ES5 / Aleph JXnp S

Front View of the Power Amplifier

Table of Contents



In autumn 2023, my friend Uli asked me to build power amplifiers with low output power for the mid-range and high-frequency horns for his four-way horn system. I didn’t have a suitable power amplifier immediately to hand, but when thinking about a possible circuit topology, the Aleph J kept coming to mind.

I found the single-ended class A concept with the Aleph Current Source to be ideally suited to this task. However, the power amplifier had to be super-symmetrical according to my ideas. So it became an Aleph JX.

I also didn’t want to use the p-channel Toshiba JFETs in the input, which are rather difficult to obtain these days. I reversed the polarity of the input stage and used n-channel JFETs. Of course, you then also have to change the polarity of the output stages to p-channel MOSFETs. This led to the name Aleph JXnp.

The output power should be relatively low. I achieved this goal by reducing the operating voltage and halving the output stages. This gave the power amplifier its final name: Aleph JXnp S.

  • Aleph J: circuit topology
  • X: super-symmetrical design
  • np: polarities of the FETs in the input and output
  • S: seduced output power (small)

Description of the Circuit Technology


Audio Board

The input of the power amplifier is a differential amplifier with the n-channel double JFETs 2SK2145BL. They are currently still in production and are therefore easy to obtain. They can be found in all my projects from the last few years. By reducing the operating voltage to ±15V, they run in the sweet spot. No additional cascode transistors are necessary. Compared to the design of the Aleph J, I use a precise reference voltage in the current source of the differential amplifier instead of the simple Zener diode.

Due to the low output power required, I only use one output stage. However, the super-symmetrical concept means that 2 stages are required. There are, of course, no two output stages connected in parallel in this design. The operating points naturally had to be adapted to the lower operating voltage.

I use servo controllers to keep the two outputs of the power amplifier free of offset voltages. These can be deactivated for an initial manual adjustment. The power amplifier is then calibrated with the trimmers. The activated servo controllers then ensure automatic offset stabilisation. This means that the servo controllers only have to compensate for thermal fluctuations.

I stabilise the operating voltage of the output stage with two capacitance multipliers, which are equipped with adjustable reference voltages. This allows me to set the operating voltages to a defined value and keep them stable, regardless of the actual mains voltage.

One power amplifier module screwed onto the heat sink.
One Audio Channel of the ES5

I have dimensioned the power amplifier so that it achieves an output power of 10W/8Ω.

Power Supply Unit

The unregulated power supply unit starts with the mains socket with integrated fuses. The mains voltage is then freed from any DC voltage components by a 230V/AC DC filter. This prevents the transformer from being driven into saturation.

Circuit board of the 230V/AC DC filter.
230V/AC DC-Filter

The toroidal transformer was customised by me for this amplifier and built to the usual excellent quality by Müller Elektrotechnik GmbH. I decided to use one transformer for the amplifier. However, each channel has its own secondary windings. From the transformer onwards, the power supply has a dual mono design.

The rest of the unregulated power supply unit for one channel is mounted on a printed circuit board. Snubber networks follow the connection of the two secondary windings. This is followed by the bridge rectifier with ultra-fast soft recovery diodes in a TO-220 housing. Each diode is screwed onto a heat sink. The rectifier is followed by C-R-C filtering with 4x 22000μF and 0.2Ω. Due to the constant current consumption of the single-ended class A power amplifier, there is no modulation of the music at the resistors. This filter technology can therefore be used to filter out residual ripple from the DC voltage.

Circuit board of the unregulated power supply unit for one channel.
Power Supply Board of the ES5

Inrush Current Limitation

The power consumption of this power amplifier is not really very high, but I still decided to limit the rush current of the toroidal transformer when switching on. Especially as I also have the circuits for remote switching on and off on the corresponding board. In a multi-way system, it is really very helpful if you don’t have to switch on all the power amplifiers manually.

Circuit board with the inrush current limiter and the remote on/off circuits.
Inrush Current Limitation and Remote On/Off

Installation in a Housing


Naturally, I used an enclosure from Italy. This time with 4 height units and a depth of 400mm. The heat sinks are able to handle the waste heat from the power amplifier, but they still get quite warm. Which is of course normal for a single-ended class A power amplifier.

Interior view of the power amplifier with a view of the built-in electronics.
A Look Inside the ES5

The photo above shows the inside view of the power amplifier. I used a mounting plate with a hole pattern from the enclosure manufacturer. On the left and right, screwed directly onto the heat sinks, you can see the two power amplifiers. The toroidal transformer is located at the bottom centre. The mounting plate of the transformer is attached to the mounting plate with rubber buffers. To the left you can see the inrush current limiter and to the right the 230V/AC DC filter. The two unregulated power supply units can be seen above the transformer. The central earthing point is located to the right of the power supply units.

Rear of the ES5 with a view of all connections.
Rear of the ES5

The rear of the ES5, shown in the photo above, is equipped as expected for a power amplifier. In the centre is the 230V/AC supply lead. To the left and right are the audio inputs and outputs. There are also the two sockets for the remote control.

The front panel (see above) is available in black on request. The only control element there is an LED that signals the operating status.

Handles are attached to the front and rear for better handling. The handles on the back also protect the sockets.