Mark Levinson built the No. 23.5 in 1990 and stopped pretending that affordable power amplifiers were anything but a compromise. This is a 100-watt-per-channel Class A design, which means it gets hot — genuinely, dangerously hot — and costs roughly what a used Cadillac cost that same year. It also means it sounds like nothing else in the basement, and that's the entire point.
The 23.5 sits one rung below the flagship No. 33H, which cost nearly four times as much and did essentially the same job with slightly more headroom. Levinson understood something most amplifier companies still don't: diminishing returns are real, but they're not tragic. The 23.5 gets you into the room where the music stops being "a recording" and becomes an event. That's worth the price and the heat and the fact that your wife will ask if you're running a sauna.
The circuit is Class A throughout, biased hot enough that it idles at roughly 40 watts per channel with nothing playing. There are no shortcuts: fully balanced input stages, direct-coupled driver stages, and a power supply that treats the output stage like the sacred object it actually is. The transformer is potted in epoxy — you could drop it off a building and it would survive. Build quality is German-level obsessive without the German price tag.
What you hear is immediate and non-negotiable. The highs are crystalline without being thin. Strings on Joni Mitchell records have texture and space; cymbals decay naturally instead of ringing. The midrange is composed and honest — voices don't bloat, don't disappear, just exist exactly as they were recorded. The bass is granite-solid, not exaggerated but immovable, the kind of foundation that makes every other amp in the room sound like it's built on sand.
This is where the honest caveat lands: the 23.5 needs a good preamp and decent speakers to shine. Feed it garbage, and it will play garbage cleanly. It won't fix upstream problems. Sloppy phono stages, worn turntables, and crossed fingers will stay sloppy. The amp is transparent in the worst possible way if your source material isn't ready. You can't hide behind it. That's also why people who own them tend to own them forever — there's nowhere to hide anymore.
Find a 23.5 in good condition and you've found the amp that didn't need replacing twenty years later. Not because it's perfect, but because once you've heard what Class A bias actually delivers, everything else sounds hurried and slightly thin. The tweaking stops. The investment begins.