Active EQ potentiometers oopsie

[MaxSxB]

Hi everyone,

I recently bought a cheap Harley Benton PJ-4 for a little solo project and decided to upgrade it (it feels good to play and love the look !). I bought a Quarter Pound set and an Artec active EQ preamp. For the latter, here goes the problem.

I didn't want to punch new holes for the EQ pots so I went for 2 stacked pots (mid/volume + bass/treble) + 1 alone. I did my researches wrong (very wrong actually) and ordered a 500k/500k for M/V and a 250k/500k for B/T (both Allparts). I've read multiple times today (delivery day...) that I should have ordered 100k's for the EQ controls, but I couldn't find any on my usual websites in Europe.

Here's my question : what will be the consequences if I'm using these 500 and 250 on EQ bands ? I've read about taper alteration, but I don't understand the practical effets of this. Will it damage my preamp card ? Will it change the frequency ranges affected ? Is it only a matter of sensibility ? English not being my native language doesn't help...

If it's a big no-go, I'll try to send them back and punch new holes, but if there is a chance the bass will be playable correctly...

Thanks in advance for your answers !
Max

 

[MaxSxB]

OK just some further researches and I came accross the trick of soldering a resistor between left and right lugs of the pot to lower its impedance. If I can help other people in this case, here is the formula to find the resistor value you need :

1/(desired value) = 1/(pot value) + 1/(resistor value)
-> 1/(resistance value) = 1/(desired value) - 1/(pot value)

Solve the right side of the equation, then do 1/(the result) and BOOM, here's your value.

Example in my case : I want 100k, my pot is 500k
1/100 - 1/500 = 0.01 - 0.002 = 0.008
1/0.008 = 125k !

(but since I can't find 125k resistors, I went for 150k ones, giving 115k for 500k pots and 94k for the 250k pot, which is IMO acceptable)

Hope this helps !
Max

 

[RobbieK]

Yes, the filter points will most likely be shifted, and yeah the tapers will be very different, and possibly the amount of cut/boost. But it is hard to predict without seeing the schematic for the actual preamp.

Also, the parallel resistor to bring a 250K down to 100k will be more like 170K.

But you can't hurt anything by doing this, so go for it. If it sounds good, you are fine.

BTW, you are right, B100K stacks are hard to find. (B50K stacks are far more common.) I think I bought some from Ali Express or Ebay last time...