Music Thing Spring Reverb Documentation

The Music Thing Spring Reverb is a flexible, easy-to-build voltage controlled DIY mono spring reverb module. Traditional guitar reverbs are tuned to the sound of the guitar and the amplifier it is played through. This circuit is different; designed to be relatively clean and high-fi, with a lot of bass response. It can also be abused and driven into (externally patched) feedback, as the demo below shows.

Kits are available in the UK from Thonk. 

The circuit, plans and PCB/panel designs are open source and shared under Creative Commons.2013-10-13 14.33.52

  • Works with a variety of spring reverb tanks, or with the Accutronics BTDR-2 reverb ‘brick’ designed by Brian Neunaber
  • Includes PCB panel designs that can be very cheaply produced.
  • Vactrol crossfade between dry and wet
  • Tilt EQ on the reverb send to tune the voice of the reverb
  • X-Fade input so the module can also be used as a standalone vactrol crossfader (crossfade demo)
  • Attenuverter on the crossfade CV input
  • Options for reverb tank connection and placement including front panel sockets.
  • Optional (unbuffered) PCB connections for 100% wet and post-EQ dry outputs
  • 6hp wide (NB: If using the brick, mounted horizontally, the brick extends 5mm over the PCB to the left of the module, around 25mm back from the front panel, so mount the reverb next to a shallow module)
  • Around 60mm deep including a phono plug for the reverb tank coming from the back. Just 35mm deep if you mount the reverb connections on the front panel

2013-10-13 14.34.16Documentation

Spring Reverb build and user manual (PDF) – includes how to choose a spring reverb, how to calibrate the circuit, patch ideas and tips for getting the best results

Block Diagram (PNG)

Spring Reverb_Schematic (PDF)

Spring Reverb Document Bundle (ZIP)

includes manual, schematic, parts list, and design specifications for the panels

Mouser BOM – Excludes the Vactrol and 3.5mm sockets. NB, the pots are not ideal (they come it at different heights and require 9mm panel holes)

Spring Reverb_PCB Files (ZIP) – Eagle and Gerber files for reverb PCBs and panels.

Licence: This is an open source hardware project. You can use this design however you like, including any modification or commercial production, so long as you credit Tom Whitwell and share your own changes. Random Sequencer by Tom Whitwell is licensed under a Creative Commons Attribution-ShareAlike 3.0 Unported License.
Creative Commons License





  1. drip.feed says:

    I’m hitting F5 on …

  2. David says:

    Hello, I wondered if this will work on 15V supplies as well?

    • Tom Whitwell says:

      I don’t see why not although the CV response may be slightly odd. If you check the thread on Muffs there may be some discussion.

  3. John says:

    I want to add dual reverb units to my 5U modular. Do you know if there is an fpd file around for the panels ?

  4. Chris says:

    Hey there. Im really Interested in buying the kit but it all seems out of stock. do you know when there will be kits available again?

  5. Gareth says:

    We built this tank driver from a Thonk Kit – useful! The dry/wet control doesn’t sen to go full wet. Have we made a mistake?

    • Tom Whitwell says:

      Hi Gareth, It should go pretty wet – the best way to test it is with the x-fade input – put one osc in there, and another in the main input, and see how well you can crossfade between the two.
      What doesn’t work is putting one end of a cable into the x-fade to see if it can fade out to zero – the circuit doesn’t really work that way – you can’t turn it into a VCA.

  6. Adrien says:

    I ended up removing R7 on mine which effectively turns it into a fully wet signal with a VCA on its output.. i found it more useful in a mixing situation 😉

  7. Mark says:

    Have built the Module with both Spring and Digital options as part of my ‘ARCON’ Controller; after the Wendy Carlos ‘CIRCON’ Controller as developed for ‘THE SHINING’.
    I replaced the Pin/Jumper with an SPDT Switch (ON-OFF-ON) to easily change from mellow Spring to bright DSP.

    A great Module and a fun build.

