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A resistor question for CAT SL-1...help needed

Hello. I have a question about resistor values and what I should be looking for to perform this modification. I don't have the rca phono loading plugs that came with the unit so I'm attempting to make my own.

I need to add a couple of resistors to my preamp phono section (CAT SL-1) to match my cartridge output of 100 ohms (Shelter 501 Mk II, low-output mc). I'm confused about what value I should get. My preamp is currently set for 47K ohms which is not the recommended setting for my cartridge.

I'm looking to experiment with values of 100 ohms to 1000 ohms but I don't know what resistor watt value to buy...ie, 1/4 watt, 1/2 watt, etc. Also, what tolerance should I get...ie, 1%, 2%, 5%, etc.

Your help or suggestions is greatly appreciated. Thanks much!!
dogpile
bombaywalla's avatar
bombaywalla
1,958 posts
 
Marakanetz's advice is correct.
However, I want to add 1 important aspect: if you are using a MC step-up then make sure that you account for the impedance transformation owing to the xformer: whatever resistor value RCA plugs you make WILL get divided by the square of the turns of the xformer. So, if you are using a 14dB step-up, which is a 5:1 xformer then 100 Ohms effective resistor will be divided by 25. So, on the cartridge side the effective resistor WILL NOT look like 100 Ohms anymore!
So, in the step-up case, if you want the cartridge to see 100 Ohms, you should make 2500 Ohms RCA plugs (1:5 step-up case). Modify if you have any other value step-up.
The cartridge output is 0.4mV & so power developed across the phono load resistor is tiny. A 1/4W resistor is plenty.
Hope that this helps.
herman
2,216 posts
 
I agree, 1/4 watt is way more than enough, and don't worry about the tolerance. If you buy a resistor assortment at Radio Shack, any 2 of the same value will be from the same batch and will be very close to each other in value.
dogpile OP
118 posts
 
Thank you so much for all your comments, it really helped and my question was answered. Time well spent!!
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