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Stu Pitt - Help Phono stage seeting to MC or MM??

 

New member
Username: Klismith

Denver, CO

Post Number: 8
Registered: Mar-09
Hello Stu,
I finally purchased a Simaudio LP3 to go with my VPI Scout and Dynavector 20xh. I couldn't find a used Dynavector P-75 so decided to go with the Simaudio. My question is probably simple, maybe even kinda stupid. The LP3 can be configured to MM or MC. My cartridge is a high output MC, rather than low output MC. Should I still configure it for MC or does a high output MC cartridge mean I should use MM? MC seems the obvious answer but i'm confused by the "high output" thing?
 

Platinum Member
Username: Jan_b_vigne

Dallas, TX

Post Number: 17132
Registered: May-04
.

Use the "MM" setting.
 

Gold Member
Username: Stu_pitt

Stamford, Connecticut USA

Post Number: 4546
Registered: May-05
I had the same question when I bought my 10x5, so if it's a stupid question, I guess there's power in numbers.What Jan said. I have the 10x5 which is a HO MC running through my Bryston B60's phono section, which is MM. It takes a little more twisting of the volume knob to get to where I need it, but not too much.

HO MC's output is closer to MM than standard MC is.

Not sure if using the MC setting would cause damage by overloading the input or not. Jan would be better able to answer that one than I ever could.

Congrats on the setup. I really like what you've got!
 

Platinum Member
Username: Jan_b_vigne

Dallas, TX

Post Number: 17134
Registered: May-04
.

Hard to guess - without checking specs myself - whether the MC section would be overloaded by a high output moving coil. Even after checking the lack of useful information from some manufacturers would still make it mostly a guessing game. Like amps and speakers, each component in the phono section will have specs which designate certain conditions of operation such as maximum output voltage before distortion sets in plus minimum input voltage required to drive that specific gain stage to its full output without clipping or distortion. (Remember, most modern phono sections capable of MC playback will have both a conventional moving magnet phono section providing "X" amount of gain and then an additional "pre-pre amp" gain stage which is switched in circuit when you select the "MC" input. Rather than trying to build one phono stage with extremely high gain, this gain stage/pre amp feeding into a conventional phono pre amp will make the device more flexible to more users plus minimize noise in the overall circuit.) And, as with amps and speakers, those minimum/maximum voltage conditions are seldom met or maintained. Dynamic music tends to have anywhere from moderate to tremendous variations in level which will translate into similarly moderate to quite high voltage levels when they have been converted into "signal" running through a gain stage. Most often the bulk of the music signal is of such a moderate voltage level that most MC inputs could run without problem with all but the highest output cartridges for alll but the highest signal levels.


The problem is really the lack of standards for phono cartridges when it comes to output voltage. There are some incredibly low output moving coils which require some fairly dramatic gain increases within the step up device just to create a useable signal in many systems. Then there are very high output cartridges designated moving coils which bear more resemblance in their specs to the average moving magnet cartridge. As a group "high output" moving coils tend to fall somewhat lower than the lowest of the moving magnet varieties but noticebaly higher in maximum voltage output than most conventional low output moving coils. It's this somewhat nebulous middle ground that leaves most people guessing. Plus, some listeners simply think their system isn't operating properly if they have to crank the volume control above 12 O'Clock just to achieve a comfortable listening level. That can be nothing more than the trim of the control itself but most people are uncomfortable with linear type vc's where each increase in the control results in a consistent increase in dB's.

You would want to look at the specs for any cartridge and select a cartridge which meets the minimum voltage requirements for your phono stage's MC input but which never exceeded the maximum input voltage. Keep in mind most phono stages are rather vague about how much gain is supplied by the moving coil step up device itself and how much gain is coming from the phono stage alone as these are two discrete gain stages which cascade one into the other when the "MC" input is selected. Until rather recently the phono pre amp stage was one component and the MC step up device was another. The phono pre amp proper was responsible for both gain and correct RIAA equalization while the step up device only supplied signal gain. (Some phono stages also fed into the line stage of the pre amp to have more total gain within the circuit.) Now the step up device and the phono pre amp stage are more commonly paired together as one convenient, but overall less flexible, component. Of course, until the mid 1980's such things as "high output" moving coils didn't exist at all. If you purchased a moving coil cartridge in 1979, say, a Denon 103, you knew you had a low outut cartridge and you could rather easily come up with a step up circuit or a transformer which would match your cartridge's output to most conventional moving magnet phono stages. Most often in those days a MC cartridge manufacturer would also retail their own step up devices matched to their cartridges. This made it relatively easy to match a cartridge, a gain stage and a phono circuit which would be acceptable through most systems.


Just to get further into the weeds for a moment, all of this happening at the front of the system still relies on adequate matching of gain stages throughout the system plus the electrical sensitivity of the speakers, the size of the room, the trim of the volume/gain controls along with the sort of music preferences the listener might have and whether they required "lifelike" concert hall volume levels through their playback system. The somewhat ubiquitous low sensitivity (82-84dB) speakers which populated the market through the '60's, '70's and '80's made system matching - when it comes to gain stages - a bit more difficult than it is today. Low output moving coils running through lower gain phono stages than you can find in today's improved devices would, on occasion, simply fail to reach acceptable levels for those who demanded first row volume levels when they put on Mahler's Fourth.



If you're still with me by this point, one more pertinent issue raised by HO moving coils is the required cartridge loading provided by the step up device. Manufacturers have come to some degree of standardization in regards to this spec but the average low output MC will sound best when it is loaded down well beneath the 47kOhm average for moving magnets. (A few low output MC's will sound best at loadings as low as 100 Ohms.) I suspect most of today's HO MC's will work well into the typical loading of any high quality phono stage but it would certainly be worth the time to check the specs - or even give the manufactuters of the cartridge and the step up device a call - to determine whether a specific high output moving coil has been designed with any unsual loading requirements in mind. Properly loading the cartridge is as important, if not more so, than properly matching your amplifier's capacities to your speakers. If the loading isn't correct for a specific cartridge, frequency response and dynamic range will be compromised. It would be a shame, though a fairly common mistake, to spend a good chunk of cash on a high quality analog set up only to have it be compromised by such a simple error as incorrect cartridge loading. Most cartridge spec sheets suggest the proper impedance loading for a moving coil whether it is high or low output. (Moving coils are typically unaffected by capacitive loading though a few oddballs might still exist where this spec is also important.) If your step up device doesn't mention adjustable cartridge loading, you can usually assume it has been set to approximately 47kOhms to work with a moving magnet input. The difference in sound quality between correct and incorrect loading, however, is well worth the few minutes it should take to check.




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