Moving Coil Cartridge loading

[steve-z]

Most likely to be Dave Cawley of Sound HiFi, Dartmouth.

Yes, that’s the guy.


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[forsell]

but I’m a little concerned over MC compatibility as the input impedance on the MC input is only 47ohms, considerably lower than the norm used by other manufacturers of 100-200ohms.

Acoording to Shit's info given on their web site: "Input Impedance: Selectable 47 ohms or 47k ohms"

General info: you can not INCREASE an input impedance of any device by switching an additional resistor in parallel as it can only lower the resulting input impedance. Hence the only other possibility is connecting an additional resistor in series. This will increase the resulting input impedance but -as both resistor act as voltage divider- the input voltage will be attenuated though.

[steve-z]

Acoording to Shit's info given on their web site: "Input Impedance: Selectable 47 ohms or 47k ohms"

General info: you can not INCREASE an input impedance of any device by switching an additional resistor in parallel as it can only lower the resulting input impedance. Hence the only other possibility is connecting an additional resistor in series. This will increase the resulting input impedance but -as both resistor act as voltage divider- the input voltage will be attenuated though.

Andrew from Rothwell Audio mentioned earlier that a series resistance would reduce output and affect S/N ratio so not a feasible idea really.


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[Barry]

Acoording to Shit's info given on their web site: "Input Impedance: Selectable 47 ohms or 47k ohms"

General info: you can not INCREASE an input impedance of any device by switching an additional resistor in parallel as it can only lower the resulting input impedance. Hence the only other possibility is connecting an additional resistor in series. This will increase the resulting input impedance but -as both resistor act as voltage divider- the input voltage will be attenuated though.

True, and as the additional series resistor adds to the source resistance of the cartridge, the signal to noise ratio will be degraded.

If one can select the 47k load impedance on the Schiit device, whilst in MC mode (ie high gain), then fitting a 100R resistor in parallel at the input would offer the correct load to the cartridge.

[forsell]

...so not a feasible idea really.

I fully agree with you.

I am just wondering what kind of holy grail doing everything "right" some guys expect for GBP 120...

[RothwellAudio]

I’ve decided against modifying because it sound pretty good as is, there is a bit of smoothing in the treble due to the low impedance loading but I can live with it for the moment until I can raise the cash for a Rega FONO MC which allows a good choice of loadings and from reviews I’ve seen sounds excellent.

You may be hearing smoother treble than you had before but I'm not sure how you can say definitively that that's due to "low impedance loading". What else have you tried with that particular cartridge as a comparison?
I'll admit that specs and computer simulations aren't infallible but my calculations suggest the difference between a 47 ohm load and a 100 ohm load with your cartridge will be nothing but a small change in signal level with no change in frequency response up to 20kHz.

[steve-z]

You may be hearing smoother treble than you had before but I'm not sure how you can say definitively that that's due to "low impedance loading". What else have you tried with that particular cartridge as a comparison?
I'll admit that specs and computer simulations aren't infallible but my calculations suggest the difference between a 47 ohm load and a 100 ohm load with your cartridge will be nothing but a small change in signal level with no change in frequency response up to 20kHz.

My previous cartridge was a Nagaoka MP110 which is a fairly neutral performer, certainly not bright, obviously I can’t do AB comparisons as I only have one turntable, the main comparison which shows the smoother treble is the comparison with the digital version of the same music, digital frequency response obviously being flat across the audio band so differences show up clearly.
The only magazine review I could find online of the ATF7 which actually included a lab report was from Hifi World August 2010 issue, their FR plot showed a ruler flat response to 7-8khz rising by 2db to 10khz and that level maintained to 18khz, enough to add a little sparkle to the very top, they don’t state what loading they used for the test though.
I get the feeling the Mani was primarily designed as a MM stage for which it is excellent and the MC side of it was a bit of an afterthought.
The benefit I think I will find with a Rega Fono MC is it has been designed to be more focused to be a MC only stage, even the much more expensive Rega Aria which covers MM&MC cartridges has totally independent inputs and circuitry for the 2 types so not compromising either type for the sake of the other. Talk of this is a little academic atm as funding the change is unlikely to occur imminently and a smoother treble doesn’t detract from the overall improvements I’m getting from the ATF7.
http://www.soundhifi.com/images/AT-F7.pdf

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[RothwellAudio]

The only magazine review I could find online of the ATF7 which actually included a lab report was from Hifi World August 2010 issue, their FR plot showed a ruler flat response to 7-8khz rising by 2db to 10khz and that level maintained to 18khz, enough to add a little sparkle to the very top, they don’t state what loading they used for the test though.

http://www.soundhifi.com/images/AT-F7.pdf

That review states "there is the usual rise in output at high frequencies due to tip mass resonance, resulting in a +2dB plateau lift from 10kHz to 18kHz, just enough to give the sound a little extra high frequency zest."
If the rise was due to coil inductance interacting with load capacitance it could be manipulated by altering the load impedance. However, if it isn't - as claimed by Hi-Fi World - then altering the load impedance won't make any difference.
Anyway, I'm just a bit concerned that you will spend money on another phonostage based on the belief that a different load impedance will brighten things up, and end-up disappointed. Of course, if another phonostage performs differently it would still be speculative to attribute the difference to a change in load impedance.
I suppose something like the Headspace would give you some idea what effect load impedance has. It has eight load impedance settings which can be selected without altering any other parameters. Personally, I can't tell any difference with most cartridges between the 55 ohm setting and the 100 ohm setting.

[steve-z]

Anyway, I'm just a bit concerned that you will spend money on another phonostage based on the belief that a different load impedance will brighten things up, and end-up disappointed. Of course, if another phonostage performs differently it would still be speculative to attribute the difference to a change in load impedance.

If I do change the phono stage it will only be after an extended audition of a loan unit, if I get the desired result I’ll change, if not then I won’t. It’s the only way to be absolutely sure, certainly the loan of a Rega won’t be a problem as I have a good relationship with my local dealer, any other options might be more difficult.


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[RothwellAudio]

Fair enough. With fewer and fewer dealers left, all too often people resort to buying online and make their purchasing decision based on specs or reviews or forum recommendations - which may or may not lead to satisfaction.
Good to hear you're still using your local dealer - best way