# Difference between 10K and 50K Alps Pots



## danlaix

What is the difference in output when using either 10K or 50K Alps Pots??


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## KTpG

The main difference is the impedence of the pot. If I am correct in thinking this, the 10k will get louder faster since it has less resistance on the voltage. However, some sources may not appreciate driving a 10k ohm load, so 50k helps here.


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## antness

What amplifier is this for? Are you building the RA-1 clone? I think the RA-1 uses a 100K pot. I think you should use 10K.


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## danlaix

Thanks KTpG and antness for replying.

 OK. I know that for cmoy amp, using the 10K pots is sufficient.
 What about for CHA47 and also for RA-1??
 What what differences does it makes if i use 10K, 50K or 100K in this case.
 Does using the types of power supplies matters here??
 ( using batteries supply)

 Thanks.


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## Born2bwire

The CHA-47 can be thought of as a modified CMOY, the extra opamp only acts as a unity gain so you'll be fine using the same pot impedance in the CMOY as in the CHA-47. Really though, the strength of the pot also depends on the strength of the signal being sent to the amp. On my Sony PCDP, the lineout is rather strong and I found that in addition to using a 50K pot, I needed to attenuate the inputted signal by 15K ohm resistors, otherwise I could just hear the signal when the pot was at full blast. For the RA-1, I would just use what the schematics call for. Really, the impedance of the pot only controls how quickly the signal will change and whether or not there is a signal heard at full strength. Remember, all pots will goto 0 ohms of resistance so the resistance of the pot will not affect how loud the output CAN get.


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## morsel

KTpG is not correct. All pots of the same make and model should change volume at the same rate regardless of their total resistance, as the pot functions as a resistive divider, so it is the ratio, not the absolute value, that controls the volume level.

 To answer your question, choosing pot impedance is a tradeoff. The lower the impedance, the greater the demand on the source to drive it. The greater the impedance, the greater the vulnerability to noise problems. 10k-100k is the reasonable range of choice. Less than 10k may be too low for some line level outputs to handle with optimum fidelity. Greater than 100k is asking for noise trouble, with the exception of certain tube designs which need a 500k pot.

 My personal preference in descending order would be 50k, 20k, 10k, with 100k a very distant and undesirable choice of last resort. Your milage may vary. 50k is close to the (perhaps somewhat dated) 47k audio input impedance standard. It is midway between the low and high limits of the reasonable range, which suggests it might be the most balanced choice. Don't let me sway you though, 10k should work fine.


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## tangent

Quote:


 What is the difference in output when using either 10K or 50K Alps Pots?? 
 

Ignoring source loading issues, none at all. I'll get back to the source loading issue in a minute.

  Quote:


 the 10k will get louder faster since it has less resistance on the voltage. 
 

Not true. A pot is simply an adjustable voltage divider. In a voltage divider, the resistor values you use don't affect the signal you get out, as long as the upstream source and the downstream sink are compatible with the resistances. (Again, this a loading issue.) All that matters is the ratio of the values. Look up the resistive voltage divider equation in an electronics book and play with different numbers until you believe this. 

 So, if you have two pots with different total resistances but with the same taper, the ratio of the resistances is the same across the entire sweep of the pot. Therefore, the voltage division is the same at the same point in the sweep of each pot, therefore the voltage output is the same for both pots at a given position.

  Quote:


 some sources may not appreciate driving a 10k ohm load, so 50k helps here. 
 

This is true, and this is the source loading question I mentioned a few times above. Ohm's law says that if voltage stays fixed, as resistance goes down, current goes up. Therefore, a smaller value pot will cause the source to put out more current, if it can. A 10K pot is approaching the low end of what you can expect the type of sources that you'd plug into a preamp to be able to drive reliably. Some sources will do much better than others, but it's good practice to make the input resistance of any stage as high as you can get away with, to minimize loading on the source. That's why we like FET-input op-amps: they have input impedances up in the megohms range, so that we have tremendous freedom over what kind of "sources" (i.e. pots, input resistors, crossfeed circuits, etc.) we plug into their inputs. Bipolar-input op-amps have lower input impedances, so you have to be more careful when designing them.

 So now you ask, why don't we just use 10M pots? That's because as resistance goes up, so does noise. Partly it's Johnson noise -- inherent electron noise present in all resistors, which becomes more significant as current goes down, which happens with large resistances. And partly it's that large resistors do not require large currents to conduct signals. This is Ohm's law again: it takes more work to drive a signal across a 1 ohm resistor than across a 1M resistor. 

 So, we try to balance source loading with the potential for noise pickup. This is where the 10K to 100K range comes from for audio amplifiers, despite the fact that there are pots ranging from 1K to 1M easily available.


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## aos

Alps Blue is not available in values less than 50k. Only fake ones (that were discussed here a lot) can be found with that value. Of course, you never mentioned that you were refering to the "Blue" pot and Alps makes many models.


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## slammy

Since I'm new at these challenges, I'd like to know, when building guitar stomp boxes, what pots work best? B50K, C50K, B100K etc?
 It's a bit confusing. I have opened guitar pedals and have seen these types of different pots, some controlling different effects. Can I modify a pedal with a pot with a greater or lesser ohms?
 Thanks for your kind response


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## nikongod

slammy said:


> Since I'm new at these challenges, I'd like to know, when building guitar stomp boxes, what pots work best? B50K, C50K, B100K etc?
> It's a bit confusing. I have opened guitar pedals and have seen these types of different pots, some controlling different effects. Can I modify a pedal with a pot with a greater or lesser ohms?
> Thanks for your kind response


 
  
 What is the best guitar string? There is no answer because we don't know if you are playing an acoustic, electric, bass, 12-string, or one of those funny "travel" guitars.
  
 There are many reasons that a given pot may be chosen for a given application in a guitar pedal. It could be the right value based on some electrical consideration or it could be a random value because that's what the first guy who built the pedal had sitting around when he built it or it could be a combination of those. If you don't have time to reverse engineer (and or still do LOTS of experimentation) just get the part it says.


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## tangent

slammy said:


> when building guitar stomp boxes


 
  
 Why not ask on a site where they talk about building guitar stomp boxes?  Be sure to mention which circuit you're proposing building or modifying.
  


> what pots work best?


 
  
 My post above is just as true as when I wrote it 11 years ago. The best pot value is circuit and application-specific.


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## AudioNewbi3

Sorry for bringing up this old thread, but can I use a 20k pot for an 47amplifier?


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## tomb

audionewbi3 said:


> Sorry for bringing up this old thread, but can I use a 20k pot for an 47amplifier?


 

 Yes.


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## AudioNewbi3

tomb said:


> Yes.


 
 Thanks mate!


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