Author Topic: Acoustic to electric conversion  (Read 259 times)

Offline Dobly

Acoustic to electric conversion
« on: August 15, 2017, 12:27:58 AM »
After the recent and raging success of my DM10X pad conversion (here)

http://www.alesisdrummer.com/index.php?topic=7136.0

I was encourage to try a similar conversion on an acoustic snare drum.

Some of you may recall a couple of years ago I found a kit on the side of the road that someone was throwing out. A very very badly rusted and unloved kit. I spend hours removing rust and even longer converting them to electric with a metal disc system like in my DM10 kit when I first got it.
That mod took hours, was complex and did not work all the great. (it was just ok)

This mod below is simple and works great. Perfect infact.

Once again I employ the 'fulcrum' technique that worked so well on my DM10X conversion. I was sure it would work here too.

First I got a scrap bit of angle metal that I had laying around. You can do this mod with anything. The idea is you need to create a platform to set the fulcrum system on. You'll see below.

I measured up and cut some holes in it.



And mounted it on an L bracket attached inside the shell.



In that photo you can also see the rim piezo and that I have mounted the socket for the stereo plug.

Next with a ruler across the rim and a wooded skewer I measured the depth of the the base to the bearing edge.



I carefully marked the skewer and measured the depth.



56mm.

I then did some simple maths..

I know that the rubber (neoprene maybe) is 6mm high.  And the piezo will site on top of 2 of them, with one on top.

So, I subtracted the 6, then another 6 and added on 2 for the height of the piezo.

46mm.

I next cut a piece of K-Flex rubber as best as I could to 46mm. To cut K-flex I've found the best way is to hold a Stanley knife razor by the end



... and use a short fast sawing motion to cut it from top to bottom. Don't stop half way. Cut right through in one go. Do your best to keep the cut square so your k-flex is level when adding the stuff on top.

Once I had the K-Flex cut I used double sided tape and some scissors to assemble  the fulcrum tower (for what of a better term).



The rubber on top is around 3 to 4 mm above the bearing edge.

Finally I whipped out the soldering iron and wired it up.



And here is a shot of the snare mounted next to my DM10X kit for testing.



Once again this fulcrum system is a major success.. Thanks again the member ignotus for telling us about it.

The drum feels great to play. No crosstalk, no hotspots and dynamics from the softest practical hits to the hardest hits.

This mod as turned a rubbish, rusted, found on the street snare drum into an awesome electric drum.

Note as I used the unloved drum on this mod I took some shortcuts drilling holes in the shell etc.. If this was a nice wood grain kit with a beautiful finish I would not do it like this. The main point of this post is to show you the principles of the mod. You can work our your own way to mount the fulcrum tower.

If any of you do try this mod please post some photos here.




« Last Edit: August 15, 2017, 04:22:16 AM by Dobly »

Offline Dobly

Re: Acoustic to electric conversion
« Reply #1 on: August 15, 2017, 09:41:02 PM »
Update

I made the mod shorter..



This makes the mod more stable. Also show how versatility this mod is.

Offline Dobly

Re: Acoustic to electric conversion
« Reply #2 on: August 16, 2017, 02:21:47 AM »
The 'Fulcrum' system and why it works.

The method I used in the mod above works because of the way the piezo is being held. It's call the Fulcrum system. A name I got from ignotus, a member here who showed me the system.

I've done this image to try to explain it.



When you hit the head the 'force' that stroke moves to the outside edge of the head and down onto the rubber on top of the piezo. The force there is much less than you hit the drum with as you can imagine. However the force out there is perfect for a piezo.

The force moves down and triggers the piezo.

If the piezo was sitting just on a rubber base, the force of the hit would most likely move down into the base and most likely trigger the rim piezo.

In the fulcrum system the force gets dissipated. Only the edges of the thin metal peizo are attached to anything. When you think about it, how much 'force' could you pass through that tiny amount of metal at the edge of a tiny fragile piezo?

The fulcum system works both ways. Force from the rim piezo will hit the rubber base, might make to the 2 rubber bits under the piezo, might get a breath of the force into the piezo, but not enough to trigger.

There is NO crosstalk here between the head and rim. And the responsiveness of the head is beautiful. I'll do a video soon.



Offline ignotus

Re: Acoustic to electric conversion
« Reply #3 on: August 16, 2017, 05:51:56 AM »
Ha ha! I'm glad the system has such an enthusiastic adherent! Some nice graphics skills there; I have to resort to scanning crude hand-drawn sketches...

Just to add to the points you make about how it works, my explanation is that with traditional assemblies, as the piezo has a larger surface area coupled to the foam and is held more rigidly, more mechanical energy passes straight down through it and a smaller fraction is converted into electrical energy through vibration. With this system, as it is allowed -and made- to flex more, a larger amount of mechanical energy is absorbed by the piezo (remember that according to the law of conservation of energy, it has to go somewhere) and converted into an electrical signal, thus leaving less energy to travel down towards other parts of the assembly. This is also why it's so sensitive.

Not to undermine your explanation but just to add some insight as to how it works.

Keep up the fine work!
« Last Edit: August 16, 2017, 05:53:48 AM by ignotus »