How To Have A Better PC Volume Control
I don’t know if it’s only me but I have a beef with the Windows volume control. You know this sliding cursor that you actuate with the mouse.
I don’t say that it is not working – of course it is working – but it is not convenient at all. Imagine a typical situation: You are watching a video (a technical video of course!) and you had to crank up the volume because the presenter’s voice has very little volume. When the video is over you click to another video and here it comes, a blasting sponsor’s advertising, full audio power. By the time you grab the mouse, click onto the little speaker icon, wait for the volume control cursor to appear – it takes its time, usually a few seconds – by then you have woken up the wife, the kids, the cats and the dog… I know there are shortcuts but they are usually slow or not convenient. I wanted a control where I am the one controlling the volume instead of the computer doing it.
If you have an external speaker/amplifier as I do, it might have a manual volume control, so the problem is solved. You can skip this article, unless you want to read more about ancient but elegant ways of controlling the volume…
The external speaker I use has a volume control but it works only if you connect it through Bluetooth. It is a pair of digital buttons + and – , very nice but, again, not very convenient. Because of this and for other reasons I use the cable connection between the laptop and the speaker, and decided to make a manual, ergonomic and efficient volume control. All what was needed was to insert a potentiometer between the laptop and the speaker. As simple as that! But let’s do it on a practical and professional way:
All you need is a small project box, a couple of 3.5mm audio jack sockets, a potentiometer, a nice old style knob and pronto! You can also prepare a nice little overlay so it will look good:
It is easy, done in no time and it works perfectly well. Controlling the volume by turning a very accessible knob is much more natural; it has a great feeling and reacts instantaneously.
And it’s the opportunity to have a closer look at this almost forgotten component, the potentiometer. We don’t see them very often these days, except maybe as adjustable potentiometers (trim pots) soldered on PCBs.
The old “pot”, as we called it, was the way to control the volume of your granddad’s radio. But there is a twist, there are different types of potentiometers: linear and logarithmic! The one used in this mini-project is labelled “B50K”, meaning 50KOhm linear. The granddad’s radio volume control pots were all logarithmic. Why this difference and how did I get away using the wrong type of potentiometer for this function? Let’s first remember the basics of this humble component:
The figure above shows the characteristics of both, linear and logarithmic potentiometer. In the case of a linear potentiometer the output voltage Vout is proportional to the potentiometer rotation. This means that half way, at 50 % of the rotation the output voltage in this example will be 0.5V (50%). In the case of a logarithmic pot, the curve is no longer linear. For example at 50% of the rotation the output voltage is only around 10% (0.1V). Why do we need this? The reason is physiological, it’s because the sensitivity of the human hear is not linear, but logarithmic. The ear is more sensitive to lower sound levels than to higher ones. This is why we can hear such a wide range of sound levels, from murmurs to airplanes reactors… Controlling the audio volume with a logarithmic pot feels much more natural, this is why those log pots were used in grandpa’s radio.
To make those potentiometers they needed to manipulate the density of the resistive track in order to obtain the desired characteristic. This was quite an expensive process but it didn’t matter much as the demand for logarithmic pots was big. Today, there is not such demand anymore and the log pots have practically disappeared from the market. Audio volume is controlled with digital encoders or control remotes. Hence most of the potentiometers you would purchase are linear, the salesman will not even ask which type you want because he/she probably wouldn’t know the difference. But what if you want to repair grandpa’s radio and need a log pot? You might find it online but if not, there is another way around: the loaded potentiometer…
In our previous example we assumed that there was no load at the output (Nothing connected to Vout terminals). This was almost the case in grandpa’s radio because the input of the vacuum tube audio amplifier following the volume control had very high impedance. But see what is happening when we load the potentiometer with a lower value resistor:
The calculation of V2 is no longer depending only on the ratio between Ra and Rb but must consider that RL is now in parallel with Rb. For each step of the potentiometer we must calculate the value of RL parallel with Rb, which we called Rp in this example. Then we calculate V2 using Rp instead of Rb… This is hard work if you want to plot V2 for each position of the potentiometer. Thus we will use Excel so we can enter the formulas once only in the first row, then drag it down. And see what we find:
By connecting a 10K resistor at the output of our 50K potentiometer we transformed the linear pot into a near log pot! I selected this value of 10K because it is the input impedance of my speaker system. I didn’t have to change anything to get a kind of logarithmic volume control that feels very nice and natural.
So here is your solution, if you have to repair granddad’s radio and cannot find a logarithmic pot. Just use a linear pot and connect a resistor between the cursor and the ground. The value of the resistor will depend on the value of the potentiometer but you can use the example above, i.e. about 20% of the value of the pot might be fine. The lower the value, the curvier the characteristic will be; it is worthwhile to test a few values and select the one that produce the most natural volume control.
