Head Scratcher

[TBurst Std]

OK. I had the preamp in my EB MM Stingray bass replaced with a John East preamp. Originally it is 18V supplied. Reading installation notes, it requires splicing the leads to the existing power supply. (I can grab that info if you need it). Anyways tried it for the 1st time yesterday. Dead as a doornail. Pulled the batteries. The upper one was 1.7 volts. The lower 9.3 volts.

Yanked those out and stuck 2 new ones in it about 3PM yesterday. I pulled them today at about 4PM: The left one is already 8.3v. Right one at 9.3.

Something is WRONG. And I have a gig Thursday. Already decided I'll use the Spector or Ric, but what is causing this wiring gurus?

I have to presume something in that splice, but what am I looking for so I can explain it? Or is it the jack negative is grounded? Or is there a short to ground. Something is causing the circuit to stay on while unplugged.

 

[DJ Bebop]

You might have the battery leads going to the jack backward. When it is, it drains the batteries even if it your cord is unplugged from the bass.

An internal bass preamp must be wired to a stereo (TRS) output jack. This jack acts as a power switch to prevent the battery from draining when not in use. Solder the connections as follows:

• Tip: Connect the main audio output wire from the preamp (usually white or colored).
• Ring: Connect the negative/ground wire from the battery clip.
• Sleeve: Connect all circuit grounds, including the preamp ground wire, pickup grounds, and bridge ground.

 

[TBurst Std]

Thanks. I just noted that to the next person to get it right. I waited 3.5 weeks for the previous guy to do it, and this what I have been left with.

 

[TBurst Std]

OK WAIT!!!!!!
The jack is prewired to the assembly by John East. I am trusting what they did. The only oddball thing to do is splice their single battery clip to an 18v system.

As that's
18V Series Wiring Steps

• Battery 1 Positive: Connect the Red (+) wire of the first battery clip to the Preamp Power Input (+V).
• Bridge Connection: Connect the Black (-) wire of the first battery clip to the Red (+) wire of the second battery clip. Insulate this connection with heat-shrink tubing.
• Battery 2 Negative: Connect the Black (-) wire of the second battery clip to the Stereo Jack Ring (R) terminal. This serves as the automatic power switch when a guitar cable is inserted.

AND
things are simply connected wrong at the insertion of the board of GND, OUTPUT, 9-18V+VE?

 

[DJ Bebop]

Thanks. I just noted that to the next person to get it right. I waited 3.5 weeks for the previous guy to do it, and this what I have been left with.

I bought a new bass that came that way. A few folks bought the same bass with the same problem. It was discovered that was the problem, the batteries leads were reversed to the plug. The trouble is, the bass still works that way with the wires switched. A harder problem to detect when the bass works regardless.

It is an easy fix. We all fixed them ourselves.

 

[TBurst Std]

reversed to the board?

 

[TBurst Std]

I just opened this up and it looks NOTHING like the diagram online, There are boards and connections not even reference in John East's material online.
Any help desired. I'd rather not pay for bench time.

My soldering skills suck due to focal dystonia. if its only inserting a wire into a board, I can handle that.
I'll take a look at the documentation it came with. YES I know should have done that 1st.

 

[TBurst Std]

Well that was a quick trip to no where. No documentation included.

 

[DJ Bebop]

reversed to the board?

The batteries leads to the plug. On ours it was the negative battery leads were connected to the sleeve instead of the ring, and all of the circuit grounds, including the preamp ground wire, pickup grounds, and bridge ground were connected to the ring. So in our case we had to switch them. Tip has the main audio output.

So you need to check to see if your two batteries are linked together as described in what you posted and the negative battery lead is attached to the ring and and all of the circuit grounds, including the preamp ground wire, pickup grounds, and bridge ground are attached to the sleeve

 

[DJ Bebop]

Well that was a quick trip to no where. No documentation included.

I don't know how many knobs yours have. I found this:

https://www.east-uk.com/wp-content/uploads/2025/05/MMSR-3K-2B-02-1-2016-09-09-disposal.pdf

And this:

For the John East MMSR Music Man preamp, pickup wires connect via bare pins on the bass/treble circuit board (often labeled BTB-MM). For standard parallel pickup wiring, solder the black and red wires to the positive "hot" terminal, and the white and green wires to the negative "cold" terminal. [1, 2]
Exact wiring diagrams and manuals depend on your specific knob configuration:

• 3-Knob, 2-Band: Review the East UK MMSR 3-Knob 2-Band Diagram.
• 3-Knob, 3-Band: Use the East UK MMSR 3-Knob 3-Band Diagram for mid-sweep controls.
• 4-Knob, 3-Band: Follow the https://www.bestbassgear.com/wiring...jchYO8r8ybNziz1jjkPOP4TtoNWwJ2rkGjiI4apZbZVcY

 

[TBurst Std]

It’s the 4 knob. V, T M with freq range, B

 

[Theobald]

Can you measure the voltage between the red wire of the first battery and the black wire of the second battery? It should be around 18V. If it is 9V, either one of the batteries is not connected at all (the 2nd, I suspect) or they are wired in parallel.
Also, a few pictures would be helpful.

EDIT: also, unplug your bass when not in use. This avoids unwanted drain. I also had issues with a John East preamp sucking all battery power super fast because of a grounding issue in the cavity.

 

[mikecd1]

As stated by others above, the ring on your jack has to be the battery negative and the 18 volt battery pack wiring should look something like this. I can't imagine that preamp has any proprietary jack parts. From left to right in the photo with the bottom of the jack in view its tip on left, sleeve in middle and ring on the right. Hope this helps. It sounds like a wire is going to ground causing the drain.

 

[TBurst Std]

That was the issue. My old luthier sorted it out in a day. Second battery not wired correctly at all. Ground wire wired to sleeve, not ring.

 

[Theobald]

Enjoy your John East preamp ;-)

 

[TBurst Std]

Well it's NOT sorted out. Haven't had a chance to try it until yesterday. Batteries dead, Replaced them. Still doesn't sound right. No punch of sizzle: very dull sounding. Taking it to another luthier.

 

[TBurst Std]

Well that luthier turned down the work. He doesn't touch control boards (blames it on his soldering gear).
So back to the original guy I sent it yesterday.

 

[TBurst Std]

Well just got a call from them. Appears the ground circuit wasn’t presented correctly in documentation. They engineered it and redid it. Says it’s working on both batteries and has no additional drain. Also as he is not a bassist, he has a studio bassist friend of his play it and says there’s a huge range of tone. Unfortunately they did not listed to it before, but before it sounded like some foreign $10 garage sale bass find with 40 year old crap flat wounds. No typical Stingtay sound. Fingers crossed

 

[TBurst Std]

The whole purpose of this venture was to be able to switch tone by simply changing the frequency of the mids.