Author Topic: Phono stage MC (R) vs MM (PF)?  (Read 260 times)

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Offline onesixright

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Phono stage MC (R) vs MM (PF)?
« on: March 05, 2018, 09:43:43 pm »
Hi All,

I'm looking to build a phono pre amp for a MC cartridge (something like this: http://diyaudioprojects.com/Chip/Opamp-Phono-Preamp/)

I also looked at some commercial pre-amps and I noticed the MC has a configurable resistance setting, while the MM has a configurable capacitance setting  :-//

With close to zero knowledge of audio, I was wondering why is it resistance for the MC and capacitance for MM? Any simplified explanation?

Thanks!


 

Online cat87

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Re: Phono stage MC (R) vs MM (PF)?
« Reply #1 on: March 05, 2018, 11:56:41 pm »
Well, that has to do with the impedance of the cartridge on your record player. Unfortunately there are lots of cartridges out there with different impedances so if you want to build your own, find out the exact impedance your cartridge has.
With that information, you can build your pre-amp to match that exact impedance and you'll also have to implement the RIAA equalization to match. If at the end of the build, the music will sound flat and bland, then there is a mismatch between your cartridgew and the pre-amp.

One very good source of information would be Douglas Self's books. I think "Self on Audio",  "Small Signal Audio Design"  and "Electronics for Vinyl" might get you started. I'd personally start with the Small Signal Audio Design one.
Of course, he's not the only source of info out there, but he has, I think, the most "bang per buck" in those books.
 
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Offline onesixright

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Re: Phono stage MC (R) vs MM (PF)?
« Reply #2 on: March 06, 2018, 12:09:38 am »
Well, that has to do with the impedance of the cartridge on your record player. Unfortunately there are lots of cartridges out there with different impedances so if you want to build your own, find out the exact impedance your cartridge has.
With that information, you can build your pre-amp to match that exact impedance and you'll also have to implement the RIAA equalization to match. If at the end of the build, the music will sound flat and bland, then there is a mismatch between your cartridgew and the pre-amp.
Yeah, I was guessing it has to do with that.

However why is it capacitance for MM and resistance for MC? It seems, depending on the cartridge type there are different method of impedance matching?


One very good source of information would be Douglas Self's books. I think "Self on Audio",  "Small Signal Audio Design"  and "Electronics for Vinyl" might get you started. I'd personally start with the Small Signal Audio Design one.
Of course, he's not the only source of info out there, but he has, I think, the most "bang per buck" in those books.
Thanks I will look for that!
 

Online glarsson

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Re: Phono stage MC (R) vs MM (PF)?
« Reply #3 on: March 06, 2018, 12:39:11 am »
Moving magnet cartridges have many turns of copper wire. This gives them high inductance and impedance. Together with the high impedance of the amplifier input (47 kohms) the effect of the amplifier input capacitance is significant.

Moving coil cartridges have few turns of copper wire. This gives them low inductance and impedance. Together with the low impedance of the amplifier input (e.g. 100 ohm) the effect of the amplifier input capacitance is insignificant. Instead of forcing a standard input impedance (as we have for moving magnet) the manufacturers optimize their design by also deciding on the input impedance of the amplifier, usually from 20 ohms to a couple of hundred ohms.
 
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Offline floobydust

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Re: Phono stage MC (R) vs MM (PF)?
« Reply #4 on: March 06, 2018, 06:21:49 am »
Douglas Self's book Electronics for Vinyl is very good, if you want explanations and details.



 
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