'22 Standard Reverb

From the vendor

'22 Standard Reverb

Apr 17, 2022 6 min read

Updated: Aug 22, 2022

My journey with spring reverb drivers starts 3 years ago, when I salvaged a spring tank from a wrecked combo amplifier (together with the rest of the components). The tank wasn't in good condition either, since one of the wires holding a spring had broken. I had to make a new one from one strand of a copper wire, threaded through the magnet and the support and soldered into a loop, which worked surprisingly well. That's when I started working on the '19 version of this circuit with the help of a friend. That one quickly turned out into a build, which I then updated in the next years.

'19 Reverb

I want to show the '19 version without going too much in depth, just to show how far has it gone.

I hate a lot of things about it: from using LTspice as schematic editor, to the inverting input stage with 1Meg worth of Johnson noise right away. The main inspiration for this one were the circuits used in modern Fender and Marshall amplifiers, because I didn't even know how to pick some values for myself.

'20 Reverb

In 2020 I've updated the circuit. This already looks better, with a non-inverting buffer, a charge pump for bipolar supply, since I had found out that driving tanks with high enough input impedance requires more voltage; also this cleaned up the circuit nicely. The mixer at the end is less messy too. Another version after this one switched to variable gain on the recovery stage because of a misunderstanding I had about noise. I was really struggling with noise at high reverb levels because of the small voltages present on the output coil and the large gain required. Sadly, variable gain helps with headroom, which isn't really an issue when your input signal is a few mV, but not with noise.

Between 2020 and 2021 I came up with a version of the circuit I was finally happy with. I had discovered a couple of pages describing spring reverb in detail on ESP, which were an invaluable help. I don't try to hide the fact that I owe most of my spring reverb knowledge and the positive outcome of this long project to them.

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This circuit is an adaptation of an ESP one as guitar pedal, which means working with different levels and supplies. I'd finally switched to the NE5532 as driver and recovery amplifier: this beautiful but power hungry op-amp works better than the TL072 both for the driver stage, since it's able to drive heavy loads with little distortion, and more importantly for the recovery stage, where its excellent noise specs meant a world of difference from before. With my old tank having a 150 ohm input coil, I found a single 5532 to be just enough, although paralleling two in a power booster configuration is an option. I then made an 8 ohm version for a friend with a simple discrete push-pull amplifier from ESP.

A fun note is that up to this point I managed to build all the updates on the same piece of veroboard, even making a TL074->072+5532 adapter by stacki