makin a reverb tank

[lightningfingers]

can someone explain to me the workings of a spring reverb, and how to go about building one?

thanx

[Mark Hammer]

I have been working on one, and one of these days I swear I will finish it, and post a photoessay and sound clips.

Mine is a miniature unit about 8" long x 4" wide by 2.5" high, or thereabouts.

I am using a loudspeaker for the driver, some very nice springs from the hardware store, and a crustal telephone receiver cartridge for the transducer.

The spring is stretchedbetween the middle of the speaker cone and the middle of the mic cartridge.  An opening is cut in the mic cartridge with a dremel to permit soldering one end of the spring to the middle of the piezo disc.  The other end of the spring is epoxied onto the centre of the cone of a small computer "beeper" speaker or other low power 2" speaker.

The speaker is driven with a suitable driver amp.  Since it is an 8ohm load, either a suitable transformer will be needed, or else one should use an op-amp such as an NE5534/NE5532/LM833 that can drive very low impedance loads, or else a small power-amp chip like an LM386.  The transducer end will need a recovery stage with a very high input impedance, such as a bifet op-amp or a FET preamp.

The two ends will need to be held in place via a mounting bracket of some sort at a distance that does not let the spring hang loose and floppy but does not place too much tension on it either.  

Better commercial units use multiple springs for a more diffuse sound.  This can be mimicked by using a single speaker to drive the unit, but soldering several secondary springs to the main one coupled to the speaker.  So, the main spring can be a little shorter and stiffer, transmitting in a kind of Y-pattern to two, or even more, secondary softer springs, each of which is coupled to its own mic cartridge.  As long as something gets to wiggle the piezo disc for a little while after each note/pulse.

That's basically it.  Forrest Cook has some nice reverb schematics that will work well with this.

[R.G.]

can someone explain to me the workings of a spring reverb

The spring is suspended stretched a bit so it's free to rotate. The ends of the spring have a permanent magnet attached to them.

The input signal goes through an electromagnet arranged around the permanent magnet at one end. The pulsing signal causes the permanent magnet to rotate as it is attracted/repelled by the signal changes.

The rotation caused by the permanent magnet travel down the spring at the speed of sound in steel, about five times what it is in air. The long length of coil gives a longer delay. At the other end, the other permanent magnet is twisted by the spring rotation. There is a pickup coil over this end to sense the rotations of the second permanent magnet. This drives the signal recovery section.

Because the mechanical/acoustic impedance of the ends of the spring are not well matched to the spring, there are reflections of the signal vibrations back and forth down the spring, not just one travel. It's a good analog to sound in an acoustically hard room.

[and how to go about building one?/quote]
The mechanics are included in the above. But the commercial units are available for less than $20, and the degree of integration is far better than hand work can do. You have to figure out if your time is better spent working a few hours at some job or many hours hand making something that might not work.

[lightningfingers]

Thanks!!

where might i buy one online?

[Nasse]

Look for places that supply tube amp replacement parts and accessories

I was lucky, found one inside nonworking old combo amp

But it is of low quality, if you go trough trouble of makin a nice box and reliable design, ready made good ones are not so expensive

Finding suitable thin steel wire is perhaps difficult sometimes. I made diy reverb spring many years ago, I attached a drill in vice and put a suitable small diameter axle in drill and with slow speed fed the steel wire on it, was quite easy. I used a speaker to drive it and a piezo mic (it was me who took the pickup off our recco player, Mother) like Mark Hammer suggests. I had a small one watt chip amp drivin the speaker (about 75 mm diameter from old transistor radio), maybe it helped to compensate the loses in spring, the steel wire was just too heavy gauge and no pre or post eq so it sounded little dull but anyway, it was covered with snakeskin leatherette :oops:

[Ansil]

you know the only problem i seem to have was actually making suitable endpieces for the thing..  i just canibalized an old reverb tank that had no springs. and rehoused it and went to ace hard ware and bought at the time what i thought looked closest to reverb springs..  

ace hard ware ran me aproximately 3 dollars for the materials to do the springs

[Mark Hammer]

Yeah, I was pleasantly surprised by what yopu can get out there without necessitating use of commercial reverb tanks.

Just a few caveats, though.

The decay time of a reverb spring is a function of how long it takes for the spring to stop bouncing around after an impulse is transmitted.  Much like a guitar string, that decay time is a function of length and flexibility.  So, longer springs are better in this regard, and they can't be too stiff.  Of course, outside of reverb tanks, there isn't a whole lot of call for springs that are long and flimsy or highly compliant.  On the other hand, you will note that even on commercial reverb tanks, each "individual" spring is actually two springs soldered end to end.  That solder joint and the small stiff part of the spring that links to the other one provides some stiffness in the middle so that , as long as the composite spring is, it doesn't sage too much and efficiently transmits along its length.  In essence, you get some of the tonal advantages of a longer spring without the mechanical/structural disadvantages.

I've managed to find some very nice suitable springs at Home Depot that, when two are soldered end-to-end, are about 8-9" long, without being too stiff or floppy.  They cost me $1.08@+tax - a nice incentive for experimenting.  I suspect that interested parties will have to go somewhere that has a LOT of springs to choose from though.  Even though I got these at Home Depot, they were not the *best* ones for this purpose, they were the *only* ones that even came close.  Be prepared for letdown; it's not as easy as we make it out to be.

Finally, pro reverb tanks generally suspend the springs on....springs..  Look closely at the housing and you'll see that the spring+transducers sit on a kind of "trapeze, which is suspended by means of much much smaller springs hooked into the corners of the chassis.  This is to isolate the springs from mechanical shocks from speakers, drunks falling on your amp, boot-heel countoffs ("And a one, and a two...") or other sources of undesirable boing.

[Ansil]

Finally, pro reverb tanks generally suspend the springs on....springs..  Look closely at the housing and you'll see that the spring+transducers sit on a kind of "trapeze, which is suspended by means of much much smaller springs hooked into the corners of the chassis.  This is to isolate the springs from mechanical shocks from speakers, drunks falling on your amp, boot-heel countoffs ("And a one, and a two...") or other sources of undesirable boing.

very good point mark i was going to point out that when i had to replace that on a tank once i used an old fender trick..   ball point pin springs..  stretch them out ever so and they are a little more complient..