[Q] Potentiometer for controlling audio volume

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1234568

Hey. I am not sure if this is the best site to post this question in but I figured that some bright spark might be able to help.

I am making a little box that will contain a switch to allow me to direct an audio input to one of two outputs. For this I have purchased a 3PDT switch and I am comfortable with how that will work.

I also want to be able to control the volume outputted. For this I believe my best option is a potentiometer, as opposed to a rheostat. However, I am unsure what resistance and power rating I need. I would appreciate it if anyone with experience on this kind of project could help.

Many thanks
Ed
 
There are a few guys with an electronic background around the forum. Can you give more details about what the audio input is for and why you want to split it?
 
Of course. All connections will be made in standard stereo audio cable carrying line level audio. The source is my PC and the outputs are some speakers and some wireless headphones.

To achieve the switching I have ordered the following 3PDT switch. http://www.amazon.co.uk/gp/product/B008AGVBWM/ref=oh_aui_detailpage_o04_s00?ie=UTF8&psc=1

As mentioned I also want to control the volume. I was hoping that I could place the potentiometer in between the input and the switch, thus enabling volume control of both outputs.

I know that for volume control I will need a log POT. I believe line level audio is <2V. I am unsure what resistance is needed though. After reading about opinions seem to range from 10 ohm to 100 ohm.

Thanks in advance for any pointers!
 
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Volume control pots are normally install before the amplifier, and not after. Will need more info on what you are trying to install, how many speakers, over what area...etc
 
So I assume you are then feeding the amplifier(s) from the audio line......so again how many amps speakers.....as we have two methods here....4 speakers than ok, any more we need to look at 100v line....the more info we have the better we can help
 
Exactly... feeding the amplifier(s) from the audio line.

One of the amps is built into some stereo speakers.

The other is in some wireless headphones.

As far as I understand things though placing the POT in the audio line before these devices and the switch will negate their affect. This is all new to me so please correct me if I am wrong.
 
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Again.....how many amplifier speakers are you using, over what areas...?
And what are you exactly trying to install..?
 
Apologies if I am being dense and misunderstanding the question. As linked to the speakers are a 2.1 setup (2 monitors and 1 sub), that are either side of a PC screen so very small area. The headphones are also 2 speakers.
 
Again very brief info......do you want audio and video to be distributed to 2 other monitors from a computer, for teaching or entertainment....?
 
For controlling ordinary line level audio, 10kΩ log is typical. It is a compromise - too low and you form an attenuator with the source impedance, too high and your output side has such a high source impedance that it picks up interference and forms an attenuator with the load impedance at midway settings.

If you are driving it from a headphone output, then I would go for 1kΩ as the output is intended to drive loads as low as 32Ω. Remember to ground the shell of the pot if it is metal. Power rating is unimportant. If it is going to get heavy use, go for conductive plastic track rather than carbon.
 
Again presuming without info.....If were talking about one line output to multi inputs we need to balance mix......unless we get the full info here, you are all guessing
 
tazz said:
Again very brief info......do you want audio and video to be distributed to 2 other monitors from a computer, for teaching or entertainment....?
Click to expand...

Video? As mentioned it's a stereo audio feed, at line level (i.e. what your headphone out is from a computer). Going from PC to speakers or headphones.

amlu said:
double gang 10k ohm log pot should do the job...
Potentiometers (Beginners' Guide to Pots)
Click to expand...

Thank you. My research suggests 10k to 100k ohm log POT's. I am unsure of exactly what to try in this range. What makes you say 10k out of interest.

Lucien Nunes said:
For controlling ordinary line level audio, 10kΩ log is typical. It is a compromise - too low and you form an attenuator with the source impedance, too high and your output side has such a high source impedance that it picks up interference and forms an attenuator with the load impedance at midway settings.

If you are driving it from a headphone output, then I would go for 1kΩ as the output is intended to drive loads as low as 32Ω. Remember to ground the shell of the pot if it is metal. Power rating is unimportant. If it is going to get heavy use, go for conductive plastic track rather than carbon.
Click to expand...

Is a headphone output not also a line level output? Why the change from 10kΩ to 1kΩ? Thank you for the tip about grounding the shell of the pot.

tazz said:
Again presuming without info.....If were talking about one line output to multi inputs we need to balance mix......unless we get the full info here, you are all guessing
Click to expand...

Please let me know what further info you require. This is all new to me and I appreciate the help. My reading about line level (mainly the wiki article) leans me to believe that it is usually relatively similar regardless of device and so the balance should be ok. Is this incorrect?
 
