Neumann SX68 cutterhead was conceived at the end of ‘60es and now, after 30years and over, is now again a really precious audio transductor with superb performances in disc cutting. It has two separate magnetic systems for the two power drivers, made by two little coils, helium cooled. Its frequency range is flat from 40 to 16000 Hz +/- 1Db and can cut very high levels. The SX74 was born some years after the SX68 and has the same construction, but with some internal improvements: the magnets was 28% stronger, so less power for the same recorded level, more internal rigidity, more light and strong material was used, so the frequency response was widened up (7 to 25000 Hz or 20 to 20000 Hz +/- 2 Db). The internal temperature resistance was increased to 200°C instead the 120°C of the SX68 and the maximum current capability was increased too.  The SX74 is now probably one of the best cutterhead now existing in the lacquer disc cutting world and is a really myth in this field.  These two cutterheads are stronger and works with feedback, thanks to two microcoils very thick and delicate mounted inside the two channels with their dedicate magnetic fields.  The Neumann SX74 cutterhead was in origin tested by Neumann with short tonebursts at 10,000Hz@10msec with a current of 8Amperes; this power is managed by a tiny wire equivalent at the little wire of a mini radio loudspeaker coil!
This is one reason because helium coil is unavoidable if LOUD cuts are necessary, especially with LOUD trebles.

 The effect of ultrasonic audio frequencies at high power may do damages on the wire insulation, so special materials are necessary to avoid shorts and for the longer life possible of similar power coils.  Neumann SX74 feedback coils drops in response over 14,000Hz (Neumann datasheet) so, the contrary normal effect is a progressive BOOST over this frequency that will result on a cut without frequency corrections (maybe +3/+5Db at 15/16,000Hz depends by the cutter, some differences may occur).  The SX15 is a very rare and fragile old Neumann stereo cutterhead. It was made at the end of 60Â’s years, very similar to the Ortofon cutterheads. Its construction is very different by the 68/74 series because there is only one magnetic system for the two drive coils, that are parallel, not 90°angled.  The stereo movement is obtained by a mechanical “bridge” and its construction is very unique. It is a really beautiful sounding head, but less open and powerful than other new series.   It is interchangeable with 68/74 heads with some FB and breaker protection readjustments.  Its feedback coils are double-winded in air, only glowed with an amazing precision; so it is possible to repair (we did so in our SX15), but we prefer not to!!! All these cutterheads are very high precision ones made 25 to 40 years ago and completely internal glowed. In the years, the old glows may give instability problems, or the internal power coils-wire may be damaged by the heat, strong vibrations-accelerations, or simply by the years working......   Sometimes at very high cutting levels, some instability like “larsens” can start at normal feedback level...WE CAN FIX THESE PROBLEMS with the latest compounds we have found.


 

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