Author Topic: FV-1 Programmable FX Unit a.k.a. "The Sandwich"  (Read 5964 times)


FV-1 Programmable FX Unit a.k.a. "The Sandwich"
« on: August 28, 2008, 08:21:40 PM »

This is our take at the FV-1 chip - a programmable FX unit designed to be used in guitar amps with up to 4 channels. Itís a cooperative work including me and a friend of mine. The idea came from M16_24 :: Fixed program module found on Spin's site but we needed more control and flexibility.
The module consists of 2 PCBs. The top one is the control board. The bottom one is where the real action is taking place. Dimensions are 60x100mm (2.36"x3.93")
The heart of the module is PIC18F4423. Four digital pots (AD5263) are used to enable storing presets. You can update the firmware and load  different combinations of effects into the EEPROM using an your PCís COM port . Spin's software is used to create different combinations of effects and generate a HEX file which is then loaded into the EEPROM with the help of a small software.

The module has 2 modes of operation.

1/ In Program mode you can build and store up to 100 presets. For example if you have a 3 channel amp and you have a song where you need Chorus for the clean channel, Reverb for the drive channel and Delay for the lead channel you just dial (via rotary encoder) the number of the program, select channel one from your amp footswitch, press Edit, select the effect you need, adjust parameters and hit Store. If you don't need effects on channel 2 the module will be bypassed (via external relay).

2/ In Manual mode you can select the effects one after another in ascending or descending order. The parameters for each effect last dialed are memorized automatically .

Each effect parameter has 20 steps you can choose from using the pots from the control board. All changes are visualized with the use of a 2 digit 7 segment LED display.
The module has 4 channel inputs and needs a 0 level to recognize an amp channel (whem it's on). You can take a ďzeroĒ from channelís LED for example or from a relay. Optocouplers are used at PICís dedicated inputs to transfer the zero.

Analog mixing circuit is used to mix the dry signal with the processed one. The parts of that circuit were deliberately left through hole in order to allow experiments. In bypass mode the whole module together with the analog mixing circuit is bypassed (out of the sound chain) using an external relay.

We had some issues with LED display noise leaking into the audio. This is the place to thank Frank from Spinís forum and FV-1ís developer Keith Barr who were very kind to give us some ideas how to deal with it and solve the problem.

The pictures below show each side of the module. The bottom one is messy because of some tweaks we made to solve the problems mentioned above and make it work as required. A new version of the PCB is cooking and it will look prettier.

I would appreciate your comments and ideas how to make the module more functional to satisfy more peopleís needs.


Re: FV-1 Programmable FX Unit a.k.a. "The Sandwich"
« Reply #1 on: August 29, 2008, 11:45:17 PM »
Some sound clips would be nice for a start. I saw this chip being used on Tonepad and was wondering when someone would start tinkering with it. Further along than me I must say. ;D


Re: FV-1 Programmable FX Unit a.k.a. "The Sandwich"
« Reply #2 on: August 30, 2008, 05:54:29 AM »
Sure there will be clips.