Sprung 2

A while back, I designed a module to power a Mod 8EB2C1B spring reverb tank* as part of a series of low-effort reverb modules. I’ve been a fan of spring reverb since I first encountered the effect back in the 90s. Yet, I rarely found myself patching into the module. I began to suspect that I had outgrown its simplicity, so I set about designing the sequel. And, like all sequels that are better than the original, its name is a not-so-subtle nod to the classic Breakin’ 2 Electric Boogaloo.

Sprung 2 is redesigned from the ground up to be more interactive, with a wider array of possible effects. There are individual controls for Wet volume and Dry volume, to better dial in the desired level of reverb; CV-controllable Boost, which sends a boosted signal to the reverb tank, for pinging the tank; CV control over the Wet volume; switchable Feedback modes–one mode is normal and the other inverts the audio signal, creating phase-cancellation effects; and a “resonant” feedback path.

*It’s called Sprung!, in case you were wondering.

Schematic

As with any schematic found on the internet, exercise caution when building. Test the build before plugging it into your case. If you find mistakes in the schematic, or you have recommendations for improving the design, feel free to contact me and let me know.

BOM

• Capacitors
  • 470pf (1) – C1
  • 10nf (1) – C5
  • 470nf (1) – C4
  • 1uf (1) – C2
  • 22uf (1) – C3
• Resistors
  • 9.1R (1) – R21
  • 100R (1) – R20
  • 470R (2) – R4, R12
  • 1k (3) – R3, R9, R22
  • 2k (1) – R18
  • 4.7k (1) – R14
  • 10k (5) – R1, R5, R6, R7, R17
  • 47k (1) – R13
  • 100k (3) – R2, R8, R15
  • 120k (1) – R11
  • 470k (1) – R16
  • 910k (1) – R10
  • 1M (1) – R19
• Potentiometers
  • 1k (1) – RV4
  • 10k (1) – RV1
  • 100k (2) – RV2, RV3
• Transistors
  • 2N7000 (1) – Q1
  • J112 (1) – Q2
• ICs
  • TL074 (2) – U1, U2
• Diodes
  • 1N4148 (2) – D1, D2
• Switches
  • SPDT Center Off (1) – SW1
  • SPDT (1) – SW2
• Audio Jack (3) – J1, J3, J6
• Switched Audio Jack (1) – J2
• RCA Jack (2)* – J4, J5

*RCA jacks are included in the schematic to indicate how they should be wired. For my build, these connections are hard wired to an RCA cable on the back side of the module. Do what feels right to you.

Design Notes

This is designed specifically for the spring reverb tank I own. It’s calibrated for an insulated input with an 800R impedance and a grounded output with a 2.5k impedance. These factors play a crucial role in the design of the drive and recovery stages–moreso than you would normally find in a Eurorack module.

If your reverb tank has different grounding configurations or different impedances, this circuit is not likely to work for you. But, nihil desperandum! I do have another module in the works that has a different set of specifications.

Demo

Coming soonish.