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Sci.Electronics.Basics -> 10% THD?
There are 47 messages in this thread.
You are currently looking at messages 20 to 40.
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Author: Phil AllisonDate: 20:49 09-04-08
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"BobG"
** Hey Bob,
take a breath - you are not talking about the same topic as others here !!
Peak clipping ( = hard clipping ) of a CONTINUOUS sine wave is VERY audible,
even at low percentages. The harmonics generated go up to 5, 7, 9 and 11
times the fundamental - if they fall in the range of 1 to 5 kHz their
presence is obvious us to anyone who is not deaf.
OTOH - occasional transient clipping of a music or speech signals is
virtually inaudible, specially if each clipping event is under 2mS
duration. Such occasional transients may be clipped at high percentages of
their unclipped amplitude and still remain hidden to listeners.
Some power amplifiers have fast acting signal clipping indicators ( ie the
Crown IOC system) and it is easily demonstrated that the LED clipping light
will flicker regularly on normal music program WELL before any listener
can hear a problem.
..... Phil
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Author: BobGDate: 20:57 09-04-08
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On Apr 9, 8:49=EF=BF=BDpm, "Phil Allison" <philalli...@tpg.com.au> wrote:
> ** Hey Bob,
>
> take a breath - =EF=BF=BDyou are not talking about the same topic as other=
s here !!
=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=
=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D
I claimed that one cannot see 3% distortion in a sine wave on a scope.
I got a response that this is utter nonsense, and its easy to see 1%
THD on a scope. So I want to synthesize a waveform with fundamental of
amplitude X and 3rd harmonic down at 0.03X. Then I will plot it and
see for myself if in fact 3% is easily visible and my claim was utter
nonsense. Of course, I'll be using a computer monitor with about 3
times the vertical resolution of most scopes, but that should just
make the distorion easier to see.... I'm making the test harder for
myself. I wouldnt want anyone to say my experiment was biased in favor
of my claim. Just trying to defend myself against the assertion that I
have spoken utter nonsense.
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Author: Phil AllisonDate: 21:06 09-04-08
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"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
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Author: Michael A. TerrellDate: 21:44 09-04-08
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BobG wrote:
>
> On Apr 9, 12:55�am, "Michael A. Terrell"
<mike.terr...@earthlink.net>
> wrote:
> > � �I have seen 2% THD described as sounding like a barrel of nails in a
> > cement mixer.
> =============================
> But in court, this would be objected to as hearsay. We have all heard
> horrible distorted clipped hash coming from and amp, but was that .5%,
> 5%, or 50% THD we were hearing at the time? Anyone can hear a diff in
> an AB comparison with a graphic EQ in and out, but few can characteris
> it quantatatively and within about an octave. Unless they have a
> couple decades experience in live sound reinforcement like me and a
> couple of buddies. They could win a bet in a bar if you took in a
> signal generator and a spectrum analyzer. Perfect pitch.
Right. Where are you going to find a judge, lawyers and a jury who
know ANYTHING about electronics, let alone how to do the proper tests,
or even know what test equipment was needed?
If you ever heard 2% THD you wouldn't argue. 2% at full rated power
was the standard spec for school intercom systems and background music
systems in stores. They would buy the smallest amp they could squeeze by
with, which sounded like crap. They were always amazed when I put in an
amp with a lower distortion rating. They could understand the messages,
and the background music didn't make your skin crawl, like it was trying
to get away from the noise.
WTH does perfect pitch have to do with recognizing distortion? I was
in the commercial sound business for over 20 years.
--
aioe.org is home to cowards and terrorists
Add this line to your news proxy nfilter.dat file
* drop Path:*aioe.org!not-for-mail to drop all aioe.org traffic.
http://improve-usenet.org/index.html
Use any search engine other than Google till they stop polluting USENET
with porn and junk commercial SPAM
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On Apr 8, 10:16 pm, mrdarr...@gmail.com wrote:
> On Apr 8, 9:58 pm, Eeyore <rabbitsfriendsandrelati...@hotmail.com>
> wrote:
>
> > BobG wrote:
> > > But 'visible clipping' is
> > > about 10%, and is surprisingly inaudible.
>
> > Absolute nonsense. You can easily see clipping on a sinewave on a scope at
> > less than 1% and it's CLEARLY audible due to the high harmonic content.
>
> > Graham
>
> 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/
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Author: EeyoreDate: 02:29 10-04-08
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BobG wrote:
> On Apr 9, 8:49�pm, "Phil Allison" <philalli...@tpg.com.au> wrote:
> > ** 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.
And the only 3% distortion you'll see from a modern solid state amplifier is
CLIPPING distortion.
