At your risk. Always protect your ears.
Signal path, setup:
Electro-Voice RE15 (low cut on) - Pleiades V5 mic head preamp - Pleiades 2N3053 power amp - Sennheiser HD580
Most previous Pleiades experiments were done with the HD580 2x300Ω headphones been driven either by the realistic disco mixer or the Sony TC-D5 pro.
Since it was recently found that just one 2N3053 bipolar transistor can drive in class A directly the headphone voice coil with superb sound, what would more logical than to connect a Pleiades electron tube battery mic pre preamp directly to it. This Pleiades 2N3053 power amplifier uses one 2N3053 transistor per channel and is operated by just a 1.3V battery.
But would it be adequately driven by just 2 electron tubes so that a high intensity sound can be heard by using a microphone? When one just sings softly to the microphone?
Well it does.
The overall gain is such that even birds from far away can be heard through the headphones when the RE15 is connected.
And it is a beautiful sound.
First of all the so low noise floor hiss sounds creamy smooth as everything in this setup is battery powered. Or is it the complete silence of the setup and what is heard as noise floor is now the acoustic noise floor high frequency content?
The sound of male singing voice is very clear as expected from a full class A (electrons flowing all the time setup). Smooth, excellent midrange. Dynamic. Smooth and extended treble. Great bass. But above all natural sound.
There is some instantenious peak limiting at high singing levels as this is a very low power amplifier since the 2N3053 is at the moment powered by only 1.3 volts for ear safety. But precisely is this what makes it sound in the direction of a good reel to reel tape recorder peak limiting at large signals and increasing the average signal level? It sounds a bit like a good quality reproduced voice from a vinyl record source.
In order to get as much gain as possible the signal from the second stage EF183 of the Pleiadss V5 head amp is taken from it's anode through an external 820nF capacitor to the input of the Pleiades 2N3053 power amplifier. The input transformer primary inductance of the Pleiades V5 head amp is 47mH and the turns ratio is 1:10. So there is a lot proximity bass compensation and the fabulous RE15 mic can be used as close as 1in-2in for flat frequency response from producer's to listener's brain.
This setup with the 2N3053 power amp should be also be tried driving the 800Ω Philips AD5046N loudspeaker, see reference. How would it sound?
Summary:
Just 3 battery powered single ended class A amolifiing stages can provide a gain high enough to directly power the voice coil of high Z headphones with source the voice coil of a studio microphone. The sound is fabulous as it is a minimum count component setup. Just 2 electron tubes, 1 transistor per headphone voice coil, one input transformer, 3 capacitors, a few biasing anode to grid collector to base resistors, load resistors and 3 batteries. The electron tubes are powered by just 7-8 volts including anodes (see references). Would it be possible to feed the transistor base directly from the anode eliminating one capacitor? An electron tube is a current output device and a transistor is a current input device. Electrons dancing to the music signal transfer the information by their electromagnetic force interaction.
It is possible to have a light weight, portable, low consumption, minimum electronic component count production reproduction setup of world class studio quality. Operating in class A (electrons flowing all the time).
References:
http://euroelectron.blogspot.gr/2018/03/madonnas-voice-coming-from-point-source.html
On preserving electron tube transconuctance at as low as 3 volt anode potential - euroelectron
Operating Features of the Audion - E.H. Armstrong
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