Log Pot Tip In

[wrl]

Hi everyone,

I recently switched potentiometers in my active crossover (using with electrostatic loudspeakers) for bass level and volume control from cheapo radioshack Alps pots to some nicer motorised Alps blue pots.

Both were 100Kohm, but the problem with the new pots is that the "tip in" is ridiculously strong. I.E. it goes from nothing to far too loud with only a tiny turn. This is also true for the bass unit although it is even worse in that the lowest setting is still loud and then it gets slighly louder as the pot turns.

The setup is essenially that these pots are between a unity gain circuit and the split to the two panel and bass sections so they should be working essentially with the output from the cd player.

Do I have these hooked up wrong by chance (I didn't notice this problem with the other pots, but perhaps I made a mistake in the wiring) or is this common? Also, can I fix this easily by soldering a resistor in series or something? I'd rather not have to order new pots because these were expensive and I've customized my chassis to them already.

Any input is welcome and I can provide more information about my exact setup if it would help.

Thanks in advance,

WRL

[roender]

Hi
I think that you had inverted two pins. Let the middle one as it is now and invert the others.

[wrl]

I had tried this with the bass level previously. It made it so that the max output was at the fully counter clockwise position. When I swapped the pins, I now have max output at the fully clockwise position, but strong tip in.

I haven't tried this with the volume yet, but I would expect similar results. Perhaps I am misunderstanding something?

Thanks,

WRL

[Javin5]

Could it be that you have linear pots instead of logarithmic pots?

[richie00boy]

Originally posted by Javin5
Could it be that you have linear pots instead of logarithmic pots?

That's what I'm thinking.

[Minion]

Originally posted by Javin5
Could it be that you have linear pots instead of logarithmic pots?

Wouldn"t it be the other way arround?? a Log Pot has about 50% of it"s resistance in the last 25% of the pots rotation which sounds like the problem he is haveing ......

a Linear pot shouldn"t be touchy at the end of the rotation but a Log pot will.....


Cheers

[richie00boy]

He said the sound goes from nothing to too much, too quickly. Which is what you would expect a lin pot to do when it should be a log one.

[Javin5]

If I understand him correctly, his problem is at the beginning of the rotation (i.e. fully counterclockwise), not at the end.

[AndrewT]

Hi,
I'm more inclined to blame a wiring error.
I doubt that Log law or Linear makes that much difference as the volume is turned from zero to just on.
I would expect all pots to register no more than 0.2% (-54db) at the start of the track and really good ones could be as low as 0.01% (-80db).
The db cut at the start of the resistive track is quite massive and the gain as the pot is turned up should be very noticeable.

I wonder if the lower end of the pot is not connected to the audio ground? A variable resistor would cause the symptom being described. But, that would not account for the actual turn off unless the pot track is broken. Confusing.

[Javin5]

If it is indeed a linear pot and you don't want to change it, here is a potential fix: Connect a resistor from the wiper to ground.

The smaller the resistor, the more of an approximate pseudo log characteristic is obtained. However, the input impedance will now be depending on the rotation angle (which I personally don't like). Still, this trick is used in many amplifiers, since it allows for relatively good tracking of the stereo channels. It is also cheaper than a really good log pot.