Center detent craziness! Preamp fried as well?

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Center detent craziness! Preamp fried as well?

Postby zuma » Thu May 07, 2009 8:52 pm

Long story short (and excuse my ignorance as I am pretty weak in the electronics dept.) I just had my bass repaired but I don't think the job is done.

My "bass" knob (from the three band active EQ) was replaced with a more generic pot instead of the center detent pot like the mid and treble have. Is this even close to being correct?

Is there a big difference between a center detent pot and a regular pot of the same value? (Besides the detent in the pot, of course)

Also, probably unrelated to the pot, my bass makes a sort of "warm-up" distortion sound when I first plug it in. Kind of like when you turn on a tube amp and keep playing it until it settles in. It only "warms up" for a couple of seconds, though. I am wondering if the preamp still needs replaced in this thing or what.

Here is a pic so you can get a good look at the pots:

Image

So, the one on the upper left is the one that was replaced. It should look like the other two below it.

I've had no luck Googling a B50K center detent pot. The tech said he couldn't find one either.

Any help is greatly appreciated.
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zuma
 
Location: East Los Angeles

Re: Center detent craziness! Preamp fried as well?

Postby noahvale » Fri May 08, 2009 6:30 am

Center detent pots are not common, but you can get them. Bartolini uses them in a lot of their preamps. You should be able to get one from them, or at least get one through one of their dealers. I've called them before, they are very helpful. I found a 50K center detent pot listed on their website: http://www.bartolini.net/information/ac ... sories.htm
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Re: Center detent craziness! Preamp fried as well?

Postby zuma » Fri May 08, 2009 6:47 am

Thanks for the link. It is really helpful. Another question: Now, let's say we stick with linear pots for a moment. Is the preamp "tuned" so it is flat at 25,000 Ohms in my case? This is a boost/cut preamp (so I think) and I am just wondering what really dictates center or flat. Does that question make sense? In other words, how does a boost/cut circuit work when it comes to pots?
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zuma
 
Location: East Los Angeles

Re: Center detent craziness! Preamp fried as well?

Postby noahvale » Fri May 08, 2009 7:01 am

It all depends on the circuit. What preamp is it? Most preamps use linear pots, flat in the center, boost/cut when turned.
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Re: Center detent craziness! Preamp fried as well?

Postby zuma » Fri May 08, 2009 7:25 am

It's the stock preamp from my Bossa OB-5 bass. It's a one man shop, as far as I know the builder designs them exclusively for his basses. I do believe that it would be as you describe though - linear, flat in center, etc.

Assuming that kind of a circuit, why is the middle flat? Why is 25,000 Ohms flat? The pot is dumb so I am assuming the preamp will register the middle of the pot as "flat?"
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zuma
 
Location: East Los Angeles

Re: Center detent craziness! Preamp fried as well?

Postby noahvale » Fri May 08, 2009 7:57 am

Basically, the way it works is that the pot controls the output of an IC chip by increasing or decreasing the voltage applied to the control circuit of the chip. That's not all of it, I'm not an electronics engineer, but I do have some limited experience with preamps. Most players want a boost/cut setup because that is what they are used to. Musicman and Sadowsky both use boost only controls. It's just a matter of preference.
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Re: Center detent craziness! Preamp fried as well?

Postby zuma » Fri May 08, 2009 12:19 pm

That's helpful, thanks. I assume then that a preamp with center detent pots would be boost/cut or else what would be the point? Right?

Just to give you an update, my Bossa began having fits again (cutting in and out) so I think the preamp is going after all. I'm getting it replaced under warranty. Might as well take advantage of having one.
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Location: East Los Angeles


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