experiments in DIY pickups, part two
A couple of months ago, I built a Zeppelin Labs cortado instrument pickup from a kit. I ended up using it on stage, attached to my octave mandolin with a plastic clamp.
It worked well enough, but needed a fair bit of equalisation, plus there was that whole “giant blue clamp” thing. It also had a fairly metallic sound, which is either good or bad, depending upon what you’re looking for. In this case, that was good, but that’s not always true.
So I had an idea - I’d try to work around all of the above by building a second pickup, with this one’s piezo disc affixed to a hardwood plate. To do that, of course, I’d need a new bridge for the octoman, just so the strings wouldn’t be pushed super-high up in the air by the addition of the plate. Fortunately, those are cheap on eBay.
And now I’ve built it. To wit:
It’s Alive
Installed on the octave mandolin
I was hoping for something akin to the sound I got with the clamp… no. That’s not true. That still had issues. No, I was hoping for the held-down-by-hand sound, the best sound I could get with version one, which I could get no other way, and thus no useful way, since I kind of need my hands to play the instrument. They’re too busy to also press the pickup plate onto the face of the octoman. Hence: this approach.
The result… it’s better. But I didn’t quite get there. I didn’t even get the amount of bass pickup I did with the clamp solution on the first pickup. But what I did get was a more naturalistic sound, and more importantly, a better curve of sound, one that I could get into the area of live sound with a simple single-point parametric equalisation curve.
That curve looks like this. Simple, clean, ignore the red line (unrelated) and the small jagged spikes (room noise):
Simple… but kind of a lot. (+19db peak)
Here’s the riff from “Thirteen,” played back with that single curve added. If you want something in more normal octave mandolin tuning, here’s a short bit of Pirate Bill, played with medium force. I find this instrument really uncomfortable to play in GDAE, so forgive the shakiness. I really don’t like the way the fretboard works on this thing.) No other processing, including compression; those are just the raw recordings plus that one EQ point added.
It’s not where I hoped to get, but it’s pretty good - particularly for live. I think that the clamp - and my fingertip, holding the pickup down directly - has been damping down the high end, the higher frequency sounds. The pickup still needs EQ when I do that, just less, and this has the advantage of being… well, it’s a large shift, but a simple one. That has major advantages in real life.
Part of the problem is, honestly, that these little discs are really sensitive, which is good, but that sensitivity starts falling off pretty hard below 300hz. They still pick up the sound, but not nearly as strongly. That in turn implies that the dampening approach might be best, but that has its own problems, even if the idea of building in some sort of adjustable pressure device is kind of hilarious. And… maybe worth trying anyway, actually. Hm.
Regardless, given that the amount of LOUD in this kit is very goddamn high - it’s very sensitive, with a nice low noise floor - I’m wondering if a low-pass filter in the pickup circuit hardware itself would be the best approach. Sure, you’d lose some signal, but it currently needs so little amplification that a subtractive approach might just be… fine.
After making those recordings, I added some tape to hold down the cord - wouldn’t want to yank that cable off the kit, now would we:
I’ve got one more of these kits, and I want to build a boundary mic with it. And I’m wondering whether I can add such a filter directly onboard. That might be all it needs.
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