Diy Piezo Spring Reverb

[mac]

Admittedly it's not the fairest of tests; the steel spring is not a great spring, but it was made in exactly the same way as the copper spring - it demonstrates that doing this in steel without a special machine for it as PRR noted is a semi waste of time - the spring just uncoils all over the place

Looks like a used guitar string
That's why I did not consider steel to make the spring.

mac

[Rob Strand]

That's why I did not consider steel to make the spring.

Most springs in the world are steel.  They use special tools and jigs to wind them.
Copper is more DIY friendly.


[How to make springs:
http://educypedia.karadimov.info/library/springs.pdf]

[moid]

Thanks Rob - the world of spring construction is a lot more complex than I had previously considered.

[mac]

Thanks Rob - the world of spring construction is a lot more complex than I had previously considered.

Plate reverb next 

mac

[moid]

That's how this started! I was trying to build a small plate reverb in a metal box without realising how large they had to be to work when someone here (Duck_arse I think) told me to put some springs in the box instead. I originally tried to persuade my wife we really needed a 2m x1m sheet of steel in our house but she disagreed with that idea (the only place I could see it fitting was hanging from the ceiling in the dining room, but that wasn't her idea of good interior decoration). Anyway I finally assembled my spring reverb today and lots of it doesn't work... I'll put the info in my thread to stop me from cluttering your thread up. Go here if you want to look:

https://www.diystompboxes.com/smfforum/index.php?topic=120755.40

[mac]

Anyway I finally assembled my spring reverb today and lots of it doesn't work... I'll put the info in my thread to stop me from cluttering your thread up.

You can post your results here.

I originally tried to persuade my wife...

"Don't make me choose between you and the plate!"

mac

[Sooner Boomer]

Just throwing out a crazy idea here, but is there any way you could anneal the spring wire?  This would take some of the stiffness and "springback" out of it.  One way to do this would be to wind it on a form (like a steel rod or tube), and heat it in the oven.  About 45 mins. to an hour at 450 F should do it.  This will give it a very mild annealing under stress.  If you want to go full on, you can heat the wire with a torch until red, then allow to cool in the air (don't quench).  This will significantly affect the properties of the wire.

[Sooner Boomer]

One other thing, and please forgive me if I'm overexplaining things; there are three modes of propagation in a spring. 

The first is what I would call a "mass effect" - the wave or impulse travels down the spring, compressing and expanding it, much the way a sound wave moves through air.  I think this is the way most spring reverbs work.

The second method is through the metal (or other material) of the spring at the velocity of sound through that material.  It doesn't matter whether the material is coiled into a spring or stretched out straight.  I don't think this is very usefull to us.

The third mode of propagation is torsional; through the twisting of the coiled spring.  If you had a transmitter and receiver (for lack of better terms) that worked *only* in this torsional mode, it could solve a lot of problems.  It would reduces the effects of outside stimulation (being knocked around) to almost nothing.

One other thing I've noticed.  A stretched out spring that has a compression/expansion wave traveling down it, will have the wave reflected back from the opposite end.  This might be (just guessing) why a lot of the reverbs were made from two springs connected together.

[mac]

I recorded a quick demo of the new version, a speaker coil driven by a LM386, and a neo magnet at one end of the copper spring.
You can see in the video that the magnet is rotated to get torsional and transversal waves. Compression waves, if any, can only stretch the spring because the sewing thread restricts the magnet movement.

IMHO sounds better than the speaker version.

Again, thanks Rob for pointing me in the right direction.

Guitar w/old strings to reverb circuit to small SS amp.

mac

[Rob Strand]

I recorded a quick demo of the new version, a speaker coil driven by a LM386, and a neo magnet at one end of the copper spring.
You can see in the video that the magnet is rotated to get torsional and transversal waves. Compression waves, if any, can only stretch the spring because the sewing thread restricts the magnet movement.

IMHO sounds better than the speaker version.

You have done well persevering and refining that project.
Sounds pretty good.
The only objection is a kind of fast "patoinggg" at about 1:50 in the clip.  Not sure if it's propagation speed or the need for some damping at the ends.

