Sowter Type 8055

Phono Cartridge Transformer

Coloured Leads 8055-F
8055 frequency response 8055 dimensions
APPLICATION For matching low impedance (5-15 ohm) 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. Recommended for ORTOFON MC SUPREME series cartridges. Can be used with coax or twinax cartridge cables and feed a balanced or unbalanced amplifier.  Two transformers are required for a stereo system.
FEATURES Mumetal core for minimal harmonic distortion. Balanced two chamber winding and 4 separate electrostatic screens for the ultimate in rejection of hum and noise in the cable connecting between the cartridge and transformer. Accurate output balance for phase split drive to balanced amplifier if required. Multiple interleaved windings ensuring exceptionally good bandwidth. High bandwidth and very low phase shift even at 10 Hz ensures excellent transient response. Mumetal can for magnetic shielding. OCC wire option.
RATIO 1:10
DC RESISTANCE Standard wire

Pri = 0.72 Ohms.Sec = 102 Ohms

OCC wire

Pri = 0.86 Ohms. Sec = 84 Ohms

MAXIMUM LEVEL 0.5 % THD at 50 Hz (40 ohm source) -3 dBu (550 mV)
FREQUENCY RESPONSE 3 Ohm source 3K ohm 150 pF load +/- 0.25 dB 10 Hz to 70 kHz
8055 application circuit options 8055 connections
E A Sowter Ltd
The Boatyard Cullingham Road
Tel:+44(0)1473 252794
Fax:+44(0)1473 236188

055 moving coil transformer loading
The following information was kindly provided by Morgan Jones.


Although the 8055 transformer can be used without considering the cartridge=s DC resistance and the secondary loading imposed by the pre-amplifier, greatly improved results can be obtained by considering these factors.


The first oscilloscope trace shows the effect on the leading edge of a 1kHz square wave when the primary is fed from a 10 ohm source and the secondary loaded by 2k7 ohm in parallel with 60pF.

Alternatively, the transformer can have a Zobel network tailored to the cartridge=s DC resistance added across the secondary, the second trace shows the effect. Note that not only has the ringing virtually disappeared but that the output from the transformer has increased from 301mV to 366mV, improving the S/N ratio by 1.7dB.



Cartridge DC resistance

4 ohms

6 ohms

8 ohms

10 ohms







The Zobel network consists of a series 2k4 ohm resistor and capacitor determined by the table. The transformer also requires 6k8 ohm in parallel with 190pF total capacitance connected directly across its secondary. All pre-amplifiers have input capacitance, so this capacitance must be subtracted from the 190pF to find the required additional capacitor.