Thread: PLZ pre-preamp
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Old 2nd March 2019, 02:19 PM
bikerhifinut bikerhifinut is offline
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Join Date: Jan 2006
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Default Re: PLZ pre-preamp

All cartridges, generally speaking, can be retipped by a competent technician. As well as Soundsmith there are people like Len Gregory and Dominic harper in the UK that offer cartridge overhaul and retipping services.
That's quite useful as at a price, you can have your stylus not only replaced but possibly upgraded to a better/different profile.
There are many opinions on stylus profile, and the most advanced and expensive don't necesarrily guarntee a better audible performance.
That stereohedron is simply a brand name for a line contact variation I think possibly a Microline. The Shibata was initially developed to play Qudraphonic LPs where the decoding information etc was up beyond the 20 khz region and so a stylus and suspension had to be developed to be able to trace those high frequencies.
Other really effective profiles are, for example, the Fritz Gyger types and the GygerS and II amongst others are used by Goldring in theoir cartridges. I happen to like the Gyger profile a lot as well as the Ortofon Fine Line which for me are every bit as good as the way more expensive Shibata profile which can be a bit edgy to my ears.
Other factors are things like tip and cantilever mass and stiffness. This seems obvious of course. And brings me to why the output of moving coils is so low. In order to have a manageably low mass and thus low inertia, the coil on the end of the cantilever has to be light and constructed of extremely fine wire with very few turns. This means that the magnet assembly around the coil has to be incredibly strong and the field highly focussed in order to produce a useable output voltage, which is still in the order of a couple of hundred microvolts or so. Moving coils have really only taken off since the development of very strong magnets using rare earth metal alloys etc, making them easier to design and manufacture.
So this brings us to the good old Moving magnet, for which I shall include variations such as moving iron and variable reluctance which are all basically variations on a theme. As you will know, a moving coil works by waggling a coil in a magnetic field to generate a voltage, and therefore by the same token if you hold the coil steady and "waggle" the magnetic field around the coil you will again get a voltage generated. The advantage here is that you can wind a nice big coil to get a more effiecient generation of volts at the cost of a smaller magnetic flux density as the magnet on the end of the cantilever has to be tiny in order to keep mass down, or the magnetic alloy in a moving iron design that alters the field from an external magnet and then induces the coil voltage. On balance however the advantage is an output some 10 to 20 times that achievable by a moving coil. And there are many very good cartridges indeed with high outputs.
The issue here though is the DC resistance and inductance of a larger coil will cause its own problems with matching and frequency responce, especially at the higher frequencies, this is why most magnetic cartdiges need a 47k loading and are very susceptible to capacity effects from circuitry and screened cables due to the RC and LC low pass filters created thus.
So there are a few very low output moving iron and moving magnet cartridges, basically all that is, is fewer turns on the pickup coil which brings the advantage of MC in terms of matching and less susceptibility to capacitance effects.
Magnet technolgy has benefited these designs to the same degree in that the inertia from tip and cantilever mass can be reduced which allows the fancy line contact stylus to actually respond at the high speed (ie frequency) demanded.
I've heard a Grado low output moving iron and very nice it was but I felt the responce was skewed at the frequency extremes. There are articles out there that suggest we should alter the RIAA response filtration for MM and MC/LOMM because of the effects of electrical loading and ability to trace higher frequencies more effectively. It's more than just that simple step up which really only has to be linear from Lf to HF.
Loading in MC is also a very contentious subject, for the most part a MC cartridge is unaffected by capacitance issues, which is a good thing and also usually anything above 25 ohms depending on the DC resistance etc of the coils, which is usually never more than 4 ohms or so on the better carts, will not have any material effect. I havent noticed my Ortofon MC cartridges to ever be fussy about DC loading. I can't speak for other brands. I suspect the improvement I hear with MC is down to the reduced masses being accelerated in the groove and so we hear less mistracking and a better detail, combined with a much reduced interaction with the various capacity, resistance, and inductance related effects in the electronics and wiring. The same result may be reasonably expected with low output magnetic types for the same reasons.
A long post Stuart but maybe explains the reasoning?

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