JP15 preamp issues

[bubucci]

Hi guys,
I bought used JP15 guitar and it doesn't play well plugged in. The sound of DiMarzio Illuminators is very weak and somewhat choked. I suspect buffer circuit because piezo works, boost works too and when I plug one ot he pickups straight to amp, it sound much more powerfull and what it should sound. Any tip for bypassing buffer circuit or whole magnetic pickups circuit ?
Thank You.

 

[beej]

First off, congrats on the new guitar!

Ok- you have two output jacks- mono and stereo. When you say, "plug one ot he pickups straight to amp", do you mean using the stereo jack? Plugging a mono cable into the stereo jack bypasses the preamp. That is how you bypass the buffer. So that sounds ok and like you expect?

The mono output mixes the magnetic and piezo pickups through the buffer (and you select which you hear via the toggle switch on the upper horn). You're saying that through this jack you hear the piezo pickups but the magnetic pickups don't sound right?

 

[bubucci]

I tried both outputs with mono cable and it doesn't seems that mono cable in stereo output bypass the preamp. Boost still work on both outputs.
By straight into amp I mean that I de-solder cables from pickup and put them on another cable with jack female and plug into amp.
Is there way to skip the preamp (on the PCB) for magnetic but piezo still working ? I am from Europe so replacement board will not be easy to get.

 

[beej]

If you have a look at the "controls" section on this page, it shows how the outputs are routed:

JP15

The JP15 features a lightweight Okoume body with a figured maple top. Available in Sahara Burst (with roasted maple top), Trans Black Burst, Cerulean Paradise and two new colors, Tiger Eye (with roasted maple top) and Purple Nebula. Each beautiful finish complements the flame or quilt figuring...

www.music-man.com

For the stereo out, the passive magnetic signal is on the tip of the output (directly, not wired through the preamp), and the output from the buffer is on the ring. When you use a mono cable you ground the buffer, so you're only getting passive output. If that isn't sounding right then you likely have a wiring issue and not a preamp issue.

When you unsoldered the pickups, you're connecting them to a cable without the volume or tone potentiometers? Just pickups -> cable? That's definitely going to sound different than the guitar naturally would.

I'm wondering if there's a basic wiring problem with the pickups/pots/etc. In other words, the connections before the preamp.

It's so hard to diagnose this kind of thing remotely, without having the guitar to look at. Can you post a picture of the cavity wiring?

 

[bubucci]

If mag pickups go straight to the tip of stereo out, guitar should play without battery, right ?
I took some pics of cavity amd connections.

 

[bubucci]

Meanwhile customer service give me some advice, I tried connect Mag in wire to mag out to go straight to output and humbuckers as they should have, thick and full. Volume pot doesn't work because it is connected to circuit. Anybody know what value is volume pot and possibility to get a schemtics ? Thanks.

 

[beej]

Hmm ... the soldering of the pickup leads to the boards looks a little messy. I'm wondering if they had been removed/reinstalled prior to your purchase? If that's the case, anything could have happened- would be easy to overheat the board, etc.

If you're already talking to customer service, then you're in the right place. They'll be able to help you more than we can.

 

[bubucci]

Soldering is not perfect, previous owner has changed wiring to fit the original JP scheme with middle position split coils instead push-push pot. But it is not issue because output from pickups switch PCB (white wire) gives full signal if I wire it directly to output (violet wire). This is one of the solution, make the mag pickups independent from active electronic with replacement of 25kohm volume pot for 500k one.

 

[beej]

In any case, it's really hard to know without being able to play with it. But separating the two, as you've said, is a good option if you can't have someone qualified take a look at it. That's probably what I would do too.