distortion with Class B (with NFB) vs Class AB

May 24, 2014

On Saturday, May 24, 2014 8:02:44 AM UTC-7, Jim Thompson wrote:

On Fri, 23 May 2014 20:26:01 -0700 (PDT), mrdarrett@gmail.com wrote:

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

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

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

...

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

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

from the opamp output to the speaker.

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

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

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

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

similar idea.

George H.

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

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

Thanks,

Michael

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

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

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

impressive how many really, really bad audio circuits there are

around. And there is a positive correlation between circuit badness

and web page pontification.

--

John Larkin Highland Technology, Inc

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

Any suggestions?

Thanks!

Michael

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

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

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

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

Michael

UC Davis? Good professor there knowledgeable in electronically

commutated DC motors. Can't remember his name now, but I visited him

there in the late '90's when I was designing the Bosch motor control

chip...

http://www.analog-innovations.com/SED/DC_Motor_Electronically_Commutated..jpg

I'm sure there are some good ones, but the ENG 17 class was all theory and nothing fun. Even worse, the professor sold us at the bookstore a photocopy of ALL her lecture slides, and I found myself yawning during class because there was nothing to write.

One notable thing: she told us the day before an exam that a student oncee drew a picture of a Star Trek phasor when she asked for a "phasor diagram," saying "this one is set to stun," "this one is set to kill" and threatened to fail anyone who did something like that again.

It wasn't until my brother-in-law repaired the car stereo (that *his* brother had installed with the polarity reversed) that I recovered my interest in electronics. He de-soldered the chip amp and soldered in a new one.

Michael

May 24, 2014

You might want to have a look at the print for the Phase Linear 400 Series Two.

They specify the bias as a voltage across R128, which is a 10 ohm resistor across the bases and the commons of the emitter resistors of the outputs. It specifies 0.35 to 0.40 volts.

It seems that the intention is to actually have the drivers drive the load at very small power levels. The outputs would not kick in until you have about another tenth of a volt or so, across that ten ohm resistor.

Yet the thing seems to meet distortion specs, or did. I don't have the equipmnt for that but of course it was tested when they were new and for sale. Right ?

The thing must have a quite high open loop gain, because I don't see how this could be linear. Obviously the feedback is taking care of it. With a rated damping factor of 1,000, it's more than just having ten ohm shunt resistors on the outputs.

If you play with the bias of an amp whie watching the waveform coming off the voltage amp, you will see the crossover distorion, well not really, you are seeing the correction applied by the feedback to attempt to eliminate the crossover distortion.

Another thing that didn't take off but could be a viable option is high frequency AC bias. It may actually be more efficient. Keep it well away from the audible range and that little output choke will eliminate it, yet it still varies the quiescent operating point enough to get rid of any crossover distortion. It probably doesn't really need to thermally tracxk the outputs' temperature either, as long as no significant load is presented to it at that frequency.

May 24, 2014

On Saturday, May 24, 2014 10:09:53 AM UTC-7, jurb...@gmail.com wrote:

You might want to have a look at the print for the Phase Linear 400 Series Two.

They specify the bias as a voltage across R128, which is a 10 ohm resistor across the bases and the commons of the emitter resistors of the outputs. It specifies 0.35 to 0.40 volts.

It seems that the intention is to actually have the drivers drive the load at very small power levels. The outputs would not kick in until you have about another tenth of a volt or so, across that ten ohm resistor.

Yet the thing seems to meet distortion specs, or did. I don't have the equipmnt for that but of course it was tested when they were new and for sale.. Right ?

The thing must have a quite high open loop gain, because I don't see how this could be linear. Obviously the feedback is taking care of it. With a rated damping factor of 1,000, it's more than just having ten ohm shunt resistors on the outputs.

If you play with the bias of an amp whie watching the waveform coming off the voltage amp, you will see the crossover distorion, well not really, you are seeing the correction applied by the feedback to attempt to eliminate the crossover distortion.

Another thing that didn't take off but could be a viable option is high frequency AC bias. It may actually be more efficient. Keep it well away from the audible range and that little output choke will eliminate it, yet it still varies the quiescent operating point enough to get rid of any crossover distortion. It probably doesn't really need to thermally tracxk the outputs' temperature either, as long as no significant load is presented to it at that frequency.

Oh, wow, a complete schematic included with the manual?

http://bradshirakawa2.files.wordpress.com/2013/06/phase-linear-400-ii-instruction-manual.pdf

Impressive THD and IMD specs!

May 24, 2014

I think that manual is in error. The THD was stated at 0.09 %, not 0.009 %.

I doubt that particular circuit is capable of getting it that low.

Of course rare is the ear as well as the source material that enables one to hear 0.09 % THD.

May 24, 2014

Scans of th original manual are at BAMA.

