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Advice on MM/MC phono pre-amp please.

I have a Rega Planar 25 with a Dynavector 20X-H high output moving coil cartridge. I just bought an Accuphase Integrated amp with switchable MM/MC Phono. The Rega plays through either one, however it is much louder through the MC.
The Manual for the Accuphase says that the input impedance is 47 kilohms when switched to MM. It is 100 ohms when switched to MC.
The Manual for the Dynavector says recommended load is 47 Kohms / 30 Ohms.
Obviously the MM stage is the perfect match at 47 ohms.
My question is can the MC be used with this cartridge, and what damage (if any) can occur as a result?
Sorry for the long post.
Thanks in Advance.
Ag insider logo xs@2xmuzikat
4 responses Add your response
herman
2,259 posts
 
No damage will occur in either case.

Your cartridge was designed to be used with the MM stage. The MC stage is louder because the gain is higher to accomodate lower output MC cartridges. Since yours is high output you don't need the extra gain from the MC stage.

It really isn't 2 different stages anyway. When you switch to MC it is inserting an extra gain stage that then feeds the MM stage. As long as you are getting enough volume with the MM stage then you are probably better off since it goes through less stages, and as you noted, it has the proper load for your cartridge.
twl
3,251 posts
 
Also, it may be noted that running a high output cartridge into a MC section with high gain, can overload the phono section and cause distortion. And using a severely low load for the cartridge(compared with what it was designed for) is counterproductive to good results from the cartridge. In this case, louder is not better. I concur with Herman, use the MM phono stage.
sean
6,231 posts
 
Twl mentioned the first thoughts that came to my mind i.e. front end overload. While you will get greater volume out of the MC section, the sound will end up being more compressed and / or distorted. That is, unless you are playing recordings that are VERY quietly recorded and lack dynamic range. As such, stick with the MM section and adjust the loading inside the preamp to what the manufacturer calls for. You should still have enough gain to reach the desired SPL range while retaining a higher level of accuracy without distortion. Sean
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eldartford
4,262 posts
 
Improper (not as designed) loading of the pickup will probably affect its sonic qualities (eg: frequency response) as well as volume. There is no risk of damage.

I have not seen the schematic of the Accuphase amplifier, but I don't think you can always assume that the MC input involves an extra stage of electronics. I have a Tandberg 3008A preamp with MC and MM inputs. It has two completely separate phono preamp stages, with identical circuit topography but different component values as necessary to yield high and low gain performance as appropriate.
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