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Dean Hillsboro single bass eq question

STANSHEMI

STANSHEMI

Nov 30, 2012
48
20
Pickering Ontario
#1
Hi everyone need some help with something I just picked up a Dean Hillsboro single bass used and i was cleaning it and throwing on some new strings so I decided to open it up and check out the electronics.
Now this is supposed to be a two band eq bass and treble but the eq says 3 band the wires for bass and treble are hooked up but they taped up the wires for the mids . Know to me it looks like I can just drill a hole in the pick guard and add a pot in. My question is one why would they do this second what kind of pot would I use . I have put volume and tone pots in passive bass's in the passed but never in a active system.
Any help would be appreciated.
 
#2
STANSHEMI said:
My question is one why would they do this
Click to expand...

There are many reasons. Firstly, not everyone likes three-band equalization on a preamp. Many people either dislike the behavior of the mid control (frequency center, bandwidth, etc.) or desire simplicity. Second, sometimes you don't have space for many pots.

STANSHEMI said:
what kind of pot would I use
Click to expand...
You will need to find information about the particular preamp.
 
#3
line6man said:
There are many reasons. Firstly, not everyone likes three-band equalization on a preamp. Many people either dislike the behavior of the mid control (frequency center, bandwidth, etc.) or desire simplicity. Second, sometimes you don't have space for many pots.


You will need to find information about the particular preamp.
Click to expand...
Hi the pre amp seams to be stock it does says B&G on it but as far as room there should be enough . They do have signature model that has a three band eq.
 
#5
If no luck contacting the manufacturer, I can tell you that 95% of three-band EQ's are pretty much the same circuit topology. And because your treble and bass still works without the mid pot connected, here's how I'd work it out:

First, check the value of the treble and bass pots. If they are linear then that's also a sign that my theory is correct. Use a mid pot that's the same value and taper - most likely 50K linear.

But which wire is which? You have three wires and three lugs on the mid pot. With the treble and bass controls centred, measure the voltage at all three wires. Two should give you a voltage that is close to half the battery voltage, these are the outer lugs. One wire will not give a DC voltage reading. Connect this to the the wiper (centre lug) of the pot, and connect the other two wires to the outer lugs.

If the pot cuts mids when you turn it clockwise, simply reverse the wires to the outer lugs.
 
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#6
RobbieK said:
If no luck contacting the manufacturer, I can tell you that 95% of three-band EQ's are pretty much the same circuit topology. And because your treble and bass still works without the mid pot connected, here's how I'd work it out:

First, check the value of the treble and bass pots. If they are linear then that's also a sign that my theory is correct. Use a mid pot that's the same value and taper - most likely 50K linear.

But which wire is which? You have three wires and three lugs on the mid pot. With the treble and bass controls centred, measure the voltage at all three wires. Two should give you a voltage that is close to half the battery voltage, these are the outer lugs. One wire will not give a DC voltage reading. Connect this to the the wiper (centre lug) of the pot, and connect the other two wires to the outer lugs.

If the pot cuts mids when you turn it clockwise, simply reverse the wires to the outer lugs.
Click to expand...
OK thanks guys I'm going to pull the pick guard and check the pots.
 
#7
Here's what I mean:
Simple%203-band%20Tone%20Circuit.gif


This is the basic topology for most 3-band bass preamps. Stingray, fender, etc they all use this. (Although, the circuit shown is designed for a bi-polar supply, so for a bass pre, the earth at the non-inverting input of the 2nd opamp will be 4.5V instead.) If you imagine it without the middle pot, you'll see that the outer lugs are connected through resistors to the output of the 2nd opamp. This will be at 1/2 the battery voltage. And you can see that the wiper is connected through a (0.022uF) cap, so you won't be able to measure a DC voltage at this wire.

Simple! :)

Disclaimer: There is a small chance that your preamp has something completely different going on. But really, those wires are meant for a pot, and if you connect one, even the wrong one and with the wires around the wrong way, you won't hurt anything.

Best of luck, and keep us posted!
 
#8
Ok so I measured the bass and treble pots and found the are 50k pots so I wired up a pot for the mids and it works. drilled a extra hole in the pick guard and now I have a three band eq and it only cost me $4.00. Still don't know why Dean would put a three band eq and then sell it as a 2 band.
Thanks for the help.
 
#9
Nice one! Glad it worked out for ya.

I've come across this a few times over the last few years. I guess it's easier and simpler for a company to just get the one circuit board done for several diferent models. I did exactly what you did on a Low End Jazz (if memory serves) 6-string last year. I put the treble and bass together as a stack and then installed a mid pot in the vacant hole. It has all the components on the board, plus three solder pads for the wires, but no pot. The bass was a fretless and the mid pot really made the preamp much better for the bass.

I own a cheap and cheerful EUB that has a circuit with three buffered inputs and three gain trim pots. But the bass only has two piezos - one under each bridge foot. I guess there's a higher model with perhaps a magnetic pickup as well...
 

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