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Old 26th April 2013, 10:59 PM   #2091
Salas is offline Salas  Greece
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Its test tone THD is nice, but clean it up by several dB for harmonic noise. I hope its not an indication of some form of oscillation. It will not be if it changes with grounding, positioning etc.
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Old 26th April 2013, 11:20 PM   #2092
Salas is offline Salas  Greece
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Quote:
Originally Posted by stajo View Post
Should I use 100% now for measuring?
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.
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Old 28th April 2013, 08:57 PM   #2093
stajo is offline stajo  Sweden
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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...
Attached Images
File Type: png Soundcard day 2.png (72.9 KB, 144 views)
File Type: png m1.png (86.1 KB, 142 views)
File Type: png m2.png (26.4 KB, 136 views)
File Type: png m3.png (87.0 KB, 130 views)
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Old 29th April 2013, 01:35 PM   #2094
stajo is offline stajo  Sweden
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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

Attached Images
File Type: png SB.png (67.9 KB, 104 views)
File Type: png m1.png (70.2 KB, 21 views)
File Type: png R.png (62.0 KB, 21 views)
File Type: png L.png (70.0 KB, 16 views)
File Type: png SB R-R.png (63.8 KB, 15 views)
File Type: png SB R-L.png (71.3 KB, 15 views)
File Type: png SB L-L.png (62.3 KB, 14 views)
File Type: png SB L-R.png (62.9 KB, 14 views)
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Old 29th April 2013, 01:47 PM   #2095
Salas is offline Salas  Greece
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Run only one card's channel in tests and experiment with ground lifting.
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Old 29th April 2013, 01:55 PM   #2096
iko is offline iko  Canada
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To me, the very obvious thing is that you might want to clean up your power supply. I don't know why, after calibration, you don't show a test of the preamp, but with no 1kHz test signal through it. That will show you how bad the 50Hz and related harmonics really are.
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Old 29th April 2013, 02:23 PM   #2097
stajo is offline stajo  Sweden
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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.
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Old 29th April 2013, 02:31 PM   #2098
iko is offline iko  Canada
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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.
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Old 29th April 2013, 02:33 PM   #2099
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Perhaps itīs time you split the PSU and amp and put them far apart while investigating where the problem is.

You have taken the hard aproach with both chokes and PSU in the same enclosure.
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Old 29th April 2013, 02:46 PM   #2100
stajo is offline stajo  Sweden
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Quote:
Originally Posted by iko View Post
Understand?
Capishe. Thanks Iko, I will investigate how to do that.

Quote:
Originally Posted by flatheadmurre View Post
Perhaps itīs time you split the PSU and amp and put them far apart while investigating where the problem is.

You have taken the hard aproach with both chokes and PSU in the same enclosure.
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.
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