Friday, January 27, 2017

Important Notes on the Pleiades Electra II

At your own risk.


The battery supply voltage adjusts the sound quality.


One must be very careful, exceeding a few milliamperes may damage headphones.


There is a delta function type clicking sound when the amplifier is connected-disconnected to battery. Headphones should not be worn during these transients to protect hearing.


A resistor pad is recommended to make while experimenting for the protection of ears.


Perhaps the amplifier can be redesigned with less power output tubes. One would have more of the instantaneous clipping of peaks that make tubes sound so natural and loud and it would be more kind to ears (the effect starting happening at lower power output). (Tubes vs Transistors is there an audible difference - Russel O Hamm - JAES. Also Robert Orban and www.261.gr).


Under heating is used as on the Neumann U47 electron tube condenser microphone. Less electron cloud traffic around cathode and grid seem to naturally increase information extraction if this is the reason. On this particular Pleiades amplifier underheating was discovered accidentally as the lead acid battery was discharging while listening).


The biasing resistor affects sound quality too.


The values published are the ones found to be optimum while listening on the Sennheiser HD 580. Source was a SONY CDP-50 player. 2 potentiometers were being adjusted one with each hand as synthesiser operators do. One may arrive at the borderline of damaging hearing without knowing it. When you wear headphones you do not realize and keep increasing the volume. The log volume control was connected the wrong way round which made matters even worse. Very dangerous!


High heater voltage, anode voltage, high anode voltage sounded to me unnatural and may blow your headphones and your ears.


Listening levels should be low. If one damages their hearing by headphones especially, it can be irreversible. So use Extreme Caution.


The ear is possibly the most sensitive instrument on the planet.


It is not very practical that the batteries are separate from the amplifier. it is only practical for quickly change types of batteries and listening to the difference.


Perhaps with li ion 3.7V batteries it may be possible for a great designer to design a great looking transparent, batteries including version.


An amazing designer is Jocob Jensen of Bang & Olufsen (B&O).


Viva the transparent look and sound of the Pleiades amplifier.


The wiring had been chosen to be as thin as possible for ease of soldering and high speed of electrons. There is work by Malcolm Hawksford published on electromagnetic theory and wires which has not been read yet. I used advice from The Preamplifier Cookbook - Allen Wright to use very thin wire.


Hliana, her mother and www.junkbox.com played a very important role for the Pleiades amplifier coming to existence. www.junkbox.com came as search result on Google while searching for low plate voltage tubes used as front end at radio telescopes. The book Audio Amplifiers - J. R. Davies p.41 was possibly the first influence, showing Class A operation collector current through a loudspeaker. This is the basis of the Pleiades speaker power amplifier.










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