Resistive Ladder Volume Control


[jefffolly] published some straight forward plans for a passive volume control. It uses a resistive ladder built across the contacts of 12W rotary switches. Each resistor provides a 5dB difference, and he recommends using 0.1% tolerance resistors to maintain accuracy. The use of discrete resistors instead of volume pots means that the output is much more predictable. All of the RCA sockets were connected using oxygen-free copper wire.

26 thoughts on “Resistive Ladder Volume Control

  1. Well to actually be a constructive comment, resistors + rotary switches have been done many times before, the real goal of using resistors is that you can better approximate either linear, log, anti-log, or other functions without having to rely on rotary potentiometers.

    AFAIK, log or anti-log pots are made by having 2 separate gradients of resistive material in linear fashion to approximate the log/anti-log curve.

    But I still have to say, this isn’t much of a hack, just an oldschool radio builders trick from when reliable potentiometers needed to tune (or rotary encoders for a digital tuner) were not available, and precise values were needed.

  2. Stereopotentiometers tend to have different values between both channels, the more deer they are the less they have this effect. With resistors you can limit this effect (which will make one channel noticeably louder than the other) to a minimum. OFC cables are standard now and cheap, what is your problem, rasz?

  3. That’s strange. I’ve never noticed any noticeable volume difference between 2 channels on any system, not even on 15+ year old walkmans. There must must be something wrong with my ears.

  4. @ragnar, even if it’s relatively cheap and harmless ofc is one of thsoe things marketed to people who think they can hear a difference which sound physical analysis can prove does not exist, and proper engineering types tend to get bent out of shape that the whole market exists because it is, for the most part, a total scam. (The difference between an 8 ft and a 10 ft cable, or 12 vs. 14 gauge, is huge compared to the difference between normal copper, ofc, silver, and gold.)

  5. As someone who enjoys listening to music, I can appreciate what this accomplishes. Ever adjusted the volume on an old stereo and heard a nasty crackling sound? Dust can get into some pots and make them useless — sound will cut out, and crackling is bad for speakers. As well, some stereos have a separate volume pot for each channel.. it makes sense to have each channel set at the same volume — but then again, people don’t actually sit down and listen to music anymore, do they :)
    Just tired of people assuming that anything audio related is snake oil.

  6. I’ve used this method before, not for the audio quality (audiophile? more like audidiots) but for the durablity. A cheap rotary switch will last longer then a cheap volumepot. And with well picked steps (not nessasarily logaritmic) it works great.

    Don’t dismiss it just because the voodoo audio idiots use it. Judge for yourself if it’s true and if it’s any use for you.

  7. I know this comment is a bit late, but I just used this trick a few days ago. Not for volume, though. This allowed me to read a six position rotary switch with an AVR using only one analog pin. The levels returned are very consistent. I could easily read many more steps than that, but 6 was all that I needed.

    Thanks Hack a day.

  8. Mike,

    You need to contact Symbol corporation and make arrangements to pay license fees for their patent, #7,248,195, which you are infringing upon with your rotary-switch and resistors idea.

    Yes, it may seem trivial and obvious to a practitioner of the art (in fact, I just reinvented it myself last night, with the exact same circuit layout as the one in the patent, for a little project of mine), but that doesn’t matter to the USPTO. They want you to challenge the patent in court.

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