At your risk.
Paraphrasing the quote by Brian Eno.
Thursday, August 6, 2026
Beginning of the Pleiades IRFS450 single MOSFET audio power amplifier in class A operation (electrons flowing all the time)
At your risk.
Possibly the first time experimenting with a MOSFET in the Pleiades lab.
I think it is same to IRF450 on a different case.
It is placed on a relatively small heat sink.
In order to check the MOSFET is in order, a digital mulimeter was used at resistance measurmnet. Drain to source resistance reading was infinite.
But when an exhauted 9V battery giving 5.6V was connected from source to gate, the MOSFET had tuned on and Source to Drain resistance was of the order of 0.3 ohms.
Thia condition was preserved even after removing 5.6V to gate. Gate keeps the charge.
Promising. I am curious how will it sound with an output transformer driving the Marzntz Imperial 5-G loudspeaker, MOSFET driven by the SONY D-EJ758CK line out.
Update on the Pleiades derivative of simplified no negative feedback Musical Fidelity A1
At your risk.
Refering to the original Musical Fidelity A1 schematic.
The idea is to try just a BD135 driving a 2N3055 driving an output transformer and no negative feedback.
A BD139 was used instead, a Mitsubishi 2N3055, a bifilar 1:1 output transformer istead of perhaps a more suitable 2:1 output trasformer. Air gap is made by sticking a layer of 3M scotch invisible tpae on the stacked Es.
Vb is 12V.
BD139 is mounted on a small heatsink. 2N3055 is mounted on a larger audio cassette case size heatsink, black aluminium. It run bare touchable hot at 24V.
4R7, 100 ohms, 300ohms resistors are used as on the Musical Fidelity output stage schematic.
Bias is adjusted by a 220Kohm in series with 1Mohm variable resistor from Vb to the base of BD139.
2N3055 Ic was set to about 400mA.
Signal path:
various CDs, Dire Straits, Barbara Streisand, Year of the Cat - Al Stewart - Sony CD Wlkman line out, Pleiades simplified striped down Musical Fidelity A1 - Marantz Imperial 5-G
It worked, it sounded loud, even louder at Vb=24V, Ic=800mA.
Changing 4R7 to 6R8 made for a somewhat more open sound.
Quick changes are posble thanks to using Wago snap connectors.
But there was lack of treble, as if one or two high octaves were missing.
Going back to such a single 2N3055, the sound so softer, less power output but better sound quality, a bit more treble.
Going back to the Pleiades Darlington BD650. It sounded much more open with extended high frequency bandwidth and deep bass too, as if 2 more high octaves were added. Loudness was between the 2 above extremes.
Why does it sound much better? Is it because there are no resistors around the transistors? Should a BD135 driving a 2N3055 be tried in this way with least possible resistors?
The Darlington BD650 at Vb=12V sounds great at just Ic=100mA, saving charged battery time.
On a small heatsink it run luke warm.
Moving closer to the spekaer at abot 1m from 3 m the sound is even more impressive.
WHat makes this so simple Darlington amplifier stand out is how alive drums sound, hi-hat sounds for example as if there is a hi-hat inside the room, for example of Sultans of Swing - Dire Straits, or On the Border - Al Stewart.
Pleiades 2N2146 single Germanium transistor class A power amplifier
At your risk.
It worked but there was some lack of treble. If memory is correct there is an earlier post on this.
Monday, August 3, 2026
Borrowing an idea from ribbon microphones to low voltage single ended zero feedback power amplifiers in class A
At your risk.
The impedance of a ribbon could be for example 0.2 ohms.
It is stepped by an internal to the microphone signal transformer to typically 25 ohms or 200 ohms etc.
If we use a MOSFET for a power amplifier we may choose by suitable bias an operating point of 1A at 1.5V. This could mean an output impedance of 1.5 ohms. We have high current but little voltage in order to drive an 8 Ohm loudspeaker.
But if we can also see things upside down we may use a step up transformer instead of a step down transformer as used on electron tube high impedance amplifiers.
So just a few turns for the primary like on a ribbon microphone. And more turns of less thick wire for the output.
Will it work?
The transformer will be fun to make winding few turns for both windings really. Even the secondary can be of the order of only two hundred turns even if using an air gap to avoid DC saturation on a single ended class A power amplifier.
The power supply could be easy too, just for example a D type 1.5V battery in series with a suitable protective fuse. Just one battery will save from the expense to buy may good quality Bulgin battery holders.
Today at Pleiades labs were found a few IRFS540, IRF222, BUZ54A MOSFETS.
Will it work or sound great?
Girls Just Wonna Have Fun - Cyndi Lauper
At your risk.
It was heard today on Easy 97.2 MHz FM radio in Athens, Hellas.
It sounds amazing played on the piano too. Key is F sharp major, so you have all those nice black keys.
The bass code is very interesting, like good Bach's music.
For example from 3:22.
Bass F# with A# C# F#
Bass B with A# D# F# ie B major 7th
Bass C# with A# C# F#
Bass F# with A# C# F#
Bass B with A# D# F#
Bass C# with A# C# D# F#
Bass F# with A# C# F#
(this is from memory there may be mistakes as it was figured out on the piano about an hour ago).
It stands alone very well as only bass and melody played together on the piano, bass which is of course only one note at the time played with left hand and melody which is also one note at the time played with right hand. the intervals are so interesting and out of the ordinary. it is a worthy addition to the Melody Book.
This music is very close to the Bach instruction to his students figured bass code found at the appendix of the Bach's biography by Spitta.
It is likely that in a few centuries people of the future may regard such songs as the classical music of the 20th century, it may be already happening.
It is interesting to note again that in music bass or melody are by definition one note at the time, just one note.
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