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Old 12th December 2012, 01:42 PM   #1
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Default Cartridge loading

Hello all,
Bought an Audio Technica AT150mlx to see if I could be happy w/ a MM design. It would be nice to have a user replaceable stylus, as I've yet to figure out that late night listening sessions coupled w/ vodka # 2 and loose pajama sleeves don't make for a happy cantilever. ( Snapped the original one on my nuded Denon DL103r and the Soundsmith ruby replacement ). Slow learner.

My phonostage is a Sonic Frontiers Phono 1 w/ 62db of gain. The front end was clearly overloaded w/ the cartridge run straight in. According to the specs I should have had sufficient headroom, but SF must have been quoting the overload margin @ the 44db gain version. So not to be outdone, I yanked my trusty old NAD 3020 out of mothballs and gave it a shot. Not too shabby, but as others on the net have pointed out pretty bright @ 47k. So I constructed a loading box so I could play w/ various resistive loading schemes, and so far 22k//47k already there started to sound pretty good. I'm going to keep going lower yet, just didn't have the resistors laying around. There was still some residual harshness to the sound, which I figure is attributable to the phonostage in the NAD. So I would like to use the SF, but I don't want to go in to change resistors to knock it down to the 44db gain version. So I came up w/ this idea, and I'd like your guys thoughts as to whether it would work or not.

I'd like to put a simple resistive voltage divider across the input of the SF to both load down the 47k to the 15k the above combination works out to, and to also pad down 20 db of gain. I'm no engineer, I do simple tube stuff. When I looked at this, I figured the cartridge sees the resistance of the entire divider network, but the lower resistor that will feed the SF is actually in parallel w/ the 47k already there, and needs to be sized accordingly.

So the simple question is is this a viable method to accomplish both of my goals of adjusting the loading and padding down the gain. I know this will add some noise, but what I'm really trying to do is to get a feel for the proper tonal balance through the SF, w/o going inside the unit.

As always, thanks in advance for any help

Cheers, Crazy Bill
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Old 12th December 2012, 01:54 PM   #2
SY is offline SY  United States
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I have a 150MLX as well- great cartridge. BUT... it does not like much capacitance in the load. You want to have the lowest capacitance cables you can find, and make sure that you're using a phono stage with a low input capacitance. 100-150pF total is as high as you want to go.

Padding down the input with resistors will severely compromise the signal to noise ratio- you should either change the gain of your phono stage (you want something like 40dB at 1kHz) or use a transformer to step down. Again, this will compromise the S/N but not nearly as much so as resistive padding.
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Old 12th December 2012, 02:23 PM   #3
DF96 is offline DF96  England
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The best compromise might be 10dB attenuation before the MC input, then 10dB after to knock the level down a bit more. Adjust as necessary. The idea is to preserve as much S/N ratio as possible, while keeping within the preamp's headroom.
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Old 14th December 2012, 06:18 AM   #4
h_a is offline h_a  Europe
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Sy is perfectly right on this, that's a typical load capacitance issue.

Quote:
various resistive loading schemes
That's for MC only; MM is a different beast.
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