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A headphone output is similar to a line level output but it is optimised for driving a lower load impedance, as typical headphones offer 32-120Ω load compared to a line input's 10-100kΩ. The signal level (voltage, not power) of a headphone output is also typically lower. However, a headphone output will serve quite well as a line output and they are often used as such. Some equipment offers you a mode selection for the output socket, with line mode delivering a higher level.

Any value from say 470Ω to 47kΩ will work with a line output, with varying degrees of excess signal attenuation. Given that you expect to drive it from an output capable of driving a 32Ω load, I would tend towards the lower end of that range for best results. The lower the pot end-end value, the lower source resistance it will present to the amplifier and hence the less attenuation will occur there and the less sensitive it will be to noise pickup.

I note you mention a 3PDT switch. Do not switch the grounds, join them all together, otherwise if the ground connection breaks first as you switch, you might get a loud thump.
 
Lucien Nunes said:
A headphone output is similar to a line level output but it is optimised for driving a lower load impedance, as typical headphones offer 32-120Ω load compared to a line input's 10-100kΩ. The signal level (voltage, not power) of a headphone output is also typically lower. However, a headphone output will serve quite well as a line output and they are often used as such. Some equipment offers you a mode selection for the output socket, with line mode delivering a higher level.

Any value from say 470Ω to 47kΩ will work with a line output, with varying degrees of excess signal attenuation. Given that you expect to drive it from an output capable of driving a 32Ω load, I would tend towards the lower end of that range for best results. The lower the pot end-end value, the lower source resistance it will present to the amplifier and hence the less attenuation will occur there and the less sensitive it will be to noise pickup.

I note you mention a 3PDT switch. Do not switch the grounds, join them all together, otherwise if the ground connection breaks first as you switch, you might get a loud thump.
Click to expand...

Thank you very much! This is starting to make more sense in my head. I didn't realise there was a difference between headphone output and line level. I will read up more on these differences and think how they relate specifically to me.

Also, great tip about the grounds. If I am joining them all together would a DPDT switch have done the job?
 
One at a time, he said. In practice with average consumer equipment you can get away with dozens or even hundreds of loads from one source before the attenuation becomes a problem. Only if the input impedance is unusually low or the output impedance unusually high, would you have to limit the fan-out to one or two loads.

Obviously it is better to buffer outputs to a low impedance and this is done in all pro gear. Ideally, there would be a buffer after this volume control, but because it is not driving a long cable or a low load impedance, one can manage without. The lower the pot end-end resistance, the stiffer the source it provides, hence my choice of a lower value where possible.

If I am joining them all together would a DPDT switch have done the job?
Click to expand...

Yes.

Now there is another factor to consider with switching, and that is that an open switch has capacitance across its contacts and when the load impedance is very high, this can pass enough current at high audio frequencies to be audible, and a floating input is very prone to picking up hum and static. Therefore, the correct way to switch audio is to switch unused inputs to ground, not merely disconnect them from the source. That would require a 4PDT switch.
 
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It's in post 7 Tazz:
Exactly... feeding the amplifier(s) from the audio line.
One of the amps is built into some stereo speakers.
The other is in some wireless headphones.
Click to expand...

I haven't followed the links because my internet connection is a piece of wet string that takes 5 minutes to load a page, but I can take a punt on the input specs of those items because most consumer products have similar specs to ensure compatibility.

I would also say that in my 25 years experience designing and building professional audio gear, I have hardly ever met a situation where a 10k pot didn't work tolerably well as an unbalanced line level volume control in solid-state equipment. Not always the best, but it will work. Here, I've suggested 1k, elsewhere I might say 47k, but they will all usually work. Valve equipment is different, impedances are higher, 100k - 1MΩ will tend to be more suitable. But I guess it's not a valve laptop.
 
So Lucien....how many line outputs are you feeding....are you going to use a line pre amp and mixer to feed the unknown amount of outputs....will all the said amount of inputs be the same impedance ...?
 
Unless I've misread it, the OP wants to feed only one device, either the speakers or the phones, at a time. I don't know where you are seeing that there are many destinations in parallel.
 
Exactly.....no mention of how many...nor information...A diagram might help us all...???????
This is just a total guessing game.....give the info, or forget wasting our time
 
Lucien Nunes said:
Unless I've misread it, the OP wants to feed only one device, either the speakers or the phones, at a time. I don't know where you are seeing that there are many destinations in parallel.
Click to expand...

Thank you Lucien. You seem to understand my question perfectly.

As you say, consumer line level seems very standardised and the required spec of the pot will not vary much. I have taken your advice (which mirrors other sites) and ordered a 10k pot. I will let you know the outcome.

tazz said:
Exactly.....no mention of how many...nor information...A diagram might help us all...???????
This is just a total guessing game.....give the info, or forget wasting our time
Click to expand...

