PAC LC-1 Passive Volume Control Review

[shrimp_dude]

I would be interested in measurements of this unit: https://www.aliexpress.com/item/32840083176.html

Not quite a cheap passive pot and not quite an expensive stepped attenuator...

 

[amirm]

I would be interested in measurements of this unit: https://www.aliexpress.com/item/32840083176.html

Not quite a cheap passive pot and not quite an expensive stepped attenuator...

Unless implemented very well, you are likely to get slow response and static as you change volume. I am not a fan unless you need precise channel matching.

 

[laudio]

Good price but if you are dyi'ing something just buy a genuine alps and wire it up. Will last longer.

 

[billmr]

I use one of these to control subwoofer level -- without getting on my knees, reaching around to adjust the pot on the back of the sub, and getting back to my listening spot to check if I got it right. Seeing as that's essentially a very low frequency mono application, this gadget is just dandy for the job -- small, absurdly cheap, and very handy.

THIS

 

[JWAmerica]

-0.8db at 20khz. Inconsequential.

 

[tktran303]

Thanks for the test data

Sadly this is one of those products where a sample size of one is of limited value, Simply due to the variability of the potentiometer.

 

[xema]

use a good step attenuator instead
will not cost too much.

 

[Rja4000]

This is the review and detailed measurements of the PAC LC-1 passive attenuator. It was kindly purchased new by a member and costs just $9.50 including shipping from Amazon.
View attachment 207656

I must say for such a cheap device, the RCA cables feely nice and supple. And volume control itself is smooth. Inside there is a tiny PCB where all the cross connections are made. From documentation it seems that it is for car stereos but obviously you can also use it for home audio as long as all you want is attenuation.

PAC LC-1 Measurements
I used the LC-1 between my Audio Precision APx555 unbalanced input and output across two 6 foot sections of cabling. Here is the dashboard:

View attachment 207657

So at this volume level, performance is completely transparent. Let's see how good channel separation is:
View attachment 207658

So there is a distinct hit but it is still more than good enough for most things.

The issue with passive volume controls is that it messes with the impedance of the device you are connecting to. This in turn causes a frequency response error as you can see below:

View attachment 207659

The level of attenuation may be worse in your device. As is, it is not too bad at roughly 1 dB at 20 kHz.

What I didn't like is the taper that they selected. Most of the range is useless as you only get meaningful attenuation once you are below 12:00 o'clock. That accentuates the channel differential in the pot used:
View attachment 207660

Of course your example may be worse or better than this. Company rates the unit at ± 8 dB. Not sure how you get +8 dB from a passive control. Assuming they only mean -8 dB, then they are meeting spec.

Conclusions
A passive volume control is going to be bring its native problems so there is no getting around that. In that context, for less than $10, you are getting what looks like a high quality little box and cabling. Yes, the box is plastic but still, I like the total package and am going to recommend the PAC LC-1.
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As always, questions, comments, recommendations, etc. are welcome.

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@amirm
For such a device, or even for an active preamp, I think an important question is:
How does it perform compared to digital attenuation ?

So, maybe, a set of a few SINAD measurements, starting from a normalised input (2V unbalanced here) with an attenuation of min, 6dB, 24dB, 42dB, 60dB, compared to a typical DAC SINAD (SNR) slope ?

I know. It's more work.