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| Question: Cheap pure sine wave genertor 1khz? |
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| Kleinstein:
--- Quote from: Grandchuck on June 27, 2021, 12:45:30 pm ---Thanks. Lots of bits makes for low THD: THD(%) = 1/(2^N) x 100 (where N is the number of bits) That is the ideal case. In practice, the THD is higher. i.e. my Siglent 14 bit generator gives about 0.008% (ideally, 0.006%). --- End quote --- The formula includes quite some simplifiaction. Looks like it assumes very high BW to also include the very high harmonics. With a limite BW (even the usual 22 kHz with Audio) quite a bit of the digital step noise gets removed, especially with an oversampling DAC, which is the norm. In addition there are INL errors from the DAC and following stages. So real world noise can be higher of lower. The Elector Wien bridge circuit is the very basic one, not specially made for low noise. So it hase relatively high demand on the OPs. It is more like good for testing the OPs than actually generating a very low noise sine. For lowest destortion it often helps to have 2 OPs in the oscillator itself with the OPs working as inverting vonfiguration and this with zero (or near zero) common mode voltage. This avoids the distorion from the limited CMRR. |
| rhb:
The canonical schematics are in: "Max Wein, Mr. Hewlett and a Rainy Sunday Afternoon" by Jim Williams. Because he understood transistors at the most basic level, he was able to achieve better performance than the best instrument available. Have Fun! Reg |
| Grandchuck:
Found on ebay: https://www.ebay.com/itm/224549490206?hash=item3448314e1e:g:ziEAAOSwhvJhAApb Very impressive distortion specs. |
| rhb:
Wow! They claim no measurable distortion using a 24 bit sound card. If it meets the specs it's an excellent soundcard calibrator. Though switched frequencies in octave steps from A 22.5 Hz would be far better. Have Fun! Reg |
| Grandchuck:
Has anyone built one of these? https://www.ebay.com/itm/184691239077?hash=item2b0074a8a5:g:q6wAAOSw4tNgTC70 Schematic shown here. |
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