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Old 24th January 2021, 06:39 PM   #81
SMABB is offline SMABB  Denmark
diyAudio Member
Join Date: Oct 2012
Location: Denmark
Finally - I now have had the opportunity to test the MC-2 with different load resistors, keeping gain constant as suggested by Hans Polak and others.

I chose to keep gain constant at 6,7 in line with the recommendations of Electrocompaniet, when using load resistors in the range of 33-43 Ohm and gain resistors from 470-560 Ohm. Also keeping in mind Hans Polak´s comments about not exceeding gain of 10 with this design.

A small change is, that I now use a Benz LP-S as signal source, which has a slightly lower generator impedance of 38 Ohm compared to the 45 Ohm of the Ruby ll previously used here. All calculations have been updated to reflect this change.

I used load resistor values of 0, 15, 37.4 and 45 Ohm and changed gain resistors accordingly to keep gain constant at the predefined 6,7 level. Calculation of gain resistor values was done using method described by Hans Polak in post #73.

Basically - I found the same observations as in post #64.
With only a bare silver wire as load (load = 0) the sound was immensely open, spacious and flowing. It was also light in bass and treble was emphasised; a tonal balance tilted towards focus on upper registers.
Opposite - with a load of 45 Ohm everything was much more balanced, the sound gaining more bass without loosing the airiness and spaciousness.
When comparing to the LP-S signal going directly into the phono stage of ARC SP-11 loaded with 300 Ohm, there still was sound traits normally associated with transistors. In addition the sound was not so airy and spacious, as when the MC-2 was in the signal path.

However - changing the load on the SP-11 to 100 Ohm made the whole sound landscape collapse, but gaining immense depth. A strange and distant sound emerging from the speakers. Going the other direction and loading with 1.000 Ohm made everything fall into place. The airiness and spaciousness so impressive with the MC-2 was now present, when the signal flowed from the LP-S directly into SP-11.

For me - the 1.000 Ohm loading of the LP-S gave me all the significant traits of the MC-2, but retaining the tonal colour, vividness and bloom of the SP-11.

Much to my surprise the noise level of the LP-S going directly into SP-11 is of no significance. Whether with or without the MC-2 in the signal path, the noise level between tracks is on a par, ie. identical. I was worried, that the lowish output of the LP-S (0,35 mV) would be too low for the SP-11 to handle without noise being noticeable present. Not so - I could not detect any significant reduction in noise level between the two setups.

I will keep it this way, the signal passing from the LP-S directly into the SP-11 loading the cartridge with 1.000 Ohm.

To sum up - we can now conclude, that the design and functionality of the MC-2 has been described and analysed for others to use. The calculation and effect of load and gain resistors has been shown and indications on, what to expect has been subjectively indicated.

I want to thank everyone, who has contributed with knowledge or followed this thread, which started with me looking at a black box, not knowing how and what it was capable of and with no clue to its functionality. I believe the contributions on here have made clear, what can be had from a MC-2 (if you can find one).

Thank you all - stay safe in these times of pandemic crisis!
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Old 25th January 2021, 12:43 PM   #82
Hans Polak is offline Hans Polak  Netherlands
diyAudio Member
Join Date: Mar 2005
Location: Blaricum
Thanks for your observations, very well done.
It shows the excellent quality of your SP11.
I have the same Benz, loaded with zero ohm.
Probably since my preamp has a very high loop gain and a flat FR independant of input resistance for a certain gain, I could not detect any difference in sound or bass reproduction between zero ohm and 33R in series with the Cart.

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