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PostPosted: Fri Nov 04, 2016 7:28 pm 
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Long time lurker.

Although I haven't attempted it yet, in theory could R23, R24 and R25 be connected in a way to select different FV-1 internal programs? Obviously the two pots would have to be added back in place of the set resistors as well.

Any thoughts on this possible modification?

Thanks!


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PostPosted: Sun Nov 06, 2016 10:45 am 
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There is an Easter egg on the pcb to do this. I'm not familiar with the details of the fv-1, but there are traces to cut on the pcb to do this.

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PostPosted: Sun Nov 06, 2016 10:01 pm 
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Ah! I see the note on the back of the pcb. I'm assuming at this point to just cut the one(?) trace, and wire the three 22k resistors with your choice of switch(es) to ground like the fv-1 schematic?


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PostPosted: Mon Nov 07, 2016 11:25 am 
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hewie wrote:
Ah! I see the note on the back of the pcb. I'm assuming at this point to just cut the one(?) trace, and wire the three 22k resistors with your choice of switch(es) to ground like the fv-1 schematic?



You can find the list of programs and how to activate them correctly in the datasheet: http://www.spinsemi.com/Products/datash ... 1/FV-1.pdf

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PostPosted: Mon Nov 07, 2016 12:02 pm 
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To get right to the point, yes. All you need to do is cut that one trace and it will open up access to the FV-1's other programs.

You need to use pins 16, 17, and 18 as binary input to determine which program you are using. As it is, the li'l reverb has pin 16 low, and pins 17 and 18 high (via the 22k pull up resistors to +3.3v). Pin 16 is connected to +3.3v via a 22k resistor as well, but ultimately, it is shorted to ground (by the trace you will need to cut). If you understand this, then you should understand that the binary code that is being sent to the FV-1 is "011", which in decimal means program number #3, right? Because 011 is binary for decimal 3, which would be "pitch shift" according to the data sheet. But this assumption would be incorrect, obviously since we are using one of the reverb programs.

In programming, you are often times given the option of reading binary in "least significant bit first" or "most significant bit first". Normally, when you read anything, you go from left to right, whether it's binary or decimal. So the number 173 in decimal is made up of 100 + 70 + 3. This is MSBF. If you were to write dec 173 in LSBF, you'd simply write it backwards as 371. The FV-1 uses LSBF, so this means that 011 is actually program #6, "reverb 1". This is because in binary LSBF, you read the 1's column first, then the 2's column, then the 4's column, i.e., you just read it backwards.

This is why the data sheet refers to PIN 16 as "program select LSB", and PIN 18 as "program select MSB". But the data sheet doesn't explain that the input is read as LSBF. It's important that you understand this first, so you know which programs you are selecting.

Cutting that one trace disconnects pin 16 from ground. This gives you a binary code of "111" or program #7 (reverb 2). You have many options for 3-bit decoding. The simplest option in this case would be to use three separate SPST toggle switches. Connect the pole of one switch to one program select pin. Connect the throws of all the switches to ground. When a switch is "off", it leaves that program pin high and gives you a "1". When the switch is on, it shorts that pin to ground and gives you a zero.

If you do this, you will probably want to add POT1 and POT2 as well, because you won't have control over some important parameters in other programs. If you compare the Li'l Reverb schematic with the datasheet, you'll see that POT1 and POT2 are actually already there, they are simply hardwired to be at "noon". So to use actual potentiometers, you'd remove the 22k resistor pairs. You'd connect Lug 3 of your pots to 3.3v and lug 1 to ground. Connect the center lug or wiper to its respective pin.

IMO, there is absolutely no difference between reverbs 1 and 2. And program #5, doesn't do anything at all. It simply passes unaffected signal, which as the "test" program, is all it's supposed to do. This information may be of some significance if you are deciding to use a rotary switch of some sort, as you would only need 6 positions. This may make it easier for you to find/design a suitable switch/interface

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PostPosted: Sat Apr 21, 2018 12:21 pm 
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I am curious to try this mod. I was wondering what adding the extra presets and pots does to the reverb pedal. Do the reverb and decay pots still work...


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PostPosted: Mon Apr 23, 2018 10:56 am 
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simon wrote:
I am curious to try this mod. I was wondering what adding the extra presets and pots does to the reverb pedal. Do the reverb and decay pots still work...


Depends on what program you have the FV-1 in. It has 7 different programs and the knobs do different things depending on which program you are in. It's explained in more detail in the datasheet. This is only for the "decay" pot however. The decay pot is connected to the FV-1 as POT 0. If you were in the pitch echo program, it would control the pitch shift parameter. POT 1 and 2 are hardwired with fixed resistors to act as if there were pots there set at noon. The "reverb" pot on the li'l reverb is analog and controls the amount of wet signal that is mix back into the dry signal, so that knob will never change regardless of what program you are in. The pitch shift and reverb programs do not have built-in mix (or blend or level) paramaters, so it would be useful with those programs. The chorus, phaser, trem, and echo programs have mix controls, so it would be redundant on those programs.

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PostPosted: Thu Apr 26, 2018 4:37 pm 
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I have added two pots and three spst switches. It sounds great I really enjoy the presets that it has. It works great when it was out of the enclosure, but when I put the jacks in the enclosure it shorts. I'm not sure what is going on with it, but i'm sure that it is some dumb noob mistake.


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