  8. michael says:

    hey – great reverb. i love in my system. out of curiosity, i messed around with it in my valve amp’s fx send/return today. sounds great…. little feedback but still fine.

    do you think the circuit will be ok @ +-4.5V . I’m thinking about making it as a pedal.

    • Tom Whitwell says:

      Not sure about +/-4.5v, haven’t tried it – you can try with other lower voltage op amps in those slots

  9. Martin says:

    Hey Tom,
    I cooked something inside the Spring Reverb. I routed a tube amp signal, which was meant to go to a speaker, through it. The resistance of the Spring Reverb was too low, of course.
    When I switch my rack on now, the dry/wet LED still lights up first, but goes off after (in smooth fades). Does this give a hint?
    I just know how to solder, but nothing about actual electronics. Can you help? Thanks.

    • Tom Whitwell says:

      Sorry, I have no idea. I’d start by replacing all the op-amp chips – they’re cheap and it’s an easy step.

      When it fades out, do the yellow fuses on the back of the module get really hot (you can touch them, but be careful)? If so, there is a short somewhere in the module – but I’ve no idea where.

  10. Martin says:

    Thanks for replying. No, the fuses don’t get hot. Op-amp chips will be my first attempt. Will let you know how it went.

  11. david says:

    would it work with the BTDR-3 chip as well?
    would be great to add another pot for the decay time!


  12. Nick Torres says:

    Hi Tom,

    I’ve been interested in this module for quiet some time now. I was wondering how well the spring reverb pairs with the mikrophonie and radio music modules? I am planning on using the spring reverb predominantly with microphones and samples, and was wondering if the sound produced was clean or muddy?

    • Tom Whitwell says:

      Sorry for the late reply; it’s a pretty clean spring reverb if properly set up, but it’s not clean like a digital reverb.

  13. Taran_te says:

    Love this module and use it all the time. I also installed the
    Accutronics BTDR-2 and a spring tank.

    The spring tank volume is very good but the Accutronics BTDR-2 is barely noticeable. Is there a way to increase the volume of the Accutronics BTDR-2?

    • Tom Whitwell says:

      The module isn’t really designed to use two different tanks – you probably have to adjust the gain trimpot between the two types.

  14. matt says:

    paired it with a Accutronics AMC2BF3 (small blue tank) and the sound of the spring it nice and loud but not getting any signal thru, ideas?

  15. tappazee says:

    Hi any idea when these will be available again on thonk?

  16. tappazee says:

    Hi Tom, thanks, they said not until some time in the new year. I can’t find any other UK stockists – are there any I’m missing?

  17. ekke says:

    I have one question about accutronics 8BB2C1B tank.. Probably because the low impedance my spring reverb is not driving the springs at all. Is there any possible mod to make the schematics work with 8BB2C1B as well?

    Thanks and happy new year!


    • Tom Whitwell says:

      If it’s outside the values in the documentation, I don’t know how to make it work for that tank.

  18. Romain says:

    Hi Tom,

    Do you have any estimated date for when this awesome kit will be back in stock?



  19. Robin says:

    Hi Tom
    Any news on when the updated spring reverb will be available?

  20. Eric Junge says:

    Any updates on the V2 Spring that I saw on youtube??

  21. Russell Duke says:


    I’ve spent all weekend building the Spring Reverb and I’m having major issues. I can’t get anything from the brick or the control knob. The IC’s are getting really hot but I can’t see a short circuit. I’ve been through the whole schematic and checked all the connections do you have any advice? I’ve built the expander and added a spring reverb and I have a response from that. Any advice would be much appreciated.

    • Tom Whitwell says:

      If the ICs are getting hot, it’s likely you’ve reversed either the ICs or the power diodes. The ICs may be damaged if they’ve got seriously hot.

  22. Wade says:

    I’ve installed the 78L05 voltage regulator the wrong way around.
    Have I killed the module?

    Yes, turned it on before I realised.