volume control problem

[mozikluv]

can anybody help me with my problem on a dual ganged potentiomenter which is used for stereo? am tired of changing my stereo volume control due to scratchy noise at least 3x a year. We dont have here in the Philippines log pots and its quite expensive. the single type performs better but you cant use it on stereo. Can anyone provide with a circuit I can use or direct me to a website who has this? your help would be highly appreciated. thanks

 

[stevez]

I have no experience with "digital pots" but you might try looking at the Dallas Semiconductor (Maxim) Digital Potentiometers Design Guide. I pulled it off their site.

My understanding of a digital pot - to the circuit installed it looks like a normal pot - has voltage an current limits same as traditional pots. There are various methods of control. It appears that this is exactly what you might find in many modern portable (and otherwise) electronics where you push a button to increase or decrease volume or some other variable.

 

[lavenatti]

You can actually repair a scratchy pot fairly easily.


A small amount of powdered graphite mixed with a little oil does the trick.
Make a mixture of the two, it still needs to flow a little so not too thick.

Drip a tiny amount into the pot, right onto the resistive material if possible.
Turn the pot back and forth a few times and try it out. I've done this at least a dozen times and it has always worked perfectly, the graphite fills in all the little cracks that make the pot noisy and the oil keeps everything in place.

 

[Mosfet]

Maxim's DS1802 dual audio pushbutton pot:
**broken link removed**

National Semi has a dual volume, balance & tone chip:
**broken link removed**
It uses single linear pots to control all functions.

Rod Elliot shows how to make a linear pot into a log pot:
**broken link removed**
[he puts a 15k resistor on the wiper to ground of a 100k pot]

 

[Mosfet]

A small amount of powdered graphite mixed with a little oil does the trick.

lavenatti,
your oil/graphite mixture sounds similar to 'lock-ease'
that stuff you spray or squirt into frozen car locks
ever use it on pots?

 

[lavenatti]

No, I haven't. If I see some in the store I'll pick it up.

You aren't really supposed to oil locks, so Lock Ease may be a suspension of graphite in a solvent that evaporates, I'll have to check it out.. Oil in locks collects dirt and stains your clothes when you put your keys back in your pocket. Not that graphite is pretty, but I think it works its way around the pins and stays off the key after a few turns of the lock.

I usually make a pretty thick mixture, any oil (petroleum, not vegetable) seems to work ok.

 

[pebe]

I did a 'temporary' repair to a TV volume control using WD40 oil. It lasted until I threw the TV out about a year later - with the pot still going strong.

 

[mozikluv]

thanks to u guys

to stevez: have visited your suggested site & have seen the item but my problem is its not avalable here.
:lol: to lavanetti: I will try to look for the powdered graphite and mix it with WD40.
:wink: to mosfet: the manufacturer has discontinued this item
to pebe: thats something I cant afford.
To all you guys thank you very much for your replies!

 

[tansis]

A soft pencil is a good source of grapite.

Or you could build log pot circuit from an up/down counter and analog switch ic's

 

[olly_k]

I use 'electronic switch cleaner with lubricant' I don't know if you can find any?
I don't understand why you can't get hold of a replacment log pot though???

 

[Mosfet]

Re: thanks to u guys

the manufacturer has discontinued this item

No they have not.
Both are in production and available for purchase.
**broken link removed**
**broken link removed**

 

[mozikluv]

to tansis: thanks for the tip,but am not good with digital circuits. if you have the circuit for this, please provide me with one. I would be mighty grateful if you could provide for me.
:? to steves: sorry, my mistake by saying national has discontinued this item, I mistook it for another item, anyway its no longer available here in the Philippines. I have visited a lot of electronic stores here in our city, Bacolod and even in Manila, they all say its no longer available. If I order for one unit, the cost of freight would be very prohibitive. Have tried the rod elliot approach and I find it good and am using it now.
Again thanks to all the fellas who responded.

 

[lavenatti]

Use motor oil or 3 in one oil rather than WD-40. WD-40 will evaporate and leave you with the same problem. Heavier oils stick around, WD-40 is great for loosening a stuck bolt or cleaning glue off of something, but it really has no long term staying power.