May 24, 2014

On Saturday, May 24, 2014 10:50:24 AM UTC-7, Jim Thompson wrote:

On Sat, 24 May 2014 10:18:47 -0700 (PDT), mrdarrett@gmail.com wrote:

On Saturday, May 24, 2014 10:09:53 AM UTC-7, jurb...@gmail.com wrote:

You might want to have a look at the print for the Phase Linear 400 Series Two.

They specify the bias as a voltage across R128, which is a 10 ohm resistor across the bases and the commons of the emitter resistors of the outputs. It specifies 0.35 to 0.40 volts.

It seems that the intention is to actually have the drivers drive the load at very small power levels. The outputs would not kick in until you have about another tenth of a volt or so, across that ten ohm resistor.

Yet the thing seems to meet distortion specs, or did. I don't have the equipmnt for that but of course it was tested when they were new and for sale. Right ?

The thing must have a quite high open loop gain, because I don't see how this could be linear. Obviously the feedback is taking care of it. With a rated damping factor of 1,000, it's more than just having ten ohm shunt resistors on the outputs.

If you play with the bias of an amp whie watching the waveform coming off the voltage amp, you will see the crossover distorion, well not really, you are seeing the correction applied by the feedback to attempt to eliminate the crossover distortion.

Another thing that didn't take off but could be a viable option is high frequency AC bias. It may actually be more efficient. Keep it well away from the audible range and that little output choke will eliminate it, yet it still varies the quiescent operating point enough to get rid of any crossover distortion. It probably doesn't really need to thermally tracxk the outputs' temperature either, as long as no significant load is presented to it at that frequency.

Oh, wow, a complete schematic included with the manual?

http://bradshirakawa2.files.wordpress.com/2013/06/phase-linear-400-ii-instruction-manual.pdf

Impressive THD and IMD specs!

As John Larkin said, build some small projects first... and only move

up when none of those "flame out" ;-)

Yes, I plan to! I'm encouraged that reasonable volume can be made from just the 5V coming out of USB...

Jim Thompson · May 24, 2014

On Fri, 23 May 2014 20:26:01 -0700 (PDT), mrdarrett@gmail.com wrote:

On Friday, May 23, 2014 5:42:26 PM UTC-7, Jim Thompson wrote:
On Fri, 23 May 2014 16:22:22 -0700 (PDT), mrdarrett@gmail.com wrote:

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

...

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

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

from the opamp output to the speaker.

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

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

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

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

similar idea.

George H.

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

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

Thanks,

Michael

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

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

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

impressive how many really, really bad audio circuits there are

around. And there is a positive correlation between circuit badness

and web page pontification.

--

John Larkin Highland Technology, Inc

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

Any suggestions?

Thanks!

Michael

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

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

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

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

Michael

UC Davis? Good professor there knowledgeable in electronically
commutated DC motors. Can't remember his name now, but I visited him
there in the late '90's when I was designing the Bosch motor control
chip...

<http://www.analog-innovations.com/SED/DC_Motor_Electronically_Commutated.jpg>

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

Jim Thompson · May 24, 2014

On Fri, 23 May 2014 21:31:22 -0700, John Larkin
<jjlarkin@highNOTlandTHIStechnologyPART.com> wrote:

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

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

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

...

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

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

from the opamp output to the speaker.

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

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

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

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

similar idea.

George H.

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

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

Thanks,

Michael

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

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

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

impressive how many really, really bad audio circuits there are

around. And there is a positive correlation between circuit badness

and web page pontification.

--

John Larkin Highland Technology, Inc

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

Any suggestions?

Thanks!

Michael

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

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

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

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

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

transistor amps.

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

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

Then try things to make it less horrible.

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

--

John Larkin Highland Technology Inc

www.highlandtechnology.com jlarkin at highlandtechnology dot com

Precision electronic instrumentation

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

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

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

Much appreciated!

Michael

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

Jim Thompson · May 24, 2014

On Sat, 24 May 2014 10:18:47 -0700 (PDT), mrdarrett@gmail.com wrote:

On Saturday, May 24, 2014 10:09:53 AM UTC-7, jurb...@gmail.com wrote:
You might want to have a look at the print for the Phase Linear 400 Series Two.

They specify the bias as a voltage across R128, which is a 10 ohm resistor across the bases and the commons of the emitter resistors of the outputs. It specifies 0.35 to 0.40 volts.

It seems that the intention is to actually have the drivers drive the load at very small power levels. The outputs would not kick in until you have about another tenth of a volt or so, across that ten ohm resistor.

Yet the thing seems to meet distortion specs, or did. I don't have the equipmnt for that but of course it was tested when they were new and for sale. Right ?

The thing must have a quite high open loop gain, because I don't see how this could be linear. Obviously the feedback is taking care of it. With a rated damping factor of 1,000, it's more than just having ten ohm shunt resistors on the outputs.

