Loading the GE RPX and VR Cartridges

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edgarryan
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Loading the GE RPX and VR Cartridges

Post by edgarryan » 11 Jun 2019 21:01

I want to experiment without opening up my phonostage. The recommended loading of these old GE mono cartridges is 100K ohms. My phono preamp is 47k ohms. How do I change the loading? Is it possible to do it this way:

Turntable --> Resistor --> Phono preamp?

If so, what resistor value do I use, and where do I connect it?

Coffee Phil
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Re: Loading the GE RPX and VR Cartridges

Post by Coffee Phil » 12 Jun 2019 18:04

Hi edgarryan,

I believe that you are correct about the recommended load resistance for those cartridges. I don't know what the recommended capacitance is or even if GE published that.

To load the cartridge with 100 k Ohms you would put a 47 k Ohm (or more precisely 53 k Ohm) in series with your 47 k Ohm input. You should put a capacitor of the input capacitance of your phono stage across the resistor.

You will get a 6 dB loss but the RPX has a whopping output as magnetic cartridges go, so it may be OK.

My RPX is mounted in a "knock-off" SME type shell and connected to both channels so it sees a ~ 25 K k Ohm load. I know that is not ideal, but it sounds pretty good with my 78s and mono Lps.

Phil
edgarryan wrote:
11 Jun 2019 21:01
I want to experiment without opening up my phonostage. The recommended loading of these old GE mono cartridges is 100K ohms. My phono preamp is 47k ohms. How do I change the loading? Is it possible to do it this way:

Turntable --> Resistor --> Phono preamp?

If so, what resistor value do I use, and where do I connect it?

edgarryan
member
member
Posts: 80
Joined: 25 May 2010 13:04
Location: Pasig

Re: Loading the GE RPX and VR Cartridges

Post by edgarryan » 12 Jun 2019 18:59

Thanks for the reply. Basically, my problem is this: my VR and RPX have distorted highs and not enough bass. I read somewhere that changing the loading would correct this. If I were to use some sort of passive attenuator, would that work? If so, what resistor values should I use; more specifically, if I'm going to connect 47K to the signal, what resistor value should I connect to the ground? I'm no electrical engineer, so I'm not really sure about what I'm doing.

Coffee Phil
vinyl addict
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United States of America
Posts: 5550
Joined: 20 Sep 2008 08:22
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Re: Loading the GE RPX and VR Cartridges

Post by Coffee Phil » 13 Jun 2019 04:47

Hi edgarryan,

What I described in my last post IS a passive attenuator.

If you would like I’ll draw up a schematic and post it. With what I posted I assumed that you want to connect the cartridge to a single channel 47 k Ohm input of a phono stage. Is this so? If you want to go to both a right and left input, I’ll draw a circuit for that.

What is the input capacitance of your phono stage?

Phil

edgarryan wrote:
12 Jun 2019 18:59
Thanks for the reply. Basically, my problem is this: my VR and RPX have distorted highs and not enough bass. I read somewhere that changing the loading would correct this. If I were to use some sort of passive attenuator, would that work? If so, what resistor values should I use; more specifically, if I'm going to connect 47K to the signal, what resistor value should I connect to the ground? I'm no electrical engineer, so I'm not really sure about what I'm doing.

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