Low-distortion Audio-range Oscillator

[Bernhard]

Variation of that lowpass with notches at h2 and h3 as those seem to be the main problem in oscillators...

 

[Bernhard]

Passive LC notch with 2 coils (0.8mm wire), -40dB @ 1 kHz, 1dB loss @ h2

 

[Bernhard]

R&S UPA generator - passive notch - LME49720 40dB preamp

 

[Bernhard]

R&S UPA generator - passive bandpass - passive notch - LME49720 40dB preamp

Everything far from perfect, it adds almost 2 zeros.

Could a 2 stage preamp be better ?
20dB + 20 dB instead of 40dB ?

 

[maouna]

hello.can you give me a schematic of a low distortion sine generator?there are a lot of posts and is a bit difficult to find. will this simple one do the job?


Low-distortion Audio-range Oscillator - RED - Page82

or this one ?

Project 174

 

[Vovk Z]

R&S UPA generator - passive bandpass - passive notch - LME49720 40dB preamp

Everything far from perfect, it adds almost 2 zeros.

Could a 2 stage preamp be better ?
20dB + 20 dB instead of 40dB ?

It is to noisiy. It is hardto tell something about harmonics until noise is higber then harmonics. You have to clean it up first, I think.

 

[maouna]

Which one is the latest updated schematic of victor's oscillator?what part values need to be changed for frequencies of 100Hz and 10Khz?

 

[vicnic]

The latest schematics:
https://content21-foto.inbox.lv/albums/e/elterra/OscillatorNew/Gen1kHzN8.png
https://content21-foto.inbox.lv/albums/e/elterra/OscillatorNew/Gen10kHzN8.png
Simplest way for to get the 100Hz is to increase values of the 1kHz version capacitors C4, C6, C7, C11, C12, C16, C18 ten times. I recommend little different frequency instead of 100Hz for better separating the oscillator frequency harmonics from the power line voltage harmonics.

Vic.

 

[diyralf]

What does the star next to the resistors mean? 0.1% tolerance?

 

[KSTR]

I would think the * denotes resistors for fine-trimming frequency and JFET Rds_on compensation
As for precision, I think R10 and R17 should be well-matched, so a use for 0.1% types here. Everything else is fine with 1%.

 

[vicnic]

What does the star next to the resistors mean? 0.1% tolerance?

These resistors can have different values.
R20, R21, R29 - for to adjust the frequency.
R18 - for the d-s voltage across the FET (app. 25mV p-p on last boards).

 

[LKA]

I tried to lock the Vic's 1k oscillator frequency according Jan's method. It works very well. As a reference clock I used usb soundcard.


setup:
Modified 1k osc: SMA connector,560kOhm 0.4W resistor to IC2 pin6
Ref clock: X-Fi USB HD USB, output level -25dBFS, notebook on AC power, sw REW
Analyzer: ESI Julia PCI, desktop PC on AC power, sw REW

 

[jan.didden]

Neat!

Jan

 

[phofman]

LKA: very nice work. Does your Juli@ really distort so little at -8dBFs, or is the chart produced artificially in REW by incorporating parameters of a notch filter? Thanks.

 

[LKA]

notch was not used (direct connection oscillator -> sound_card_input)

and this is the STXII in the same PC, ref clock at -26dBFS, at -29-30dBFS the syncing is not effective anymore

 

[1audio]

Can you provide more implementation details? Connection points, voltages etc? I want to duplicate your measurements. I'm not sure what voltage dBFS would translate to.

 

[jan.didden]

notch was not used (direct connection oscillator -> sound_card_input)

and this is the STXII in the same PC, ref clock at -26dBFS, at -29-30dBFS the syncing is not effective anymore

You can sync at low level by decreasing the series R into Vic's oscillator.

Jan

 

[LKA]

120mVrms (-25dBFS) injected via 560kOhm into the IC2 pin6 (LME49720).

 

[Vovk Z]

Can you provide more implementation details? Connection points, voltages etc? I want to duplicate your measurements. I'm not sure what voltage dBFS would translate to.

0 dBFS for Xonar Essence STX is 2 V RMS (I think for STX II the same). Or it is not Asus STX card?

 

[Vovk Z]

notch was not used (direct connection oscillator -> sound_card_input)

and this is the STXII in the same PC, ref clock at -26dBFS, at -29-30dBFS the syncing is not effective anymore

- seems the same locked and unlocked from my first site?