Help: Need low noise stable amplitude audio signal generator or design

[Vovk_Z]

Chinese low distortion audio range generator kit
...
Ideally, for this project, a generator that stabilises in amplitude (<60uV/min) within ~30 min and has less than 30uVpp noise on a 1v/1KHz signal would be OK.
....
How good is your audio frequency generator for amplitude and noise in a metrology role?

If I'm not wrong 60 uV is 60 ppm for 1 VAC signal. This is not 'stable' but this is 'ultra-stable' I think.
I worked with a Chinese low distortion audio range generator kit (1 kHz) it was the most stable of all several different simple analog oscillators I had in my hands. It works at 50 Hz in my case. I guess it is as stable as used passive components are (plus some semiconductor drift caused by heating). I had something like 100-200 ppm amplitude stability with that oscillator over time. (I don't have more accurate AC voltmeters to make a deeper investigation, unfortunately).

[enut11]

Thanks @Vovk_Z
I came to the same conclusion about that single frequency chinese audio signal generator kit. My requirement is 20Hz-20KHz minimum which can be done with switched caps and variable resistors.

The plea for help from Forum members was to see if other solutions existed.
enut11

[David Hess]

If I'm not wrong 60 uV is 60 ppm for 1 VAC signal. This is not 'stable' but this is 'ultra-stable' I think.
I worked with a Chinese low distortion audio range generator kit (1 kHz) it was the stablest from all several different simple analog oscillators I had in my hands. It works at 50 Hz in my case. I guess it is as stable as used passive components are (plus some semiconductor drift caused by heating). I had something like 100-200 ppm amplitude stability with that oscillator over time. (I don't have more accurate AC voltmeters to make a deeper investigation, unfortunately).

Precision could be improved by temperature compensating the rectifier circuit better.  That would be a good place for a precision monolithic matched pair used as diodes.  Jim Williams used the same configuration to stabilize the amplitude of his Wien Bridge oscillators and noise sources.  Leveled RF sources use the same type of circuit but with faster diodes.

Wouldn't a precision rectifier be more stable?

[Roehrenonkel]

Hi,
 
maybe the smallest solution could be the Apex SWR200, impressive datasheet:
"SWR200 is a Precision Sine Wave Reference providing an ultra stable sine wave output of +7.071V at
±0.5% initial accuracy and temperature coefficient as low as 20ppm/°C over the full military temperature
range".
I guess you have to bring a big wallet. ;-))
In the 1980s there was a simimlar hybrid-circuit ROJ20 from Datel but i don't remember the data.

[enut11]

Big wallet indeed - $374 each!

[enut11]

If I'm not wrong 60 uV is 60 ppm for 1 VAC signal. This is not 'stable' but this is 'ultra-stable' I think.
I worked with a Chinese low distortion audio range generator kit (1 kHz) it was the stablest from all several different simple analog oscillators I had in my hands. It works at 50 Hz in my case. I guess it is as stable as used passive components are (plus some semiconductor drift caused by heating). I had something like 100-200 ppm amplitude stability with that oscillator over time. (I don't have more accurate AC voltmeters to make a deeper investigation, unfortunately).

Precision could be improved by temperature compensating the rectifier circuit better.  That would be a good place for a precision monolithic matched pair used as diodes.  Jim Williams used the same configuration to stabilize the amplitude of his Wien Bridge oscillators and noise sources.  Leveled RF sources use the same type of circuit but with faster diodes.

Wouldn't a precision rectifier be more stable?

The Chinese audio range generator is good if you have a very stable +/- power supply.

I have also tried this design which has a precision rectifier (U3) plus voltage reference (TL431) to control the output level but it is very very noisy - pity.

[Conrad Hoffman]

Did Apex get the Thaler designs? They had some nice references, including an AC reference.