Help: how to build a rotary remote volume control

[amirm]

Hello everyone.

One of the key measurements for headphone amps and integrated speaker amps is distortion versus level. This is normally done by setting the physical volume control on the unit to max, but then sweeping the input level from low to high. Problem is, this is not how people use the products. Input level is usually high/whatever the DAC/music dictates. It is the volume control that is used to determine how loud it plays, rather than messing with input level.

Now, some products perform the same in both situations. But for a number of one, performance can be different since we don't know whether the source of noise/distortion is in the front-end of the amp or output stage.

My question is for those of you in the maker world, or mechanical engineering, is there a ready-made, or kit of some rotary control mechanism that I can drive with a computer? That is, I like to clamp something to the volume control which of course has varying size, and then under computer control step it one notch at a time and measure the distortion. Probably need to be belt driven or have overload detection as to not push the volume control past max.

Any ideas?

 

[March Audio]

Found this

https://www.pololu.com/product/3131

 

[amirm]

Oh, the electronics is the easy part. I am looking for something close from mechanical point of view.

 

[restorer-john]

So I gave this some serious thought.

What you should consider is that a rotary control mechanism would be of very limited use due to the fact that most volume controls are no longer 270 degree turn pots anymore, they are rotary encoders with all different velocity sensing algorithms and no start or end stop.

Most rotary encoder volume controls can offer anything from zero to full volume in half a turn or many turns, depending on how the designer has set the rotational ballistics. Some take many rotations where the physical movements are small incremental steps. Many can drop to 0.5dB steps for 20 degree turns. Some offer no gain change in the last 5-10dB, so the rotational position means nothing.

Some other units you will be testing will have 'up' and 'down' volume control buttons and no 'knob'.

The rotational position of even a conventional pot is not directly linked to the gain in a log way. Some very expensive stepped or thick film printed resistor calibrated pots (Alps black beauty etc) of days gone by came close. No two brands were ever the same however.

As you know, S/N and distortion are always measured with the volume wide open. I agree, there are many (if not most) instances where S/N and distortion deteriorate (or even improve) at positions other than wide open and these are positions where people tend to 'position' their volume controls. I have long been a proponent of realistic volume pot position/rotation and use, but ever since the introduction of CD, we have had 2v sources into 150mV sensitivity front ends with the consequent volume pot (conventional 270 degree hardware pot) being around 9pm to the 11:30pm position (on the clock face). This position in many vintage amplifiers was arguably the worst in terms of S/N, channel tracking and often THD.

I would suggest picking a reference output power or a listening level reference SPL, based on an arbitary efficiency level speaker. It would be easy to consistently repeat and would have some meaning.

I understand the difficulty with the integrated units as you are testing a complete unit and are looking for the stages that are causing the results you are seeing. It is no different to the integrated amplifiers of old. Integrated amplifiers with switchable preamplifier and power amplifier stages were tested as a whole, reviewed as a whole, flaws and all.

 

[amirm]

Thanks for the thoughts. It is definitely a challenge. I can mitigate some of them (e.g. the analyzer measuring the power rather than relying on known position of the volume control) but not all.

 

[DonH56]

I have not looked for a while but there used to be various mechanical volume controls available, either steppers or motorized pots. A better option might be one of the volume control chips that are essentially digitally-controlled analog pots or steppers.

https://duckduckgo.com/?q=digitally+programmable+potentiometer&atb=v98-2_g&ia=web

 

[amirm]

Hi Don. What I am looking for is a mechanical device that turns the existing volume controls on audio products. Not one to build into one.

 

[March Audio]

Oh, the electronics is the easy part. I am looking for something close from mechanical point of view.

Buy their stepper motor, hub and mounting bracket plus an elastic band and plank of wood to screw it all to.

https://www.pololu.com/product/2267

If you need to make a specific metal part you could use front panel express. Their design software is easy to use.

https://www.frontpanelexpress.com/products/machine_parts/

 

[March Audio]

Hi Don. What I am looking for is a mechanical device that turns the existing volume controls on audio products. Not one to build into one.

I think this one is going to have to be a DIY solution, I will be surprised if you find something perfect for the job off the shelf

 

[DonH56]

Hi Don. What I am looking for is a mechanical device that turns the existing volume controls on audio products. Not one to build into one.

Ooops. misunderstood, sorry. Tend to agree with @BE718, probably not a COTS solution...

 

[Wombat]

Hello everyone.

One of the key measurements for headphone amps and integrated speaker amps is distortion versus level. This is normally done by setting the physical volume control on the unit to max, but then sweeping the input level from low to high. Problem is, this is not how people use the products. Input level is usually high/whatever the DAC/music dictates. It is the volume control that is used to determine how loud it plays, rather than messing with input level.

Now, some products perform the same in both situations. But for a number of one, performance can be different since we don't know whether the source of noise/distortion is in the front-end of the amp or output stage.

My question is for those of you in the maker world, or mechanical engineering, is there a ready-made, or kit of some rotary control mechanism that I can drive with a computer? That is, I like to clamp something to the volume control which of course has varying size, and then under computer control step it one notch at a time and measure the distortion. Probably need to be belt driven or have overload detection as to not push the volume control past max.

Any ideas?

This??

https://www.waste.org/~knobs/arduino_remote_stereo_volume_control.html

 

[maverickronin]

Someone at SBAF just posted a write up on an Arduino based volume control.

https://www.superbestaudiofriends.o...olume-control-laziness-and-unemployment.6955/