10% THD?

[Phil Allison]

"BobG"

** Hey Bob,

take a breath - ?you are not talking about the same topic as others here
!! ==============================================

I claimed that one cannot see 3% distortion in a sine wave on a scope.

** But you can see 3 % clipping distortion.

The tops of the sine wave are flattened and in most cases 100 / 120 Hz
power supply ripple becomes visible too.

I got a response that this is utter nonsense,

** Which it is - in the context of this thread.

and its easy to see 1%THD on a scope.

** Which it IS when the distortion is hard clipping of a pure sine wave.


You are now off on a tangent all your own.

Take your lunch and a warm jumper.

It may get cold and lonely.



...... Phil

 

[[email protected]]

Perhaps you have better ears than the rest of us. ;-)

There's a cellphone ringtone that supposedly only teenagers can hear,
no one over thirty - so if they get a call, their parents/teachers are
none the wiser.

Michael

How would that be possible?



Adam
Do something good today. Fight cancer with just a click! - Global
Cancer Research Institute
http://gcri.blogspot.com/

 

[Eeyore]

==============================================
I claimed that one cannot see 3% distortion in a sine wave on a scope.

And the only 3% distortion you'll see from a modern solid state amplifier is
CLIPPING distortion.

Graham

 

[[email protected]]

How would that be possible?

Adam
Do something good today. Fight cancer with just a click! - Global
Cancer Research Institutehttp://gcri.blogspot.com/

http://www.freemosquitoringtones.org/

 

[[email protected]]

How would that be possible?

Adam
Do something good today. Fight cancer with just a click! - Global
Cancer Research Institutehttp://gcri.blogspot.com/

.... and this
http://saunderslog.com/2006/06/12/the-mosquito-ring-tone-this-adult-can-hear-it/

 

[Phil Allison]

"Bob Masta"

For most modern amp designs, the curve of distortion versus power
output at 1 kHz looks like a lopsided valley: At very low outputs,
there is moderate crossover distortion, which essentially is a
fixed-size discontinuity near zero so it becomes a smaller percentage
of the total at output power rises. So distortion decreases linearly
until some mid-power region (1-10 watts, say).

** Totally false !!!!!!!!!!!!!!!!!

The characteristic rise in published THD curves at power levels below about
1 watt is almost * entirely * due to supply frequency hum and wide band
random noise.

NOT any mysterious x-over region effects !!!!!!!!!!

The general definition of THD *** includes *** hum and noise - which
tends to be a fixed level at all power outputs.
So the PERCENTAGE increases the signal level reduces !!!

Obvious - right ?

At any rate, the manufacturer has to make a judgement call about
what power level to claim.

** Bollocks.

The typical power output difference between the 0.1% THD level and 0.01%
THD level is trivial for the majority of hi-fi quality SS amps. Maybe 102
watts as compared to 100 watts.

Only by doing THD measurements on * real amplifiers * can one have any
insight into the facts of the matter .

Which I do all the time.

While Bob does not.



....... Phil

 

[Bob Eld]

I called them again (the phone lines were clear this time).

Confirmed that, yes, it is 10%. (Tech guy asked his supervisor).

okay then...

Either way, the manual said 8 ohm to 16 ohm impedance only... I was
thinking of using the 4-ohm subwoofer speakers I got (great deal on
car audio) that I currently use on my Onkyo.

Oh well..

"Nobody in their right mind..." ha ha ha.

Thanks guys

M

Well, maybe I should change it to nobody in their right mind would BUY such
a lousy amplifier. You certainly can do better than 10%THD but at what
price, I don't know. This thing might fit your needs if sound quality is not
a big issue.

Four ohms is going to make things worse because if the amp struggles with 8
ohms, 4 will require more current loading the amps even more. However, a
sub-woofer may not care, the speaker will not respond to the higher
harmonics anyway.

In my mind, a bigger issue is intermodulation distortion. If it produces
high harmonic distortion, you can bet it has high IM as well. This is also a
nonlinear distortion and is curiously not even spec'd on the data sheet.
What does that tell you?

 

[Eeyore]

Well, maybe I should change it to nobody in their right mind would BUY such
a lousy amplifier. You certainly can do better than 10%THD but at what
price, I don't know. This thing might fit your needs if sound quality is not
a big issue.

I think you're missing the point.

I have little doubt that this amplifier is capable of 0.1% THD at say 60W.

The 10% THD figure has simply been used in order to produce an inflated power
rating. This is considered normal practice with car audio.

Graham

 

[Bob Eld]

I think you're missing the point.

I have little doubt that this amplifier is capable of 0.1% THD at say 60W.

The 10% THD figure has simply been used in order to produce an inflated power
rating. This is considered normal practice with car audio.

Graham

Yep, apparently that must be the case. However, this isn't car audio. Here's
the device:
http://av.jvc.com/product.jsp?modelId=MODL027647&pathId=5&page=2

Also, can this POS deliver 100 Watts of its distorted power on all five of
it's channels simultaneously? I'll bet not. The rating must be one channel
at a time run for just the few seconds it takes to get a measurement and no
longer.

