Cartridge Break-In

Onhwy -- it's not a hard and fast specification by any means, however it's based on (and borne out by) a few (unforunately very few!) cartridge makers who DO specify optimum load values for their cartridges. And also the concensus of a lot of audiophiles who report their results. I have compiled these anecdotal reports, and it's amazing how consistently the results work out to the 25x (the resistance of the cartridge in question.)

As for science, it's pretty simple, though again, not hard and fast, because of so many other variables like cable length and composition, phonostage design etc. However if you take an average gain of 50dB (most MC phono stages are between 40 dB and 60 dB I'd say) and an average output of 0.40 mV (most cartridges have outputs somewhere between .20 and .60 mV) you will come up with (again this is an average) an impedance matching differential that requires the driven impedance be (at least) 25x the impedance of the driver. Notice I said "at least". So why wouldn't say 47K ohms be even better since it's way above the "at least" minimum? That's a fair question. the answer has to do with the miniscule value of the driving voltage, as opposed for instance to the (usually) healthy voltage with which preamps drive amps. In the cases of both cartridge-to-phono preamp (always) and preamp-to-amp (sometimes, but often enough to cause problems), when the driving voltage falls to near the minimum input sensitivity of the driven device, it's important that the match be closer to the theoretical ideal (minimum) to insure flattest frequency response and best efficiency (input voltage to output voltage) for the driven device. If you need proof of that, think of the many discussions you've (probably) read where somebody is complaining that their magabuck preamp and their megabuck amp are producing thin, or glarey, or bass-shy sound and they can't figure out why. The problem lies not with the equipment, but with the combination. And why BTW, we have all these expensive ICs with network boxes (like MIT and Transparent) which allow better impedance matching (load adjustment) of preamp to amp. Personally, I don't think this would be necessary if the equipment were well matched to begin with. But I digress, sorry.

So this 25x factor is really a rule of thumb which is meant to get things to a point (ballpark) from which you can be pretty sure that an optimum value (obtained by listening) will be found within a range that's easy to work with, practically speaking. I usually recommend 50% +/_ This means for instance that if a cartridge had an internal resistance of say 30 ohms (sometimes spec'd. as "output impedance") and therefore (IMO) a theoretical ideal load of 750 ohms, that you would probably find your best sonics somewhere between 375 ohms and 1125 ohms. If you were to start out at 750, and depending on what you hear, it's not hard to tell if you should go up a little or down a little (and after you do, you may decide to stick with 750 ;~)) What you WILL avoid however, is sitting there for two weeks with a huge bag of resistors (and a soldering iron, if the person who designed your phono preamp thought you should only have to do this once!!) until you zero in on the optimum load for your setup.

I can say one thing for sure about any MC cartridge (not HO of course) without fear of being made to eat my phono cables: It's never going to be 47K, and it's never going to be equal to the internal resistance of the cartridge (like 6 to 30 ohms). I mention this because that's the range most @#^?*! cartridge manufacturers give you. Yeah, great! So where are you supposed to start?! Try 25x to start, it might not be absolute perfection, but it will save you a lot of time and aggravation getting there.

I enjoyed reading some of your proposed alternatives, especially the one about the subwoofer ;~) I think the best way is still playing records as Steve said. However, you can break in a cartridge while you're away by using the Cardas sweep/burn in record. It has white noise bands that are continuous (don't run out.) The record is made of extra hard vinyl just for this purpose, and if you leave your whole system on at low/moderate volume, you get some additional burn-in for your system too.

RE the recommended break-in time: I don't know why cartridge manufacturers all seem to quote such low break-in times! If you ask around, you'll discover that most folks will tell you a new moving coil cartridge requires a minimum of 100 hours (150 just to be sure) so I don't understand the manufacturers' lack of candor on this pooint. And that would take about four to six days playing the Cardas record 27/7. Which is what I did, and it worked just fine. However, I heard no difference after the first 60 hours (the manufacturer recommended 30!) It was bright and glarey, and I thought I'd made a terrible mistake! But after 100, everything changed and continued to get better and better until 125-150 or so.

It would be a lot smarter for the manufacturers to be honest and not raise expectations unnecessarily.

Onhwy61, what kind of cartridge is yours? I ask, because if it's a MC, then 47K ohms is WAY too high a loading and will give you "tipped up in the treble and the bass is uneven" no matter how long you break it in.

A good rule of thumb (starting point) for MC load is 25 times the specified coil resistance.

I can't think of a (safe) quicker way to break in the cartridge than using the Cardas record. I also have an AT stylus cleaner (which vibrates at a single frequency, I don't know what it is exactly) It's an intriguing idea, but I'm not sure I'd want to use it on my cartridge for 100 hours -- it seems a little strong, to say nothing of the batteries it might use up. And I agree with you, I'd be nervous about leaving that kind of setup unattended!

The reason BTW for the 100 hour +/_ break-in time we all talk about, is because the modern polymers used in suspensions require a certain number of flex/relax cycles before the long-chain molecules settle into place and get as tightly packed as they're going to. So it's not really not about how hard you flex the material as how many times.

Of course it's just my own personal style, but given the choice, I almost always go for the more moderate approach . . . .

Neil

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Onhwy, if Raul says:

"Just play records, forget about break-in and enjoy the ride."

You should remember that is the "Gospel according to Raul", but not necessarily the gospel Truth!

Please remember that Raul and others have personal opinions which they have a habit of expressing as absolute facts. Do not misunderstand me, I have nothing against opinions -- I just think they should carry a proper disclaimer.

I have given you some verifiable information about the stress performance of modern polymers, and you can research this further, as I have, by using the modern miracle of Google.

Further, re cartridge loads, only a few manufacturers (like van den Hul, for instance) bother to state an optimum load for their products, even the very expensive ones. Most give a range that starts at the coil resistance (5 to 30 ohms or so) and goes to 47K ohms. That doesnt tell you a hell of a lot does it? However, there is a very definite electrical relationship (called impedance matching) between a cartridge's internal resistance and the load it is working into (just like between a preamp and amp). The customary starting point is usually a multiple of 25 times the cartridge's internal resistance. This has been arrived at through both experience and experiment. Using it will definitely get you in the ballpark, otherwise you'll be starting outside the stadium parking lot!

If you don't know the coil resistance of your cartridge, give me the make and model and I'll be happy to look it up for you. It may also be listed at www.cartridgedb.com

I hope this helps clarify some of the mystery.

Doug, you're quite right, none of this applies to stepup transformers. Just to confirm you findings (somewhat), if you take the 25x factor and apply the +/_ 50% range, it would come out 12.5x to 37.5x, which is another way of calculating the range. Add the extremes together and divide by 2 to get the mid-point.

One technique that works very well when breaking in cartridges, especially those with the latest temperature and moisture resistant polymers every manufacturer seems to use now for the supensions, is to slightly 'over-deflect' or 'over-stretch' the polymer for the first 50 hours or so. I know this sounds scary, but it won't hurt the cartridge and only requires just a slight amount.

Basically, for the first 50 hours, you want to apply a VTF that is like a quarter of a gram ABOVE the maximum tracking force recommended by the cartridge maker. Doing this will temper/condition/stretch (whatever term you like) the elastomer suspension material just a bit BEYOND the highest VTF you will ultimately use -- insuring that if you track your MC cartridge at the upper limit of the manufacturer's suggested range (as many of us do) that the polymer suspension will be fully 'conditioned' just PAST that tracking force, rather than at the 'cusp' of its break-in conditioning.
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