SOWTER TYPE 1495

APPLICATION

A competivitly priced transformer for use with most current out Digital-to-Analogue Converters. Works well with any current out DAC. Provides current to voltage conversion, voltage gain to achieve at least a line level signal (0 dBu 0.775V) depending on the I/V resistor used. Presents a low impedance to the DAC output for best frequency response and quantisation noise reduction. Provides significant sound quality improvement when compared to other interface methods. Ensures full isolation of digital noise in ground and supply rails. 

We recommend that the I/V resistor is placed across the secondary of the transformer but a primary resistor may be used instead for a different filtering characteristic. (higher roll off frequency). The I/V resistor value should not exceed 100 Ohms referred to the primary (See below).  Lower values may improve the sound but will reduce the output level. Can be configured to drive 9335 attenuator without loss of bandwidth. Can be used driven from multiple parallel DAC's to increase output level.

The secondary must be connected to a high impedance amplifier. 100K Ohms or higher.

FEATURES

Mumetal core for minimal harmonic distortion. Mumetal can for magnetic shielding. Twin secondary windings for driving differential (push-pull) amplifier. These may be used in parallel to give a ratio of 1:8 which will improve the bandwidth and reduce the output impedance. Package options.

HOW TO CALCULATE THE I/V RESISTOR (example)

Current out = +/- 1 mA = 2 mA p-p = 2 / 2.82 mA= 0.88 mA RMS.
Configuration: Seconday coils in series. Ratio = 1:18
Secondary current = 0.049 mA
Secondary load resistor for line level (0.775V) = 0.775 / 0.000049 = 15.8 KOhms.. Allow 10% for copper loss. Use 18K Ohms. DAC wil see about 65 Ohms.

Configuration: Seconday coils in parallel. Ratio = 1:9
For line level out use 4.2K Ohms secondary load. DAC will see about 70 Ohms..

Suitable DACS:

AD1860N AD1862 AD1865 DSD1792 PCM1702 PCM1704 PCM1738 PCM1792 PCM1794 PCM1795 PCM1796 PCM1798 PCM2702 PCM56 PCM63 TDA1540 TDA1541A TDA1543 TDA1545A TDA1547