For a long time, I have heard that one of the problems with a potentiometer as a volume control in audio equipment is that the volume level of the right and left channels do not track each other very well. I understood there are often large and variable differences between the volume of the two channels and the tracking errors are the worst at low volume levels. Furthermore, I have heard that one of the advantages of a stepped attenuator is that volume level of the two channels track each other with greater precision over the whole range of attenuation when compared to a potentiometer.

My last blog post on September 24th, 2025 showed that indeed the attenuation of the left and right channels of my DÆ v4.2 stepped attenuator are well matched. The measurement showed ±0.2 dB over the attenuation range of -60 dB to 0 dB.

By way of comparison, the tightest tolerance for the Alps RK271 potentiometer is a gang error of 2 dB max between -60 dB and 0 dB. The gang error tolerance is even greater at ± 3 dB for lower volume levels with attenuation between -70 dB and -60 dB. Gang error is the difference between the attenuation of the right and left channels at a particular shaft angle. The shaft angle sets the volume level or attenuation. The Alps RK271, also called Alps Blue Velvet, is a well regarded potentiometer by the audiophile community.

It further check the claims for tighter channel matching for a stepped attenuator compared to a potentiometer, I bought three Alps RK271 potentiometers from Digikey and prepared a jig to test them. The jig is shown below. It has 24 equally spaced markings so the I could measure the attenuation of the potentiometer in similar increments to the steps provided by the DÆ v4.2 stepped attenuator.

Jig to test gang error for Alps RK271 potentiometer.

And here are the results for one of the Alps RK271 potentiometers . The results for the other two potentiometers where nearly the same. The attenuation was measured with a 1 kHz, 1 volt RMS tone and a QuantAsylum QA401 Audio Analyzer.

The blue line is the target attenuation for the DÆ v4.2 stepped attenuator which is linear with shaft angle except at position one which is a “mute” setting. The orange and green lines are the attenuation of the left and right channels of the Alps RK271 potentiometer which are nearly on top of each other except at positions one and two. The Alps potentiometer has a logarithmic taper instead of the linear taper of the DÆ v4.2 stepped attenuator.

The red line is the gang error for the Alps potentiometer which can be compared with the solid black line which is the gang error for the DÆ v4.2 stepped attenuator. Certainly the gang error for the stepped attenuator is lower (better) than the gang error for the Alps potentiometer. This was to be expected.

What stood out to me is that the gang error for the Alps potentiometer is lower than I expected. The measured data is well within the tolerance bands (dashed black lines) except for attenuations greater than -70 dB. Probably not much listening goes on at that very low level. In fact the gang error is less than ± 0.5 dB over most of the range which would be inaudible.

So yes, the stepped attenuator is more precise but the potentiometer is really very good - better than I expected. Another potential benefit of a stepped attenuator, beyond just being cool, is lower noise over time. After years of use, even high quality potentiometers can become noisy producing a scratchy, crackling noise when adjusted . Hence the use of Deoxit and other chemicals to clean the controls of vintage audio equipment. The reed switches used in the DÆ v4.2 stepped attenuator are hermetically sealed so the contacts should be immune to contamination over time. I have only been using the reed switches in my stepped attenuators for a couple of years and much longer testing is required. I think potentiometers in audio equipment can become noisy after ten years or more - so I have a long time to wait to prove or disprove the longevity advantage of a stepped attenuator!