AliExpress cheap low distortion analog sine generator - review and measurements

[IVX]

If the Use AES17-2015 standard notch option is selected the fundamental power for THD and THD+N calculations will be the power within a one octave span around the fundamental frequency. If that option is not selected it will be the power in the main lobe of the fundamental. When the fundamental level is not well above the noise floor using the standard notch will produce a higher figure than the fundamental main lobe, in those cases it is better not to use the standard notch setting.

John, slightly off topic, but I've been suffering for about one year since you changed the error handling logic in REW. I'm using REW for ADC calibration, and every time I unplug the USB cable causes two new error windows. So, I have to close them before using the next ADC unit. The 2023 versions or earlier had more tolerant error handling, and I was quite happy. Could you please roll back that error handling?

 

[pma]

When the fundamental level is not well above the noise floor using the standard notch will produce a higher figure than the fundamental main lobe, in those cases it is better not to use the standard notch setting.

I have just tried it on one of the long wav records of the generator output - with std. notch I get THD+N = -115.9dB, without the notch I get THD+N = -115.5dB. I assume in this case the difference is negligible.

 

[JohnPM]

John, slightly off topic, but I've been suffering for about one year since you changed the error handling logic in REW. I'm using REW for ADC calibration, and every time I unplug the USB cable causes two new error windows. So, I have to close them before using the next ADC unit. The 2023 versions or earlier had more tolerant error handling, and I was quite happy. Could you please roll back that error handling?

Meaning a message about the device list changing? Java does not react well to USB device changes. It can take some time for the change to propagate to the Java runtime (up to 1 minute on Windows), trying to use the device in the intervening period causes errors and can lock up the runtime's audio handling. The message you see is a way of handling such a change to avoid more serious problems.

 

[pma]

So far I measured the generator as it was delivered, without any additional settings. Adjusting the trim pot VR (see schematics in post #1) it is possible to reduce distortion slightly, especially H2 almost disappears. It is not sure if there is not a distortion cancellation of H2 between the generator and the Cosmos ADC, then. @IVX , your thoughts on Cosmos H2? Also the forest of low level high order harmonics (>= 7th) might be IMO a product of the ADC.

 

[IVX]

So far I measured the generator as it was delivered, without any additional settings. Adjusting the trim pot VR (see schematics in post #1) it is possible to reduce distortion slightly, especially H2 almost disappears. It is not sure if there is not a distortion cancellation of H2 between the generator and the Cosmos ADC, then. @IVX , your thoughts on Cosmos H2? Also the forest of low level high order harmonics (>= 7th) might be IMO a product of the ADC.

View attachment 475792

Almost 100% of Cosmos ADC/ADCiso have H2 at <-145db.

 

[Buckness808]

This is classic haha I love these niche finds

 

[audio_tony]

Mine arrived today (took 6 days to get the UK - impressive).

I paid £12.27 for mine.

Plugged into my Asus Xonar Essence sound card (which is what I use for all my testing) I'm seeing 0.00017% THD (-115.39dB)

I don't know which has impressed me more - the sound card or the oscillator!

 

[pma]

Welcome in the club .

 

[audio_tony]

I've replaced the NE5532 (the IC in pink on the schematic) with an OPA2134.

THD has dropped to 0.00013% (-117.72dB) (it went up to 0.00014% when I took the screenshot lol)

The spike at ~35kHz is an artefact from the sound card.

 

[audio_tony]

I replaced those cheap IC sockets with some turned pin sockets which has straightened the ICs out. I've also mounted it in a small aluminium box, fitted a decoupling cap and a volume control (none of which has affected the THD).

I now have two variable outputs, and a single fixed output (3 sockets).

 

[capslock]

I wonder if further reduction can be achieved by:
- replacing the second 5532 IC
- replacing the film caps (other than those around the 072 chips) which look suspiciously like polyester film with PP or even better, COG/NPO caps

PS: COG up to 470 nF (!) seem to be availeable in SMD

https://cdn-reichelt.de/documents/datenblatt/B300/KEM_C0XXX_C0G_DB-EN.pdf

 

[pma]

I've replaced the NE5532 (the IC in pink on the schematic) with an OPA2134.

THD has dropped to 0.00013% (-117.72dB) (it went up to 0.00014% when I took the screenshot lol)

Do you know the distortion limits of your sound card? It is highly unlikely that the replacement of NE5532 by OPA2134 would result in distortion reduction. In fact, the OPA134/2134 series has higher distortion at 7V level than NE5532. Your result might well be due to distortion cancellation between the generator and the soundcard (depending on phase of distortion harmonics). Asus Xonar is unlikely to have intrinsic distortion low enough to measure the generator properly. Not speaking about the elevated noise level as well (you show THD+N = 0.00088% which equals to -101.11 dB only).

 

[audio_tony]

Do you know the distortion limits of your sound card?

According to tests carried out by Asus, 0.0002% (-113dB) - see attached test report for full tests. No doubt this will vary from batch to batch, and some may measure worse than this (and I suppose some may even measure better).

I've also included a test I did from a DAC - the results seems to be consistent across various software (Arta, AudioTester, WaveSpectra etc.)

 

[pma]

According to tests carried out by Asus, 0.0002% (-113dB) - see attached test report for full tests. No doubt this will vary from batch to batch, and some may measure worse than this (and I suppose some may even measure better).

It is still not good enough. I have repeated your test and below are the results.

1. Original JRC5532D part

2. Replaced by OPA2134

Please note much lower both distortion and noise than you get with the Asus. The measuring device has to be at least as good as the source and preferably better to get some meaningful results. Please also note that the OPA2134 did not bring any improvement. Please note that phase of H2 and H3 have changed after IC replacement.

 

[audio_tony]

Please note much lower both distortion and noise than you get with the Asus.

Which comes as no surprise, given that the E1DA is a far superior device.

The measuring device has to be at least as good as the source and preferably better to get some meaningful results.

I am well aware of this, please don't take me for an idiot.

Please also note that the OPA2134 did not bring any improvement. Please note that phase of H2 and H3 have changed after IC replacement.

I did note a change in harmonics, I shall go back and measure again - I was only reporting what I found by swapping the 5532 for the 2134.

I'm sorry if it doesn't agree with your own measurements, but I'm only reporting what I see.

Something I have found with the 2134 is the oscillator takes a while to stabilise (several minutes) - so I'm currently experimenting with other options.

Are you sure the 2134 you tested with is a genuine part? I know mine is.

 

[IVX]

OPA1656? For the H2, I believe you may add some symmetry adjustment(trimpot).

 

[pma]

Yes, H2 can be adjusted by the “VR” trim pot.

 

[Ixnay]

This could be useful to me if it could be set to produce a 60Hz wave.

 

[Janfi67]

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 ?

By the way @audio_tony , I see you're powering the oscillator with a small switching power supply. Do you have a link to the one you're using? The ones I've tried seem too noisy for this purpose. Thanks.

 

[audio_tony]

Do you have a link to the one you're using?

Here you are: https://www.ebay.co.uk/itm/315963681245 (the price has almost doubled since I bought mine about 5 years ago!)

I could only find this on UK Ebay. You might find it on ALi Express - I tried a quick search but found nothing. Audiophonics used to sell them - but not any more.

A note of caution though; The stated input voltage is 5v to 12v - the module seems to self destruct when run continuously on 12v and highish current (it's rated to 1.5A) - it also has a USB input socket - I found that running it off USB creates noise issues (ground loops etc.) hence I use a pre-regulator to step down to 5v - and then I run it off a linear PSU for minimum noise.