Bass guitar and piezo: undersaddle or contact?
 

Hi, I'm a new member to this forum. I'm not strictly a guitarist (although I do have a crap but cute Eko Ranger VI), I joined because you acoustic guitarists might actually be better informed on this matter.

I bought a quirky bass guitar which is nominally semi acoustic and it has a magnetic pickup + a piezo at the bridge.

It's this one, by the way: https://www.italiaguitarsusa.com/wp-...***_ICR_01.jpg

The piezo actually sounds quite nice, if only the E string weren't much lower in volume. The piezo is encased in epoxy inside the arch-top style bridge so it can't be moved or replaced.

So, I'm having a new bridge built for it. The original was just too flimsy anyway and I suspect it is the main culprit for the weak sounding E string, even with the magnetic pickup. (The bridge never stays in place and it is held in place by two tiny screws which are a bit bent). The new bridge will be a full rosewood block, screwed into the mahogany body (it's a plastic top with a mahogany frame + centre block underneath) and with an acoustic-style bone saddle. Action won't be easily adjustable but I don't really need it to be.

Anyway, piezo pickups come in two varieties + two materials:

- undersaddle piezos, which have lots of "volume" but often pick up a lot of string noise
- contact microphones, which I would stick to the rosewood block

Likewise, you can get

- ceramic piezos, which have a high output and are really inexpensive, but tend to have a very coloured response apparently

- metal foil piezos, which have lower output and cost a lot more, but should be much higher quality

Also, you can get piezos in shielded and unshielded varieties.

FWIW, the current piezo preamp has huge volume compared to the magnetic pickup. Having lower volume would not be a problem at all. Also, I could build a probably better preamp if I want (the only challenge is finding an opamp that consumes a low enough current - let's say 3mA for a dual - yet has low-ish noise, especially if I want to implement a charge amplifier that should essentially sidestep around the issue of shielded vs unshielded, assuming it's a problem at all).

Could you help me out?

I'm not following exactly what your question is.

If it's any help, I've built 3 short scale bass guitars and used a Baggs Element transducer under the saddle and the preamp that is part of the Element VTC system. I'm quite happy with the resulting sound.

Fretless bass with Baggs Element undersaddle

I realise I may have been unclear. I want to fit it with a piezo, but I don't know what I should go with.

For acoustic instruments piezoelectric pickups are typically under saddle transducers (UST's) or Soundboard transducers (SBT's). Neither of these are microphones - they're piezoelectric materials that give off a millivolt signal in resonse to strain (vibration).

An UST is made for a fixed bridge flat top with removable saddle, and doesn't look like the bass you're linked to could use an UST unless your new bridge will have a removable saddle.

I've used SBT's in dozens of acoustic instruments from fiddles to ukuleles, all the different sized mandolin family instruments, flat top, arch top and pliage Sel-Mac guitars, banjos and double basses. They work great in these applications. I mount them inside, against the bridge plate or soundboard under the bridge.

Again, the bass you linked to isn't really acoustic - it looks like a semi hollow body. I don't believe you can access the inside by the bridge.

But since you're getting a new rosewood bridge made, you can have piezo's embedded in the bridge. It will essentially function like a UST. There are several bridges made for archtops, mandolins, upright bass, etc. that have this. I'm not familiar with what's available for electric bass guitar but Google can surely help.

IMO the best tone you're likely to get will come from a good magnetic pickup. If the one you have in there isn't working I would look at upgrading that to a dual coil with adjustable pole pieces, and select strings that work best with it.

The new rosewood bridge will feature a bone saddle, just like an acoustic bass guitar (or an acoustic guitar, for that matter). Yes, it's not a true acoustic, and it is essentially a solid body bass with a plastic "casing" (reminiscent of certain instruments in the '60s). There magnetic pickup does work, it's the piezo (encased within the bridge) that works but only on three strings, and it cannot be repaired (and the current bridge is the bass's weakest point anyway). Since I'm actually having a new bridge made, I get to decide whether to install an undersaddle pickup or a contact pickup (that would go below the top, stuck to the rosewood block). The idea is that the piezo would almost never be used alone, and is there to supplement the neck pickup. Still, the nicest tone I can get from the piezo the better, right?

To be more precise, I was looking at the following products:

This:

https://www.te.com/commerce/Document...%7F11026275-00

Or this, with the polymer coating (I have no idea what this does, apart from maybe protection?):

https://www.te.com/commerce/Document...%7F11029806-00

to the fancier, shielded version:

https://www.te.com/commerce/Document...%7F11031263-00

These should all be usable as contact microphones (in a pair, located on the rosewood block, each sensing two strings) right?

Otherwise, I could go with a piezo cable, and fit it under the saddle, like the Baggs Element:

https://www.cbgitty.com/guitar-instr...rument-pickup/

I've experimented a little with the film type piezo elements, they really need to be under some pressure to have good sound and output, like under the foot of a floating bridge for example. Simply stuck to a surface they have very low output.

SBT dots and UST are both widely used and work well. Dots give you more flexibility in location if you want to experiment with tone. One should be all you would need. If you go the UST route you might consider:

https://www.amazon.com/Replacement-S.../dp/B07KX9T8PH

Also MGB in Florida has a whole bridge assembly exactly as you’re describing for $20 but currently out of stock.

I’m guessing the preamp you’d build would be onboard since you’re looking for low current. Artec makes several prewired circuits specifically for blending piezo and magnetic pickups, the MB__ series, that could be worth investigating.