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The Morgan Jones Mini Tube Headphone Amplifier

The Morgan Jones Mini Tube Headphone Amplifier

It has a grounded cathode input stage with an idling of about 3mA. The output stage is a push-pull White follower, which provides low output impedance without the need for global feedback. It idles at about 10mA and can swing ±20mA in push-pull.
The output impedance is about 10 ohms (the calculated value was 6 ohms). The overall gain of the amp is about 22 (the calculated value was 28). Jones used an ECC88 input tube. The original EarMax has an ECC81 input tube, but he felt that the low anode current required for this stage would lead to noise and gain problems with the ECC81. The EarMax output tubes are ECC86. Jones used the similar ECC88, later used in the EarMax Pro’s output as well. He rated the amplifier to drive headphones from 200 to 2000 ohms.


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