Build spring reverb?

[Guitarist]

I've had some good reverb pedals of late but also heard two real Accutronics reverbs (stereo). This was unforgettable and absolutely killer as they were from a pair of VT-22 Ampegs. having looked over one tube reverb, it wouldn't be that hard to make a good standalone reverb and maybe put it in the rack.
Anyways, today I sold a TC Noca reverb and note that the Hall of Fame looks great but WIDE stereo reverberations are hard to come by ( I even called into their tech support and the "stereo" is more so to preserve prior routing) but a pedal is rather convenient Anyone else mused on this for days?

[Justin Thomas]

I don't think anyone's built an Ampeg-style reverb instead of Fender-style... I prefer the Ampegs myself... sure it wasn't the circuit instead of just the tank? Check it out - no transformers! Just work around the oddball tubes Ampeg used to make many of their verbs - 6U10, who knows what else...

Wish <I> had a pair of VT-22s to take through! Yes, I crank them...

Justin

[Mick Bailey]

I've built a standalone capacitor-coupled reverb that uses a wide range of tanks due to having a MOSFET driver, which eliminates the transformer. The rest is tube. Still needs a little work, though it is finished, cased up and fully working.

[Mick Bailey]

Here's a pic. Still never got round to covering it - it's been on the back-burner for a while now, along with tens of other projects.

[jamesmafyew]

I just finished this reverb last week:



It's transformer coupled into an 8-ohm tank, driven by a 6V6 running in triode mode. I too was interested in a big stereo sound, but went about it differently: this unit has a small 20W power amp (supplied by an old laptop SMPS) so it can directly drive a cabinet with the 100% wet reverb sound. I really really like how big and full that sounds, mixing in the air with a 100% dry amp/cab.

[Guitarist]

That looks and must sound so deluxe eh! Nice build for some series 'verb

[Mark Hammer]

I've experimented with entirely DIY reverbs. And while I really do have to build one up completely, and document the process, preliminary experiments have been positive.

Many hardware stores will carry a variety of relatively compliant springs with a diameter about the size of a pencil. I've bought some at Home Depot, I believe. These can be soldered to create longer transmission times, and pulled to whatever length you like to achieve different compliance and resonant properties. For instance, a person can make a Y, with one "driver" spring branching out to two subsidiary coupled springs, one stretched a little tighter than the other.

The end of the "driver" can be epoxied to the cone of a small speaker, driven by any of the little 8-pin sub-1W power-amp chips. I've cut out some of the cone from the speaker such that the movement of the cone is unobstructed but it moves less air, making it less audible on its own. The spring is affixed to the cap of the voice coil, and the voice coil does the "shaking" of the spring.

At the other end, the spring can be either soldered or epoxied to a piezo disc, whose output feeds a high-input-impedance recovery amp. And that's it, more or less. Yields a very flexible and acceptable quality reverb.

Apart from price, the nice thing about this approach is that one has a great deal of flexibility in design, and a whole lot can be built into a relatively small package. Imagine a chassis that allows you to mount the receiving end on a retractable bracket so that you could adjust the relative tension of several springs, and play with their relative outputs via mixing the levels of their separate recovery stages. There is certainly something wonderful about a 6-spring long pan, but those springs all turn into one single output. What I'm proposing yields far more ammunition for experimentation.

[52 Bill]

I really like the idea of multiple springs with different delay lengths, resonant frequencies and phasing all being able to be mixed separately into one output. Might make for a very complex sounding delay.

I'm not sure how well the speaker as driver will work. There just seems to be too many mechanical/acoustic problems to deal with. Maybe something more like a horn driver.

Please keep us updated.

[Mark Hammer]

Your concerns about use of a speaker as "shaker" are legitimate. All speaker cones are precariously balanced, and have whatever degree of compliance or stiffness is required for them to do the job they are engineered to do. So, some voice-coil caps might be able to survive the mechanical attachment to a spring that I propose, while others would simply dislodge the coil and cone and leave them dangling, damaged and useless.

It is fair to acknowledge that the bandwidth of pretty much any spring-based system will be severely restricted at both ends, simply by virtue of the mass and compliance of the springs themselves. So, a stiff, small-cone speaker, of the 2"-3-1/2" range is probably best suited for the job. Stiff enough by virtue of its size. Not too much bass, and little treble to squander; i.e., if it can do 200hz-3khz, it's good enough.

A horn may have the requisite structural properties...or not. I suspect you have to judge on a case-by-case basis. Keep in mind they are designed with respect to pushing air, and not with respect to withstanding the tug of an externally attached spring.

[jamesmafyew]

I remember reading somewhere that in the usual Accutronics spring tank, the tranducers are actually twisting the springs, rather than pushing/pulling or wiggling. That is to say, the mechanical 'signal' is a torsional wave rather than a longitudinal or transverse wave. But of course now I can't find a source on that.

Does it actually matter whether the spring is being driven with torque/rotation or piston action? My gut says that the torsional drive would be less sensitive to mechanical interference from nearby speakers, but again, no evidence to back that up.

[J M Fahey]

I'll post some pictures of my own made Hammond type twisting magnet reverb tanks.
No big deal, except you need the pencil lead sized hollow magnets, magnetized radially, not axially.

I had to order the proper tiny dies made, get 1 kilo of ceramic magnet dust from the factory, press them (got about 5000 ) and then carefully carry them to magnet factory to have them sintered: cooked in a special oven until ceramic dust melts and each grain sticks to the ones around, into a solid mass: the ceramic magnets we all know and use.

The mechanical part and winding the coils is easy.

[Mark Hammer]

"Artisanal" reverb?

[Mark Hammer]

FWIW, I think your reasoning is sound. My own thinking was simply guided by the principle of: how could I throw something together, cheaply, with stuff lying around the garage? The most exotic component of what I made was the piezo discs. The springs were readily available from several hardware places in town. Transverse transducers might be salvageable from surplus gear, but I have little speakers with stiff cones coming out the wazoo, so that's what I tried.

What I did worked, although there is little doubt in my mind that it could be done better, and maybe transverse is the "better" to be aimed for. Naturally, as with ALL spring-based systems, optimal compliance is the principal challenge (can't be too stiff OR sag), with insulation from extraneous vibration the secondary challenge.

Meanwhile, there are all manner of DIY projects for plate reverb posted around, as well as the Belton bricks, and similar circuits using multiple PT2399 chips. There is always the Panasonic MN3011 and MN3214 multi-tap BBD chips that were intended for the solid-state reverb market, though MN3011s are über-rare and pricey. I've never even seen a 3214 for sale anywhere, let alone a project or product using one; just the datasheet.

[J M Fahey]

Here they are:

[Steve A.]

FWIW Craig Anderton has plans for building a ss reverb on pages 152-154 in the 1978 edition of "Home Recording for Musicians". I built two of them in 1985 and they worked great using the springs from my 1965 Pro Reverb and 1977 Peavy Back Stage amps.

I got the Yamaha 4 track cassette deck with my tax refund in 1985 using the mixer I built from the book. (I had to wait for my 1986 tax refund to buy the Yamaha mixer and patch bay.)

Steve A.