adjusting step of remote contoled volume?

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sapek said:
I have Rogue Audio Magnum 66 preamp. It has remote controlled volume implemented using an electric motor moving the pot. The single step is too large. Is it possible to make some modification to adjust the step of the motor?


How many steps does the motor have? Depending on the type of motor you could use half-step or even quarter-step stepping. Really fancy you can get with micro-stepping but that's probably too involved.

Jan Didden
I apologize for not responding earlier. I'm new to the forum and I thought that I will get an e-mail notification about activity on the thread but I didn't.

I'm not sure if this is stepper motor. The pot is not stepped but continuous. When I press remote button, the motor moves the pot in a smooth motion. The haven't counted how many steps there are two a full circle but my estimate from memory is that about 20-30. Cutting the step in in 4 or even in 2 would be great. Currently one step changes volume of my speakers by about 4dB.

I can open the preamp and get specifics of the motor. What kind of information should I look for?

I counted 8 steps of the motor to turn pot by 90 degrees (from 9 to 12 o'clock).

There is following marking on the motor:


It is connected to the pot which is marked:

147t 100KAX2

What changes are needed to make the motor steps smaller? I would appreciate any information/help.

Does anyone have any advice?

I was thinking about trying to put a resistor between motor terminals - the idea being that it would lower voltage applied to motor and make it move slower (this assumes that the controller moves the motor for a specific period of time for each step). Is this crazy? Can I damage something this way?

If you turn the motor by hand, with the system off, can you feel any sort of detent-like steps, during the rotation? If you can, then count how many of those there are, in 90 or 180 or 360 degrees of rotation. If you can't feel any "steps", then it's probably not a stepper motor.

If it's not a stepper motor, you might be able to make it run more slowly, more easily. But I don't know if putting a resistor across the terminals would be a good idea. You could stress whatever is driving the motor, by trying to draw too much current. If it's a DC motor, maybe you could put a resistor in series with one of the leads, instead. At any rate, wait until we've figured out what type of motor it is, at least.

Also: Can you see the wires that go to the motor? How many are there? What do they come from?

Have you tried to find the schematic?

Do you have an oscilloscope?

How many turns can the potentiometer travel, total?
Thanks for the response gootee.

There are no discernible steps when I turn the pot by hand.

There are two wires going to the motor.

I have done some searching on the net and I think that it might be an integrated ALPS motorized potentiometer. It looks something like this:


I don't have a schematic for the preamplifier. I also don't have an oscilloscope.
to put a series resistor is the best I believe. I can not imagine any way that you would damge the anything with that.
I would rather put a potentiometer in series and find a slowest position where the motor still turns and just turn a bit back so it still turns in cold. An 500 ohm pot shold handle that current if it is not an ultra small SMD verion.

If that does not work, than is is more complicated. You need to build a circuit, based on a monostab multi, so for example instead of 1s pulse you only let the motor turns for 0.5s, but the polarity change makes it a bit more complicated. You need cut the lines and insert a small signal relay to switch, driven by a monostab multi which is fed by a bridge from the 'like AC' lines.


This appears to be a DC motor driving a pot. I doubt whether the diodes or resistor shortens each change; that timing surely is set in the pot control driven by the remote. Using diodes or resistors in series will probably get you to the point that it doesn't move at all anymore.

I have built such a system some time ago with a microcontroller so I could set each change duration in the software. Most probably that is also the case here, and there isn't much you can do to change that.

In that case, one possible option would be a timer with a 555 or similar, that switches the power to the motor with the power that activates the motor after a remote command. The 555 then switches off the motor power *before* the remote command terminates. But be aware that there is also a minimum time: once the motor moves, it cannot be stopped within a few milliseconds, it moves a bit on itself due to momentum.
You need to decide whether you really want to go through all that; is it that important?

Jan Didden
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