Even in LA phono of the month seems to be at the audiophiles heart. I have several in the works.
Doug, I somehow get the impression you have never tried to ELIMINATE hum from the usual unbalanced phono input system in real life.
If you are writing a book about the electronics of phono playback systems, you should at least include a chapter on how to do this in practice ... all the caveats & gotchas with earthing etc. And don't forget the RFI issues too.
You've made a statement that its trivial to get unmeasurable hum with an unbalanced system.
I would very much to know how you achieved this feat.
Having said all this, you may want to go through Wayne's threads on the subject and check out his detailed measurements. He says it is MUCH easier to achieve unmeasurable hum with a balanced system and he backs it up with measurements too.
He also shows one (two?) way(s) to achieve near 1dB 'NF' for both MM & MC with a balanced input. You'll probably find the MC situation slightly more difficult to achieve your unmeasurable hum.
Last edited:
Bruce Hofer from AP told me they went over to MLCC NPO/COG for all new products because they are superior to whatever film caps they can get. Cheaper and smaller too.
I'm not normally an 'I have it on authority' guy but for this I make an exception ;-)
Jan
Richard, I think gentle persuasion with some hard data would go a long way. I've never had until just now a TT without a DIN5 connector and I think it would be nice to at least to put the information out there for folks to experiment with other possibilities. Doug is not going to update a book saying everyone should go and find a tech to rewire their Thorens TT's and go full differential. This approach just makes the whole idea threatening.
Having said all this, you may want to go through Wayne's threads on the subject and check out his detailed measurements. He says it is MUCH easier to achieve unmeasurable hum with a balanced system and he backs it up with measurements too.
He also shows one (two?) way(s) to achieve near 1dB 'NF' for both MM & MC with a balanced input. You'll probably find the MC situation slightly more difficult to achieve your unmeasurable hum.
So give me a link that works.
It's not the lack of hard data, it's the lack of even a theoretical mechanism for how common-mode rubbish can get into a cable with just a floating coil at one end.
Unless of course you have an electrically unscreened cartridge, which seems to me a crazy way to carry on.
And then the hum won't be a true common mode signal; I dare say you could have a 'balanced' input in which you set the gain of each input separately so you could try to null out a sort-of-common-mode signal. Good luck getting that to stay nulled as the arm moves across the disk.
In standard grounded shield single ended applications common mode has no meaning. Grado's MI cartridges have probably 10's of thousands of happy users and I'm sure there are a few others. For one thing they don't use the cap loading to tune against the cantilever resonance.
Quite, but we are talking about a balanced input with a floating source across it. A common-mode voltage is possible, but where can it come from?
Are they really happy users? Typing 'Grado hum' into google gives an avalanche of hits.
Here's one, titled 'The awful Grado cartridges':
http://www.vinylengine.com/turntable_forum/viewtopic.php?f=19&t=27154
Last edited:
Any hints, new or already published?
Using any MLCC NPO/COG parts
Suggest to Doug
Tackle a SMT design, or at least discuss the design requirements and techniques. THT is coming to a limited availability end, so why use parts that are becoming obsolete? This is small signal design after all.
So many design books written, but so few having actual designs, pcbs, boms.
CAD is a bit of a problem, because so many are available and learning curves.
But there are free or low cost pcb cad pkgs that can be used, ie diptrace, eagle.
Designer's have to learn to do pcbs and not through them over the wall, to people like me
. I start to through them back now that I can It is all part of the design process, isn't that the idea of a circuit design book, to make something work in real life? I have the same input to Bob Cordell too, not sure if he is listening to me ramble on
Last edited:
IMVLE I'm not aware of deliberate screening in any of the moving coil cartridges I owned over the decades, but I might have missed something.
I currently have one HOMC (a Benz Ebony H) and three Ortofon LOMCs: an SPU A95, an SPU Royal N, and a Windfeld.
The Benz definitely isn't screened and this is easy to see as it sits in a wood body that is entirely open on the bottom. Hum has never been a problem as long as screened leads are used. None of the wood bodied Benzs are screened.
Harder to tell with the Ortofons, but I have no reason to believe they are screened either, there certainly is no external evidence for that.
I've also owned a ZU Denon DL-103, the aluminum body provides some electrostatic screening if it's grounded (not always the case) and is open on the bottom. Unmodified DL-103 and DL-103D were not screened.
I've owned a fair number of other MCs over the years, and had a brief and very unhappy flirtation with a wood bodied Grado that also was not screened. (Hum was not a problem with this induced iron cartridge.)
