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Old 21st April 2010, 12:00 PM  
SY is offline SY  United States
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Join Date: Oct 2002
Location: Chicagoland
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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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5th November 2012
PET-240
diyAudio Member
Gday Sy,

Still haven't heard from Mr Gregory, will email again to be sure, anyway, asa thought, had you looked at the 6N2P tube? If the D3a is all over the shop, not sure the sound or ease of use, im sure you would know by looking at it.
Also, if I wanted to get a balanced output, what's the process here?

Thanks,

Drew.
5th November 2012
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SY
diyAudio Moderator
Easiest way to get a balanced output is to use a transformer. Otherwise, you're looking at adding another stage. IMO, balanced brings nothing to the table between preamp and power amp for home installations.
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
20th February 2013
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luvdunhill
diyAudio Member
Many, if not all phono preamps for MC have switchable loading resistors. I'm curious, is that not needed in your opinion, or is there something about the design that makes this unnecessary?
20th February 2013
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SY
diyAudio Moderator
My experience with low output MC is that they tend to be very noncritical of loading. If you do want to play with that, do it on the primary side of the input transformer.
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
22nd February 2013
gortnipper
diyAudio Member
I just inherited a nicely built up HMN that a a late friend of mine did last year before he passed.

He built it up with Jensen JT-44K-DX transformers, but he did not add the Jensen recommended Zobel after the secondary.

http://www.jensen-transformers.com/datashts/44kdx.pdf

Now, I have these same transformers in a standalone SUT I have used for years with various carts (with varying degrees of success), and it uses the recommended implementation.

In the HMN w/o the Zobel , the sound is very bright and the bass is very thin in comparison - which is consistent with what I have read should be the case in this type of standalone implantations of the JT-44K-DX w/o it.

Do you forsee any issues in adding this immediately after the tx secondary in the HMN?
22nd February 2013
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SY
diyAudio Moderator
No, I don't see an issue- if you want to be thorough, load the transformer with the proposed Zobel and ~100pF in parallel, then drive it with a square wave from a source impedance equal to the DCR of your cartridge at 0.1mV or so (a resistor voltage divider is your friend here!). See what the square wave looks like.

While you're at it, double check that the EQ components are all correct.
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
22nd February 2013
gortnipper
diyAudio Member
"While you're at it, double check that the EQ components are all correct."

This may be beyond my nascent abilities. See the attached pics that show a break in the traces on the board adjacent to C7. From the wiring coming from the output end of the board, it looks like the two boards on the end of the chassis have been inserted into this break point.

I will have to figure out what these are for.

Any ideas?
23rd February 2013
gortnipper
diyAudio Member
OK, so the photos I attached earlier didnt show up. You can see them here - Flickr: gortnipper's Photostream
6th April 2013
SMOTH
diyAudio Member
Hey there...

I'm a bit new to this of thing... I've read the article several time and I love the sounds of this project! I'm just wondering if I could build this for a mm cartridge, and skip the need for a step up transformer? If that would indeed work, would I have to make any further modifications? Apologies if this is a rudimentary question, and thanks in advance for any advice.
7th April 2013
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SY
diyAudio Moderator
Two caveats: first, you obviously lose the advantages of the balanced input. Second, the input capacitance is quite high, which some MM cartridges tolerate and some don't.
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

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