Phil, or at least take your meds.

LTSpice schematics are text files, and that's what that was. I cut it and pasted it into a text file and it worked _just fine_ in LTSpice.

Because it _is_ a schematic.

I'll leave the conclusions about what that says about _your_ intelligence, wit, and state of mind to the general audience.

--
My liberal friends think I'm a conservative kook.
My conservative friends think I'm a liberal kook.
Why am I not happy that they have found common ground?

Tim Wescott, Communications, Control, Circuits & Software
http://www.wescottdesign.com
Reply to
Tim Wescott

"Bill Bowden = RETARD "

Yes, slew rate may be the problem. I was using a LM358

** ROTFLMAO.

Will this tenth wit moron never learn ANYTHING !!

Reply to
Phil Allison

e.

e

ot

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

George H.

Reply to
George Herold

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.

=A0 =A0 ...Jim Thompson

=A0 =A0| =A0 =A0mens =A0 =A0 |

=A0 | =A0 =A0 et =A0 =A0 =A0|

=A0|

=A0 =A0 =A0 |

ide quoted text -

Reply to
George Herold

I like "sliding" class-A... 1/2 the normal standby power. ...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  |             |
| Voice:(480)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.
Reply to
Jim Thompson

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

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

Reply to
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 ?

Reply to
Phil Allison

a

od

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.

=A0 =A0 ...Jim Thompson

=A0 =A0| =A0 =A0mens =A0 =A0 |

=A0 | =A0 =A0 et =A0 =A0 =A0|

=A0|

=A0 =A0 =A0 |

ide quoted text -

Reply to
George Herold

a
d
n

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

Reply to
Bill Bowden

ElectronDepot website is not affiliated with any of the manufacturers or service providers discussed here. All logos and trade names are the property of their respective owners.