Self contained small DIY spring reverb

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Here's a little project from the last couple days. I almost posted this in the lounge, but I suppose it is close enough to a stomp box to post it here...

Here's a clip of it in action:
http://www.youtube.com/watch?v=dIIYrrs6c8E
Controls left to right are: straight gain, reverb input volume, reverb output volume, dry/wet mix.

Here's the physical setup of the spring/exciter/piezo in the box:


I don't have schematics, but here is the layout I used, I omitted panel wiring for clarity.


And here is a description of what's going on"
1) Input comes in and is split to two JFET gain stages based on Tim Escobedo's utility boost
2) One gain stage goes to the output for the clean mix - this stage has a gain control on the front panel.
3) The other gain stage goes to a voltage divider volume control for reverb driver input level
4) Volume control from #3 feeds into a 386 amp circuit set up basically in a standard datasheet setup
5) 386 feeds an "exciter" (see the "transduce anything" thread on this board) which is directly glued/soldered to a thin wire spring (see pic)
6) Piezo is soldered directly to spring (see pic)
7) Piezo signal brought back to the circuit board and goes through another boost stage, with a pretty small cap on the front to filter out a lot of low frequencies (something I may modify or add a switch for as it is a little thin for my tastes right now)
8) Piezo gain stage mixed into a standard "blend" control with the straight signal for wet/dry mix.
9) I've also included voltage regulation on board to clean up wallwart noise as that is the type of supply I use.

Gain stage schem, for those interested - it's a great simple circuit for amplifying mics, guitars, piezos, line signals as well... stays pretty clean up to the last 20-50% or so, depending on what is coming in...

[John Lyons]

COol! Mechanical reverb is a lot of fun.
You could probably add a spring or two to add complexity to the
sound. A lighter weight spring will excite easier and resonate
more freely. fun fun fun

[Mark Hammer]

Kudos for actually doing it.

I've had a couple of different versions of something like this sitting disassembled for a couple years.  I keep meaning to finally put the damn thing together into a package, but just never got it together.  Preliminary tests indicate that it CAN work, and your demonstration confirms that in glorious dinkiness.

My own spring arrangement is a small speaker epoxied to the spring driving it, and piezo telephone receiver mic cartridges soldered to the other end.  Where it differs is that I have a Y arrangement with the principal spring driving two secondary springs, with all of them soldered together at their junction.  There's juuuuuust enough rigidity to keep the 3-spring arrangement from sagging too much.  The nice thing is that you can get a longer decay by cascading springs, and a richer reverb sound by having different arrival times.  The springs themselves were about a $1.20@ at the hardware outlet, and are about the same length as yours.

BTW, that's some tricked-out SK-1 you got there!

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Yea, you are right John and Mark, I had thought of adding a second spring. This is just what I had on hand though.

The one I used is actually pretty thin wire despite the large loop. It is actually from one of those "echo mic" toy reverb mics.

I've built one other reverb similar in the past (though larger and with no mixing circuitry) and it was a heavier spring and had poorer HF response.

If I come across another spring it could easily be added to this setup.

[JKowalski]

Neato!

I have a special springs drawer in my mechanical parts organizer just for this kind of thing, if I ever get around to it. I was thinking of super-miniature two spring arrangement. Just haven't thought of an elegant, cheap-y way to drive the springs yet.

[Top Top]

an elegant, cheap-y way to drive the springs

$1.99/pair ($1 per exciter!)
http://www.parts-express.com/pe/showdetl.cfm?Partnumber=309-148

Or is that not mini enough?

Some people also use a DC motor driven by an audio amplifier. I've seen it but never tried it.

[JKowalski]

an elegant, cheap-y way to drive the springs

$1.99/pair ($1 per exciter!)
http://www.parts-express.com/pe/showdetl.cfm?Partnumber=309-148

Or is that not mini enough?

Some people also use a DC motor driven by an audio amplifier. I've seen it but never tried it.

Thanks for the suggestions but yeah, it's not mini enough.

I might end up winding a tiny transducer. I have these two small springs that will be stretched out to around 2-2.5 inches, both are the same diameter but with different tensions, should offer a little more complexity in sound. What I have in mind is hooking them both up to a small metal rectangle plate and driving the plate, picking up the sound off the other plate.

