Seeking advice for self-teaching skills for passive conversion

Mar 3, 2024
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I’m planning to convert my bass (an EHB1005F) to a fully passive bass.

In terms of controls, it has one toggle switch and four knobs.

The portion of the planned conversion that I’m most hoping is possible consists of the following controls:
* An On/On/On switch to toggle between serial/parallel/parallel out of phase
* Two push/pull volume knobs, one for each pickup, that toggles between split coil and humbucker on push/pull
* A rotary knob that’s a custom varitone circuit, bypass option included

The last knob I have two ideas for, but I’m unsure based on what I’ve been reading if the interaction between the circuits would have unintended effects on the resulting eq.
The first, and the one I probably prefer to install assuming it won’t interact negatively with the varitone circuit, is a push/pull knob that switches between a bass cut and a treble cut.
The second option is a rotary knob that switches between predefined high/low pass filters. I would install the filter knob assuming the cut knob interacts poorly with the varitone and the filter doesn’t, otherwise I would install the bass/treble knob and only use it when the varitone is bypassed.

With all that said, I’m looking for some advice on building up the base electronics knowledge to understand diagrams and design this myself. There’s a lot of knowledge out there, I don’t have to do everything from scratch, but I don’t want to Frankenstein other people’s designs, I want to understand what I’m doing. I have the Art of Electronics marked down as a worthwhile reference source; if the answer is just buy a book and stare at diagrams until you comprehend them I’ll be a little sad, but I’m up for it!

More confident in the resources I know of with regard to soldering, which will involve practice regardless of knowledge…

If it changes anything, I’m planning on running this converted bass into something like a zvex SHO (high input impedance clean gain pedal). I’m not worried about a little signal loss, just bad interactions from the electronics.
 
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I could lead you down the path of least resistance, but I don't have the time to work on this with you.
So, I'll try to keep it direct and to the point.
If you're doing this project on that bass guitar to learn how things work and educate yourself, go right ahead of course.

Otherwise I'll make some points.
-Active is superior to passive in every way.
-You could simply change your preamp if you aren't happy with the current one that's installed.
-Then add your pickup switching, S/P etc.
-Add a passive/active switch that bypasses the preamp if need be.
-Add a passive tone control or the varitone circuit you mention to the passive mode. Stellertone Tonestyler is a nice one.

If it's output impedance you're worried about, that could be solved with this contraption.
https://reverb.com/item/45178509-dpfx-pedals-impedance-changer-input-output

I've done all of the things you're wanting to try and learn about. It was fun but ultimately a waste for me because in the end I switched to a simple active EMG 2 band setup and have never sounded better.
Granted I had to demo many string types and gauges to get there.

If you use the correct search terminology in this forum, most of the answers have already been given within.
That's how I learned over the years, including lots of trial and error.
I also utilized Google to search talkbass by using this in the search bar before my search term.
site:www.talkbass.com
But you may already know that one.

If you do go down this road and people chime in here to help you. I'd recommend this repository to pick your wiring diagrams from, 322 of them to be exact. Wiring Diagrams

Best of luck.
JL
 
This is definitely mainly an educational project.
In the future, I’m planning on making a couple custom instruments for me and my siblings, and this bass is partially a platform for experimentation.

As for active vs passive, I just prefer the gain to be on the pedalboard. I hate the idea of messing around with batteries forever, even though it’s really not a big pain point! It somehow offends my sensibility. Much nicer when you just plug stuff in…

Regardless.
The theoretical future instruments, I imagine, will be much simpler in terms of controls (one tone circuit, volume per pickup, pickup/pickup combo switch) but I want to try pretty much every passive eq option on this one first (most importantly the Rickenbacker bass cut on the bridge pickup to restore the mids when both pickups are on, or the aforementioned varitone circuit).

Thank you for the wiring diagram link! I’ve been saving as many as I can find, mainly from this forum, and always appreciate more information.
 
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I'm not trying to dissuade you here, but did want to make a few more things clear.

All of my gain is still done from the pedalboard. I mostly use the basses onboard eq to cut, not boost.

A lithium or MAX 9v battery will last ages. It's still just plugging in, except you'll need to plug in a new battery every 3-5 years. That's how long my lithiums tend to last.

An active blend control (superior to passive blend) like on the EMG preamp is far easier to manage than a 2 volume setup when blending pickups.

It might be worth keeping those things in mind once you complete you're project and maybe decide to try active again one day.

Also, as for the wiring diagram link I shared.
Protip: Flickr has on option on there to create and download a zip file of all of the images and diagrams. Once you download that, the image file names make it easier to discern what the diagrams are actually for.
 
Will definitely keep in mind, trying to absorb as much info as I can!

Also not throwing away the preamp, fwiw; if I get through the process and want to put it back in, I’m only out the labor time and some material cost.

In that scenario though, I’ll probably try one recommended here often, like an EMG or Audere preamp.
 
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