If you play with the bias of an amp whie watching the waveform coming off the voltage amp, you will see the crossover distorion, well not really, you are seeing the correction applied by the feedback to attempt to eliminate the crossover distortion.

Another thing that didn't take off but could be a viable option is high frequency AC bias. It may actually be more efficient. Keep it well away from the audible range and that little output choke will eliminate it, yet it still varies the quiescent operating point enough to get rid of any crossover distortion. It probably doesn't really need to thermally tracxk the outputs' temperature either, as long as no significant load is presented to it at that frequency.

Oh, wow, a complete schematic included with the manual?

http://bradshirakawa2.files.wordpress.com/2013/06/phase-linear-400-ii-instruction-manual.pdf

Impressive THD and IMD specs!

John Larkin · May 25, 2014

On Sat, 24 May 2014 09:44:01 -0700 (PDT), mrdarrett@gmail.com wrote:

On Saturday, May 24, 2014 8:04:38 AM UTC-7, Jim Thompson wrote:
On Fri, 23 May 2014 21:31:22 -0700, John Larkin

jjlarkin@highNOTlandTHIStechnologyPART.com> wrote:

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

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

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

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

...

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

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

from the opamp output to the speaker.

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

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

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

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

similar idea.

George H.

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

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

Thanks,

Michael

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

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

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

impressive how many really, really bad audio circuits there are

around. And there is a positive correlation between circuit badness

and web page pontification.

--

John Larkin Highland Technology, Inc

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

Any suggestions?

Thanks!

Michael

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

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

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

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

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

transistor amps.

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

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

Then try things to make it less horrible.

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

--

John Larkin Highland Technology Inc

www.highlandtechnology.com jlarkin at highlandtechnology dot com

Precision electronic instrumentation

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

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

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

Much appreciated!

Michael

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

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

OpAmp.

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

Michael

And then bias the transistors on some.

May 26, 2014

>"I'm encouraged that reasonable volume can be made from just the 5V coming out of USB... "

Some people would be surprised at how loud just one watt is. Take whatever amp you got and put a meter on it, on an eight ohm speaker run it up to where there is 2.83 volts read on the meter going into the speaker.

Pretty loud actually, louder than alot of people listen to music or the TV, whatever.

Then take it to double the voltage which will be four times the wattage, and see how much louder it ISN'T.

This is why crossover distortion needs to be addressed. Things are a bit different down in the milliwatts. Really, alot of people listen to things at like a quarter watt or so. Down there is where you can really hear crossover distortion. Crank it up to ten watts and it'll be clear as a bell, kinda. The distortion is still there but it is only a small part of the output.

Let's not even go into what an acoustic watt is. Levels like that'll blow you right out of there. I forgot what it is, but an acoustic watt is LOUD.

Jurd · May 27, 2014

On 5/26/2014 11:53 AM, jurb6006@gmail.com wrote:

"I'm encouraged that reasonable volume can be made from just the 5V coming out of USB..."

Some people would be surprised at how loud just one watt is. Take whatever amp you got and put a meter on it, on an eight ohm speaker run it up to where there is 2.83 volts read on the meter going into the speaker.

Pretty loud actually, louder than alot of people listen to music or the TV, whatever.

Then take it to double the voltage which will be four times the wattage, and see how much louder it ISN'T.

This is why crossover distortion needs to be addressed. Things are a bit different down in the milliwatts. Really, alot of people listen to things at like a quarter watt or so. Down there is where you can really hear crossover distortion. Crank it up to ten watts and it'll be clear as a bell, kinda. The distortion is still there but it is only a small part of the output.

Let's not even go into what an acoustic watt is. Levels like that'll blow you right out of there. I forgot what it is, but an acoustic watt is LOUD.

No kidding. Guitarists seem especially bad about this. I'm constantly
hearing guys insist they need these high powered tube amps (pushing two,
four or eight 12" speakers) or similar, and yet they'll probably rattle
their teeth loose if they turn it up past 3. A lot of other things
factor into SPL (speaker, cabinet, what freqs are emphasized, etc) but
my main amplifier (Laney ProTube AOR) is rated 22W RMS into the speaker.
It is PLENTY. I had a 50W version of the same amp and it was ungodly
loud- too loud (and heavy) for me to use on a regular basis. I can't
imagine how deafening it was in the 1970s when touring musicians played
in front of a wall of 100W Marshall JTMs going full tilt. Amazing sound
but those volume levels were absolute madness I'm sure. Madness I say!

Meanwhile, I have a pile of LM386 chipamps that I practice with
regularly. I think a couple are 250mW and one is 500mW. They're quite
adequate. I've made a few for some guitar buddies and they're always
amazed at how loud they are for being so low-powered.

