Don't have your line in volume up to 100%. 
Do these steps:
1) set the volume out on your sound card to generate 1V RMS at about 400Hz and measure it with whatever you have
2) set your volume on "line in" so that Arta gives you 0dB for that output which you set in step 1)
3) now measure your noise level with no cables on the input (Arta set on "external" not sine)
4) cable from LINE OUT to LINE IN, measure distortion; this is the distortion base level of your sound card
5) do things with your preamp
Do these steps:
1) set the volume out on your sound card to generate 1V RMS at about 400Hz and measure it with whatever you have
2) set your volume on "line in" so that Arta gives you 0dB for that output which you set in step 1)
3) now measure your noise level with no cables on the input (Arta set on "external" not sine)
4) cable from LINE OUT to LINE IN, measure distortion; this is the distortion base level of your sound card
5) do things with your preamp
You should always use whatever checks real 1VRMS as 0dBV spike, nothing else. And don't use more drive for the Sounblaster input DUT included. Its enough to check average level behavior and have a picture of what is your hum/buzz level for now. Monitoring that you know what you really do each time you tweak fast, and without need to listen for noises each time until best effort is done.
I've done some more wackoo experiments today. First I fiddled with my SB and Arta again. Everything seems to completely change after a night and a restart or two (Windows and Creative, well what to expect...) so I made a new calibration. Heres 78% out and 50% In (pic 1)
Then a new measure on same patient but I moved around stuff a lot. New grounding, some shielding, an inch shorter twisted pairs between SSHV and anodes, and the filament CCS moved to the audiocurcuit side. Awful curve but nicer values on THD and THD+N (dunno why). Thats pic 2.
Pic 3 is chokes tied to audioground (floating before).
Pic 4 is ONE SSHV instead of two and the circuits closed at audioside. SSHV upped to 60 mA. No major difference.
Thats measuring side. Listening side is fairly good. Hum inaudiable in the sofa but easy by the speakers. That is usually the same as no good grip in bass and thats exactly what it is. Flumsy.
Interesting thing (Flathead): Microfony is still there but it differs a lot between tubes. Last example was some Philips that had a lot of bass in right channel when i nail-pinged it. Then I shifted tubes left right and the behavior came in the left channel.
So I measured CSS-feeded filament voltage and the high microfony came in both cases from the tube with 6,2 VDC. The tube with 6,05 VDC had a mere brigtht and much lower ping sound.
Extremely sensitive to filament voltage in this config apparently. Maybe to the type of voltage too. To be examined...
Then a new measure on same patient but I moved around stuff a lot. New grounding, some shielding, an inch shorter twisted pairs between SSHV and anodes, and the filament CCS moved to the audiocurcuit side. Awful curve but nicer values on THD and THD+N (dunno why). Thats pic 2.
Pic 3 is chokes tied to audioground (floating before).
Pic 4 is ONE SSHV instead of two and the circuits closed at audioside. SSHV upped to 60 mA. No major difference.
Thats measuring side. Listening side is fairly good. Hum inaudiable in the sofa but easy by the speakers. That is usually the same as no good grip in bass and thats exactly what it is. Flumsy.
Interesting thing (Flathead): Microfony is still there but it differs a lot between tubes. Last example was some Philips that had a lot of bass in right channel when i nail-pinged it. Then I shifted tubes left right and the behavior came in the left channel.
So I measured CSS-feeded filament voltage and the high microfony came in both cases from the tube with 6,2 VDC. The tube with 6,05 VDC had a mere brigtht and much lower ping sound.
Extremely sensitive to filament voltage in this config apparently. Maybe to the type of voltage too. To be examined...
Attachments
Did some more tries today, and recalibrated soundcard to 1012 mV in and 0 dBV out (pic 1).
Then I pushed in some RCA black anodes that took 5,6/5,8 VDC from the filament CSS (pic 2).
For fun I pulled left channel in and out (pic 3)
Then I run only left channel in/out (pic 4)
I did loopback on soundcard again R-R (pic 5). 50 Hz and small harmonics.
R-L (pic 6) small 50 Hz bigger harmonics
L-L (pic 7) No 50 Hz no harmonics to talk about
L-R (pic 8) 50 Hz medium harmonics
Then I pushed in some RCA black anodes that took 5,6/5,8 VDC from the filament CSS (pic 2).
For fun I pulled left channel in and out (pic 3)
Then I run only left channel in/out (pic 4)
I did loopback on soundcard again R-R (pic 5). 50 Hz and small harmonics.
R-L (pic 6) small 50 Hz bigger harmonics
L-L (pic 7) No 50 Hz no harmonics to talk about
L-R (pic 8) 50 Hz medium harmonics
Attachments
Pic 1 is loopback calibration Iko + 0,1 dBV. Pic 2 is same but thru preamp -1,1 dBV.
I opened it up and found a broken sense wire. Dont know if it was or if it broke when I opened. Ethernet twisted pair, nicely twisted but they break very easy.
Im rewiring back to 1 SSHV per channel, will measure B+ on live circuit with (new!?!) scope.
I opened it up and found a broken sense wire. Dont know if it was or if it broke when I opened. Ethernet twisted pair, nicely twisted but they break very easy.
Im rewiring back to 1 SSHV per channel, will measure B+ on live circuit with (new!?!) scope.
What I'm saying is, show pic 2 but with no 1V signal through the preamp. Understand? You can set Arta instead of "sine" to "external". So, after you calibrated the sound card, you use no cable on the input to the preamp, and connect the output of the preamp to the input of the sound card. Then run Arta set on "external" signal. Then the 50Hz and related harmonics dBv are relative to the 1V and you will finally get a good idea of how bad/good it is.
Capishe. Thanks Iko, I will investigate how to do that.
Yea thanks I'm gonna dummy load measure it and live circuit measure it again. I did measure on dummy b4 and it was flat like a salt desert.
Tho I agree that I'm cutting corners a bit. Need to investigat the parts.
I need to figure out the 50 Hz and also if the harmonics are from that or from the 1 kHz
The up side is that I'm learning a lot on tools. The bad side is that I'm boring you of course.