[sdiy] How do reverb tanks work?

[Ray Wilson]

Both sides of the reverb tank are similar they differ mainly in the 
impedance of the coil circuit. The "input" side is generally lower impedance 
and yes your are driving a coil that is causing a fluctuating magnetic field 
to cause the magnetic ferrous bead attached to the reverb spring to wiggle 
causing the spring to wiggle so that on the other end another magnetic 
ferrous bead wiggles and induces a voltage into the "pickup" or output coil 
(generally higher impedance) than the other coil. The signal on the second 
coil is the actual reverb signal which you amplify and mix with your 
original signal to get the classic spring reverb type effect.

The coils are wound with the teeniest wire in the world and fixing them is 
next to impossible. Notice I say... "next to" because with enough patience, 
care, light and magnification I suppose one could reconnect the coil wires 
to the input/output terminals and the thing would be as good as new.

Cheers and Good luck.

Ray
----- Original Message ----- 
From: "RMC" <RMC at richardcraven.plus.com>
To: <synth-diy at dropmix.xs4all.nl>
Sent: Friday, November 24, 2006 10:08 AM
Subject: [sdiy] How do reverb tanks work?


> Hello
>
> I'm interested in spring lines and most specifically, the transducers 
> used. Does anyone know the detail of how the output transducer works?
>
>
> The input transducer uses the motor principle to develop torque which 
> imparts torsion to the spring, but how does the output element work?
>
> Having just dismantled and repaired a broken springline (the output 
> transducer coil had gone open circuit where the lead-out flex solders to 
> the coil turns, due to 1970s corrosive flux!), I can't understand with 
> certainty how it works.
>
> The ends of the spring seem to have tiny ferrite beads mounted on them, 
> which are lined up to occupy an air gap in the output transducer. Either 
> that, or they're magnets.
>
> In the former case the gap reluctance presumably gets modulated by 
> movement of the ferrite bead. In the latter case, an MMF gets generated by 
> the magnetic flux cutting the core (aluminium laminations??) and hence 
> inducing a current in the output coil which is common to the magnetic 
> circuit thus formed.  As far as I can tell, the circuit that receives the 
> tank output doesn't provide a constant current through the coil so there 
> isn't a method of detecting the relucatnce - it must be that the little 
> beads are magnets. Is it true?
>
> I managed to leave out a couple of tiny little brittle black (plastic?) 
> "plugs" which appeared to act as some kind of spring damper, where the 
> spring end feeds into a tube, where it gets anchored. This is after it has 
> passed through the output trasnducer. However, it works without these 
> components (which shattered, hence why they're not re-fitted).
>
> There are a load of picrues on my website - which the ISP has just shut 
> down because I exceeded my storage allowance. I'll post a link if I get 
> that problem resolved.
>
> Cheers
>
> RMC, England
>
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