AliExpress cheap low distortion analog sine generator - review and measurements

[audio_tony]

@Janfi67 I found a cheaper version of the same thing.

1pcs Single Voltage To Positive Negative Regulated Power Supply Module Low Noise | eBay UK

Description: The board input voltage is 4-12V DC. HIFI class low noise low internal resistance single voltage to positive and negative power supply output regulated power supply, the maximum output current is up to 1.5A, the output voltage range is positive and negative 8V to positive and...

www.ebay.co.uk

 

[Janfi67]

Thanks a lot @audio_tony for the links and for your advices.

With eBay pictures, I’ve found it on Ali too : https://a.aliexpress.com/_EJBepS4, https://a.aliexpress.com/_EQZkJlS.
More expensive than other boards, probably less noisy too. I’ll do some comparisons.

I think I will use a small DIY centralized 5V linear power supply to power this oscillator as well as other stuff (like an ADC ...) powered by USBc. I’ll take care not to use the soldered plug of the DC-DC converter.

 

[audio_tony]

With eBay pictures, I’ve found it on Ali too : https://a.aliexpress.com/_EJBepS4, https://a.aliexpress.com/_EQZkJlS.
More expensive than other boards, probably less noisy too. I’ll do some comparisons.

That's a good find. It looks like an updated / revised version. These power supplies are very quiet, I've used them in DACs and preamps as well - they are just as quiet as using LM317/337 and associated transformer.

 

[Ixnay]

Given the price, I'll give this oscillator a try.
The distortion probably depends on the appearance of certain capacitors and resistors, I'm not sure all units are equally good.

Does anyone know how to set the frequency to 10 kHz ?

Hey Jan,
The coneheads here are too wound up chasing crazy numbers to actually give any useful information so here:
If you hit the vendor link in the original post, it takes you to the product listing with a picture of the part locations.
You can page the picture down to the schematic that shows you which parts do what. Presuming that you've seen oscillators before and can recognize the frequency-determining components, there you have it. Just get out your slice rule, scale the part values to get what you want.

 

[audio_tony]

You can page the picture down to the schematic that shows you which parts do what.

I didn't even notice that previously!!

The capacitors that control the oscillation frequency on the board are selected and paired using a digital meter. The resistor that controls the oscillation frequency is a 3.3K resistor and a 200 ohm 3296 multi turn potentiometer connected in series. The pairing is adjusted by measuring with a digital meter to ensure the accuracy and low distortion of the output frequency.

matters needing attention:
In theory, R10=2R13， C3=2C4， Minimal distortion.
2. The data in the figure is a value of 1KHZ. If there are other frequencies, besides R6, R7, C1, and C2 that need to be adjusted accordingly, R11 should also be modified according to the frequency.
For example: 50HZ, R11=447K, 60HZ, R11=408K.

 

[Janfi67]

Hey Jan,
The coneheads here are too wound up chasing crazy numbers to actually give any useful information so here:
If you hit the vendor link in the original post, it takes you to the product listing with a picture of the part locations.
You can page the picture down to the schematic that shows you which parts do what. Presuming that you've seen oscillators before and can recognize the frequency-determining components, there you have it. Just get out your slice rule, scale the part values to get what you want.

Thanks a lot @Ixnay.
Unfortunately your message didn't help me much.

I already knew the schematic and comments around.
But I’m not comfortable with this kind of oscillator and I don't trust simplistic formula without explanation, especially about an ultra-low distortion oscillator.

Fortunately, the WEB is a goldmine for those who take the time to search.
https://sound-au.com/articles/sinewave.htm provides excellent explanations about State Variable Filter Oscillator and tips to reduce distortion.

 

[mlloyd1]

@pma (and others):
Thanks for this testing. I had a couple of these purchased a few years ago but hadn't used yet. After reading this, I fired one up and noticed clipping on the negative side with a peak to peak output of ~28V. So, I won't even bother yet to try to measure distortion. Did any of you have to do anything to your oscillator to bring the output level down to a sensible level? A couple of pics attached: oscillator image and waveform on scope.
mlloyd1

 

[Janfi67]

no, my two samples worked out of the box with a peak to peak output of 21.3V well centered around 0V.
Perhaps something wrong around the amplitude stabilization control (D1,D2,D3, TL071, JFET, 1/2 NE5532...) ?

But I have to adjust the frequency, it is around 920 and 930 Hz in my case.
And to check the distortion with an appropriate tooling. I just don't see any harmonic on the FFT of my scope, better than an average AWG.

 

[mlloyd1]

no, my two samples worked out of the box with a peak to peak output of 21.3V well centered around 0V.
Perhaps something wrong around the amplitude stabilization control (D1,D2,D3, TL071, JFET, 1/2 NE5532...) ?

But I have to adjust the frequency, it is around 920 and 930 Hz in my case.
And to check the distortion with an appropriate tooling. I just don't see any harmonic on the FFT of my scope, better than an average AWG.

thanks for replying. interesting. are yours a recent vintage or older? mine are from 2017.

 

[Janfi67]

Bought 3 weeks ago. They looks like pma's one, same PCB, same capacitors...

 

[Janfi67]

First quick mesure with an E1DA ADC iso grade B in stereo mode.

Good for the price and quality seems to be consistent across samples.
The oscillator is powered by a small isolated +5V -> ±15V booster.

A Chinese 3590S 1KΩ potentiometer at the output doesn't seem to degrade performance and should ease the usage.

Still some work to adjust the frequency (an DUT doesn't care but a notch filter does), get the other running at 10KHz, try to optimize SNR and THD and to put them in a housing.