The main cutting amp.

If you plan to use Tube amplifiers, we can UPGRADE your SX68 and SX74 doubling the internal impedance to 9-10 Ohm power drive coils instead standard 4,7Ohm, (SX68 and 74) to obtain a true better matching impedance. Using the same kind of super hi-quality flat wire for nominal repairs, but calculated for 9 Ohm instead the 4.7, the impedance will be slightly higher, but the advantages will be also if you want to use standard SAL74 or VG66 solid state (old) amplifier. The advantages are: less charge to the amplifier, better charge agreement to the common 8Ohm standard output of audiophile Tube amps, not last, solid-state amplifier BRIDGED, normally works better with charges higher than 4 Ohm; Less thermal internal dissipation of the cutterhead, so IMPROVED insulation SAFETY, because more wire turns means, with the same power drive, the same performances but with LESS CURRENT=LESS HEAT inside. Our main SX74 tube drived, was modified so and was hardly misused to voluntarily burn.

 


 

The misuse was: FB channels inverted for some seconds; FB level over maximum (14-15Db) for some seconds in larsen; FB hardly disconnected during a cut of +6Db@5cm/sec.Normally this operation can destroy also some mechanical parts, otherwise is the only way to fully understand limits and how ruggedness can be the materials employed for repairs. Only with a full power 20kHz continuous RIAA encoded with no Helium cooling gas for several seconds the cutter lost the insulation and PARTIALLY shorted to 4Ohm...only in Left channel.. but again was able to cut. After the internal check at stereomicroscope, the wire was again crystal clear, not burned, it only partially lost the 250°C varnish. The current inside the cutterhead coils is not DC continuous, but sinusoidal at different frequencies, especially the hi-end of the audio band because the RIAA standard vor vinyl disc cutting physically MAKES A BOOST of +20Db at 20,000Hz@1000Hz ref and a drop of -20Db at 20Hz@1000Hz ref.

 

 
 

 

40Db of difference traduced in audio power is an enormous difference; consider that only +3Db means DOUBLING the power of an amplifier.. to the ears the difference is just audible! Finally, we don't promise MIRACLES... only, Robby makes test test tests to assure the best results for these OLD but mythic cutterheads, again capable of give incredible sounds and performance to the vinyl discs in the 2000 years! Note: For the use of 9Ohm cutters with Neumann SAL or VG amplifiers it is necessary to slightly change the parameters of the cutterhead current/thermal protection, because they works with the value of the cutter copper-wire resistance change with the heat, with the use of a DC bridge... if this parameter isn't changed, maybe the protection disconnect the cutter automatically without give power; this because the original value decode the 8,2Ohm like a temperature of 200°C. Westrex 3D cutter is about 12 Ohm of drive coils and 13 Ohm for the Neumann SX15

Another tube RIAA encoder

 

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