Handling hot signals with an FV-1

[mark2]

Anyone here using companders or other methods to deal with boosted signals into an FV-1?

I've just always assumed that everyone puts their signal to unity before time or modulation effects, but I've talked to people who find this unacceptable. Curious if they were outliers, I posted a question on the r/guitarpedals forum and sure enough, plenty of people insist digital pedals are rubbish if they can't accept a hot input.

Have you taken any steps to try to accommodate a wider range of inputs in your pedals? I've not (yet?) gotten into synth, but I can see this being an issue  if you want to use your pedal with either guitar or synth.

Or does anyone know what CBA or OBNE do? (I'm going to go try feeding them hot signals later today, and take a closer look under the hood)

[Cybercow]

IME, having some sort of control/circuit to manage the input levels to an FV-1 circuit is circuit-chain dependent. All of the FV-1 circuits I work with (primarily pedals) have (at the very least) a buffer of some sort the input. On the SpinSemi FV-1 Development Board I have, (which has only a pair of resistors & caps on the FV-1's input), my '79 Strat can be plugged directly into it without issue. And according to the datasheet, the FV-1 can handle up to +0.5V above the Avdd/Dvdd supplies respectively. (With the typical Avdd/Dvdd supplies tied together using 3.3V

Of further importance, regarding the FV-1, are the patches employed thereof. If they are poorly crafted, the output will reflect that in one way or another.

All that said, I've not had great success with getting extremely dirty input signals to produce anything with any clarity from an FV-1 circuit. As I see it, the FV-1 was designed to accept clean, low-level signals (about 0.3V up to a max of 2.0V) for defined processing.

For greater detail, lookup the SpinSemi FV-1 Datasheet.

[FiveseveN]

plenty of people insist digital pedals are rubbish if they can't accept a hot input.

Well, plenty of people are dumb Just add a sticker that says "Operation of this product requires basic understanding of gain staging".

[ElectricDruid]

All that said, I've not had great success with getting extremely dirty input signals to produce anything with any clarity from an FV-1 circuit. As I see it, the FV-1 was designed to accept clean, low-level signals (about 0.3V up to a max of 2.0V) for defined processing.

This doesn't come as a huge surprise. The chip is running on a 3.3V supply, so the *maximum* headroom is going to be somewhere around 3V, depending how close to "rail to rail" they got. It may well be significantly less.
With a typical input sample rate of 32KHz, a lot of distortion products going in will cause all sorts of chaos. Most FV-1 designs seem to be *very* light on pre-sampling filtering, basically assuming that there won't be any out-of-band frequencies coming in. Which is probably ok if the FV-1 is the first thing after the guitar, but is a pretty ropey assumption if it's further down the chain. It should really have some decently heavy filtering in front of it (like -24dB/oct at 16KHz or less as a minimum) to make sure there's no alising in the ADC. You don't see it much on typical FV-1 schematics though.
 

[Cybercow]

All that said, I've not had great success with getting extremely dirty input signals to produce anything with any clarity from an FV-1 circuit. As I see it, the FV-1 was designed to accept clean, low-level signals (about 0.3V up to a max of 2.0V) for defined processing.

This doesn't come as a huge surprise. The chip is running on a 3.3V supply, so the *maximum* headroom is going to be somewhere around 3V, depending how close to "rail to rail" they got. It may well be significantly less.
With a typical input sample rate of 32KHz, a lot of distortion products going in will cause all sorts of chaos. Most FV-1 designs seem to be *very* light on pre-sampling filtering, basically assuming that there won't be any out-of-band frequencies coming in. Which is probably ok if the FV-1 is the first thing after the guitar, but is a pretty ropey assumption if it's further down the chain. It should really have some decently heavy filtering in front of it (like -24dB/oct at 16KHz or less as a minimum) to make sure there's no alising in the ADC. You don't see it much on typical FV-1 schematics though.

Precisely to what I was alluding.