 

[[email protected]]

Yep, apparently that must be the case. However, this isn't car audio. Here's
the device:http://av.jvc.com/product.jsp?modelId=MODL027647&pathId=5&page=2

Also, can this POS deliver 100 Watts of its distorted power on all five of
it's channels simultaneously? I'll bet not. The rating must be one channel
at a time run for just the few seconds it takes to get a measurement and no
longer.

IIRC, the mannual says the power supply consumes 155W, 200VA.

I'm guessing the power supply won't appreciate being driven on all 5
channels with subwoofers.

Don't you love it when a device is spec'ed at 500W output, with less
than 200W input. I explained it to my wife this way: how can a
business collect only $200 a day, but spend $500 a day, and stay
afloat?

But this isn't unique to JVC. Sherwood's unit does something
similar. (Power cable says 200W, and it's rated at 500W or more.)

Which is why, I guess, if I want 500W per channel, I'd better build
the darn thing myself. ;-)

Michael

 

[BobG]

Yo Phil.... theoretical question.... I have two hi quality sine
generators and a THD meter. If I set generator 1 at 1V 1KHz and
generator 2 at .03V 3khz, thats the only 'distortion component', 3rd
harmonic thats 3% of the fundamental. I guess I could square it and
sqrt it, but since thats the only harmonic, would it show 3% THD on
the meter? Thanks.

 

[Phil Allison]

"Bob Masta"
"Phil Allison"

(I'm not sure why you are calling crossover distortion "mysterious"...
I suspect it is the main source of the residual distortion at the
bottom of the valley around 1 watt or so.)

** The crossover region in most SS amps is around the 10 - 20 mW power
level - a bias setting of 25mA allow class A operation up to 50 mA peak
at 8ohms = 10 mW .

10 mW is 40 dB below 100 watts and so 40 dB below the quoted s/n ratio for
such an amp.

Allow the measured s/n ratio to be 90dB unweighted, then the s/n at 10 mW is
only 50 dB and -50 dB equates to 0.3 %.

The distortion residual at 10 mW output ( as seen on a scope after removing
the fundamental) is usually much lower than 0.3 %.

QED.


........ Phil

 

[Phil Allison]

"BobG"

Yo Phil.... theoretical question.... I have two hi quality sine
generators and a THD meter. If I set generator 1 at 1V 1KHz and
generator 2 at .03V 3khz, thats the only 'distortion component', 3rd
harmonic thats 3% of the fundamental. I guess I could square it and
sqrt it, but since thats the only harmonic, would it show 3% THD on
the meter? Thanks.

** You are no longer talking about waveform distortion - but a spurious
signal.

Once the 1kHz wave is removed, the 3 kHz is left alone.

So it will give a 3% reading, like you say.

But so would some 60 Hz hum or a supersonic signal.



....... Phil

 

[z]

Are they serious?

http://av.jvc.com/product.jsp?modelId=MODL027647&pathId=5&page=2
"100 watts per channel, 8 ohms at 1kHz, with 10% THD"

10% THD sounds like a lot.

Michael

you used to see this kind of spec all the time for junk-grade audio.
but jvc? sad.

 

[z]

There's a cellphone ringtone that supposedly only teenagers can hear,
no one over thirty - so if they get a call, their parents/teachers are
none the wiser.

there are 6 "mosquito" ringtones from 15 khz up to 20khz. i've tested
them all (vzw tones, motorola krazr) on a 5 year old and an 11 year
old that didn't know they were being tested, and neither even looked
up.

 

[z]

I think you're missing the point.

I have little doubt that this amplifier is capable of 0.1% THD at say 60W.

The 10% THD figure has simply been used in order to produce an inflated power
rating. This is considered normal practice with car audio.

Graham

exactly. this may well be a fine amp at 60 watts or 70 or whatever.
some middle management moron undoubtedly decided "this amp needs to be
100 watts! make it 100 watts or you're out!" so the engineer just
decided "OK..... have it your way" and the moron doesn't know the
difference.

 

[z]

I've learned recently that speaker manufacturers are similar.  The good ones,
when specifiying frequency response, will tell you that it's, e.g.,
100Hz-10kHz at -1dB or -3dB... the less-reputable ones will often spec it
at -20dB !!! ...and of course usually not mention the level.

off topic: just ran into this:

"A favorite demonstration of mine was to plug the [McIntosh] ML-4
woofer section into the 120-volt wall outlet. This really captured the
attention of visitors who questioned the power handling of the system,
and it was also very loud. "
http://www.roger-russell.com/lsd1.htm

This guy's whole site captured more for an afternoon.

 

[[email protected]]

you used to see this kind of spec all the time for junk-grade audio.
but jvc? sad.

Yep... I've noticed that lots of car audio manufacturers even refuse
to publish THD data.

Hmm...

Michael