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
Atmasphere......The Ah-Ha moment! http://www.atma-sphere.com/en/mp-1.html Is this the company you represent? I apologize that I did not recognize you as a tier one supplier of high quality phono stages. I will study your web page further. Thanks for being involved with Audiogon and sharing your knowledge!! Lou |
That is not the case in this instance. The measured frequency response of both cases is within 0.1dB within the audio band and the 1:40 has a 2dB low Q resonance at 90kHZ and the 1:8 has a 6dB peak @ 235kHz. To isolate the contribution of the SUT I left the 1:40 unloaded to reflect 187Ω and placed a 200Ω resistor across the primary of the 1:8. I then level matched them and am hard pressed to tell the difference between the two. This gives me confidence in my belief that the load on the cartridge is responsible for the sonic changes that I reported above. dave
|
I don't doubt that it could be affected. Loading the cartridge causes the cantilever to become stiffer (more work is being asked of it and that has to come from somewhere: the cantilever is thus harder to move)- and thus can introduce the possibility that even though the bandwidth of coil is unaffected, the mechanical aspect of the cartridge will be affected by that added stiffness- possibly making it less able to respond to higher frequencies. |
The distinction between virtual and actual ground is a subtle one. When an opamp inverting input is used, the virtual ground is extremely similar to a real ground as the action of negative feedback makes it so. The difference is in the error term- i.e. the output voltage divided by the open loop gain of the amplifier, together with any impairments added by the amplification system. This difference can be extraordinarily small, so arguing that the virtual ground is not a real ground is largely facile. As far as the source is concerned there can be essentially negligible difference between a real ground and a virtual ground. Claiming, arbitrarily, that it is prima facie audibly different as far as the source is concerned is not reasonable. To put this in context. The error term is a function of the opamp gain bandwidth product, open loop DC gain, and the internal sources of distortion, both the intrinsic input non linearity and the output stage non linearity. With high gain bandwidth and high open loop DC gain the error voltage is extremely small in the audio band, and with low intrinsic open loop distortion at the signal levels present at the non inverting input when negative feedback is applied the resultant distortion component of the error signal is also extremely small. These facts make the virtual ground , when opamps of sufficient quality are employed, extremely close to an ideal ground, in fact just about as close to an ideal ground as any "real" ground that you can actually construct. |
