TSE measurement over time

[Evenharmonics]

Anyone kept a log of their TSE measurements over the years? Below are what I compared. White graph is from 2010 and green is from today. Granted, the measuring device calibration has been changed slightly since but I wonder what could possibly make the two graphs look so different from same amp 2.5 years later. Any thoughts? THD and THD+noise numbers haven't changed much but the extension of harmonics is somewhat scary (to me).

 

[rknize]

Have you checked the spectra of your source? That looks like signal generator noise to me.

 

[Evenharmonics]

I did and it's fine.

 

[Evenharmonics]

On thing I should add, both channels produce about the same characteristics so I'm guessing it's a common source.

 

[rknize]

Anything funky about the output wave form? Is the heater supply quiet?

 

[Evenharmonics]

Have you checked the spectra of your source? That looks like signal generator noise to me.

You were kind of right. It was the source in an indirect way. The sound card and signal were fine but for some reason, when it entered the amp, something got added. Static maybe?

Anyway, I redid the measurement today and it looks normal. While I'm at it, I decided to play around with bias. As George mentioned in his TSE build steps, trying different bias and see how they sound, I measured 3 different settings below. First is set at 58 mA, second at 62 mA and the third at 72 mA. I find it interesting that as bias goes up, THD decreased but high order harmonics increased. As bias went down THD increased and high order harmonics decreased. How do they compare in terms of sound? It's going to be a time consuming and difficult process because there is no way for me to change bias quickly enough to make an accurate comparison. I'll report back in a few days if I audibly notice something between these bias settings.