Tech Question - MM JP7 9V Battery Tone

[StreetLethal91]

Hey All,

I'm still very new to my MM JP7 I just bought a month ago. I've noticed that the guitar even with new strings sounds kind of dull and dark. Almost as if the tone knob has been rolled off even though its on full. As I understand, the 9V battery on the guitar helps to power the preamp boost and Piezo system, but does this also affect the tone of the pickups? Are the passive pickups also affected if the 9V battery is low? Considering the simple things first before swapping pickups. I'm not new to active pickups and know when the 9V that powers those are low. Trying to better understand how everything is connected on these guitars before I start swapping parts and throwing money at things.

Thanks!

 

[elvis2]

May or may not. Swap it and see. Also check if the tone knob makes it even more dark, or if it seems to be not really doing anything...

 

[StreetLethal91]

I think I may have found the answer to my question. Looking at a wiring diagram for the JP7 it appears the pickups are connected to an active preamp that controls the magnetic pickup volume and boost. The Piezo system has a separate preamp and volume on a separate circuit. However, BOTH circuits are powered by the 9V battery which explains why things aren't sounding great. Going to replace the battery and hopefully that cures things. Looks like the JP6 guitars again have separate circuits for magnetic and piezo, but only the Piezo circuit is powered by the 9V battery.

 

[elvis2]

So what powers the mag circuit in the JP6?

 

[StreetLethal91]

So what powers the mag circuit in the JP6?

JP6 appears to be a regular circuit that receives power from the input cable. Only the piezo circuit is powered by the 9V battery. Now on the JP15 6-string models, both circuits are powered by the 9V battery.

 

[beej]

The tone of the buffer shouldn't be affected by the battery until it's almost dead. At that point you're going to lose headroom and it will start to sound distorted. Doesn't sound like what you're describing. But certainly worth trying to see.

With the older instruments that had piezos and two outputs, the mag only output isn't buffered, however the other output is. The piezo requires a buffer, and it's also necessary when combining mag + piezos into a single output.

 

[StreetLethal91]

Brand spanking new 9V and she's back to being crunchy and brooooootal!!! Doing the tongue test on the leads of the original 9V it wasn't very spicy, new 9V is very spicy.

 

[elvis2]

JP6 appears to be a regular circuit that receives power from the input cable. Only the piezo circuit is powered by the 9V battery. Now on the JP15 6-string models, both circuits are powered by the 9V battery.

There is no power on the cable. Is it just a passive tone/volume circuit? No buffer or boost?

 

[StreetLethal91]

I also should have mentioned that I was using the mono input most of the time. Knowing now that that input is buffered it explains why the low battery affected the guitar's tone the way that it did. Using the stereo input bypasses the piezo and doesn't use up the battery. I have been using this input now mostly because I don't use the piezo often.