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Old 21st April 2010, 12:00 PM  
SY is offline SY  United States
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Default His Master's Noise: A Thoroughly Modern Tube Phono Preamp

After more than 25 years of faithful service, it seemed that it might be time to redo my phono system. After all, I like to think that I've picked up a few tricks in the intervening years... The old system consisted of a VPI HW17-II, a Linn Ittok LVII tonearm, and a Troika cartridge. The Troika was...

Last edited by Variac; 2nd April 2011 at 12:17 AM.
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30th December 2013
Brinkman
diyAudio Member
Regarding my last post, after a little googling, I have discovered that the noise contribution of an RC network is dominated by the kTC of the capacitor. In the case of the Zobel network Jones recommends, a 500pF cap would introduce about 4uV of noise.

Perhaps the 6k8 input R in combination with the miller capacitance was satisfactory enough to tame the 8055x? Still curious if the circuit was tried with the Zobel network.
30th December 2013
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SY
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I left the network out because, with the cartridge I was using, the combo of 6k8 and the input tube's Miller ended up giving me nice looking square waves.

Any noise from the Zobel is shunted by the source impedance, so is somewhat smaller than the noise of the network alone. That's dropped another 20dB as well when it's input-referred.
You might be screaming "No, no, no" and all they hear is "Who wants cake?" Let me tell you something: They all do. They all want cake.- Wilford Brimley
30th April 2014
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6L6
diyAudio Member
I'm a bit unclear on the requirements for the input transformers ... I have a set of custom Electra-Prints made for the Denon DL-103, 40ohm input to 100ohm output. Two-wire primary, two-wire secondary. Can those be used?
30th April 2014
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SY
diyAudio Moderator
You'll have to tweak the RC network across the secondary. Do you have a square wave generator and a scope? If so, it's easy and I can walk you through it.
You might be screaming "No, no, no" and all they hear is "Who wants cake?" Let me tell you something: They all do. They all want cake.- Wilford Brimley
30th April 2014
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6L6
diyAudio Member
That's it? Awesome! I was concerned about the balanced wiring thing.

Yes, I have a generator and scope.

I'll order the boards from Jack right now.
30th April 2014
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SY
diyAudio Moderator
You'll still want to run balanced in- the noise advantage is remarkable. All it takes is making up some cables (I used mike cable) and the right connectors (my prototype used DIN, my "nicer" build uses mini-XLR).
You might be screaming "No, no, no" and all they hear is "Who wants cake?" Let me tell you something: They all do. They all want cake.- Wilford Brimley
30th April 2014
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6L6
diyAudio Member
I fully intend to.

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