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
I don't usually get too caught up in the Interface methodz being discussed in the descriptions offered. Using the Manufacturers recommendations, has been quite successful for my own purposes. I have a selection of Cables, as well as few SUT's and cam also have the use of Head Amp's I will swap different configurations to see what develops in the SQ. I also have a Phon' with a methon to control input capacitance, input impedance and adjust gain. I will use this to learn if a chosen configuration is able to be improved upon. |
Dear @intactaudio : " and 100Ω values are odd but that is secondary to demonstrating the effect. "
and something important is that PM is the only gentleman that showed/measured in that regards, The critic made by atmasphere is useless and for any one is easy to post that kind negative comments. Could be better to prove with measures that PM is wrong, this is the way to do it but obviously till that happens PM it's not wrong and in this regards a congratulations to him is the least we can do for. Again, thank's for your PM information that trully and finally puts the " ligth " we all need it about.
R.
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Transimpedance phono sections have the cartridge driving the 'virtual ground' of an opamp circuit. That's quite a bit different from driving an actual short (0 Ohms)! For example, if the cartridge isn't present, the virtual ground does not exist. They really aren't an example in this context. Try placing a 5 Ohm resistor across the output of any LOMC cartridge and see what happens 😁
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I didn’t mention a dead short and was only referring to the two terminal impedance the coil of a cartridge sees. Any reference to ground be it real or virtual does not factor into the load seen by the coils. Surely there has to be an actual input impedance for a current amp and it has to be low otherwise the coils will not generate any current to amplify. I am not trying to get into an in depth analysis of how various transimpedance amplifiers work but address the general first order behavior of the system and believe that a cartridge operating into a ideal voltage amp behaves differently than the same cartridge into an ideal current amplifier primarily due to the fact that the loads are at opposite ends of the spectrum.
that depends on what load the input of the following stage gives. If it is a voltage amplifier with 47kΩ, a 30Ω cartridge loaded by 5Ω it will be 17dB down. When you replace that 30Ω cart with a 2Ω cart the output will only be down 3dB. If it is a current amplifier with a 1Ω input impedance a 5Ω parallel load will lower the current into the 1Ω input node by1.6dB with both the 2Ω and the 30Ω cartridge. The absolute currents will be different for the 2Ω and 30Ω carts but the relationship of how the 5Ω load affects a 1Ω input impedance stays the same. dave |
