SOWTER AUDIO TRANSFORMERS
1465 DAC INTERFACE TRANSFORMER

IMPROVES THE SOUND EXPERIENCE OF CD PLAYERS AND NETWORKED MUSIC SYSTEMS.

Product under development.
These plots are the target.


Sowter DAC transformer

APPLICATION Our most popular transformer for use with most current out Digital-to-Analogue Converters. Works well with any current out DAC. Provides current to voltage conversion with 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 (See below). The transformer has sufficient inductance for good quality operation with higher values to increase the output level..  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. Twin primary windings are provided for use with twin DAC's fed with complimentary data. This approach has been used in order to cancel out quantisation noise.

The I/V resistor across the secondary of the transformer instead of the primary has yeilded the best result according to some customers.  The value of the resistor should be increased by the ratio squared.  The table below suggests values for rexperiment.

FEATURES Exceptionally large and high performance transformer.  Twin secondary windings with geometric balance for driving differential (push-pull) amplifier. These may be used in parallel to improve the bandwidth and reduce the output impedance.  Mumetal core for minimal harmonic distortion.  Mumetal can for magnetic shielding. 

HOW TO CALCULATE THE I/V RESISTOR (example)

Current out = +/- 2 mA = 4 mA p-p = 4 / 2.82 mA= 1.43 mA
Configuration: Primary coils in parallel. Seconday coils in series. Ratio = 1:10
Secondary current = 0.143 mA
Secondary load resistor for line level (0.775V) = 0.775 / 0.000143 = 5420 Ohms. Allow 25% for copper loss. Use 6.8K Ohms

Configuration: Primary coils in parallel. Seconday coils in parallel. Ratio = 1:5
For line level out use 3.3K Ohms secondary load. For increased output level increase load in proportion.

Suitable DACS:

,AD1852, AD1853, AD1860N, AD1862, AD1865, AK4396, AK4399, AK4440, AK4490, AK4495S/95, CS43122, CS4390, CS4398, DSD1792, ES9018, EVM1702, PCM1702, PCM1704, PCM1738, PCM1792, PCM56, PCM63, SAA7350, TDA1540, TDA1541A, TDA1547, WM8740, WM8741
CAN DIMENSIONS
45 mm Dia. x 52.5 high
PRIMARY INDUCTANCE (each coil)
5.0 H Typical 
PRIMARY DC RESISTANCE (each coil)
6.7  Ohms  Typical
SECONDARY DC RESISTANCE (2 coils in series)
1.29K Ohms Typical
RATIO
1+1:5+5
FREQUENCY RESPONSE (Typical)
Parallel secondary windings
+/- 1.5 dB 5 Hz to 100 kHz
Series secondary windings
+/- 1.5 dB 5 Hz to 50 kHz
Sowter DAC transformer
Sowter DAC transformer