I replaced the volume pot on my tube preamplifier.
Replaced the two mono Alps pots in phono preamp with Tocos (Tokyo Cosmos), RV24 units. I heard good things about these pots on other forums. Fair bit of work getting them to fit into the Croft 25R. I had to loosen the tube boards and drill out the mounting holes for the larger threads. The pots were only $26 for both inc tax and shipping. Huge improvement in speed, clarity, solidity, and transparency. I'm blown away.
@mashif That’s a specification - 50,000 ohm input impedance, x2 for stereo (2 gang) - not a model number. If you were looking at an RK50 model you’d think "wow!" - it’s massive, shiny, beautiful and gold :) The RK50 doesn’t imply 50,000 ohms either (though that is a very common choice); it comes in a few different impedance values. |
The Alps "Blue Velvet" RK27 is almost ubiquitous in analog preamps and headphone amps below $10K - especially tube units which are less likely to use a digital volume chip. Which is a shame, because EVERY TIME I’ve compared this pot to a better alternative - RK50, TKD (the 2CP-2511 is fantastic!), stepped or ladder attenuators - the RK27 has been exposed as a significant performance bottleneck. JUST like you’ve found. Alps used to make an RK40 "Black Beauty" pot which was better, and much more reasonably priced than RK50, but sadly it’s long discontinued :( Now every time I see a component with that dark blue plastic Alps pot inside, it’s enought to make me lose interest. If it's also above $10K MSRP, I cringe. I think it’s become so common for its low relative cost and motorized option (and laziness on the designer’s part). I’m pretty sure a digital volume chip sounds better than RK27 too, but I haven’t compared them on "relatively equal" terms - just guessing here. |
Agree! I’m normally a fan of "affordable, but reliable and sounds good" parts (like resistors, caps), and get a little hesitant to just blindly go in for exotic $$$ parts which can sometimes change the sound a little too sterile, bright, or analytical IMO. But the Alps Blue is defintely NOT a good sounding part in a very critical position; most of its alternatives sound better :) |
The only MZ2 pics I see online clearly show an RK27 - some motorized, some not. An RK50 wouldn't even fit in there without a motor - it's massive. IIRC motors for RK50 have to be custom made; VAC is the only one I know of doing it in their preamps, which start at $30K. Never heard of an "RK50A". If you're seeing a huge shiny brass cylinder, then it's definitely an RK50. Getting a great sounding analog volume control with good granularity (at least 40+ steps) and reasonable price is hard enough. Adding motorization / remote control just adds to the challenge. No wonder some (like Audio Research) have gone to digital chips. Khozmo Poland is worth a mention; they produce some very good looking analog volumes w/ controllers, high quality resistors, and fine-grained steps (60+). Lots of flavors to choose from: Shunt, Ladder, Stepped. "Ladder" sems to be the most premium of discrete options. Verified good sound:
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