Measurements

[SoNic_real_one]

This is 19+20Khz 1:1 on my NOS TDA1541a.... to be honest, I don't really know what I am (supposed to be) looking at.... enlighted me..

What I was looking for is the "grass" that is present in-band and also out-band, past the 20kHz mark.

For PCM61 the higest off-band alias apears at -84dB, for TDA1541 at -70dB (worse), for PCM1791 at some -110dB (best).
In-band I have some "grass" between the spectrum at noise floor level.
You have two huge off-band spikes mirrored around the 22.05kHz and you have a lot of in-band "grass" that rises numerous times to -80dB (don't know what the averaged total would end up). That is distortion of the original signal.

Now... What I don't know is why you don't have any beats between the fundamentals in your signal. What ADC are you using?

 

[SoNic_real_one]

I redid my measurements with different setup for the ballanced inputs (to accept unballanced signal). No change.
Loopback E-MU1820m, PCM61@0dB, PCM61@-60dB, PCM61@19+20kHz@-3dB. I still don't get what's up with the beats...

 

[SoNic_real_one]

Same measurements for TDA1541@0dB, TDA1541@-60dB, TDA1541@19+20kHz/-3dB. Same OpAmp (LM4562) as PMC61.

 

[SoNic_real_one]

And for PCM1791@0dB, PCM1791@-60dB, PCM1791@19+20kHz/-3dB.

 

[ThorstenL]

Hi,

LPF... How? Where? In Arta?

In the signal. Generate a test signal, for example using Audacity etc...

Ciao T

 

[Bernhard]

I redid my measurements with different setup for the ballanced inputs (to accept unballanced signal). No change.
Loopback E-MU1820m, PCM61@0dB, PCM61@-60dB, PCM61@19+20kHz@-3dB. I still don't get what's up with the beats...

For -60 dB, did you adjust the MSB ?
You can do it using a headphone, adjusting for most pure tone
and watching the live measurement, grass sinking in the noise floor.
Also try other pcm61 chips, you may find better ones.

 

[SoNic_real_one]

I did ajust the MSB, it did affect the 2nd harmonic the most. Maybe I can redo the adjustment now, with the better card.
I have (6) PCM61 but didn't really had time to rotate them. I was thinking to parallel them when I am bored