-J

May 27, 2014

On Monday, May 26, 2014 12:14:17 PM UTC-7, Jurd wrote:

On 5/26/2014 11:53 AM, jurb6006@gmail.com wrote:

"I'm encouraged that reasonable volume can be made from just the 5V coming out of USB..."

Some people would be surprised at how loud just one watt is. Take whatever amp you got and put a meter on it, on an eight ohm speaker run it up to where there is 2.83 volts read on the meter going into the speaker.

Pretty loud actually, louder than alot of people listen to music or the TV, whatever.

Then take it to double the voltage which will be four times the wattage, and see how much louder it ISN'T.

This is why crossover distortion needs to be addressed. Things are a bit different down in the milliwatts. Really, alot of people listen to things at like a quarter watt or so. Down there is where you can really hear crossover distortion. Crank it up to ten watts and it'll be clear as a bell, kinda. The distortion is still there but it is only a small part of the output.

Let's not even go into what an acoustic watt is. Levels like that'll blow you right out of there. I forgot what it is, but an acoustic watt is LOUD.

No kidding. Guitarists seem especially bad about this. I'm constantly

hearing guys insist they need these high powered tube amps (pushing two,

four or eight 12" speakers) or similar, and yet they'll probably rattle

their teeth loose if they turn it up past 3. A lot of other things

factor into SPL (speaker, cabinet, what freqs are emphasized, etc) but

my main amplifier (Laney ProTube AOR) is rated 22W RMS into the speaker.

It is PLENTY. I had a 50W version of the same amp and it was ungodly

loud- too loud (and heavy) for me to use on a regular basis. I can't

imagine how deafening it was in the 1970s when touring musicians played

in front of a wall of 100W Marshall JTMs going full tilt. Amazing sound

but those volume levels were absolute madness I'm sure. Madness I say!

Meanwhile, I have a pile of LM386 chipamps that I practice with

regularly. I think a couple are 250mW and one is 500mW. They're quite

adequate. I've made a few for some guitar buddies and they're always

amazed at how loud they are for being so low-powered.

-J

Oh! How many watts are typically required for a rock concert?

M

Maynard A. Philbrook Jr. · May 28, 2014

In article <19e13d0a-978a-4af9-89e5-dc20eaa62b64@googlegroups.com>,
mrdarrett@gmail.com says...

amazed at how loud they are for being so low-powered.

-J

Oh! How many watts are typically required for a rock concert?

M

What ever it takes to get those rocks a flying!

Jamie

Jurd · May 28, 2014

On 5/27/2014 1:01 AM, mrdarrett@gmail.com wrote:

-J

Oh! How many watts are typically required for a rock concert?

M

All of them!

As I'm sure you know the modern-ish (and better) solution is miking the
amp at practice volume and sending it through the PA to fill the room.
Even clubs and small shows do this for a better, more even sound. The
last couple of times I saw Dick Dale there weren't any amps on stage at
all, he was connected to some hidden backline via wireless.

I don't know why they didn't figure that out long ago, when you had to
hit the back of the stadium with stage volume.

-J

May 28, 2014

>"Oh! How many watts are typically required for a rock concert?

Actually none.

May 28, 2014

On Wednesday, May 28, 2014 2:30:52 AM UTC-7, jurb...@gmail.com wrote:

"Oh! How many watts are typically required for a rock concert?

Actually none.

Like this?

http://memeheroes.com/83e90-just-listening-to-some-rock/

May 29, 2014

She looks doable...

As for the THD, to eliminate that, glue it to the floor.

If she protests your advances, glue her to the floor as well.

Problem solved. And don't start bitching about that, some girls really like it.

Just hope for the best, if not, see you in twenty years or whatever.

Jurd · May 29, 2014

On 5/28/2014 12:12 PM, mrdarrett@gmail.com wrote:

On Wednesday, May 28, 2014 2:30:52 AM UTC-7, jurb...@gmail.com wrote:
"Oh! How many watts are typically required for a rock concert?

Actually none.

Like this?

http://memeheroes.com/83e90-just-listening-to-some-rock/

Nothing like cute girls who listen to heavy rock. I'm a bit concerned
about the THD of that rug it's sitting on, though.

-J

JW · May 29, 2014

On Wed, 28 May 2014 16:27:39 -0500 Jurd
<guitardorkspamspameggsandham74@gmail.com> wrote in Message id:
<lm5kbm$fpj$1@news.albasani.net>:

On 5/28/2014 12:12 PM, mrdarrett@gmail.com wrote:
On Wednesday, May 28, 2014 2:30:52 AM UTC-7, jurb...@gmail.com wrote:
"Oh! How many watts are typically required for a rock concert?

Actually none.

Like this?

http://memeheroes.com/83e90-just-listening-to-some-rock/

Nothing like cute girls who listen to heavy rock.

Better yet, cute girls who play heavy metal.
https://www.youtube.com/results?search_query=meytal+cohen

Yum!

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