All of these cartridges have source impedances that would be considered low compared to an MM. My LOMC types are all 6 ohms or less. (200uV - 300uV unloaded @ 5cm/sec lateral recorded velocity)
I generally use SUTs as step ups but also have a 26dB head amp a friend designed for me a few years ago. Because of the way I put things together I've never had the possibility of an easy way to evaluate whether balanced connections would improve performance, they definitely do not work with conventional RCA cables. (It was easy to try)
SY is a firm believer in balanced operation with LOMCs and given his propensity for scientific rigor (i.e. he forms a hypothesis and tests it rigorously) I have to believe in so far as LOMC cartridges are concerned there is a significant improvement. I believe he touches on this in his "His Master's Noise" phono pre-amp article.
Peace Doug, you are truly indefatigable to use an old expression. The Grado crowd will have to look elsewhere. Always respect your contributions, for me there is always a little room for professional disagreement.
Err.rrh! The missing data is that supporting Doug's incredible claim on unmeasurable hum in an unbalanced phono playback system.
I'm sure all of us can provide examples of how difficult it is to achieve very low hum in such a beast .. especially with Lo Output MC.
Wayne shows one successful method with an IA approach .. but if Doug has a method which doesn't require IA, rewiring bla bla ..
... I'm sure ALL of us will want to know how to do it too.
Err.rrh! I've posted the link(s) 3 times now, the last time in #74. I didn't realise you weren't interested in looking through them.
For your convenience, one set of measurements is on page 14 of
Pro Audio Design Forum • View topic - Flat Phono Preamp Based on John's P10 and 2SK389
from #74.
On the same page, is a caveat about earthing turntables.
Wayne also reminds me that many arms had a 5p DIN connector; the evil SME gold plated phono cables going from that to the preamp. The wiring from that 5p DIN to the cartridge terminals is usually floating with shield. That means its not that difficult to achieve floating into balanced like Wayne.
Doug, there's also stuff about earth straps on cartridges etc which you might want to include in your How to achieve unmeasurable hum phono system with unbalanced inputs
Some of this will be familiar to practitioners of the black arts like "how to deal best with the evil SME phonos".
There's more measurements in the other thread(s) on his website. I think I posted a link to an other in $74.
And I apologise. He doesn't achieve unmeasurable hum like you do.
But he does find noise & RFI advantages too.and also really good stuff about de-clicking, EVIL LME49860 etc.
Err.rrh! That's a the bumblebee can't fly argument.
If 'theory' and practice don't coincide, guess which is wrong.
The 'screened' cartridge is one of the gotchas you need to address in your chapter on unmeasurable hum. Wayne comments on this at several points. You have to look at cartridges which don't make electrical contact with the arm too.
__________________
I'm sure discussions on passive vs active RIAA EQ, Neumann poles bla bla will be interesting to readers of your new book but is unlikely to actually help them get better sound.
But unmeasurable hum WILL result in better sound.
__________________
May I ask you a question Doug?
Do you actually have and use a phono playback system at present or have a good friend who is amenable to you conducting experiments?
There's no shame in answering "No." I'm sure many, even in this august forum, will be the same. My phono system and records are all in my sister's shed on the other side of the continent.
But it would give context to your pronouncements on phono playback systems.
Wayne and Gold on Wayne's website still do and Gold does vinyl mastering for a living so their comments have some weight.
If you go for analog - although DSP having arbitrary precise RIAA filter function is clearly an option- then there are basically these options
a line out level at "0dB" 1 khz is specified and also the input at 0db ( 5cm/s)
thus follows the necessary gain
one could opt for linear amps and a passive RIAA low pass filters between
one could opt for linear amp input driving passive 75 µs and output active providing for 318 µs and 3180 µs
or just changed the sequence input active providing for 318 µs and 3180 µs
driving passive 75 µs and linear output
or input active providing for 318 µs and 3180 µs driving a "subsonic" hi pass
- warped disks could require such- and an inverting output with the 75 µs
in these four possible topologies how to split gain
I have never used a professional microphone, dynamic, ribbon or condenser that was not balanced. What advantage would balanced give them that it would no give to a phono cart? Or is it just the cable length difference?
Anyhow, it would be nice to see some different approaches covered. Balanced, DSP, passive vs active or split and so on.
Anyhow, it would be nice to see some different approaches covered. Balanced, DSP, passive vs active or split and so on.
- Status
- This old topic is closed. If you want to reopen this topic, contact a moderator using the "Report Post" button.