Current-Mode Driver for Reverb Pans

When people began steering away from thermionic based designs, and replaced the basic building blocks of music amplifiers with solid-state equivalents, one of the things they did was replace the high impedance class-A approach to driving reverb (spring) pans to a low-Z op-amp one … I always considered this suspiciously wrong for number of reasons // fidelity being one of them … I’m sure some readers will agree that these circuits can tend to sound harsh, even at their best // the worse thing for me is seeing an “otherwise” all-tube amplifier design that has an op-amp based reverb interface circuit sandwiched in there (argh!) … an obvious mod there is to bypass the reverb circuit


And so, to investigate the wrongness of all this “op-amp drives a reverb pan” madness I thought about alternate ways of exciting a coil for the purpose of producing accurate signal transfer down a spring delay line … of course, any solution has to replicate the network parameters that the original tube circuits did // but not necessarily in a class-A manner … the solution that I propose (and verified to work perfectly on this day) achieves the kind of interface parameters the input coil of a reverb pan likes to see in order to maintain high fidelity, and the circuit that does this is highly linear in nature to boot … the combination allows a down-to-DC frequency response that is distortionless // … simply respecting proper rules of network theory, that’s all … (and yes, it is cheap to build)

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