Over a cup of morning coffee still in bed I asked Perplexity Deep Research how many watts an Aleph J outputs. Pretty amazing how it summarizes, and the need for spending half a day scrolling threads and documents becomes unnecessary. Well, one ofc has to take the info with a certain amount of salt, but still.
# The Power Output Characteristics of the First Watt Aleph J Amplifier
The First Watt Aleph J amplifier, designed by Nelson Pass, represents a refined iteration of the classic Aleph series, blending technical innovation with a focus on sonic purity. This report examines its power output specifications, contextualizing them within the amplifier’s design philosophy, performance characteristics, and practical usability.
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## Technical Specifications and Rated Power Output
The Aleph J’s nominal power output is
25 watts into an 8-ohm load at 1% total harmonic distortion (THD) when measured at 1 kHz[1][3]. Under clipping conditions, the amplifier can deliver up to
30 watts[2][3]. These figures are achieved with a power consumption of 200 watts, reflecting its single-ended Class A operation[2][3]. The disparity between input power and output wattage underscores the inherent inefficiency of Class A topologies, which prioritize linearity and low distortion over energy efficiency[3][4].
The amplifier’s gain is specified at 19.6 dB, requiring an input signal of 1.5 volts to achieve its full 25-watt output[2][3]. This moderate gain structure ensures compatibility with both solid-state and tube preamplifiers, particularly those with high output impedance, thanks to the Aleph J’s input impedance of
242 kΩ (RCA) and minimal capacitance[1][3].
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## Design Philosophy and Performance Context
Nelson Pass designed the Aleph J to address listeners prioritizing “naturalness and musicality over specifications”[3]. By reducing negative feedback by 15 dB compared to earlier Aleph models and eliminating electrolytic capacitors from the signal path, the amplifier achieves a distortion profile dominated by second-order harmonics, a trait often associated with tube amplifiers[1][3]. This design choice results in a subjectively “liquid” sound signature while maintaining measured performance comparable to modern solid-state designs[3].
The Aleph J’s
damping factor of 20 indicates moderate control over speaker driver motion, making it best suited for high-efficiency loudspeakers (≥90 dB/W/m)[2][3]. While this limits its utility with low-impedance or complex loads, the amplifier’s stability remains uncompromised, as noted in its ability to drive any load without risk of damage[1][3].
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## Thermal Management and Practical Considerations
Operating in pure Class A, the Aleph J dissipates significant heat, with users reporting heat sinks reaching temperatures requiring caution during prolonged use[4]. Anecdotal evidence from DIY builders indicates that heat sink surfaces can exceed 60°C in ambient room temperatures, necessitating adequate ventilation[4]. Despite these thermal challenges, the amplifier’s reliability remains a hallmark, with no reported failures attributable to thermal stress in the reviewed documentation[1][3].
For users requiring lower power output—such as those with high-efficiency full-range speakers—modifications to rail voltage and bias settings can reduce heat generation. For example, lowering rail voltages to ±11 V could theoretically yield a 5-watt output variant, though this requires careful recalibration of the current source and power supply components[4].
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## Comparative Analysis with Predecessors and Competing Designs
The Aleph J distinguishes itself from earlier First Watt models like the F1 and F2 through its
voltage-source architecture, a departure from the current-source designs of its predecessors[1][3]. This shift improves compatibility with conventional loudspeakers while retaining the Aleph series’ characteristic simplicity. Compared to the original Aleph 3, the J variant offers 15 dB lower noise and improved power supply filtration, reducing voltage ripple by 20 dB[1][3].
When contrasted with tube amplifiers, the Aleph J achieves similar harmonic richness without the maintenance demands or output transformer limitations. Its
frequency response (-3 dB at 6 Hz and 80 kHz) exceeds typical tube designs, ensuring extended bandwidth for modern high-resolution audio formats[2][3].
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## Conclusion
The First Watt Aleph J delivers 25–30 watts of single-ended Class A power, optimized for high-efficiency loudspeakers and listeners valuing tonal accuracy over raw output. Its design refinements—including reduced feedback, JFET input stages, and robust thermal tolerances—make it a compelling choice for audiophiles seeking a bridge between solid-state precision and tube-like musicality. Future iterations could explore adaptive biasing for improved efficiency, though such changes must carefully preserve the circuit’s core sonic identity.
For potential users, pairing the Aleph J with high-sensitivity speakers (≥95 dB/W/m) and a high-quality preamplifier will maximize its performance, ensuring that its modest power rating translates into satisfying real-world dynamics.
Sources
[1] Aleph J
https://www.firstwatt.com/product/aleph-j/
[2] Review: First Watt Aleph J Power Amp
https://forum.polkaudio.com/discussion/199702/review-first-watt-aleph-j-power-amp
[3] AJ Power Amplifier.PDF
https://www.firstwatt.com/wp-content/uploads/2023/08/prod_aj_man.pdf
[4] Low watt Aleph J
https://www.diyaudio.com/community/threads/low-watt-aleph-j.179662/
[5] Aleph J - Recommended Preamplifier?
https://www.diyaudio.com/community/threads/aleph-j-recommended-preamplifier.394414/
[6] NELSON PASS designed Aleph J class A 25 watt power amp with balanced inputs only | eBay
https://www.ebay.co.uk/itm/286047063632
[7] First Watt Aleph J Build (Introduction)
[8] General Asylum
https://www.audioasylum.com/cgi/vt.mpl?f=general&m=751548
[9] 6moons audio reviews: First Watt Aleph J
https://www.6moons.com/audioreviews/firstwatt3/alephj.html
[10] First Watt Aleph J Power Amplifier
https://www.firstwatt.com/pdf/prod_aj_man.pdf