MC impedance & compliance confusion

[Apolek]

Decided to take a shot at a moving coil cartridge (my first), and I’m pretty sure I’ve settled on the Audio-Technica AT-F7. I’m planning on running it through a Schiit Mani pre-amp, and that into the aux input of my Onkyo TX-NR535. While looking at the specs for the cartridge, I see a recommended 100 ohm minimum load impedance. Reviewing the specifications for the Mani… no mention of load impedance, but it does say: “Input Impedance: Selectable 47 ohms (typical for MC cartridges) or 47k ohms (typical for MM cartridges)”. I’m not familiar with all the inner workings of the MC/preamp setup, so I’m left wondering if this is a suitable combo; and if so, how does one go about calculating/measuring load impedance. Other question is if this cartridge is suitable for my tonearm. Plan on using a JVC VL-8 with stock tonearm, but no data can be found that defines the mass of the arm. Assuming it’s a medium(ish) tonearm for now, but wondering if there's a formula or specified range called out for matching a cartridge to a tonearm.

 

[hirscwi]

The input impedance of the Mani (set at 47ohms) could be a bit low for best sound. It won't hurt the cartridge to try it and see how it sounds but generally the manufacturer's recommendation is good. You can always add a high quality (1% metal film) resistor in series with the phono section input to bump it over the 100 ohm recommendation. Or it may be simple to modify the Mani internally.

 

[lini]

(...) You can always add a high quality (1% metal film) resistor in series with the phono section input to bump it over the 100 ohm recommendation. (...)

Bad idea - 'cause by doing that one would basically create a voltage divider and reduce the output of the cartridge to ca. 1/3rd. So in case the 47 kOhm are also availabe in combination with MC gain, it would be way smarter to install a resistor per channel in parallel (for example in the plugs of the phono cable) to reduce the 47 kOhm instead.


Ap: Haven't tried that myself, as I don't own an AT-F7, but Andreas (alias akem), one of the experienced phono fans over on the German Hifi-Forum(.de) suggests to rather load it with roundabout 1 kOhm for better sound quality. So I'd suggest to install a 1 kOhm resistor per channel in parallel in combination with the 47 kOhm setting on the Mani.


Greetings from Munich!

Manfred / lini

 

[hirscwi]

Of course you are correct. I had not thought about it that way. Of course you could go into the preamp itself and swap the loading resistor.

 

[Apolek]

Thanks, guys. I'll look into making something to add resistance to both channels. I was hoping that it was simply a nomenclature thing and that Schiit's input impedance was not synonymous with load impedance. Or, maybe I'll look into other cartridges.

 

[Apolek]

Hmmm... wondering if the changing the gain switches on the Mani have the same effect as varying the load impedance

 

[mprince]

Hmmm... wondering if the changing the gain switches on the Mani have the same effect as varying the load impedance

Gain and load are not related. Think of gain as volume controls and impedance as tone controls.

 

[lini]

(...) Of course you could go into the preamp itself and swap the loading resistor.

Certainly. However, to me Ap's initial posting rather seemed to imply that he hasn't bought the Mani yet - and typically one rather wouldn't want to mod a brand new piece of equipment in order not to void the warranty. And as Ap might yet want to determine the optimal load for his taste and system environment anyway, I'd tend to suggest using splitter adaptors and loading plugs for a start.

Gain and load are not related. (...)

Technically not, but in many cases the MM/MC switching implementation only allows for switching both at the same time. The Mani seems to sport individual switches for that, though - and apparently even separate ones for each channel.


Greetings from Munich!

Manfred / lini

 

[Aerobat]

Bad idea - 'cause by doing that one would basically create a voltage divider and reduce the output of the cartridge to ca. 1/3rd. So in case the 47 kOhm are also availabe in combination with MC gain, it would be way smarter to install a resistor per channel in parallel (for example in the plugs of the phono cable) to reduce the 47 kOhm instead.


Ap: Haven't tried that myself, as I don't own an AT-F7, but Andreas (alias akem), one of the experienced phono fans over on the German Hifi-Forum(.de) suggests to rather load it with roundabout 1 kOhm for better sound quality. So I'd suggest to install a 1 kOhm resistor per channel in parallel in combination with the 47 kOhm setting on the Mani.


Greetings from Munich!

Manfred / lini

Yep, 47K in parallel with 1K results in 979 ohms.

 

[Apolek]

Certainly. However, to me Ap's initial posting rather seemed to imply that he hasn't bought the Mani yet - and typically one rather wouldn't want to mod a brand new piece of equipment in order not to void the warranty. And as Ap might yet want to determine the optimal load for his taste and system environment anyway, I'd tend to suggest using splitter adaptors and loading plugs for a start.




Technically not, but in many cases the MM/MC switching implementation only allows for switching both at the same time. The Mani seems to sport individual switches for that, though - and apparently even separate ones for each channel.


Greetings from Munich!

Manfred / lini

Sorry about the misunderstanding... I've had the Mani for almost a year now and have been very pleased with it. Been using it with a MM cartridge, so the MC issue hasn't come up until now. Literature says it could do MC, and can "handle any cartridge you can throw at it", so I went off that. And, yes, the Mani has what appears L&R switches for gain and load.

 

[Apolek]

So, what I'm looking at is adding resistors (one for each channel) across R ground, R+, and L ground, L+, using the resistance in parallel formula to achieve a desired resistance? I can do that. May even use a pair of decade boxes for flexibility.

 

[Aerobat]

So, what I'm looking at is adding resistors (one for each channel) across R ground, R+, and L ground, L+, using the resistance in parallel formula to achieve a desired resistance? I can do that. May even use a pair of decade boxes for flexibility.

Yes.