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Morgan Jones E88CC OTL  2005

 

One year later I already made plans for my second tube headphone amplifier, the Morgan Jones Mini Tube headphone amp from the Headwize site. It started life as an improved version of the famous 'EarMax' headphone amp and was initially drawn by Morgan Jones and later improved upon by Alex Cavalli to provide more current swing into low impedance headphones. It uses three E88CC double triodes or its derivatives 6922, CCA or 6N23P with a cathode grounded input stage and a push pull White Cathode Follower as output stage.

Again I partially adapted the schematic to my liking and included a classic EZ81 rectifier tube and LC filtering in the power supply but left it mostly unchanged otherwise. This project was deliberately chosen to be a bit simpler and less expensive than how I built  the previous C3G OTL ;).

 

 

 First schematic:

 

 

The schematic above is very close to the one posted on the Headwize site except for the psu. All parts values were carried over since it was a proven circuit. The input stage idles at about 3mA and the output stage at 10mA with a supply voltage (B+) of 220V. The amplifier worked flawlessly from the beginning and sounded nice and natural but also somewhat slow and uninvolved. Overall dynamics and resolution were less than with the C3G OTL.

 

In order to improve the sonic qualities I began converting the first stage to LED bias and even started a thread on Headwize. There I eventually got some nice tutoring from the Master himself, Mr. Morgan Jones. He guided me with his input to carry out the conversion with a few parts values adapted and moderate feedback added... in fact it was an easy change but I learned my lessons about short and proper wiring and layout! The change improved the sound quality with tighter bass and slightly better imaging, but the amplifier still lacked the certain "magic".

 

Lesson learned: OTL will not really be my cup of tea since you are going to great lenghts to improve every single part in an amplifier and then you are passing the precious audio signal through big electrolytic capacitors.

 

 

 

Images