I recently purchased the Sennheiser HD600 headphones second-hand and realised that their full potential could only be met with the highest quality amplifier. Hence this project!
Output transformerless designs either use direct coupling or capacitor coupling. In the former case the possibility of DC appearing at the output is very real, either at switch on or when plugging the ‘phones in and out (when the common connection in the plug can short the right channel jack output). With capacitor coupling it is usual to use a delayed muting switch to prevent switch on and off “thumps”. Generally speaking, there are no turn on and off thumps on transformer-coupled amps because the current in the output valve tends to build up and decay slowly, a fade-in and fade-away type of effect. Muting circuits on other designs are fine, but a transformer does offer the ultimate in terms of protection (damage to the headphones and electric shock).
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