Bench data
What actually fails on Pass Labs.
1,331 repair records mention Pass Labs — Aleph, First Watt, and the big class-A amps. The most-discussed topic is the one the design makes famous: bias.
Pass Labs is the second-most-discussed brand in the corpus after McIntosh. It's a solid-state house — the heavy tube mentions in its records are mostly comparisons, because the conversation around class A is always about heat, bias, and whether solid-state can sound "warm."
How we count
- 9,561 repair records in the training corpus: forum repair discussions and bench transcripts, tagged by gear type, symptom, and topic.
- Per-brand counts here are keyword co-occurrence across those records — a record counted once per brand and per symptom it mentions.
- These are conversation counts, not diagnoses: they say what people talk about when a brand comes up, not what every unit on earth fails with.
Counts computed from the database, August 2026.
Class A runs hot by design — bias drift is the topic
130 records mention bias, the brand's signature topic. Class-A amps like the Aleph run their output stages at full tilt by design: the heat is the sound, and it's also the stress. The failure pattern in the records is drift — bias that creeps as parts age, showing up as rising heat, offset, or hum that wasn't there before. The fix is a bias check and set, not a part swap.
The supply is the life of a big class-A amp
144 power-supply mentions and 142 transformer mentions — the big rails that keep a class-A output stage honest. When these amps fail, it's the supply that gives: filter caps aged by decades of heat (83 capacitor mentions), fuses doing their job (104), or a transformer starved by the rest of the supply. Same story as every brand in the corpus, running at class-A temperatures.
Hum in solid-state is a ground story
127 records mention hum. With no tubes in the chain, the causes are the boring, fixable ones: ground loops between components, coax and Ethernet picking up the room, or aging supply caps in the amp itself. The check order that resolves most of it: different outlet, kill the cable grounds, then suspect the caps.
Before you open it
- Hot is normal. Class A runs hot by design — check bias before you suspect a fault.
- Bias drifted? that's a set, not a part. Most bias complaints resolve with a check and adjust.
- Hum? grounds first, caps second. And never open the supply without discharging it.
Not sure what's wrong?
Describe the symptom to the Customer Service Wizard. It's trained on this exact database, plus bench experience, and it will tell you what to expect: likely fixes, effort, and whether it's a bench job.