Cartridge Loading.....Part II
I read last night the below noted discussion with great interest. It's a long post but worth the effort and I found it interesting.
It started me thinking about the amount of loading on my moving coil cartridges. Years ago I purchased my first MC Cart, a very nice Benz Micro Glider, medium output of 0.5 mV as I recall. At that time I inquired about loading here on Audiogon. I was convinced, via discussion, by another member, that 300 Ohms was the magic number, so I thought.
Time moved onward and my second MC Cart is currently a Lyra Delos, again medium output 0.6mV. Both carts had Boron cantilevers', 6 nines oxygen free copper coils and line contact diamond stylis. When I set up the Delos I did not change or even consider 'loading' changes. That was a grand mistake.....
Well, thanks to this specific thread I started to second guess myself . (you can do this when retired and more time is on your hands....)
My take from this recent thread is as follows. Load at 100 Ohms or at 47K Ohms with a quality MC cartridge. I opened up my Conrad Johnson EF1 Phono Stage this afternoon. Found it set at 500 Ohms loading. 100 Ohms is not an available setting. Damn...All these years I've been running the wrong loading, and on two carts, back to back... I don't recall why I set the loading at 500 Ohms. Faulty logic.
I reset the loading to 47K, buttoned things up and called the wife in for a listening session. Sure as heck both of us noticed the highs were crisper and more 'apparent' than in the recent past. Not a huge difference, but yes, a difference.. Hard lesson learned!
So, you smarter folks on this site might banter amongst yourselves, but in reality there are those of us, behind the curtains, reading and listening! I just wish I hadn't wasted all those years listening to the incorrect load setting!
Ending with a sincere thank you very much!!
Lou
Ralph, The two statements you quoted from me seem to align well with each other and I was unaware that there was a different versions of ohms law for static vs dynamic loads
I agree it is an interesting choice but his measured results clearly show signal and if if anything a lower noise floor so I fail to see where the issue is or how it invalidates his results. dave
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In the case of a transimpedance input, feedback is applied to the output of the cartridge. Its a fair amount of feedback too- the more output the cartridge has the more feedback. That is quite a bit different than a simple resistor- you can’t equate a virtual ground with a static resistance- for one thing, you need an opamp to even create a virtual ground. Ohm’s Law certainly is in play (how could it not be), but the issue here is that while a cartridge has its output at a virtual ground, that is significantly different from having the cartridge drive 0 Ohms (IOW, if it were actually tied to ground). In the case of the former, the actual input impedance is dynamic and isn’t actually 0 Ohms, so amplification can occur because a signal is present. In the case of the latter, the load is actually a short and because the signal is shorted out, no amplification can occur. ’Virtual’ means ’almost or nearly as described, but not completely or according to strict definition.’ If the 0 Ohms of a virtual ground is conflated with the 0 Ohms of actual ground, confusion is the direct result. Real ground is when a terminal is connected physically to the ground or earth, whereas virtual ground is a concept used in opamps in which a node is assumed to have the potential that of the ground terminal.
I say Peter threw off his numbers because he chose a value that no-one would ever use (and a static value at that, no opamp involved, so the load was causing the output of the cartridge to change in a significant way, whereas real-world loads have negligible effect) since its a reasonable expectation that if you are going to use a load on a cartridge, you’d likely start with one that is 10X the source impedance of the cartridge. I can see using static values lower than that, but not one that’s actually lower than the the source impedance! Barring a good explanation for that, when I read that in his article I found I simply had to take his results in abeyance. I’d have to read the article again (Google defeated my attempts to locate it just now), but IIRC he had some variables left uncontrolled that I felt at the time might affect his results. One way around this is to ignore that transimpedance inputs exist and simply focus on what happens to the output of any source when the load is a fraction of that of the source. That’s really what I’m getting at here, if Peter was actually suggesting that we use such loads both back then and now the extra gain needed would be impractical. |
Dear friends: Looking to the PM charts that @intactaudio shared with us yesterday I took in count that ( for my self. ) I can measure it too due ( as I posted several times in this forum. ) that I own around 20+ different vintage comercial test LPs from: CBS, Shure, JVC, Stereo Review, HiFI, Vanguard, B&K, Ortofon, Audio Technica, etc. etc.
Through them I have 4 tracks IMD dedicated and rigth now I'm talking with some of my audio friends looking for the ritgh phono stage that permits in easy way changes in the cartridge loading because in my unit I can do it unsoldering/soldering resistors . As I said I will do for my self satisfaction and with withness of the gentleman that will share his phono stage for 3-4 hours any day in the afternoon.
So " stupid " I'm that having a solution I did not see way before.
R. |
Dear friends: Looking to almost all my vintage LP test recordings I found out that I have some even sealed as one from Micro-Acoustics and the Ortofon serial 003 that yesterday opened and listen to it. It's not a test tones and the like but the lovely tracks are MUSIC, this LP is an Ortofon collaboration with the label Opus 3 that in the past ( too ) made 3-4 test LPs. Well, first than all this Ortofon LP is really good centered with no waves you can detect and even that's a vintage recording not only is a great recording but the LP recorded surface is dead silent, even the band that separates the tracks is dead silent.
If you can find out buy it, it's a good investment for you and your room/system set up.
R. |
On the subject of phono input impedance as it relates to the discussion between Atma-sphere and Intact Audio, one should also keep in mind that every "current drive" phono stage seems to be a bit different from every other "current drive" phono stage, at least on the subject of input impedance. Most advertised "current drive" phono stages do have a finite input impedance greater than zero, whether that is virtual zero or whatever. A couple of years ago, I looked at 4-5 different products and the range of measurable input Z was from a few ohms up to as much as 20 ohms. A unit with a real 2-ohm input Z will probably react differently to a LOMC with an internal resistance of from 2 to 10 ohms than a unit with a 20-ohm input Z, current, voltage or whatever. The water gets really muddy. They want to dumb it down for us consumers. |
