Any opinions or improvements suggestions about this low thd 1 khz sine generator ?

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gaetan8888

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Hello

Any opinions or improvements suggestions about this low thd 1 khz sine generator ?

Thank

Bye

Gaetan
 

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gaetan8888 said:
Hello

Any opinions or improvements suggestions about this low thd 1 khz sine generator ?

Thank

Bye

Gaetan
Click to expand...

For what purpose do you need a 1khz Low THD sine wave generator?
Also, the 071 could use a 100pF cap across pins 1 and 8 (check the datasheet).
 
Such devices are as much 'art' as 'science', and I recall that it's easier to get low distortion using a bulb rather than an FET in the feedback - from HP I seem to remember?.
 
The key question is what is your spec for THD? -60 dB? -80dB? -100 dB?? then how will you verify it? If -60 dB, the solution to both could be a Software Sig Gen. and Spectrum Analyzer. Audacity.exe generate anything you can imagine and detect with AUX input.
 

Well that's not how you measure THD, it's in percentages (such as 0.01%) not dB's, and PC hardware is nowhere near capable of the requirements for decent quality audio measurements.

However, pretty cool thing Audacity - and would be VERY useful for less critical applications.
 
Nigel Goodwin said:
Well that's not how you measure THD, it's in percentages (such as 0.01%) not dB's, and PC hardware is nowhere near capable of the requirements for decent quality audio measurements.
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Yes of course, but Spectrum Analyzers measure in dB then you convert that to %THD . Last time I used an electret mic with tower Turtle sound card, I was surprised by the SNR and THD it recorded using Audacity. The mic also had a DC response with bias nulled. Let's see how much %THD is -120 dB for the waveform in memory.....
 
AnalogKid said:
Uhhh ... a dB is a ratio, as is a percentage.
Click to expand...

Except a percentage is in reference to a known point, a dB isn't - and regardless, you don't give distortion figures in dB - just as you don't give the weight of jewlery in metric tonnes.
 
AnalogKid said:
Uhhh ... a dB is a ratio, as is a percentage.

ak
Click to expand...

I've somehow avoided working with db to this point and recently confronted with a similar ratio question. This THD scenario frames it well.

If measuring THD, and there is a 10% positive and 10% negative deviation from the input signal, (i.e. output waveforms deviate from input from 90% to 110% of input), would THD be expressed as 0.9db (for the negative deviation) to 1.1db (positive deviation).
 
Last edited:
Nigel Goodwin said:
Except a percentage is in reference to a known point, a dB isn't - and regardless, you don't give distortion figures in dB - just as you don't give the weight of jewlery in metric tonnes.
Click to expand...
How can db be a ratio without a denominator?
 
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