Notice the funky brown on my A4 knobs compared to the RYTM? I got the A4 for 700$ used because the seller said people were complaining about the funky smoke smell, and look apparently. After a few weeks the funky smoke perfume smell went away, and I tried alcohol pads on the knobs. Being that my studio is kinda dark anyways, I just rolled with it. Nothing is wrong other than the funk on the knobs(not the kind of funk i want) Any suggestions that have worked?
It looks like gold. Just paint them gold anyway - and sell for a premium 
Another possibility is plastic infection. Not well reported in the medical literature - inflammatory plasticosis - most common organism is Plasticosum Plantarum.
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Most likely nicotine stains. You aren’t going to get rid of those so either paint 'em or replace 'em. There is a lovely toxic compound that people use to restore yellowed plastics on old computers (Apple IIe, for example) called Retr0bright but you have to mix it up yourself and I reckon that would be overkill.
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I’d just ask Elektron how much it would be to replace those knobs. I couldn’t live with that, they look foul!
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Close the door, smoke a lot, you won’t care after. 
I’d change too.
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Asking Elektron costs nothing
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That sure looks like nicotine staining. The previous owner must have liked a smoke whilst creating music.
Might be worth asking Elektron if you can buy replacement knobs?.
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That’s definitely nicotine stains. Any solvent worth it’s weight to try to remove it would not only potentially destroy the integrity of the knob’s compound, but would probably be futile anyway because nicotine is of course an oil and by looks of it, has permeated the knob’s surface more than surface deep, along with tar. Replace the knobs, but you can count on the rest of the A4’s surface outside and inside to be as likely polluted.
Also be wary of purchasing equipment from people that vape. The nicotine is still very much present with the added displeasure of the glycerin slime from vape juice. Nasty habit.
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I can’t even imagine how much smoking for how long would make that happen, and I’m a smoker!
Edit:I don’t smoke inside
Had same problem, made ticket with support and got a new set for a good price delivered to my door
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i almost threw up in my mouth when i saw that. someone should teach that person how to wash their hands.
Better an A4 than a Rytm. Those pads would be trashed.
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Looks like a pipe smoker´s work! Standard cigarette brands cannot do this kind of damage. I had gear that was parked 10 years in a heavy smoker´s room and it was basically fine. I once got an APC40 from a pipe smoker, I could not tell which LEDs were on due to the dirt on the pads. I tried lots of thing to clean it but in the end I was unsucessful. So my +1 for replacement from Elektron.
It DOES do that much damage when a smoker pretty much exclusively rolls their own. It then is even more pronounces on the fingers in addition to regular atmospheric smoke. A self-rolled cigarette also usually does not typically have a filter unless a small mechanical machine is used to “roll them” with filter on tubes.
Those knobs look like a friend of mine’s Yamaha RM1X step buttons who also happens to roll his own cigs. When he received that RM1X it had been painstakingly serviced and all new encoders and switches and buttons. It only took him 1 1/2 years to make it needed servicing again and when it was opened-up, it was enough to make him switch to vaping and eventually quitting. The tech told him that his lungs likely looked as bad if not much worse.
Nicotine and Tar also can eat away at printed circuit boards in the way something is so alkali on scale it’s acidic.
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Seriously - wtf… forget cleaning them, why would you even want to touch them? 
Like everyone says, spend a cpl of bucks buying new knobs from Elektron - I cant imagine them costing more than $5-10 bucks…
Find your local electronics shop and pimp your a4 out.
I quit smoking since last november, woo hoo to me.
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And the poster’s name is knobs… Member from 2015, you can’t change your user name right?
Go figure…
I would think some anodized red knobs would look really nice that match the red on fascia of A4/AK if rubber knobs cannot be located in suitable shape/form-factor. If Liberace were alive today, his Analog Keys would have embedded rubies on the knobs. 
Thanks for all the suggestions, I’m just going to order some new ones. I didn’t really have the funds when I first got it, but now I do.
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Do tell us how much Elektron quote for new knobs.
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