Moving magnet cartridge with MC input

[Notnilc]

Hello and Happy Saturday,
I have a question for all the MM vs MC guru’s. I just upgraded my preamp and the 2nd phono input is MC. While I do have the ability to adjust the ohms on the McIntosh C2300, can I take it down low enough to use a MM cart on the MC input?

I can always switch to a MC cart, but I just bought an Ortofon Bronze for my 2nd table and I really want to use it.

 

[Redd House]

Don't you want more resistance, not less? A typical MM cartridge wants to see 47,000 ohms whereas a typical MC wants to see 100 ohms. Also an MC preamp will be boosting the signal a lot more than is required for a typical MM cartridge.

 

[trinhsman]

I made the mistake once doing this. Sounded horrible with my turntable. Not sure if it could work for you. Try it with volume levels completely down, and then adjust volume to see what happens. IMHO

 

[tnsilver]

Plug an MM cart to an MC input and you're likely to overload the phono stage. It'll sound muffled and murky.

 

[sqlsavior]

It is going to depend on how much headroom your phono stage has. You can try it at low volume without hurting anything. Some phono stages have lots of headroom, others very little. If it sounds good, it is good, and if it sounds bad, don't use it that way.

One thing to beware of is if it sounds good, except for occasional loud passages sounding bad. IMO, that would be too risky to run at loud volumes.

 

[lini]

Plug an MM cart to an MC input and you're likely to overload the phono stage. (...)

Shouldn't be that bad, actually, depending on the input impedance of the MC stage. I.e., if the latter is pretty low, most of the generated voltage will rather already drop at the internal resistance/impedance of the cartridge. So overload is less likely, than one would initially think - whereas...

(...) It'll sound muffled and murky.

...that would be very likely, indeed.

Greetings from Munich!

Manfred / lini

 

[Montycat]

I inadvertently used the MC setting with a Moving Magnet the other day. It did indeed sound muffled and murky.

 

[tnsilver]

^ yeah, that's true but lini's point was that's it's not happening on account of overloading but rather on account of impedance mismatch.

 

[Notnilc]

Don't you want more resistance, not less? A typical MM cartridge wants to see 47,000 ohms whereas a typical MC wants to see 100 ohms. Also an MC preamp will be boosting the signal a lot more than is required for a typical MM cartridge.

Thank for the reply. Yes, the MM have much less resistance

 

[604man]

 

[Notnilc]

Shouldn't be that bad, actually, depending on the input impedance of the MC stage. I.e., if the latter is pretty low, most of the generated voltage will rather already drop at the internal resistance/impedance of the cartridge. So overload is less likely, than one would initially think - whereas...



...that would be very likely, indeed.

Greetings from Munich!

Manfred / lini

Thanks. So the moral of the story is use an MC cart and be done with it.

 

[W9TR]

The C 2300 has an outstanding MC phono stage and deserves a nice MC cartridge to go with it. I run a Dynavector 17D3 with my C 2300 and love it.

 

[tabarddn51]

Not sure if you can go this way. If you want to reduce the ohms all you need to do is add a couple of resistor plugs to a RCA ''Y'' connector. But i do not know if it will work adding a couple of 4700 ohms resistors. but try it, it would only cost about $10 to set up.

cheers

 

[W9TR]

The problem is not reducing the resistance. The C 2300 MC input has a max resistance of 1000 ohms which is waaay too low for a normal MM cartridge which requires 47 kOhms or thereabouts.

 

[tabarddn51]

Yes I know, however I as I said it may be that what is important is the 1st resistance the cartridge see's, I do not know as I am not an electrical engineer. for $10 it may be worth a try
Also although I rarely use them I read there are several MM's that can be used with a lower resistance.

Cheers

 

[lini]

t51: No, that wouldn't work. I.e., whatever resistor one would add via external parallel loading - it would always just decrease the total load impedance. And in fact, if you'd check various existing phono stage implementations, you'd find, that even internally the total input impedance is not rarely implemented by two resistors in parallel.

And before you ask: No, one can't increase the input impedance by an external series resistors either, 'cause one would rather implement a voltage divider that way.

Similar problem with capacitance: Another capacitor in parallel would always increase the load capacitance - and with a capacitor in series one would rather implement a high-pass filter.

So for both increasing input impedance and decreasing input capacitance there's no way around opening the device and swapping or removing parts.

Greetings from Munich!

Manfred / lini

 

[wyn palmer]

Yes I know, however I as I said it may be that what is important is the 1st resistance the cartridge see's, I do not know as I am not an electrical engineer. for $10 it may be worth a try
Also although I rarely use them I read there are several MM's that can be used with a lower resistance.

Cheers

A "typical" MM cartridge (the Shure V15 in this case for example) will have c.1300ohms and 500mH inductance.
So at 100Hz the impedance will be c. 1.3k, at 1kHz c. 3.3k, and at 10k c. 30k (at 20kHz it's 60k- higher than that of the load R)
So into a 100 ohm load you will get about 22dB attenuation, 30dB at 1k and 50dB at 10k.
That indeed will sound muffled etc.
It will also bring the gain down to normal MM levels.
Incidentally, the effect of loading at 10k and above helps to explain why MM cartridges require a small load cap to resonate with the inductor and flatten their HF response.
Also, very few preamps have 20dB or more broadband overload margins at the maximum cartridge outputs before miss-tracking.
It's likely that if you change the load to 47k that you will indeed overload the preamp- probably at the HF end- which will have all sorts of negative consequences.
Using the volume control will not generally help to alleviate this, depending on the preamp gain partitioning.

 

[rothwellaudio]

This thread is baffling.

While I do have the ability to adjust the ohms on the McIntosh C2300, can I take it down low enough to use a MM cart on the MC input?

How would reducing the input impedance make an MC input more MM friendly?

Don't you want more resistance, not less? A typical MM cartridge wants to see 47,000 ohms whereas a typical MC wants to see 100 ohms.

Exactly.

Yes, the MM have much less resistance

Much less resistance? Less than what?

Yes I know, however I as I said it may be that what is important is the 1st resistance the cartridge see's...

Does the cartridge see any kind of secondary resistance?

Am I the only one confused by all this?

 

[sregor]

You could always add a series resistance to the input - with the input set to 1k in, add a 47K resistance, and you will have a 48 K load. However, you also get a 1/48th signal in (which could be a good thing, as no overload) but probably a lot higher noise level. If cartridge can use a lower resistance, will increase signal. YMMV Just my 2 cents.

 

[wyn palmer]

You could always add a series resistance to the input - with the input set to 1k in, add a 47K resistance, and you will have a 48 K load. However, you also get a 1/48th signal in (which could be a good thing, as no overload) but probably a lot higher noise level. If cartridge can use a lower resistance, will increase signal. YMMV Just my 2 cents.

Well, this is actually a sort of reasonable suggestion, so it deserves a bit of a calculation.
Ignoring the cartridge impedance, and components such as the input bias current noise.
The combo of the two Rs will produce c. 28nv/rtHz (the 48k) divided by the voltage gain (goes to c. 0.55nv/rtHz) root sum squared with the 1k noise (4nv/rtHz) to produce c 4nv rtHz. combined at the input of the MC preamp This is only about 12dB worse than a relatively quality. MC preamp. However, the signal level is dropped by c.34dB (a factor of c. 50) for a source that is usually about 20dB larger than a normal MC cartridge output.
So, the S/N ratio would degrade by about 26dB- which is, alas, not quite good enough.