Piezo and magnetic together - tone knob problem

[Andy G.G]

Hi everybody, new poster old reader here.

It is about my electro acoustic bass recently upgraded with magnetic pick up as in addition to its original piezo one. ⚠ Problem - tone pot on magnetic doesn't work (no change in tone when turned in any direction).

 

1. Piezo.
Bass has original preamp with EQ for its piezo, standard thing:

💡 Note: It works fine when alone as well as after adding magnetic to the same jack output.

2. Magnetic.
I had this idea to put some spare P pickups into the sound hole. Managed to put it there:

Added two pots: 1 vol 1 tone:

Wired them to standard Fender schematics and connected to that stereo jack output to which piezo has been attached, but tone didn't work. Tried all other wiring ideas I found online or in my other basses, but no joy.. This is current wiring:

(Red caps: 0.047uf, 0.047uf, 0.022uf. Green cap 0.0022uf) 💡Note: the same result when green cap is not connected.

💡 Note: Sound is bright and clear no matter how you turned that tone knob.

So I replaced pot, replaced cap, replaced wires, tried different caps (single 0.047,  two same value, two mixed value or 3 as above), no joy..

💡 Note: All that time volume pot (for magnet) and piezo system have been working fine. I can mix their levels no problem, eq piezo no problem.

3. Output jack.
Output wires from magnet and from piezo are connected to a stereo jack originally supplied with guitar:

💡 Note: Preamp for piezo and pots for magnet are not detailed in the picture but are used indeed.

4. Conclusion.
As far as I know all has been soldered correctly, because when testing magnet direct to amp it dumps the tone down nicely as expected (even with 3 different caps and that green one as shown before). However when connected to a jack along with piezo - tone pot stops working and sound doesn't change, tone is not dumped down anymore.

It looks like that piezo system somehow doesn't allow my mag tone pot to dump the high frequencies down to the ground..

Why? How?
I'm sure someone has heard similar story before and solution was found.
Electric gurus please help.
I can't sleep anymore. 
 

[Hellzero]

Suppress the green capacitor, ground the case of your tone control and put a single 22 nF (or 47 nF) capacitor : everything should work. In fact your tone control is simply not grounded...

Making decent solders is also a good starting point. 

[Andy G.G]

2 hours ago, Hellzero said:

Suppress the green capacitor, ground the case of your tone control and put a single 22 nF (or 47 nF) capacitor : everything should work. In fact your tone control is simply not grounded...

Making decent solders is also a good starting point. 

All has been done already.

As mentioned in first post single cap was tried, no green cap was on and tone case was also directly grounded as per Fender schematics. As a matter of fact in current wiring the signal is grounded through the cap to the case on vol pot.

Here are the wirings I have already tried:

💡 Note: Magnet wiring is fine - it works when connected to amp alone (when piezo is disconnected from the circuit).

It only stops working when connected through the jack shared with piezo. So the piezo system is to be looked at.

 

Thanks for the input.

[Ghost_Bass]

First thought is that you have crosstalk between piezzo and magnetic. Either a blend pot for both circuits before sending to the jack or a couple of resistors to avoid crosstalk on the end of each circuit before soldering on to the jack - kind of like the old fender stacked vol/tone circuit.
This is from my mind, haven't spend time investigating those circuits you have there to be sure of what i'm writting.

[Andy G.G]

On 14/06/2018 at 15:40, Ghost_Bass said:

... a couple of resistors to avoid crosstalk on the end of each circuit before soldering on to the jack...

That may be actually a solution. I don't have any resistors handy but have played around with a spare pot - I connected output of piezo into one lug and jack to the other lug while having magnet directly into a jack and all of a sudden tone pot started to work again.

There were some hums as well but it proves that resistor will be an answer. I'll put two, one for each pickup. 

What values do you suggest so I can order them soon?

[Ghost_Bass]

Sorry but i don't know enough about electronics to recomend a resistor value, the ones i used was in a passive independent stacked vol/tone circuit. You have an active circuit there so i can't say for sure the same values would be OK. Best option is to do some searches in the web and try to get an opinion from real techs.

Here's a starting point with some links to help you: 

It's an old thread, so no pictures since the site upgrade but will get you some info on the subject.

Cheers

[Ghost_Bass]

Maybe try messaging @KiOgon on this forum, he does some nice wiring looms for basses, maybe he can build you what you need.

[Andy G.G]

A quick update to the topic.

I've put two 1k resistors between output jack and each of the signal wires.

And it works!

Tone for magnet is now back and running. 🎸🎶

Thanks for hints everybody!

[Ghost_Bass]

Great! I'm glad it worked out