I have just bought an old spring reverb unit called the Great British Spring off eBay. It sounds great but if I feed any drums through it, or a percussive synth sound, it makes a weird 'ping' sound. I've had a look around the Internet and can't find much if any info on the thing. Can you help?
SOS contributor Steve Howell replies: The Great British Spring was very popular in the '80s — I had one myself. One of the first affordable, decent-quality spring reverbs, it arrived at a time when Fostex were bringing fairly serious eight-track reel-to-reels to the market — it was a marriage made in heaven for the emerging home studio market. That said, the GBS was of serious enough quality to have been adopted in 'proper' studios as a cost-effective way to add extra reverb channels to supplement the main plate reverb.
Spring reverbs work by feeding the input signal, typically from an effects/aux send, to a transducer that 'excites' one or more of the springs. The signal travels down the spring and is picked up by another transducer at the other end, then sent to the output and on to the effects return. But it's not quite as simple as that, as the signal also 'bounces' back along the spring, colliding with other signals on their way down and causing complex pseudo-reflections. We perceive this as a reverb effect, and the more springs a unit has, the more diffuse the reverb effect is.
The length of the spring dictates the reverb length and density — the GBS's springs are quite long and give a nice hall reverb effect. However, as with all spring reverbs, percussive attack transients can cause the springs to become temporarily unstable, generating all sorts of unpleasant audio artifacts, as you've found out.
The simplest solution is just to reduce the level of the signal going to the GBS. This will prevent the springs from getting over-stimulated and thus will eliminate (or at least reduce) the 'ping' effect. The down side to this is that to have the same level of reverb on the sound, you will have to increase the reverb return level which will, of course, increase the amount of noise — these electro-mechanical devices are not known for their noise-free operation! However, even that can be overcome. You see, the frequency range of the springs is limited so, by bringing the reverb returns back through channels that have EQ, you can roll off the top end to reduce the hiss coming from the unit without adversely affecting the reverb sound too drastically, if at all. In fact, given the simplicity of the GBS (and spring returns in general), using EQ can add a lot of creative as well as correctional possibilities.
A more elaborate solution is to run the effects/aux send that is feeding the GBS via a limiter set pretty hard, so that the signal never reaches the level that will cause the springs to become unstable. Many more expensive spring reverbs had just such a facility built in.