Article updated with archive photos from the very early days of my business: I apologize for the image quality, but I decided to keep them because they clearly show the “before and after” of the work performed.
When speaking of musical, elegantly voiced tube amplifiers, the name Audio Note inevitably comes to mind. The Audio Note P1 embodies this philosophy: an essential integrated amplifier for those who value naturalness and micro-detail over sheer power. Created to deliver the unmistakable “Audio Note sound” in an accessible format, the P1 captivates with its warm timbre and open soundstage that remain memorable even after long listening sessions. The unit featured here also has a small backstory: purchased years ago by a classical and jazz enthusiast, it accumulated countless hours of music without any servicing until internal failures finally made a complete overhaul unavoidable.
Initial Diagnosis
When the amplifier arrived at my workshop it was in rather worn condition. Several electrolytic capacitors were completely exhausted, some resistors had burned out, and one of the JJ Tesla output tubes had suffered an internal short circuit, worsening the situation. Before taking measurements I therefore carried out a thorough inspection of the wiring and grounding to ensure that no secondary faults were hidden.
Restoration and Replacements
After the diagnosis I replaced all the faulty components and proactively renewed the most worn capacitors. All the tubes were replaced except for a pair of ECC83 still in perfect condition and well matched, which I kept in the phase splitter section, thus preserving a touch of the amplifier’s original “voice.”
Output Transformer Analysis
During the preliminary inspection I observed that, in the output transformer, the final layer of the secondary winding did not completely fill the bobbin window. This construction choice, which may depend on specific design considerations or winding requirements, suggests a possible influence on leakage inductance. Subsequent measurements confirmed characteristics consistent with this configuration.
Measurements and Performance
- Maximum power: 10 W RMS, in line with the specifications.
- Bandwidth at 1 W: 20 Hz (–0 dB) ~ 17 kHz (–3 dB).
- Bandwidth at 6 W: the low range is more stressed (distortion already below 30 Hz), while the high range shows a slight improvement, indicating partial compensation of the leakage inductance.
The measurements show a frequency response with –3 dB attenuation already at 17 kHz. This means that, when listening, the amplifier may sound slightly lacking in the upper range and give an impression of a darker or more subdued character compared to designs with wider-band transformers. Without replacing the output transformers it is not realistic to achieve a substantial improvement in this respect; conversely, choosing loudspeakers known for a bright top end could partially offset this tendency, resulting in a more neutral tonal balance. The damping factor, equal to 8, remains very good, but is achieved through rather strong negative feedback. With a transformer limited in bandwidth, high NFB can promote instability: indeed, with no load I detected a self-oscillation around 10 Hz, a phenomenon that could occasionally occur in real conditions when the loudspeaker impedance rises during cone return.
Final Result
After replacing the critical components, adjusting the bias, and performing thorough bench tests, the P1 has regained its classic Audio Note signature sound. The intervention now ensures many more years of reliable listening while preserving the distinct “British” character that continues to make this integrated amplifier a favorite among enthusiasts.