CV range

  1. CV inputs 1-3 have a range of [0v to +3v]
  2. SRR input has a range of [-2v to +5v]
  3. D/W input has a range of [-5v to +5v] (positive voltage decreases the wet level, and negative increases dry level)

+/-5 V from mid position, and thus around 10Vpp from full wet or dry.

SRR input has that weird range because it can go much lower in frequency vs up. Positive voltages decrease the sample rate, because that is what most of the users like to do.

D/W moves from Wet to Dry with positive CV voltage, and from Dry to Wet with negative voltage. Again weird, but I was working with 100% wet signals most of the time, so my brain reversed the starting point.

CV1-3 inputs are limited to only 3.3V because some gate signals are only 4V, and attenuators are much more spread than amplifiers. And the user will need attenuator to set the desired modulation depth anyway.

0V applied to the Sample Rate does not change the default rate.

CV assignment is stored with each preset.

Target signal levels (if your effect starts to clip / crackle / glitches you should attenuate the inputs)

Can we finally accept that FX AID has the optimized levels eurorack gives to us? There is no other way to balance both high level guys and moderate level ones. It is just not possible to have other levels and not to clip at some settings. Some people want the FX AID to accept -10V...+10V at input, give -10V...+10V at wet output and magically have them both mixed without hitting 12 V rail limit.

FX AID's input should not exceed -7V...+7 V, which is a wise compromise. FX AID's output is limited to -6V...+6V, which is also a wise compromise, so dry and wet mix is never above 10 V. I deliberately limited it to 10V vs 12 V, because some other modules can be following FX AID, and them are not obliged to use rail to rail parts to be safe from nasty distortion. How can I explain to a client that FX AID's output is heavily distorted being fed to his/her X times more expensive module from a popular brand? FX AID has 3 dB Dry/Wet mixing law to avoid level drop at 50/50 mixing. This required dropping dry amplitude a bit to fit to the above described limits.

SSR input (bricks) / chip clock

You reduced the sample rate way too much, so the chip became non-responsible on such a low frequency. Please do not exceed +5V for lowering the sample rate and minus 2V for increasing it.

some words regarding the update process (levels / if it stucks)

In case someone needs it: I’m able to reliably update FX AIDs with levels from -1.2V..+1.2V down to -0.1V…+0.1V. So the range is quite broad if clean audio pass is used.

If FX AID was interrupted during the update and becomes irresponsible and no lights are active: switch off the case power, press both buttons and while they are still pressed switch on the power. FX AID will reboot to firmware update mode with two inner leds blinking asking for the proper update.

alternative ways to navigate

As requested now there are two possible ways to navigate the effects:

  1. standard browsing with sequential selection in both left and right directions
  2. new browsing option with left button selecting 1 of 4 banks and right button selecting 1 of 8 effects within this bank.

New CV assign destination is added – effect selection. So now CV can be used to switch between all 32 effects. XL version: CV should be applied to the SRR input. Just reupdate your favorite effects set via wav file to benefit from this new mode.


"Delay Sync" has "Divider" control to set the desired ratios of the incoming clock. "Delay Tap Tempo" do not need this control, as it should follow the tapped time. It can also be used with ordinary clocks and "Tone" control can be adjusted to the asked HighPass in the feedback.


List of SpinASM code for guitar effects pedals and other applications : https://mstratman.github.io/fv1-programs/


https://github.com/HolyCityAudio/SpinCAD-Designer : SpinCAD Designer is an open source Java project which allows creation and audio simulation of patches for the Spin FV-1 audio DSP chip

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