BTW, Nice chords.  The first part reminds me of the things Greg Lake used to play (from Emerson Lake and Palmer).

[mac]

Thanks Rob

The only objection is a kind of fast "patoinggg" at about 1:50 in the clip.  Not sure if it's propagation speed or the need for some damping at the ends.

I played single notes ("Set the controls for the heart of the sun", PF) and reduced the dry signal to emphazise a short delay.
The LM386 output cap is 100uf to filter lows. Lower values can be used to decrease the resonance at low and mid freqs.

About the coil, the LM386 has enough power to drive the small neo magnet (BTW, I did not try a ferrite magnet). I can see it moving.
A second coil can be placed above the magnet to avoid divergence of the field, ie, coil 4ohm - magnet - coil 4ohm. A 1cm diameter cardboard cylinder with a hole in the middle to host the magnet can do it.

As you can see the spring is held tightly with an alligator clip on the piezo side. It's better to solder the spring and the wire together to avoid overheating the piezo.

BTW, Nice chords.  The first part reminds me of the things Greg Lake used to play (from Emerson Lake and Palmer)

"The Sage" 
After the intro I thought to play the arpeggio from film "Crossroads", but instead of sounding like Steve Vai I was going to be more like Ralph Macchio without Willie Brown mojo 

mac

[Rob Strand]

About the coil, the LM386 has enough power to drive the small neo magnet (BTW, I did not try a ferrite magnet). I can see it moving.

Probably best with the neo.  It's actually cool you got the motor efficient enough to be driven by a LM386 - Like the commercial 8ohm tanks need that.

A second coil can be placed above the magnet to avoid divergence of the field, ie, coil 4ohm - magnet - coil 4ohm.

Yep, that would work.

"The Sage"   

So it is!  I haven't listened to that for while.  He used to chew gum and sing while playing that stuff.   Made it look easy.

After the intro I thought to play the arpeggio from film "Crossroads", but instead of sounding like Steve Vai I was going to be more like Ralph Macchio without Willie Brown mojo 

It sounds good anyway.

[mac]

I changed the coil.
As you can see below, I winded the coil around a cardboard former with two holes. One half of the coil is just above the holes, the other half just below.
Total DC resistance is 8 ohms.
The magnet is rotated 45ª to get transverse waves.
The flux is now almost parallel to the former axis.
I am getting a bit more decay.







mac

[Rob Strand]

Looks cool.

[mac]

I tried with two coils again.
I put the coils as shown below to avoid the field from driver to go into the other coil.

The one in the picture has more turns than a speaker and almost 3 ohms. I am driving it with a LM386. The driver could be a speaker coil too.

OTOT, the sensor must have lots of turns. It is connected to the (+) input and to vref.
Much like my Laney LC30 reverb return opamp

Same copper spring.

The sensor magnet is a bit heavy, and the coil is something I had at hand. However, the reverb is there. I can hear a short delay. Highs are filtered because of the magnet though.



mac

[Rob Strand]

I tried with two coils again.
I put the coils as shown below to avoid the field from driver to go into the other coil.

Looks like a good set-up.   The copper spring still looking the way to go for DIY.

OTOT, the sensor must have lots of turns. It is connected to the (+) input and to vref.
Much like my Laney LC30 reverb return opamp

Do you get any difference in hum when you connect the outside or inside of the coil to the opamp input?   (Obviously there's signal phase shift.)

[mac]

Do you get any difference in hum when you connect the outside or inside of the coil to the opamp input?   (Obviously there's signal phase shift.)

Hard to tell if there is a difference,
I live in a main avenue, there are all kind of EM around me.

The copper spring still looking the way to go for DIY.

What about the winding around 6th string?

mac

[Rob Strand]

What about the winding around 6th string?

I know it can be done but I suspect you need a proper spring winder.
What I've seen in the past (an also one of the posters a few pages back) is
everything looks OK when you are winding it.  Then you remove the spring from the
mandrel and it twists up and loses the cylindrical shape.  Some days come out better
than others.

This guy does it without any trouble whatsoever!
https://www.youtube.com/watch?v=XQBbGF4-t4s

The trick seems to be selecting a tube diameter with the right clearance for the
wire and mandrel.