Introduction
Another Headfone Amplifier? Yes, against all HiFi-religions, I offer a class-B amplifier with overall feed back which performs excellent (< 0.003 % distortion) with a 300 Ω resistive load like a Sennheisen HD650. |
The Diagram
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Explanation of the Diagram
The amp contains just a few components: an op amp and the brand new
buffer: BUF634. Henk ten Pierick measured the OPA134 as the best
sounding op amp in high input impedance applications. With his research
method, active components can be ranked in sound quality. Many listening
sessions approved his method. |
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The feedback
The 'power stage' does not really need feedback, so that the feedback
could be restricted to the op amp itself (the 'local feedback'). Bear in
mind that the BUF634 goes up to 180 MHz with R5 = 0! |
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OscillationsIn case the remedy should be: put a dominant pole in the amp, somewhere over 20 kHz. To make a long story short: 220 pF mica or styroflex parralel to the output of the op amp should solve the problem, according to the data sheet. |
Power SupplyThe power supply is rather simple: with a two times 15 volt toroide transformer, a rectifier quad, electrolithic capacitors and stabilisers 7818 and 7918 the supply could be constructed. In the diagram below a solution is given. Mind the 10 Ω resistors (R1 and R2) serve filtering the higher frequency noise from the stabilisers..... |
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Conclusions
Before building this amp, study the data sheet of the BUF634! It works
well at VHF, so some mounting details should be obeyed to prevent
oscillations.
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May 15 - 2011
Herbert Rutgers.