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Sci.Electronics.Basics -> 10% THD?
There are 47 messages in this thread.
You are currently looking at messages 40 to 47.
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Author: Phil AllisonDate: 23:05 12-04-08
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"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
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Author: Bob MastaDate: 09:20 13-04-08
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On Sun, 13 Apr 2008 10:49:15 +1000, "Phil Allison"
<philallison@tpg.com.au> wrote:
>
>"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.
>
Got it! Thanks, Phil. For decades I have apparently been laboring
under a misconception that there was always some residual crossover
distortion, but now that you point it out it seems totally
unjustified... and I'm more than glad to be rid of it!
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: zDate: 13:16 14-04-08
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Author: zDate: 13:23 14-04-08
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On Apr 9, 1:16=A0am, mrdarr...@gmail.com wrote:
> 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.
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Author: zDate: 13:27 14-04-08
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On Apr 10, 12:16=A0pm, Eeyore <rabbitsfriendsandrelati...@hotmail.com>
wrote:
> Bob Eld wrote:
> > Well, maybe I should change it to nobody in their right mind would BUY s=
uch
> > 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 po=
wer
> 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.
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Author: zDate: 13:32 14-04-08
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On Apr 11, 2:44=A0pm, "Joel Koltner" <zapwireDASHgro...@yahoo.com>
wrote:
> "Bob Masta" <NoS...@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. =A0The 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.
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On Apr 14, 10:16 am, z <gzuck...@snail-mail.net> wrote:
> On Apr 8, 11:35 pm, mrdarr...@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
>
> 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
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