PURE HENRY (Pair) Audiograde inductor for Amp outputs By Ben Duncan

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Product Overview

10% Off for a limited time only - Usual Selling Price per pair £60 - Now only £54

A highly-rated universal output inductor for power amplifiers. Easy to fit: Readily wired in line with speaker leads next to the amplifier. Priced per pair.


Notable Characteristics


  • A highly-rated, universal output inductor for power amplifiers.
  • Easy to fit: Readily wired in line with speaker leads, next to the amplifier.
  • Restores the performance aspects of most Hi-Fi power amplifiers in today's RF-polluted environment.
  • Does not saturate, nor vary its inductance, at any power level.
  • Stabilises amplifiers without output inductors, against the higher capacitance and low inductance of many good speaker cables - particularly woven and close-spaced types.
  • Effective operation from just above audio, up to medium-to-high Radio Frequencies (RF).
  • Designed by Ben Duncan, power amplifier engineering consultant, co-designer of several of the world's top professional power amplifiers, and author of a world reference hardback book, High Performance Power Amplifiers.
  • 100% made in UK.


Power amplifier outputs need a series output inductor for two principal reasons. In good designs, the inductor is provided and operates with other parts to progressively isolate and decouple the speaker and cable load above 20kHz. The inductor also prevent RF signals entering the amplifier casing and circuitry, via the speaker cables (which can make a good aerial). In both valve and transistor amplifiers using overall ('global') or even 'local loop' feedback, an output inductor can greatly help to prevent RF getting into the feedback loop.


Ben Duncan's Pure Henry design provides the optimum output inductance for most Hi-Fi amplifiers, when the part is absent. In this case, it can be simply fitted in line with the speaker leads, close to the amplifier. This may be accomplished without special knowledge nor any risk of causing instability.


Pure Henry can equally supersede & upgrade the cheapskate output inductor found inside almost all Hi-Fi amplifiers, subject to arranging physical fitment and correct re-wiring. However, Hi-Fi News Accessories Club cannot be held responsible for the results of replacing or altering parts inside your power amplifier, if you make a mistake !


How many do I need ?

Most users place one Pure Henry in line with each amplifiers' +ve output, i.e. two for a stereo amplifier. But when RF levels are high in the locality, additional units may be usefully placed in line also with each - ve side (black, 'earthy') output terminal.


Reference Material

Hooray Henry (DIY article), Hi-Fi News & Record Review, August 1997, pp. 54-57.

Copy of the article available from HFN Accessories Club.

Or contact Hi-Fi News magazine, for a back issue (but please note limited availability).

A satisfied user says ...

"A veil had been removed allowing me to hear more of the ambience in recordings" and

"The ... sound appeared more natural and lifelike and recordings exhibited more depth.

Bass details was enhanced and much to my surprise, the dynamic performance of the

amplifiers was improved..."


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  • 5
    Pure Henry

    Posted by Roy Chan on 7th Oct 2020

    The above item makes such a profound difference that you should not live without them if you are a audiophile and music lover.Kudos to Ben Duncan