His Master's Noise: A Thoroughly Modern Tube Phono Preamp - Page 19

21st April 2010, 12:00 PM
SY On Hiatus Join Date: Oct 2002 Location: Chicagoland	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... Click here to read the entire article Last edited by Variac; 2nd April 2011 at 12:17 AM.

12th August 2014

On Hiatus

Since the DCR is pretty similar to the Technics (14 ohm), it was a drop-in replacement; no retuning at the step-up secondary needed. Still dead quiet.

I've got mixed feelings (though mostly positive) about the 103R- there's more of the "classic MC" coloration than I'd like (slight upper midrange dip, rising top octave), and it took a few mechanical mods to optimize it. All in all, it's pretty good. I think that the Audio Technica 150MLX with my new preamp (Equal Opportunity) is better, and a low-hours Technics EPC100C Mk4 that I snagged is better yet, but the Denon is excellent for the money and very easy to listen to.

"You tell me whar a man gits his corn pone, en I'll tell you what his 'pinions is."

13th August 2014

Brinkman

diyAudio Member

Quote:

it took a few mechanical mods to optimize it.

Was this more involved than simply adding mass to the headshell? And if I may ask, was this by ear or did you take measurements? I'm curious because I'm not sure such a FR dip at the cart would match well with the LS3/5A-style speakers I have planned to build down the road.

13th August 2014

On Hiatus

I drilled a couple small holes in the cartridge body and filled the space with a filled viscoelastic polymer. I see that other people actually pull off the body and replace it, which scared me a little bit.

The trick (besides a steady hand with the Dremel and drill bit and knowing where to drill) is propping the cartridge up on its pins before injecting the uncured resin (which has to be low viscosity). Since I run a chem lab, I was able, cough, cough, to have one of the guys formulate a suitable epoxy. I filled the epoxy with some powdered high damping elastomer that I had cryoground before injection.

This sounds involved, and I guess it is, but it's easier for a chemist to pull off in lieu of precision machining a new headshell. A skilled machinist with a good Bridgeport could bypass all of this and just fabricate a tight-fitting shell.

The differences were not night and day, but my uncontrolled perception was a bit more "tidiness" to the midrange sound.

Actually, I think the 103R could be a very nice match for LS3/5A.

"You tell me whar a man gits his corn pone, en I'll tell you what his 'pinions is."

26th August 2014

luckythedog

diyAudio Member

Hi Sy, the article still stands as very worthy IMO. Thought to return a comment since the extent to which noise has been considered seems comprehensive yet there is one aspect which I recently became aware of which seems relevent and I can't see covered.

Series resistance of the the primary winding of the SU tx appears at the tx secondary output multiplied by (turns ratio)^2 as a noise source. In series with the resistance of the secondary winding itself, which might also be significant as a noise source. In the grand scheme of things when other noise sources have been reduced to the limit, intrinsic noise within the SU transformer remains potentially significant in principle I think, and should be considered as a selection criteria for the SU transformer - particularly if the SU (turns) ratio is high.

26th August 2014

On Hiatus

Absolutely true in theory. But let's put some numbers in: the Sowter I used has a primary DCR of 0R72. Compare that with the cartridge DCR (~15R) and it's pretty well buried. Likewise, the secondary DCR is about 100R, which is negligible compared to the reflected impedance of the cartridge (1k5).

But your point is valid- if we use a cartridge with a low DCR, we'll want to choose a transformer with a low primary resistance in comparison. Because the noises add in quadrature, a transformer resistance less than 1/3 that of the cartridge will be pretty negligible.

"You tell me whar a man gits his corn pone, en I'll tell you what his 'pinions is."

26th August 2014

luckythedog

diyAudio Member

Sy, yes your choice of SU tx looks spot on, and I agree in that case it's not significant. Worth noting that not all SU tx are equal, and certainly not if one subs in tx not devised for the job I think. Aside, leakage inductance of the primary also appears ^2 in series with the secondary, and that's another story and rarely specified for SU tx. Just to comment that I think these things are worth noting if subbing an alternate tx perhaps.

26th August 2014

On Hiatus

Also absolutely true, and one of the reasons that some high resistance MCs (e.g., DL103 at 40R or higher) just don't seem to play well with transformers. Appreciate you filling in the blanks!

"You tell me whar a man gits his corn pone, en I'll tell you what his 'pinions is."

26th August 2014

6L6

diyAudio Moderator

It's not that the non-permeable former MC carts don't play well with transformers, (most commonly the Denons) but that most transformers are optimized for a much lower coil inductance.

Really low primary transformers is difficult to wind and to get to couple, and so need to be used in the range they are designed for. To high coil impedance, and they get funky response.

Conversely, if the cartridge inductance and coli inductance is mated properly, all becomes happy. (And incidentally the SUT are actually much easier to make.)

I have a set of Electra-Print SUT that are centered on a nominal 40R cartridge coil. My plan was to use a Denon of some sort, either a hot-rodded DL103 or a DL-S1.

It will also be good with my medium output Benz (50R coils)

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24th November 2014

spinning wheel

diyAudio Member

Great thread !

Would the input tube handle moving magnet/iron carts as well ?
I mean when one omits the sut ? what's the input capacitance of a D3A
or E280F ?

Thx ,
Paul

24th November 2014

On Hiatus

It's pretty high, a few hundred pF. If your cartridge is happy with that (plus the 100-150pF or so of the interconnects), you can use the circuit minus the input transformer. You do lose the advantage of balanced input, though. That's why I designed the Equal Opportunity for MM use; I'm a firm believer in balanced operation of phono cartridges.

"You tell me whar a man gits his corn pone, en I'll tell you what his 'pinions is."