rogers2: Rogers'' amps used unique quadrifilar wound transformers.

Rogers took an innovative approach with their Ravensbourne and Ravensbrook amplifiers by using quadrifilar wound driver transformers instead of the more common complementary transistor arrangement.
The key points about this design choice:

Unique topology: The quadrifilar wound transformers allowed Rogers to use a split-supply output stage with two identical NPN transistors, rather than complementary NPN and PNP pairs.

Potential advantages:

• Improved matching between positive and negative halves of the signal
• Reduced crossover distortion
• Simplified biasing of the output stage
• Potentially better thermal stability

Technical implementation:

• The transformers provided electrical isolation between the input and output stages
• This allowed the output transistors to "float" relative to the power supply
• Four separate windings on each transformer enabled precise control of signal phasing

Mixed reception: While innovative, opinions on the sonic results were mixed. Some found the sound smooth and refined, while others felt it lacked transparency compared to more conventional designs36.

Historical context: This approach was relatively uncommon in solid-state amplifiers of the late 1960s/early 1970s, setting Rogers apart from competitors.

Legacy: The Ravensbourne is remembered as a well-constructed amplifier, though its sound quality was sometimes debated. The design represents an interesting transitional period as manufacturers moved from tubes to transistors.

While the quadrifilar transformer approach had some potential benefits, it also introduced complexity and potential drawbacks. As transistor technology improved, most manufacturers ultimately favoured more conventional complementary output stage designs in subsequent years.

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