Graham
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On Apr 9, 8:40 pm, gerf...@gmail.com wrote:
> On Apr 8, 10:16 pm, mrdarr...@gmail.com wrote:
>
>
>
> > On Apr 8, 9:58 pm, Eeyore <rabbitsfriendsandrelati...@hotmail.com>
> > wrote:
>
> > > BobG wrote:
> > > > But 'visible clipping' is
> > > > about 10%, and is surprisingly inaudible.
>
> > > Absolute nonsense. You can easily see clipping on a sinewave on a scope
at
> > > less than 1% and it's CLEARLY audible due to the high harmonic content.
>
> > > Graham
>
> > 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 Institutehttp://gcri.blogspot.com/
http://www.freemosquitoringtones.org/
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On Apr 9, 8:40 pm, gerf...@gmail.com wrote:
> On Apr 8, 10:16 pm, mrdarr...@gmail.com wrote:
>
>
>
> > On Apr 8, 9:58 pm, Eeyore <rabbitsfriendsandrelati...@hotmail.com>
> > wrote:
>
> > > BobG wrote:
> > > > But 'visible clipping' is
> > > > about 10%, and is surprisingly inaudible.
>
> > > Absolute nonsense. You can easily see clipping on a sinewave on a scope
at
> > > less than 1% and it's CLEARLY audible due to the high harmonic content.
>
> > > Graham
>
> > 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 Institutehttp://gcri.blogspot.com/
... and this
http://saunderslog.com/2006/06/12/the-mosquito-ring-tone-this-adult-can-hear-it/
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Author: Bob MastaDate: 08:33 10-04-08
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On Tue, 8 Apr 2008 20:35:10 -0700 (PDT), mrdarrett@gmail.com wrote:
>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
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). Then as you continue
to increase power, you soon hit a point where the distortion starts to
rise rapidly with power, as you get near to (and into) clipping. (The
distortion can rise before the signal actually hits the hard clip
point, beacuse near clipping the amp's negative feedback has less
elbow room to work its magic.)
At any rate, the manufacturer has to make a judgement call about
what power level to claim. He can pick a high level if he thinks the
customer will be impressed by watts and not know or care about
distortion. Or he can pick a lower power and correspondingly lower
distortion to appeal more to purists. (The ability of the amp to
withstand the power without damage is not typically an issue here.
Amps dissipate the most power at intermediate levels.)
As others have pointed out, music often has transient peaks that
can be clipped a fair amount before they become objectionable.
When the signal level is set so that the tallest peaks are just
hitting the 100W point, the average power is probably more like
10W or less, with correspondingly low distortion. And for most
speaker systems, this will be *plenty* loud!
Best regards,
Bob Masta
DAQARTA v3.50
Data AcQuisition And Real-Time Analysis
www.daqarta.com
Scope, Spectrum, Spectrogram, FREE Signal Generator
Science with your sound card!
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Author: Phil AllisonDate: 08:51 10-04-08
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"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
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Author: Bob EldDate: 12:00 10-04-08
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<mrdarrett@gmail.com> wrote in message
news:9318bf28-99a6-4369-945c-ebb64d28cec0@q10g2000prf.googlegroups.com...
> On Apr 9, 11:57 am, mrdarr...@gmail.com wrote:
> > On Apr 9, 11:20 am, "Bob Eld" <nsmontas...@yahoo.com> wrote:
> >
> >
> >
> > > <mrdarr...@gmail.com> wrote in message
> >
> >
>news:8b5083e5-4d3e-4117-86d6-a3213396f804@s39g2000prd.googlegroups.com...
> >
> > > > 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
> >
> > > It is a lot. Most likely a misprint. Nobody in their right mind would
spec.
> > > an amplifier with that distortion nor would they rate an amplifier at
its
> > > clipping level as has been suggested.
> >
> > > Since getting less than one percent even less than 0.1% THD is trivial
these
> > > days with modern semiconductor circuitry it would seem that this spec
sheet
> > > is probably in error.
> >
> > > Most likely the printer or web master left out a decimal point and
nobody
> > > caught it. Call JVC and ask.
> >
> > I downloaded the manual, and it also has 10%
THD...http://resources.jvc.com/Resources/00/00/90/LVT1507-001A.pdf
> >
> > Support info:http://support.jvc.com/consumer/support/index.jsp
> >
> > I called their 800 number, and heard an amazingly distorted
> > recording. Maybe distortion is company policy? ;-)
> >
> > I'll try e-mailing them (but won't hold my breath).
> >
> > Well, if it does end up a mistake, this would be a pretty good
> > product...http://www.walmart.com/catalog/product.do?product_id=5301826
> >
> > Thanks,
> >
> > Michael
>
>
> 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?
