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Post subject: Please help with my Eric Clapton midbooster
Posted: Fri Mar 14, 2014 12:06 pm
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I installed my EC midbooster yesterday. It seems to work after some trial and error. However, the volume pot does not work as it is supposed to be. The guitar produces some kind of squeeling sound. It truly sounds horrible. Also, the volume cannot be turned off.. No matter what I try, the volume will not go all the way down.

Has anyone any idea what I should do next?


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Post subject: Re: Please help with my Eric Clapton midbooster
Posted: Fri Mar 14, 2014 1:32 pm
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Bad Soldering? Did you check that you soldered the right parts together?
Did you use the right potentiometer that came with it? Did you get them wrong and took the volume pot for the boost pot?


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Post subject: Re: Please help with my Eric Clapton midbooster
Posted: Fri Mar 14, 2014 10:33 pm
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Location: Denver, CO, USA
With the Clapton mid-boost, you must use the supplied 50K pot for the volume. It's connected to the preamp after the first gain stage, not connected directly to the pickups like a normal passive pot. Using a 250K pot for the volume with a midboost will result in the squeal you're experiencing.

But not being able to turn the volume all the way down is a symptom of not having grounded the third lug/terminal of the volume pot. Normally you bend that lug over so it touches the pot's can/case, then solder it to the can/case/shell of the pot. Some people run a wire from the terminal to the can/case/shell instead -- same difference (you could even run a wire from the third terminal to some other ground point -- it just needs to be connected to ground).

On wiring diagrams, it's not always clear that you have to connect the third terminal (the one that doesn't have input/output wires attached to it) to the back of the pot. Lots of people miss that, and then the pot is acting as a simple variable resistor instead of acting as a voltage divider. In other words, it adds enough resistance to reduce the volume somewhat, but it can't shunt the signal to ground in order to completely silence the signal.

If you use the correct 50K pot but don't ground the third lug I know it would keep the pot from turning the sound all the way down, but I don't know if it would cause squealing. Maybe it would, so it's possible you used the right pot.

If you did bend the third terminal over and solder it to the back of the pot, you could have a bad solder joint -- it looks connected but it isn't really. It can be hard to solder to the back of the pot, so a bad joint there isn't all that uncommon.

Another less likely possibility is that you added an extra wire from the switch to the output jack. Then you'd have a parallel signal path -- the signal from the pickups would go both to the preamp and directly to the jack. Since the volume pot is connected to the preamp, it would have no effect on the passive signal going to the jack. If you turn the volume all the way down and then turn the midboost knob, if the tone and volume changes you didn't ground the third lug, but if the tone and volume remain the same when the volume pot is all the way down and you rotate the midboost, you have an extra wire in there.


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Post subject: Re: Please help with my Eric Clapton midbooster
Posted: Mon Mar 17, 2014 1:06 pm
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Thanks for the help guys! The problem was indeed the ground connection of the volume pot. This fixed the squealing sound and the volume problem. Thanks again!!!


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Post subject: Re: Please help with my Eric Clapton midbooster
Posted: Tue Mar 18, 2014 7:05 am
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Cool, glad it's working for you.

Missing that ground connection on the third terminal is very common when you start modding guitars. But after you've done it once you never forget again. (Been there, done that.)


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