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Old 25th December 2011, 11:50 AM   #221
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Merry Christmas,

Here is a link to the ones I purchased.
McMaster-Carr

McMaster also has sorbothane grommets which I think would even be better.
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Old 25th December 2011, 12:04 PM   #222
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Quote:
Originally Posted by merlin el mago View Post
Could you post a pic
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Old 25th December 2011, 12:41 PM   #223
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Originally Posted by SGregory View Post
Merry Christmas,

Here is a link to the ones I purchased.
McMaster-Carr

McMaster also has sorbothane grommets which I think would even be better.
Thank you guys & Merry Christmas for everybody.
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Old 28th December 2011, 10:10 AM   #224
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Default 6v6 CCS loaded CF compared to 12b4 Gyrator loaded

Attached are two curves comparing my old 12b4 gyrator loaded preamp vs. the new 6V6 CCS loaded CF. I quickly threw together my measurement system and calibrated it. Noise floor is -145db and is flat from 20 to 44kHz.

All measurements were taken with 1Vrms signal and ploteed so that 1Vrms = 0dB. The soundcard is a 1616m using audiotester software. Audio Tester has come along way from the last time I used it. Did not have one crash.

The first plot is frequency response. the -3dB for the 6V6 is beyond my measurement set-up.

The second plot is the FFT of a 1kHz signal. What immediately jumps out is the difference in noise floor. Keep in mind that the 6V6 is currently configured is using AC heaters with no attention to sheilding and a marginal ground scheme. What I havn't shown is that even with the 6V6 isolated on grommets, it isn't enough isolation. The plot used here is with the preamp resting on acoustic felt to decouple it from the counter. The remaining grass seen on the 6V6 plot is, imho, a combination of ground loops, acoustic noise polution and microphony of tube, and absolutely no shielding.

The distortion of the 12b4 measures 0.133% while the 6V6 measures 0.031%. Very nice improvement.

In general I continue to enjoy this change in my system. Certainly more tweeks to come like DC heaters, better shielding and improved mechanical decouplings of the tube.
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File Type: jpg 6V6_vs_12b4 Sweep.jpg (143.8 KB, 573 views)
File Type: jpg 6V6_vs_12b4 1kHz FFT.jpg (201.9 KB, 546 views)
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Last edited by SGregory; 28th December 2011 at 10:13 AM.
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Old 28th December 2011, 10:24 AM   #225
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Is its B+ regulated yet?
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Old 28th December 2011, 10:28 AM   #226
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Yes. Using Version One of the SSHVS. 65mA total current right now per channel.
I plan on increasing that to about 80mA since I have the heatsink and power supply available.
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Last edited by SGregory; 28th December 2011 at 10:30 AM.
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Old 28th December 2011, 10:31 AM   #227
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So there should not be much power rail hum mixed in. I think it could be lower in harmonic noise after you sort it out. But the base line got much lower already.
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Old 28th December 2011, 10:34 AM   #228
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P.S. Measure with another make also, the new Tungsol is good.
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Old 28th December 2011, 10:37 AM   #229
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I agree, lots of room for improvement. Over the next few days will build a filtered DC supply for the heaters. I don't know if I want to regulate it or not.

That reminds me that I have the heaters lifted to 100V. Need to set them back down now to around 20V
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Old 28th December 2011, 10:48 AM   #230
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The tube model is usually central to harmonic noise issues.
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