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Author: EeyoreDate: 12:16 10-04-08
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Bob Eld wrote:
> 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
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Author: Bob EldDate: 15:43 10-04-08
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"Eeyore" <rabbitsfriendsandrelations@hotmail.com> wrote in message
news:47FE3D59.1A895B20@hotmail.com...
>
>
> Bob Eld wrote:
>
> > 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
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.
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On Apr 10, 12:43 pm, "Bob Eld" <nsmontas...@yahoo.com> wrote:
> "Eeyore" <rabbitsfriendsandrelati...@hotmail.com> wrote in message
>
> news:47FE3D59.1A895B20@hotmail.com...
>
>
>
>
>
> > Bob Eld wrote:
>
> > > 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
>
> 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
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Author: Joel KoltnerDate: 14:44 11-04-08
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"Bob Masta" <NoSpam@daqarta.com> wrote in message
news:47fe0425.1356369@news.sysmatrix.net...
> At any rate, the manufacturer has to make a judgement call about
> what power level to claim.
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.
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Author: NewsGroupsDate: 19:49 11-04-08
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Author: Bob MastaDate: 09:24 12-04-08
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On Thu, 10 Apr 2008 22:51:47 +1000, "Phil Allison"
<philallison@tpg.com.au> wrote:
>
>"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 ?
>
Right. Thanks for reminding me about the hum and noise. It's the same
basic concept I was taliking about: A constant that is a bigger
percentage of a smaller total.
(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.)
Modern methods using synchronous averaging and FFTs (with a sound card
and the right software... hint, hint!) can measure the distortion
alone, by removing noise and cancelling hum. But I admit it is
purely academic at these low levels, and surely not worth the effort
for most purposes.
>> 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.
I sure won't argue. It depends on how steep the curve is for the amp.
(My suspicion is that this amp may not be in the "hi-fi quality"
department.) At any rate, they must have had *some* reason to pick
the 10% THD point to state their power rating. "100 watts" certainly
would appeal to Marketing better than, say, "97 watts".
Of course, it *could* be a typo. I can just picture Moe telling Larry
"Tenth percent THD" and Larry telling Curly "Ten percent THD".
<g>
>Only by doing THD measurements on * real amplifiers * can one have any
>insight into the facts of the matter .
Agreed!
>Which I do all the time.
>
>While Bob does not.
No fair, you peeked! Yes, sad to say that software development has
really been keeping me away from the test bench for far too long.
But I still have my monster dummy load bank (4 x 8 ohms, 200 watts
each) sitting there gathering dust. Some day, Real Soon Now....
Best regards,
Bob Masta
DAQARTA v3.50
Data AcQuisition And Real-Time Analysis
www.daqarta.com
Scope, Spectrum, Spectrogram, FREE Signal Generator
Science with your sound card!
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Author: BobGDate: 11:53 12-04-08
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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.
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Author: Bob MastaDate: 12:52 12-04-08
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On Sat, 12 Apr 2008 13:24:08 GMT, NoSpam@daqarta.com (Bob Masta)
wrote:
<snip>
>(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.)
I just realized that this statement probably marks me as an
out-of-touch dinosaur, since it is based on experiences with bipolar
output devices... now driven to near-extinction by MOSFETs as the
preferred output stage.
"Back in the day", the bias of the output stage was a critical
setting. Too little and the amp ran as class B, with heavy crossover
distortion as the positive and negative devices handed off their share
of the load near 0 volts. So the bias was adjusted for class AB,
where each half carried over just a bit across zero, overlapping with
the other half in a linear region around zero. That way, there was
always somebody there to carry the load. (Still true today, but read
on...)
The problem with bipolars, however, is/was thermal runaway: As they
get hotter, they conduct harder and that causes them to heat up still
more. So you had to be very careful, and have good temperature
compensation for the bias circuit, or the output stage would go up in
smoke. (That's not *absolutely* true: With enough negative feedback
you can get away with pretty meager bias, but there are other problems
with that approach.) I tended to be cautious, and not too concerned
about what I couldn't hear anyway. <g>
But MOSFETs (which I've never used in an output stage) have the
opposite behavior from bipolars: As they heat up, their resistance
goes up and they conduct less, causing them to cool down. So I would
not be at all surprised to find that bias is nowadays set much more
agressively, so that crossover distortion may indeed be a thing of the
past. Mea culpa!
Best regards,
Bob Masta
DAQARTA v3.50
Data AcQuisition And Real-Time Analysis
www.daqarta.com
Scope, Spectrum, Spectrogram, FREE Signal Generator
Science with your sound card!
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Author: Phil AllisonDate: 20:49 12-04-08
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"Bob Masta"
"Phil Allison"
>>
>>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 !!!!!!!!!!
>>
>
> (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
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