Sprungtrix

While designing and building Sprung 2, I started to consider further expanding the possibilities of the module by picking up some additional spring reverb tanks. The style of tank I was using comes in three reverb tail lengths: Short, Medium and Long. I had the long, and thought it might be interesting to add a short or medium for variety.

Around this time, I happened on an eBay listing for a lot of three tanks: Short, Medium and Long. I couldn’t believe my luck, and sprang on it. (See what I did there? I’ll be here all week…)

Unfortunately, I failed to read plain English and ended up with three reverb tanks whose specifications were critically different from the one I’d designed Sprung 2 to operate. I’d already started to build Sprung 2 and thought “Ah, screw it. I’ll build a second reverb module.”

And thus, Sprungtrix was born.

Borrowing from some of the Sprung 2 design concepts, along with completely different drive and recovery circuits, I ended up with something quite usable. Individual volume for Wet and Dry signals; CV control over both; a feedback gate, which turns the feedback signal on or off; “tank ping”, which sends a burst of current at the tank input to momentarily overload the reverb; individual output for the wet signal; and a very basic lowpass filter with CV over the cutoff frequency, for toning down the brightness of the reverb.

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
  • 22nf (2) C4, C6
  • 100nf (1) – C1
  • 580nf (1) C8
  • 10uf (3) – C3, C5, C7
  • 22uf (1) – C2
• Resistors
  • 22R (1) – R18
  • 47R (1) – R6
  • 200R (2) – R15, R19
  • 2.2k (1) – R16
  • 1k (8) – R4, R5, R12, R13, R14, R21, R22, R23
  • 6.8k (2) – R10, R11
  • 10k (4) – R3, R7, R8, R9
  • 100k (4) – R1, R2, R17, R20
• Potentiometers
  • 10k (1) – RV4
  • 100k (3) – RV1, RV2, RV3
• Transistors
  • 2N3904 (1) – Q1
  • 2N3906 (1) – Q2
  • 2N7000 (2) – Q3, Q4
• ICs
  • TL072 (1) – U4
  • TL074 (1) -U3
• Diodes
  • 1N4148 (2) – D1, D2
• Vactrols (3) – U1, U2, U3
• Audio Jacks (7) – J1, J2, J3, J4, J5, J6, J9
• Switching Audio Jacks (2) – J7, J8

Design Notes

The drive and recovery circuits for this module were calibrated specifically for the Mod 9ABxCxx reverb tanks. These tanks have an insulated input with 10R impedance and a grounded output with 2.5k impedance. This module will not work well, or at all, with reverb tanks of different specifications.

Demo

Coming soonish