Cort/Curbow 4 Bass with Mighty Mite pickup/preamp

[dporto]

Is anyone familiar with this bass? I've had it for quite awhile but it has never worked (long story...). Anyway, I finally got around to trying to fix it and from what I can find it's an early model with a passive pickup (Mighty Mite) and an active pre-amp. The only schematic I've been able to find is for a later model with a Bartolini active pick-up. Hence the schematic is quite a bit different from what I've got. Mine has two connectors (one five pin and one six pin) and two micro adjustment pots for mid and bass boost. The schematic for the Active Bartolini pick-up has two six pin connectors and a three pin connector with no mid and bass pots. Ive tested the pick-up and it works (it shows 11.8k resistance). I hooked it up direct to the output jack and it sounds fine, just no tone controls. I've traced the ground through the pre-amp and it's all good - beyond doing that, I'm flying blind since I don't have a schematic. Short of getting a schematic or new pre-amp I'm thinking about just running the pick-up passive, but I'd need some cap values for the tone controls...Any ideas would be greatly appreciated!

[Jazz P Bass]

If you are repairing the preamp, I would look at the ic output pins.
I usually find either bad ic's or failed coupling caps.
(along with cheesy soldering )

[dporto]

Ok, thanks... I'd like to repair it, but I haven't had any luck with re-soldering. I don't have any clue where to start troubleshooting without a schematic. I sent an email to Cort/MightyMite...we'll see what happens...

[Jazz P Bass]

I don't have any clue where to start troubleshooting without a schematic.

Very basic preamp troubleshooting.
First, you have to identify the input pin & the output pin.
(i prefer to draw the little board)
This is the start to getting your bearings around the board.
Identify the voltage pins. + & - Vdc.
An often proven tequnique is called "Divide to Conquer".
Do you have the proper voltages?
Insert a signal.
Do you have the signal at the signal in connector?
Do you have signal at the output connector?
Then you jump right to the middle.
Start on the IC's.
Pin 1 & pin 7 should both sit at 1/2 the power supply. (Vdc)
If that is true, send through a signal.
The output pins will then vary there heighth. (Vac)
Or they won't.
If they do, you move on.
If they do't, you find where it is failing.

[dporto]

Hey, Thanks again JP! First, I don't have an oscilloscope (I know that makes thing a little more difficult) so I'm just working with the output of the bass pickup - it would be so much easier if I had some visual feedback... In any case, I appreciate the help and will follow your outline for "very basic troubleshooting"

[Jazz P Bass]

Yeah, a scope & a signal generator would be ideal.
Then again, you are not repairing a "crappy sounding" unit.
This is were a multimeter will help you.
Check the dc voltages.
Then apply a signal & look at the output pins with the meter set on volts ac.
If the IC's are doing there job, then you could start looking at electrolytic coupling caps.
If they are at fault, what you will see is a good signal on the input & a bad (or nonexistent) signal coming out of the cap.

[dporto]

Damn you're quick!!! This is an onboard bass pre...everything is TINY!!! I literally can't read anything on any of the components so I can't even tell what's a resistor or a capacitor (everything looks the same) I can see at least 1 IC (I think it's got 8 pins IIRC) and I was able to determine which one was the ground...That's about it so far. I'm getting ready to dig back in (hence being online...) so wish me luck! Thanks again

[dporto]

So I've done a little more sleuthing on the preamp circuit board (with a magnifying glass this time)... it contains

1- IC # TLO 62C, 85T, D6XC
8 - ALY ... are these Caps?
1 - D105
several #'d components - 304, 394, 000, E81, 105, 154, 132, 202... caps?
several colored components - green, brown, lilac - resistors? no stripes just different colors
There is also a B+ disignation on one of the pins of the multi-connector... I assume this is the input voltage from the 9V battery?

[Jazz P Bass]

If that IC is has a standard pinout you will find pin 8 is the power pin.(B+)
Looking down on the IC, there is a dot or some marking at one end.
Using that designator, facing north, the pins are numbered from the top left (pin 1)down the left side (2, 3 4) then around to the right side (south) pin 5, 6, 7 8.
Pin 1 & 7 will be your output pins.

[David Schwab]

Instead of going through all that. I'd just replace the preamp.

The Mighty Might stuff is pretty cheap. You can find equal quality preamps on eBay for cheap, mostly made in Asia. Of you can get something a little better. The Kent Armstrong preamps are nice, and bot a lot of money.

[dporto]

Instead of going through all that. I'd just replace the preamp.

The Mighty Might stuff is pretty cheap. You can find equal quality preamps on eBay for cheap, mostly made in Asia. Of you can get something a little better. The Kent Armstrong preamps are nice, and bot a lot of money.

Yhea, if I was just fixing this for someone, that's what I'd do. In this case I'm trying to learn a little/lot in the process. In addition, I haven't been able to find a direct replacement for this particular preamp. If I could it would be really nice and easy - there isn't even a model designation on the board itself In any case, I may do that eventually, but what I've done in the mean time is to experiment with some capacitors (some that I had lying around) to create a passive tone circuit. It's not exactly what I would want, but it does give me some control over the tone...

[Mike Burgundy]

Just stumbled across this - how did it turn out? I wouldn't be at all surprised if what you have is what is available somewhere on the net as the Tobias preamp. I have a Toby pro5, which has that exact preamp and it is a mighty mite.

[dporto]

Just stumbled across this - how did it turn out? I wouldn't be at all surprised if what you have is what is available somewhere on the net as the Tobias preamp. I have a Toby pro5, which has that exact preamp and it is a mighty mite.

Hi Mike,
I was never able to find an exact replacement for the preamp despite some pretty intense searching. It's ironic that the Tobias uses the same pre. Do you know if that part is still available? If so, where from, part # etc? I'd love to replace it because although the Bass is usable at this point it's not very flexible sound/tone wise. Thanks

[Mike Burgundy]

I'm not sure if it is the same though, I just know the Toby has what I recognise as a MM. Is it this one perhaps?
www.MightyMite.com (Edit: go to electronics/bass solutions/bass pre)
Did you get around to measuring voltages (starting with all IC pins)?