3 volumes, one tone

[kk]

Hello all.
I’m looking for some input on a wiring schematic for a hofner ‘style’ violin bass. I haven’t wired it together yet (still waiting for a part) but if any one can tell me if the schematic below will work, I’d greatly appreciate it. I’d like to mention, I really don’t know what I’m doing as far as understanding electronics, but I’m good at following diagrams.

I get allot of flack about this bass… it’s small, it’s hollowbodied, it’s got humbuckers, it’s got a stupid shape, the 60s are over, I’m not paul mccartney, etc… but I love the short scale, non-fender shape/sound and the general punchiness of the thing, so f*ck ‘em. Awhile back I added a PIEZO pickup with an on/off switch that mounts directly onto the floating bridge, it gives it a switchable acoustic bass twang that is pretty useful. The only trouble is that, depending on the amp, the high-treble from the piezo can be too scratchy and requires allot of amp EQing to be acceptable. I thought of wiring in a volume pot for the piezo but instead decided to rewire the rest of the guitar too. (besides: the Hofner bass wiring does not include a tone potentiometer for any of the pickups and I thought that would be kinda helpful.)

The bass has two humbucking pickups and the piezo pickup mentioned above. I am planning on having a separate volume control for each pickup (3) and one master tone control (1). I will leave the on/off switch installed for the piezo.

Take a look at the schematic and tell me if it will work… or if it will work “BUT.”
Thanks!!

[4real]

Welcome to GN2

Hmmm, well I think you have a major problem with the piezo have a huge difference in impedance and loading everything up. I ahve and several others tried some mag/piezo things which you can find and JohnH has done a lot of the background on these things and hopefully will chime in later.

So, bit problem right there that will need to be sorted out as a piezo is not equivilent to a normal pickup and will require some kind of preamp and perhaps mixer and perhaps even some 'eq' on the pre to tame the high end or the like.

A lot of bass forums and such use piezos and many simple bass circuits exist for exactly this kind of application so a wider google search might be in order to see what is available and perhaps why this is an important aspect of any such proposal. Different pot values and such will likely be required, perhaps even preamps on the mags and piezos to work...so not a simple thing and will require a battery!

[JohnH]

These things need some active electronics to get a good result, to stop pickups fighting each other

If your piezo is just the piezo element, then it needs a buffer circuit at least.

I think the best approach is to make whatever passive tone and volume set-up you want with the mag pickups, then take the output of that to a buffer, and have a pot that mixes between the mag and (buffered) piezo, and outputs probably to another buffer.

(a buffer is an active stage with x1 gain)

This is my version, for a guitar:
guitarnuts2.proboards.com/index.cgi?board=schem&action=display&thread=3718

This is a system using a piezo with an inbuilt buffer:
guitarnuts2.proboards.com/index.cgi?board=schem&action=display&thread=4595

John

[kk]

Thanks!
I'm looking into the preamp solution.
But since i'm not looking to have piezo contribute to the sound in any way other than providing a defined hi-freq click noise(and string scratch noise) I'll try some experiments with passive hook ups also.
Currently, the piezo is hooked up passively with an on/off switch to the output jack and i like the "effect" it produces -except- that it is slightly too loud of a click and scratch noise (which can be adjusted via amp EQ).
I'm hoping that hooking up the 500k pot will tame it a bit... I'm also wondering what would happen if i used a 'blend' pot to mix the regular PU with the Piezo.

btw: the piezo pickup is a barcus berry outsider piezo pu which claims not to need a preamp. (but, it sounds much better with a preamp)

did i mention, I don't know what i'm doing.

[4real]

It's not that a piezo cant work on it's own, it will make a noise, though not that efficiently and super high freq...it is the effect it has on the oother pickups is the big worry and they are not an equivilent to mag pups.

One passive solution could be an extra 'jack' for the piezo, separate lead into it's own channel and kept quite separate. Combined with mags, there is no 'passive solution'...

[ashcatlt]

The wiring you've posted will work, BUT...

...what 4real and JohnH said, and...

...the pots are labeled 500 Ohm. Not what you want and not what you've written in your posts, and...

...the tone cap is labeled as 0.047 milifarads. That's a bit too big. Micro is properly abbreviated with the small mu μ , though we usually just use a lowercase u, and...

...you've got the V pots wired "backwards" like a Les Paul. This is good in that it allows you to turn off one or two pickups without killing the whole guitar. Its not so good in that it gives you no way to silence the cable's antenna action. Between songs or on smoke breaks if you turn all three Vs down you wont hear the strings, but you will hear a bit of hum. Don't think there's anything you can do about that without adding a kill switch or picking one pickup which will never get turned all the way down. It may not be a big deal in your situation. Heck, lots of people play Les Pauls!

It seems a little strange that you've run the output from the piezo's pot to the jack, yet collected the other two at the T pot. Electronically its all the same, it just looks a little funny. Shrug.