I have an old spring reverb of unknown brand and impedance that I would like to use as an outboard effect, essentially sending signals to it from a mixer as a FX send or from my audio interface.
My understanding is that spring reverbs need to be amplified in order to get a good signal from them. Or is it vice versa, that the signal needs to be tamed down?
So my questions are:
Is it the in or out of the reverb that needs amplification or taming down?
Are there any universal solutions to this that works without knowing the exact impedance of the reverb? I’ve heard about using headphone amps, is that a valid option?
Hopefully useful answers are;
(I’m assuming you’re talking about a raw tank and not a housed unit of some sort) Both ends of a spring tank need some amplification. Conventional tanks don’t need much amplification, you’re powering two small transducers just enough to vibrate a few very light weight and low tension springs.
The output side is pretty easy. The amplification on this side is called “recovery gain” and can usually be handled by small preamps (mic pre/ mixer inputs/ front end of a guitar amp/ most pedal inputs/ etc). The best part is that the output impedance is almost universally in a range that works for this application, few exceptions exist. It just needs a little boost to get the low level signal up to something usable, much like a passive guitar pickup.
The input can be tricky. The amplification on this side is usually referred to as “driver gain” though you’ll sometimes see it called “dwell gain”. The massive range of potential impedances is the issue. It can be just a few ohms like a speaker or it can be hundreds of thousands of ohms or anywhere in between. There’s really no way around “matching” an amp’s output impedance with a tank’s input impedance. That being said, it doesn’t have to be a perfect match, just in the ballpark, and it’s a big ballpark.
Headphone amps are popular and work well with many tanks provided the tank impedance isn’t too high. Headphone amps don’t output much energy in the sense of wattage and the transducers in spring tanks don’t need (and can’t handle) much. If the tank and amp impedances are too far apart from each other the amp won’t be able to drive the tank, it is possible for damage to occur in some cases but it’s very unlikely in a scenario where you’re testing things out with commercially available products as long as the wattage is low.
I recommend trying it. Just have all of your levels all the way down to start and bring them up gradually. If one type of mixer/ soundcard output doesn’t work, try a different one (aux/ subgroup/ headphones/ mains/ half inserted channel inserts/ etc depending on your specific gear). You’ll most likely get the best results with a headphone out but you’ll need to be mindful about feedback loops. Also, not all headphone outs have the same impedance so try different ones. If absolutely nothing works you might be stuck needing different equipment. You could make or buy a compatible amp but keep in mind that spring tanks can be found cheap, especially used, and it might make more sense to buy one that is compatible with the rest of your rig.
I hope this ramble is in some way helpful.
Not much to add, but if the impedances are too far off when
swapping a tank into a pre-existing circuit the output can be greatly reduced or inaudible.
If it’s a self-contained outboard unit, it probably needs nothing other than power. If it’s just an unloaded spring tank and you’re working with stereo mixes, even after you work out the gain factor you may still find limited use from running them through a mono signal path.
It is a raw tank that I bought of a guy doing rockabilly music. It’s a metal box that has two RCA connections for in and out. Unfortunately there are no numbers on the tank indicating model or impedance.
I’ll try the headphone amp approach and see if it works! Another potential solution that I’ve heard about is to figure out the impedance using a signal generator. Not sure exactly how you would go about it though.
Cool. I love some of that old rockabilly stuff.
Honestly I wouldn’t get too hung up on the impedance unless you can’t make it work with what you have. Just try it with various outputs on your mixer and soundcard and whatever input won’t make a feedback loop with whichever output you’re using at a given time and play with the levels until either A) you find something that works or B) you’ve exhausted your options. Treat it like an experiment and control for all of the variables you can and keep track of what you’re trying so you don’t neglect possible connections.
I’ve never heard of finding impedance with a signal generator, maybe a signal tracer like an oscilloscope? If you have a multimeter (or even just an ohmmeter for that matter) you can test for nominal impedance. Just set it to ohms and probe the positive and negative poles of each rca jack. I say nominal because impedance is dynamic and you’ll be getting a reading of it in a state where A) it’s not energized, B) it’s not part of the circuit it will eventually be a part of, and C) it’s moving parts are static. This is the same as when you check the poles of a speaker. Both are transducers with specs that are in constant flux when in use that vary depending on a number of factors. Without getting into theory or the math, for the purposes of this discussion you can think of it like a resistor whose value is always changing. The only number needed for determining compatibility is the nominal value because that’s the standard we use.
As an aside:
As you may have guessed I’m a big fan of spring reverb. Unfortunately I haven’t heard an emulation that stands up to the real thing. Many get close but unless there’s something really recent I’m not aware of, those as enthusiastic as me still need the real deal. As such I have lots of them, some commercial, some homemade, some kinda in between. My next reverb project is a spring verb using the spring from a roll up door from a loading dock that was replaced recently. It’s about a foot in diameter and about eight feet long, weighs probably 70 or 80 pounds. I have a transducer that should drive it (it’ll take about 300 watts) but I need to make one for the recovery stage. It might end up being boring sounding or it could be amazing, you never really know until you try.