Tazz I believe I have described my setup in it's entirety already.

PC line level output >>> POT >>> pc speakers OR headphones (controlled via 3PDT switch).
All of this will be connected via 1/8 jacks.
I have included the exact details of the speakers, headphones and switch via links.

What other details do you require? If I am being slow, I apologise. Repeating the question and getting hostile is a poor way to go about things. A smarter man might try rephrasing the question.

Tazz, the concept of forums is that people making positive contributions when they can. No one is forcing you to waste your time. You can leave the discussion to more contributing members. As you are a moderator I am surprised by your attitude.
 
Just a suggestion, forget the pot and control the levels via your pc and switch between speakers and cans via a switched jack socket?

HTH...
 
Last edited by a moderator:
Sorry you feel that way, but you post is basic with no explanation on what you are trying to achieve, all we know is you want to connect speakers and headphones to a pc....how may, why and what for is anyones guess.
 
Tazz why are you treating the OP like this? You are a moderator and should know better. He has said what he is trying to do. It is a not a full blown PA system so why try and over-complicate it. Well done Lucien for a decent answer. Daz
 
djw said:
Just a suggestion, forget the pot and control the levels via your pc and switch between speakers and cans via a switched jack socket?
Click to expand...

I did think of using Windows for level control but I often turn off the monitor while doing paper based work which makes this awkward. Also I have ordered the bits. If I don't get a good result with the pot this may be exactly what I do. Thanks for the suggestion!

DPG said:
Tazz why are you treating the OP like this? You are a moderator and should know better. He has said what he is trying to do. It is a not a full blown PA system so why try and over-complicate it. Well done Lucien for a decent answer. Daz
Click to expand...

This is my first thread in this forum. My voice is small but "DPG for moderator!"
 
A lot of people get put off by the very frosty responses they get
 
1234568 said:
I did think of using Windows for level control but I often turn off the monitor while doing paper based work which makes this awkward. Also I have ordered the bits. If I don't get a good result with the pot this may be exactly what I do. Thanks for the suggestion!

Are you looking to make a small enclosure to sit by your pc and adjust the level there? If so, think about using 1/4 inch
jacks and 'made-up' leads/adapters, much less fiddly soldering wise...
Click to expand...
 
djw said:
1234568 said:
I did think of using Windows for level control but I often turn off the monitor while doing paper based work which makes this awkward. Also I have ordered the bits. If I don't get a good result with the pot this may be exactly what I do. Thanks for the suggestion!

Are you looking to make a small enclosure to sit by your pc and adjust the level there? If so, think about using 1/4 inch
jacks and 'made-up' leads/adapters, much less fiddly soldering wise...
Click to expand...

Don't forget the small jacks are 1/8" rather than 1/4". Daz
Click to expand...
 
Exactly... a small enclosure is already in the post!

I am hoping to mount it via a 35mm tube clamp to my monitor stand and maintain precious desk space.

The idea is to have just an output switch and a volume control on the front of the box.

Bearing in mind the boxes planned positioning I am going for the smaller 1/8 over 1/4 components.

As a dental student I like to think I can handle the fiddliness. Although i've just jinxed myself horribly! :p
 
1234568 said:
Exactly... a small enclosure is already in the post!

I am hoping to mount it via a 35mm tube clamp to my monitor stand and maintain precious desk space.

The idea is to have just an output switch and a volume control on the front of the box.

Bearing in mind the boxes planned positioning I am going for the smaller 1/8 over 1/4 components.

As a dental student I like to think I can handle the fiddliness. Although i've just jinxed myself horribly! :p
Click to expand...

Sorry premature posting, hope it works out :)
 
Last edited by a moderator:
Sorry I haven't read through all the posts in this thread, but many other people have overcome the same problem without having to resort to soldering components together in adaptable boxes.
Personally I have an old disco mixer on top of my CPU which allows me to switch between or mix the audio signal from my PC or TV to play through speakers, or listen through headphones, or both.
Alternatively, unless I've missed something, most PC speakers come with a headphone output.
 
I could go the mixer option but I want my controls within easy reach and I have limited desktop space. The custom route means I can mount a minimal enclosure to my monitor stand. Additionally, the components are cheaper than most audio switches I saw online. Finally, I like the idea of taking on the project and learning something! ;)
 
Better still, have a look at Peter Belt's stuff. Stick a small shiny sticker on your door frame to make your cds sound better. It's worth a look. You'll all be buying them! Ha ha. Daz
 
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