[Top Top]

What about speakers from a pair of earbuds?

Could potentially be used as transducers on both ends, though will be somewhat microphonic on the receiving end, which is probably no good. Piezos are cool that way - don't have to worry about vibrations in the air.

Or could just use the type of transducers traditionally used in spring reverbs. I don't know any specs on them but they are pretty tiny when I look in the commercial tank I have.

[jasperoosthoek]

I really like this! Real spring reverb in a normal size stomp box. 

Every time you turn it on you get stuff like this: http://www.youtube.com/watch?v=F7U4V8T1VmI (at 0:14 for instance).

[gtudoran]

 I think that you could use a small headset for an exciter (to fit it in a BB type box)... just a thought. I will give it a try this night, and also you could use the other pice of headset as a input transducer (to replace the piezo element).

Best regards,
Gabriel Tudoran
Analog Sound

[jasperoosthoek]

You might be able to use two springs that hang on a little seesaw. This allows you to double the spring length and have some mass in the middle, like most regular spring reverbs.

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Every time you turn it on you get stuff like this: http://www.youtube.com/watch?v=F7U4V8T1VmI (at 0:14 for instance).

Can't see it due to some restrictions? Says it's property of Sony and can't be seen in the US? Weird.

[gtudoran]

Ok... made a test, used 2 pcs of a stereo head set, and a preamp with 3904 for the transducer... what can i say... it's working like a charm. I will put this week some pictures with work in progress and some samples anyway thank you a lot for the kick start.

Best regards,
Gabriel Tudoran
Analog Sound

[jasperoosthoek]

@Top Top

Hmm, sorry. It's medeski martin woods and john scofield. A song called 'telegraph' on the album 'out louder'. If has some reverb tank banging in it ;-). Good album btw .

[JKowalski]

This is what I was thinking so far, with the materials I have. It's pretty much the same layout as a normal reverb tank - the magnetic rings on the spring ends, vibrated between the air gap of the EM. I just wound the coil real quick - 12 ohms. The pickup will be the same. The whole thing will be in a little folded aluminum box, like a normal tank. The iron core will be fixed to the sides of the tank, so picture the size as the size of the entire core plus a little room underneath for the springs.

TO-220 for size comparison

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Ok... made a test, used 2 pcs of a stereo head set, and a preamp with 3904 for the transducer... what can i say... it's working like a charm. I will put this week some pictures with work in progress and some samples anyway thank you a lot for the kick start.

Best regards,
Gabriel Tudoran
Analog Sound

That is great man, can't wait to see/hear it. What did you mean about 3904 for transducer? You used a 3904 transistor to amplify the headset input to drive the mini speaker?

I am always amazed when something so simple can sound good.

This is what I was thinking so far, with the materials I have. It's pretty much the same layout as a normal reverb tank - the magnetic rings on the spring ends, vibrated between the air gap of the EM. I just wound the coil real quick - 12 ohms. The pickup will be the same. The whole thing will be in a little folded aluminum box, like a normal tank. The iron core will be fixed to the sides of the tank, so picture the size as the size of the entire core plus a little room underneath for the springs.

TO-220 for size comparison

Great, can't wait to see it all assembled. How tight is the tension on those springs?

@Top Top

Hmm, sorry. It's medeski martin woods and john scofield. A song called 'telegraph' on the album 'out louder'. If has some reverb tank banging in it ;-). Good album btw .

Right, I'll check it out. Some surf bands used to use it as an effect and it's in some beach boys songs as well.

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I ended up adding a tone control (big muff type) between the piezo and the post reverb gain stage, and putting a bigger cap on the gain stage following it... helps get some different reverb feels (nice deep murky or more bright/springy like it was before, or in between)



...oh and some "graphics"

[Jaicen_solo]

Any chance of some more demo's, Perhaps on guitar this time?

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Any chance of some more demo's, Perhaps on guitar this time?

Yea, I'll try to put up another one tonight with more instruments.

I also realized that the cable I was using to go from 1/8" to 1/4" was canceling a lot of the sound of the SK-1, so the sample I uploaded sounds a little weak.

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Here's a clip with a guitar

Sorry, not the best recording -- something is rattling somewhere, might be my amp.

http://www.youtube.com/watch?v=72DoW85l_eo