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MU follower - distortion

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First attempt at mu follower for headphone amp.

2 x 6N6P.

Voltage on bottom anode is 100V - led bias at about 2.0V across it.
18-20mA??

top cathode has 120 ohm resistor (1.9V-16mA) follower by 10K with bootstrap of 220K.
Small bypass cap connected to bottom anode.


Turn is up a little a it distorts quite a bit.
32 ohm phones.

For me the voltages and currents look ok.

Strange.
 
32 ohms is a pretty impossible load for a valve. I think you would need a pretty special circuit with lots of feedback. Think about the problems of designing OTL amps.I think EC8010 probably knows a lot about this kind of thing judging from some of his posts.
 
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Mu followers IMLE in most cases don't drive low impedances very well as compared to say a properly trimmed white cathode follower (WCF) or even SRPP - A properly designed WCF is inherently PP and the SRPP if designed to match the headphone impedance range will also work in PP. Mu followers work great for voltage gain in applications where the load impedance is relatively high.

I drive 32 ohm and lower impedances quite effectively with a pair of 5842 in a WCF - you only need a few mW typically for ear splitting levels with most headphones.

You need to choose a topology designed to deliver power to low impedance loads, the mu follower is great for providing voltage gain, not quite as good providing high current to a load.

I would think the 6N6P would be ideal in a WCF..
 
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