Help interpreting 2nd/3rd Harmonic values on WE datasheet

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RhythMick
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#1 Help interpreting 2nd/3rd Harmonic values on WE datasheet

Post by RhythMick »

I stumbled across a WE datasheet for the 300B which included a table of operating points showing 2nd and 3rd harmonics, expressed in dB. Screenshot attached.

Now I'm reasonably competent with maths, but will readily accept to dB being a weakness of mine. As a measurement it's a ratio, right ? So in this instance it must be expressing 2nd and 3rd harmonics as a ratio of the output ? So higher figures represent lower levels of harmonics ?
Screenshot_2019-08-19-21-36-38_compress15.jpg
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Nick
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#2 Re: Help interpreting 2nd/3rd Harmonic values on WE datasheet

Post by Nick »

Yes, so for example 40dB is 1%, 20dB is 10%
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#3 Re: Help interpreting 2nd/3rd Harmonic values on WE datasheet

Post by RhythMick »

Nick wrote: Mon Aug 19, 2019 9:53 pm Yes, so for example 40dB is 1%, 20dB is 10%
Ok thanks Nick. How do you convert dB to %
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#4 Re: Help interpreting 2nd/3rd Harmonic values on WE datasheet

Post by Nick »

So if we call the dB value above x

y = -x/20

z = 10^y

Percent = z * 100

So, x = 40 in your list,

y = -40/20
y = -2

z = 10^-2
z = 0.01

Perc = 0.01 * 100
Perc = 1.0%

Or take 48dB
y = -48/20
y = -2.4
z = 10^-2.4
z = 0.003981
perc = 0.003981*100
perc = 0.4%
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#5 Re: Help interpreting 2nd/3rd Harmonic values on WE datasheet

Post by ed »

if it's of any benefit I used to use the calculator from:

http://www.sengpielaudio.com/calculator-db-volt.htm

as shown in this doc:

http://www.vitalstates.org/diy/amplifie ... rement.pdf

part 5 shows the calcs
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#6 Re: Help interpreting 2nd/3rd Harmonic values on WE datasheet

Post by Nick »

TBH, I just use a scientific calculator on my phone to do the conversion I posted. Yet another thing that phones have taken over.
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#7 Re: Help interpreting 2nd/3rd Harmonic values on WE datasheet

Post by ed »

Nick wrote: Tue Aug 20, 2019 11:32 am TBH, I just use a scientific calculator on my phone to do the conversion I posted. Yet another thing that phones have taken over.
's'funny...I don't have a phone and for some reason I keep thinking there are others like me, that don't have one.....

I know I'm mistaken but I still keep thinking that there are others.
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#8 Re: Help interpreting 2nd/3rd Harmonic values on WE datasheet

Post by Nick »

s'funny...I don't have a phone and for some reason I keep thinking there are others like me, that don't have one.....
You have a good point, but you did post a solution that requires access to a computer connected to the internet...

My original solution can be done with a slide rule or set of log tables.
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#9 Re: Help interpreting 2nd/3rd Harmonic values on WE datasheet

Post by RhythMick »

Many many thanks. I use a calculator called HandyCalc on Android and it allows me to create functions which are really quick and easy. I'll create one for this.
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#10 Re: Help interpreting 2nd/3rd Harmonic values on WE datasheet

Post by ed »

Nick wrote: Tue Aug 20, 2019 2:43 pm My original solution can be done with a slide rule or set of log tables.
bah humbug!

I was all set to try it on my trusty castell 1/60 when I realised it doesn't have the LL scale, which is needed for the expo....
not all slide rules are created equal...

I'm not even going to look for my 4 fig tables...you got me!
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#11 Re: Help interpreting 2nd/3rd Harmonic values on WE datasheet

Post by IslandPink »

ed wrote: Tue Aug 20, 2019 2:13 pm 's'funny...I don't have a phone and for some reason I keep thinking there are others like me, that don't have one.....
I don't have an I-phone. Just a simple one for sending a few texts.
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#12 Re: Help interpreting 2nd/3rd Harmonic values on WE datasheet

Post by pre65 »

IslandPink wrote: Tue Aug 20, 2019 6:31 pm
ed wrote: Tue Aug 20, 2019 2:13 pm 's'funny...I don't have a phone and for some reason I keep thinking there are others like me, that don't have one.....
I don't have an I-phone. Just a simple one for sending a few texts.
Me too.

Infact mine is a Doro old gits phone. :lol:
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