Sowter Type 9990

1:20  Transformer for 3 to 10 ohm Phono Cartridge

Coloured Leads
Octal base
APPLICATION For matching moving coil Phono cartridge to balanced or single sided solid state or valve pre-amplifier. Ensures appropriate loading of the cartridge and correct matching to pre-amplifier. Ideal for use with low output cartridges. Suitable for most cartridges with a dc resistance in the range 3 to 10 ohms.  In order to get the correct HF roll off it is recommended to use a Zobel network consisting of 330 pF in series with 9.2k ohms.   The loading seen by the cartridge mat be adjusted by means of a secondary load resistor.See the table below. If the cartridge does not require loading just omit the resistir (R)R altogether. Two transformers are required for a stereo system.
FEATURES  Mumetal (76%Nickel) laminated core for minimal harmonic distortion and exceptional bandwidth. 4 separate electrostatic screens for rejection of hum and noise in the cable connecting between the cartridge and transformer. Multiple interleaved windings ensuring exceptionally good bandwidth with a wide range of cartridge impedances.  As shown above the bandwidth improves with lower cartridge resistances. The high bandwidth and very low phase shift ensures excellent transient response. Mumetal can for magnetic shielding. Available with colour coded leads or international octal plug for a small extra charge.  Available wound with OCC wire as an option. This transformer replaces types 7136 and 9575
RATIO 1:20  (26 dB)
TOTAL HARMONIC DISTORTION at 20 Hz (6 ohm source) typical  0.05%
FREQUENCY RESPONSE 5 Ohm source 100K load with Zobel network (330pF in series with 9.2 k ohms). These values should be used as a starting point for optimisation using listening tests with your actual cartridge. +/- 1.5 dB 3 Hz to 100kHz
NOTE The transformer should be connected as shown below. The Black (ground) lead is normally connected to the signal ground of the amplifier. You may need to experiment with different connection points to minimize hum.
E A Sowter Ltd, The Boatyard
Cullingham Road
Tel: +44(0)1473 252794
Fax: +44(0)1473 236188