At your own risk. Protect your ear from high sound levels and always use fuse in series with batteries for safety.
The Sennheiser HD580 precision headphones (300Ω for each channel) is connected to the just finished Pleiades 2N3053 on breadboard (Pro-ject board GL No.12).
It is one 2N3053 transistor per channel only driving directly each voice coil which is connected to the collector. Everything operates in class A (electrons flowing all the time) including electrons flowing through the headphone voice coils too.
Just one 1.3V rechargeable battery powers both channels.
The volume control is a variable series resistor from CD player line out to base.
No capacitors or transformers are used in this amplifier circuit.
So it goes down to a limit of 0Hz. And why not as high as a few megahertz as the 2N3053 can go.
The sound is fantastic. So big with just a 1.3V battery and so small output power.
It will not go too loud and this is possibly good news for ears. Still one must be careful when overdriving it as harmonic overtone production gradually increases.
One of the reasons it sounds so big to listener's brain must be the smooth linear sound at small signal levels and the gradual production of harmonics at peaks, (Russel O. Hamm).
Another reason is the response down to limit of 0Hz.
Another reason may be the production of sub harmonics by the presence of the produced overtones at larger levels. We know that when the ear is presented by x2f, x3f, x4f, aka harmonic series and the f is missing, our brain creates f. This is a fabulous effect used on Dansette and similar record players to produce lower bass by the electron tube producing harmonics when generously driven. It is also used by great composers such as Beethoven on Moonlight Sonata. At some point Beethoven plays F# C# F#oct on a very low register by the left hand. This is the 2nd, 3rd, 4th overtone of a missing sub bass. Of course the brain creates it and it is an unbelievable bass sound even for a piano. (Exact x2f, x3f relations are wrong, our brain needs slightly more and this is the difference between the engineering octave and our ear brain pitch octave). See also the next euroelectron post on how Beethoven creates a great bass from the piano to our mind.
Is it that the Pleiades 2N3053 makes it possible for the brain to create information below 10Hz?
Another reason for the big bass may be the impedance matching between the transistor output impedance and the headphone input impedance. See recent euroelectron posts on Nelson Pass constant current driving and euroelectron impedance matching.
Another possible reason is the increase of the average level due to instantaneous peak limiting (similar to FM radio signal processing) when the amplifier is generously harder. Fletcher Munson curves may give the answer. Would this amp make a good mastering amplifier too?
Signal path, setup:
Dionne Warwick definitive collection CD - Sony CD Walkman - Pleiades 2N3053 with 2x50K log in series rheostat at the input and 1.3V power supply - Sennheiser HD580
The 50K stereo rheostat potentiometer has to be increased as at some loud CDs the sound is already loud and even a bit distorted even when fully counterclockwise. Perhaps it is better to include a fixed series resistor and then a series rheostat connected potentiometer. Note only 2 pins are used on each potentiometer.
References:
Tubes vs Transistors (vs operational amplifiers), Is there an Audible Difference? - Russell O. Hamm - JAES
http://euroelectron.blogspot.gr/2018/04/how-beethoven-creates-great-bass-on.html
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