I said I am trying. How would you do it then?
My own point is not that high end stuff put an electrlytic cap in series with the MC cartridge. What I said was, that I have seen this. I can only speak of these and cannot generalise.
What "getting rid" of means is what I/we are trying to figure out.
1 muA = 0,001 uA = 1 nA. To me, that would mean JFET input stage for an all solid state cartridge series cap-less design.
It is also about 1000 times less that mentioned in this thread.
Good input.
Sigurd
My own point is not that high end stuff put an electrlytic cap in series with the MC cartridge. What I said was, that I have seen this. I can only speak of these and cannot generalise.
What "getting rid" of means is what I/we are trying to figure out.
1 muA = 0,001 uA = 1 nA. To me, that would mean JFET input stage for an all solid state cartridge series cap-less design.
It is also about 1000 times less that mentioned in this thread.
Good input.
Sigurd
h_a said:
How could this happen ?
Maybe you use a different system, just for clarity for me muA (mu for the greek character) are microamperes, that is 10^-6 A. 1nA (nanoamperes) are 10^-9A.
I don't have any numbers at hand for these extremely low output MC-cartridges, so I cannot quickly calculate, but I guess i wouldn't care about 10^-6 A.
What I tried to point out, was only that if an elco is an accepted 'blocker' in high-end - and it's a pretty bad blocker - the leakage current that still passes is a hint on what can be safely ignored or at least is usually regarded as such.
Not a good argument, but better than none.
Of course if that makes you feel uncomfortable, you can stick to jfet-frontends.
Have fun, Hannes
As I pointed out it really shouldn't be that difficult to get some real # on DC current effects in MC cart
how about using the bender from a $3 piezo horn tweeter as a mechanical excitation source
a sound card, Cap coupled MC preamp, power amp and a little free software
drive the piezo bender with the power amp @ 1-2KHz (bender resonance?) from soundcard, rest the MC cart stylus on the bender
look at fft of MC pre out with soundcard
apply slowly varying "DC" current to MC coil, at a frequency enough larger than the line-width of the 1-2KHz MC output you see in the fft
average as long/many fft records as needed to pull the signal out of the noise, looking for IMD products from the coil current modulation
how about using the bender from a $3 piezo horn tweeter as a mechanical excitation source
a sound card, Cap coupled MC preamp, power amp and a little free software
drive the piezo bender with the power amp @ 1-2KHz (bender resonance?) from soundcard, rest the MC cart stylus on the bender
look at fft of MC pre out with soundcard
apply slowly varying "DC" current to MC coil, at a frequency enough larger than the line-width of the 1-2KHz MC output you see in the fft
average as long/many fft records as needed to pull the signal out of the noise, looking for IMD products from the coil current modulation
jcx said:
What about a piezo buzzer @1.2KHz http://search.digikey.com/scripts/DkSearch/dksus.dll?Detail&name=668-1190-ND excited from a 50ohm, 40Vpp max, sine source? Resonance will be amortized, but I suppose strong enough to get the nominal output from the MC. No power amp required.
I may actually try this over the weekend. The only concern I have is measuring the tonearm damping, rather than the MC IMD.
as long as vibration level and linewidth are OK these types of piezo transducers seem like a good place to start
experiment seems the quickest way to show if ceramic piezo material mechanical loss and piezo hysterisis give too much line broadening in the vibration to easily make the IMD measurement - although I'd guess there is no reason the coil current modulation couldn't be raised to ~100 Hz (avioding line frequency multiples)
experiment seems the quickest way to show if ceramic piezo material mechanical loss and piezo hysterisis give too much line broadening in the vibration to easily make the IMD measurement - although I'd guess there is no reason the coil current modulation couldn't be raised to ~100 Hz (avioding line frequency multiples)
scott wurcer said:syn08,
I forgot to ask, do you see any merit in an outboard 60Hz drive amp for the TT? I also use a VPI, in fact it was the review sample for TAS (my first exposure to their review techniques
You mean for the motor? Absolutely not. Its the motor itself that indeed needs replacement with a more performant synchronous model.
What are you using as a replacement? I'm pondering myself between a VPI Scout SAMA ($400, outrageous) or a motor replacement. The original VPI model is driving me nuts with the rumble (and its not about mine being old, I have already replaced the original, no good).
.
Are you guys especially charmed by the look of the VPIs?
Technically you would be far better off with any direct drive turntable. These pushed the envelope concerning rumble and speed precision in the 80ies and - to my knowledge - are unrivaled since then. 400$ should bring you a unit in excellent condition.
Have fun, Hannes
Technically you would be far better off with any direct drive turntable. These pushed the envelope concerning rumble and speed precision in the 80ies and - to my knowledge - are unrivaled since then. 400$ should bring you a unit in excellent condition.
Have fun, Hannes
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h_a said:
TT's is probably the only area of audio where I indulge in subjectivism. I'm a big fan of SME and Graham tonearms (and happen to really dislike the VPI JMW), I also happen to like a lot Benz Micro cartridges, and Clearaudio MM. I subjectively disliked much more expensive cartridges, like the Koetsu Rosewood Signature.
My ideal TT would be a VPI Super Scout Master Reference with a Graham B44 tonearm and a Benz Micro Ebony Wood or Clearaudio DaVinci cartridge.
Otherwise, I am not qualified to do an evaluation belt drive vs. direct drive.
h_a said:
That's $400 I'd rather not bother spending, if it means a new arm, etc. it just gets more and more. I have an existence proof (to me) that after a good rub down of the belt with baby powder I get transfers that make me happy.
Yes you are right, make two consecutive copies of the same LP and put them into Diffmaker
Ahhhhh, yes the evil word
In the end everybody has his own, personal areas of subjectivism
Right. So I just didn't even start to bother and got a Pioneer PL-L1000 from which above specs are. The looks are certainly not everybodys taste, but if you happen to like them you get a truly great linear tonearm for free. Another source of distortion eliminated.
Have fun, Hannes
EDIT: forgot, the Kenwood KD-990 meets more the general taste and has also a very nice 10.5" arm. Tons of other directdrives not as popular as a SP10 available with very competitive specs at much small price.
Use caution with those early direct drive turntables. The servos are pretty primitive. While they have the correct rotation and low measured flutter they are not really "stable" and act like they have zero gain on frequency. They tend to shift up and down about the target speed. Like a primitive pll. Since the 80's PLL design has become much more sophisticated. PLL Design primer
A real rework on one of those early direct drives could have a major effect on the sound but isn't going to be successful without an understanding of the challenge. Scott is probably up to it. Its most likely too deep for me. I have an SP10 that I'm not happy with, and SP15 that seems to sound better and a granite behemoth with a Pabst direct drive that seems pretty good but too big to set up. A 50 Lb platter can do wonders for servo problems.
A real rework on one of those early direct drives could have a major effect on the sound but isn't going to be successful without an understanding of the challenge. Scott is probably up to it. Its most likely too deep for me. I have an SP10 that I'm not happy with, and SP15 that seems to sound better and a granite behemoth with a Pabst direct drive that seems pretty good but too big to set up. A 50 Lb platter can do wonders for servo problems.
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