• RE: How do I adjust the fan speed/noise of 2281S-20

    I have not seen any update nor ETA on a FW update for this.

    I did get a Keithley 2602B and it is much quieter under light loads. It will spin the fan up under heavier loads - there seem to be a few steps rather than analog proportional, but that's fine for what I do.

  • RE: How do I adjust the fan speed/noise of 2281S-20

    I think I've found a way to dramatically reduce the noise, though I'm certain it voids any warranty. Time will tell if it causes a catastrophic loss of PPMs, but so far the exhaust doesn't feel too warm, even with an 800mW load (orders of magnitude over what I'll normally have connected). I'm certain that most of the heat for the way I use it is not related to the load, but I wanted to check a load with some margin.
    A Noctua fan & a CT connector (+ soldering, heat shrink, a set of torx bits & sockets) did the trick. It is now quieter than the UPS I have under my desk - not silent, but quiet enough. Form measurements (A-weighted), I see 50 dB in the air-stream very close to the unit. I measure 38dB at about a meter away, but the noise floor for this room is 36 dB with the PSU off. I think this PSU is going to get a lot more use now.
    To be clear, I'm not advocating anyone else do this ( and if you do you need to follow electrical safety and you modify at your own risk). I'll try to post if the performance surprises me in some way.

    I would still really be interested in an SDK or some way to develop for both the fan and some voltage / current related functionality / testing. If a FW fix for the fan came out, I would probably go back to the stock fan.
  • RE: How do I adjust the fan speed/noise of 2281S-20

    Is there an SDK available for the supply OS/firmware? If there is, I'd be interested to do some development with it related to fan functionality.

  • How loud are the fans on dual channel SMUs?

    The 2604B is of primary interest, but other dual channel SMUs would be of interest too. Measuring in A-wieghted dB at 1 meter from the unit would be a good metric, but even qualitative information would be helpful since there aren't a lot of review videos of these SMUs showing them running without overdubbed audio.
    I did look in the datasheet (for "fan", "dB", and "loud") but didn't find anything. It would be helpful if this parameter was included in the datasheet.
  • RE: How do I adjust the fan speed/noise of 2281S-20

    Hi Jacob,

    Can you provide an estimate of when a FW version with a change would be available?

    Best regards,


  • How do I adjust the fan speed/noise of 2281S-20

    This fan is quite loud in my lab, and I need to make acoustic measurements sometimes. Most of the time the load I have on it is in less than 1mA, and I'll almost never exceed 0.5A. The fan is clearly under some kind of SW control since it's not nearly as loud in the boot screen.
    I know this was asked on the prior forum.tek , and the only suggestions were to regress the FW to older versions. This really is a problem, and not just a nuisance.