There are indeed more than only two kinds of potentiometers, some with specific characteristics to suit various analogue functions in scientific instruments. Some companies are still making “tailor made” potentiometers to suit any application. For a price obviously! For us, the standard linear is doing the job perfectly well.
I hope that you enjoyed this trip into the past…
Gerald Musy
Penang, Malaysia
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https://jestineyong.com/make-your-own-emi-measurement-probes/
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24 Comments
Leave a Reply
YH Wong
November 12, 2016 at 3:43 pm
Good simple gadget. I'm not sure how well is logarithmic vs linear to my ears. Haven't compare it before.
Gerald
November 14, 2016 at 2:50 pm
Hello YH,
Thanks for your comment and support. A linear control would feel like the volume varies from zero to loud with only a few degrees of the pot rotation, then no much difference until the max of the pot range.
Cheers,
GM
Gerald Millward
November 12, 2016 at 6:04 pm
Excellent Gerald - I'd forgotten all about lin/log pots and analogue volume control! Loved the loaded pot idea - first time I've come across it in more than 50 years experience.
Gerald
November 14, 2016 at 2:58 pm
Thanks for your support Gerald. Well it's almost not used anymore as we control the volume digitally with remote controls and encoders and the compensation (log curve) is done digitally.
The loaded pot is also a good school exercise to practice resistor networks calculations...
Cheers,
GM
Yogesh Panchal
November 12, 2016 at 6:32 pm
Sir,
Thanks for informative tips.
Gerald
November 14, 2016 at 2:59 pm
Thanks for your support Yogesh
Bulent NUR
November 12, 2016 at 7:47 pm
Very simple and good result, thanks for sharing.
Gerald
November 14, 2016 at 3:00 pm
Thanks for your support Bulent
Suranga Electronics Sri Lanka
November 12, 2016 at 10:38 pm
Mr, Gerald Musy,
very good idea. Thanks..!
Gerald
November 14, 2016 at 3:00 pm
thanks Suranga
HumbleStudent
November 13, 2016 at 8:42 am
This is still very vital in electric guitars and basses....the log taper pot is generally preferred...good to understand the workaround. And so naturally, if you're looking for a true logarithmic potentiometer, you might want to consult the musical instrument suppliers.
Thanks!
Gerald
November 14, 2016 at 3:06 pm
Thanks for you support HumbleStudent. Yes the electric guitar world is still using vacuum tube amplifiers or other amplifiers with very high impedance inputs, hence the need for log pots. This is a good hint, thanks.
Cheers,
GM
Ulises Aguilar Pazzani
November 13, 2016 at 11:53 am
Mr Musy
great idea thks for sharing , I will keep in ram memory
Gerald
November 14, 2016 at 3:07 pm
Thanks for your support Ulises
Parasuraman S
November 13, 2016 at 3:11 pm
Very informative technical stuff, because of which, not easy to digest for me! Shall read, re-read again and try to imbibe whatever I can!
Gerald
November 14, 2016 at 3:08 pm
Thanks for your support Parasuraman
Albert van Bemmelen
November 14, 2016 at 5:02 am
I rarely listen to the radio or to music, Gerald. (My Solar Radio however plays on brighter or sunny days automatically on its own. It is placed on the Window-ledge in my living room). Because on my age I like the quiet to be able to think. And I guess your as always excellent article can be of great help to also accomplish just that. (;)
Gerald
November 14, 2016 at 3:13 pm
Thanks Albert. Indeed I also like the quiet surrounding. I also subscribed to a few technical YouTube sites and this is where the volume control comes handy.
Cheers,
GM
Robert Calk
November 15, 2016 at 2:16 am
Nice lesson, Albert. Thanks.
Robert Calk
November 16, 2016 at 1:01 pm
Sorry Gerald, I don't know why I typed Albert.
Henry
November 15, 2016 at 1:20 pm
Very well presented and nicely explained. Like all your articles Gerald it it easy to read and to follow. Simple in style but excellent educational material. I like it, and always enjoy your postings here. Please continue with those great tips with added theoretical base.
Gerald
November 15, 2016 at 6:17 pm
Thanks for your support and appreciation Henry
Benjamin E.
November 22, 2016 at 7:21 am
If you are using YouTube, it may be your problem.
I have noticed that on some YouTube videos, the sound will start out loud and then decrease in volume after a few seconds. This happens when the video starts, and also sometimes (but not always!) when you change the slider to a different time.
It's very, very weird... I don't have this issue with other video players on my web browser. It's only YouTube ...
-Ben
Humberto
November 24, 2016 at 1:42 am
Another didactical article, as usual. Keep on and thanks.