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Old 29th December 2006, 02:58 PM   #1
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Default Cartridge Impedence Matching

Ok, I'm kindof a noob when it comes to diy, so take it a little easy.

I'm currently building a pass pearl and am trying to find out how to correctly load the cartridge with the correct resistor and capacitors.

I'm using an AT 440MLa, and I've found values for the recommended load.

Coil impedance at 1kHz: 3.2 kOhm
Coil inductance at 1kHz: 490 mH
Recommended load resistance: 47 kOhm

Does this mean I would just put a 47kOhm resistor on R1? What about capacitance?
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Old 29th December 2006, 03:13 PM   #2
Ghianni is offline Ghianni  Greece
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I think, this is going to help you: http://www.hagtech.com/loading.html
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Old 29th December 2006, 06:48 PM   #3
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Quote:
Originally posted by Ghianni
I think, this is going to help you: http://www.hagtech.com/loading.html
and you were right, that did help. thanks!
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Old 30th December 2006, 09:16 PM   #4
EC8010 is offline EC8010  United Kingdom
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I'm afraid Jim Hagerman is wrong on this one. He's quite correct in showing that different loading capacitances and resistances change the frequency response, but his assumption that a flat electrical response is desirable is incorrect. You see, cartridge manufacturers use the electrical resonant circuit to equalise for the falling mechanical response of their generator. That's why early Ortofon VMS20E required 400pF-500pF of loading capacitance and too little capacitance actually reduced the treble heard. 1970s and 80s Shures were the same.
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Old 30th December 2006, 09:57 PM   #5
Nordic is offline Nordic  South Africa
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I'm currently bussy with a layout for Graham Maynard's The "ACE" from 1975.

It has variable damping, variale input C variable input impedance, extended RIAA switch, Diffirential bass cut switch, balance control.

Most of the circuits I see take no notice of damping etc...
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Old 31st December 2006, 04:18 AM   #6
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nordic LOL @ your avatar even if it is "slightly" photoshopped
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Old 1st January 2007, 11:24 PM   #7
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Quote:
Originally posted by EC8010
I'm afraid Jim Hagerman is wrong on this one. He's quite correct in showing that different loading capacitances and resistances change the frequency response, but his assumption that a flat electrical response is desirable is incorrect. You see, cartridge manufacturers use the electrical resonant circuit to equalise for the falling mechanical response of their generator. That's why early Ortofon VMS20E required 400pF-500pF of loading capacitance and too little capacitance actually reduced the treble heard. 1970s and 80s Shures were the same.
what do you suggest then?
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Old 2nd January 2007, 08:47 AM   #8
EC8010 is offline EC8010  United Kingdom
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I suggest that you follow the cartridge manufacturer's recommendations. It's a shame they don't specify capacitance. 1970s and 80s cartridges tended to want 400pF-500pF (that's arm wiring and pre-amplifier together). Using that amount of capacitance tended to resonate the equaliser at somewhere between 15kHz and 30kHz, but the response dropped off like a stone after that. In fact, you can often get a good idea of stylus tip mass by calculating the resonant frequency of the cartridge's inductance paired with its load capacitance. As I recall, the Shure SC35 resonated at 15kHz (it was a big robust broadcast beast), whereas cartridges with lighter cantilevers and rondels needed less equalisation and had a correspondingly higher equaliser resonant frequency.

Then, CD4 appeared with its quadraphonic subcarrier that needed a cartridge response up to 50kHz. That led directly to improved stylus profiles (Shibata etc) and the necessity of reduced loading capacitance to enable the equaliser's resonant frequency to be set to 50kHz or so. Pick-up arm manufacturers responded and started making arms with greatly reduced arm wiring capacitance (it wasn't difficult and enabled them to claim that they were CD4-ready). All of a sudden, load capacitance had fallen from 400pF-500pF to about 250pF, but the majority of the cartridges were the same and needed the old capacitance. Ortofon sold a 200pF loading capacitor that slid onto the back of their VMS20E to correct the situation.

So, if your cartridge is old, try 400pF-500pF, if modern, try 250pF. Try 250pF first, then, if the extreme treble seems weak, try 450pF. If it needs 450pF, the extreme treble will improve, if not, it will get even worse.
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Old 2nd January 2007, 08:57 AM   #9
sreten is offline sreten  United Kingdom
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Hi,

Also note that capacitive loading is additional to cable capacitance, usually ~ 200pF.

/sreten.
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Old 2nd January 2007, 08:09 PM   #10
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I think I'll go w/o any additional capacitance and see how it sounds. My klipsch are awful bright so if the high end is off I'll definitely notice.
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