OTX47

OTX47
The Kraftwerk OTX47 is a modern interpretation of the classic output transformer found in the legendary EMI REDD.47 valve preamplifier modules — a key part of the sonic identity behind some of the most iconic recordings in Abbey Road history.
Rather than replicating the original transformer material stack one-to-one, the OTX47 is built as a contemporary vision inspired by original geometry, impedance structure, and inductance behavior. The core is an enlarged EI57 CRGO (M6) lamination set, selected to deliver powerful low-frequency extension, enhanced dynamic headroom, and exceptional saturation control — while preserving the signature REDD-style harmonic structure and musical midrange presence.
Every mechanical, magnetic, and winding parameter was carefully engineered to maintain the fundamental tonal architecture of the original circuit, while expanding performance in areas where modern design allows: lower noise floor, wider bandwidth, higher LF stability, and more consistent high-level handling.
 
Model: OTX47
Turns Ratio: approx. 7 : 1
Nominal Impedance: 10 kΩ : 200 Ω
Primary DCR: 505 Ω
Secondary DCR: 40 Ω
Primary Inductance: ~100 H
 
Core Material:
Custom CRGO (M6) — silicon steel
(Inspired by original mixed nickel/steel lamination topology)
Core Format:
EI57 (ungapped), enlarged edition
 
Build Characteristics
• Inspired by the original EMI REDD.47 output design
• Enlarged EI57 core for deep LF extension and high dynamic headroom
• CRGO (M6) lamination stack for focused bass, stability, and harmonic openness
• High inductance primary (~100 H) for extended low-frequency bandwidth
• Authentic working impedance: 10 kΩ : 200 Ω
• Precision-balanced winding layout for clear harmonic structure
• Smooth transformer saturation under drive — musical breakup, no loss of LF
• Full humbucking configuration for low noise
• Designed to preserve the tonal heritage while expanding performance
 
Tonal Character
Muscular lows, rich harmonic texture, and open transient detail, with the unmistakable REDD-style midrange presence — now supported by increased depth and clean headroom provided by the enlarged EI57 core. Perfect for tube stages demanding authority, warmth, and scale.