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Re: Modify a Reverb Pan??

9/14/2005 7:09 AM
Mark HammerRe: Modify a Reverb Pan??
For a little over a year now, I've been "threatening" to provide an illustrated exercise in making one's own spring reverb from absolute scratch. Unfortunately, stuff to do keeps piling up and and I haven't been able to finish it. The basics of it are pretty basic, though.  
I was able to score some decent/suitable springs from Home Depot for about $1.20@. They are about 3-1/2 - 4" unstretched, and strike that balance of rigidity and compliance I was talking about. The driver is a simple little computer "beeper" speaker (although I'm toying with the idea of using one of the wider bandwidth units I get from cannibalized MacIntoshes), to which the end of the spring is epoxied. The cone, or at least portions of it, are excised with a sharp x-acto blade. I find giving a light coating of diluted white glue stiffens the cone enough to make it easier to poke the blade through and cut. The idea is to make the driver itself still function like a speaker but be less audible, and hopefully inaudible.  
The receiver transducer is simply a nice big piezo disc. Happily, the end loop of the spring can be soldered directly to the disc. One of the things I'm toying with is using a sort of Y-configuration of springs where a single driver is ganged to a pair of secondary springs and a pair of piezo tranducers. The piezo discs can be of different sizes. Conceivably, between the different spring tensions and different frequency response patterns of the discs, a lusher sound can be gotten. I would qualify that use of the term "lush" since the whole thing would not be much longer than 8-10". Still, the idea is to get something not quite so focussed in its resonances that it sounds irritating. I might point out that the receivig discs themselvs can be positioned in a variety of ways including skewing one off to the side or placing it a little farther back for more spring tension.  
Electronics are simply whatever it takes to drive a headphone (LM386, NE5532/LM833, etc.) and whatever it takes to serve as piezo disc preamp. One of the things I like about the piezo discs is that they provide a really robust output (60mv+) with little effort, necessitating less recovery-amp gain.  
My goal was to produce somethng that would easily suit a small, portable, battery-powered amp. I have a little LM380-based 2-watter that runs off an octet of C-cells and pushes a nice 6" speaker. Such a mini-reverb setup could fit in and run comfortably.

R.G. That's a good approach to getting a... -- 9/14/2005 7:50 AM