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    1. · Premium Member
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      I'm actually working on a spring reverb, from scratch, to incorporate in the Vox UL730 amp clone I'm working on. RG Keen spotted me the Vox preamp PCB he had laid out, and accompanying documentation. He's a big fan of those solid-state Vox amps. The two-channel reverb/tremolo preamp stages are all discrete transistor, but the power stage is tube. I'm using a simple TDA2030 power amp chip as my power stage. The board RG sent me is about 1/4 the original size; made possible by the tremendous reduction in thru-hole component size, abandoning eyelets, and conservative spacing. As the pics here show, however - The VOX Showroom - Vox 730 Amp - A Look Under the Hood - Preamp Circuit - the reverb is a piece of crap, and is not one of those things that musicians pine away for. Bulky single spring (albeit long), it uses phono cartridges as sensors.

      One can find longish springs that have the right balance of tension, flexibility, and length in a number of places. I've gotten some at Home Depot and places that carry automotive parts. I picked up some "exciter" units from Parts Express, when I dropped in there a few years ago ( Home ). These are essentially powerful little coneless voice coils, that one can attached to some light moveable surface, via an adhesive pad, to use that surface as the cone. Even the little 3W units I bought work surprisingly well, delivering a wide bandwidth sound with great imaging, when used with the recommended pink insulation panel. (Look up DML speakers on Youtube)

      In any event, the plan is to solder one end of the spring to a piezo disc (I have plenty, of varying sizes), and attach the exciter to the other side of the disc. to "wiggle" the spring. The exciter is powered by a low power amplifier chip - the same LM386 used in so many little practice and headphone amps, and homebrew guitar sustainer units. The main spring that gets wiggled, is connected to a pair of secondary springs, in a Y-configuration. The secondary springs are each soldered at the output end to piezo discs, which feed high-impedance recovery circuits. Preliminary tests reveal that it works reasonably well. The Y configuration uses springs with different tensions. The principle that makes 3-spring units more desirable is that you get a mix of arrival times as well as resonances. The Y-configuration strikes a compromise, by having the two secondary springs stretched out differently. The tricky part for me will be designing some sort of structure to hold and support the driver, sensors, and springs. I imagine as well that there will be some tweaking of the tone-shaping circuitry in the driver and recovery stages. I'm pondering using one of those little PT2399 delay chips to add a bit of predelay to the reverb, but first things first.
       
    2. · Monster Replier
      '97 Strat Plus, '22 LP Studio
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      6,582 Posts
      Discussion Starter · #12 ·
      I'm actually working on a spring reverb, from scratch, to incorporate in the Vox UL730 amp clone I'm working on. RG Keen spotted me the Vox preamp PCB he had laid out, and accompanying documentation. He's a big fan of those solid-state Vox amps. The two-channel reverb/tremolo preamp stages are all discrete transistor, but the power stage is tube. I'm using a simple TDA2030 power amp chip as my power stage. The board RG sent me is about 1/4 the original size; made possible by the tremendous reduction in thru-hole component size, abandoning eyelets, and conservative spacing. As the pics here show, however - The VOX Showroom - Vox 730 Amp - A Look Under the Hood - Preamp Circuit - the reverb is a piece of crap, and is not one of those things that musicians pine away for. Bulky single spring (albeit long), it uses phono cartridges as sensors.

      One can find longish springs that have the right balance of tension, flexibility, and length in a number of places. I've gotten some at Home Depot and places that carry automotive parts. I picked up some "exciter" units from Parts Express, when I dropped in there a few years ago ( Home ). These are essentially powerful little coneless voice coils, that one can attached to some light moveable surface, via an adhesive pad, to use that surface as the cone. Even the little 3W units I bought work surprisingly well, delivering a wide bandwidth sound with great imaging, when used with the recommended pink insulation panel. (Look up DML speakers on Youtube)

      In any event, the plan is to solder one end of the spring to a piezo disc (I have plenty, of varying sizes), and attach the exciter to the other side of the disc. to "wiggle" the spring. The exciter is powered by a low power amplifier chip - the same LM386 used in so many little practice and headphone amps, and homebrew guitar sustainer units. The main spring that gets wiggled, is connected to a pair of secondary springs, in a Y-configuration. The secondary springs are each soldered at the output end to piezo discs, which feed high-impedance recovery circuits. Preliminary tests reveal that it works reasonably well. The Y configuration uses springs with different tensions. The principle that makes 3-spring units more desirable is that you get a mix of arrival times as well as resonances. The Y-configuration strikes a compromise, by having the two secondary springs stretched out differently. The tricky part for me will be designing some sort of structure to hold and support the driver, sensors, and springs. I imagine as well that there will be some tweaking of the tone-shaping circuitry in the driver and recovery stages. I'm pondering using one of those little PT2399 delay chips to add a bit of predelay to the reverb, but first things first.
      And someday I might be smart enough to see that in my own imagination.

      The possibilities are endless and I am extremely excited to begin to see how these things work.

      While I have no idea how you will do what you have described, your elementary description of your idea gives me a sense of what you plan to do. It sounds like a hell of a plan.

      For the here and now, I gotta play some monkey see monkey do so as to gain a LOT more basic knowledge of the interaction of all of these fascinating components.
       
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