Converting a design for keyboard

[auden100]

Hey, folks. I'd like to experiment with running my keyboard through some lofi or tube-sound pedals to introduce a little character. I've got a few different schemes in mind, but I'm wondering about how to optimize them for keyboard rather than guitar. As I'm still in the planning stages, I'm hoping there might be some typical guidelines for how to do this. I'm assuming that some might be:

- Increasing input cap sizes to allow lower frequencies. How low is low enough?
- Using higher DC for more headroom. What would be a good amount? 12v?  15v?

Are there some other tips I could work with, or things I should keep in mind?

[Jaicen_solo]

In my experience, you need headroom, or at least some way of padding the input down.
After that, like you say, you need to be able to deal with lots of low frequencies without unintended distortion.
This is tricky, because it's not really an issue in most guitar or bass effects, where a little distortion can often be desirable.

Likewise, you need a good frequency range, from ~30Hz into the high 10kHz+ range, depending on what type of synth/keyboard you're processing.
My own experience is that parallel processing is most satisfying, allowing a blend of clean and effected signal, particularly with distortion or compression effects.

[amptramp]

It sounds like you have the right idea.  The lowest frequency I can hear as sound is 35 Hz and I have proven that repeatedly during vibration testing of aircraft equipment (which goes from 5 Hz to 2000 Hz).  The A below middle C is 220 Hz and the octaves below that are 110 Hz and 55 Hz, so figure out what your lowest output frequency is and design for the amount of low-frequency attenuation you need.  There have been some threads on tweaking pedals for use with a bass guitar - search those.

You may need more headroom, but if you are running a synthesizer into a Tube Screamer, you do have a drive control that you can back off - you don't need to carry higher levels through the pedal chain.  If the signal goes from 100 mV for guitar to 1 V for synthesizer, you need 0.9 volts more headroom.  For most pedals, you already have enough.

You may want to change the design of certain functions.  If you have a diode fuzz, you may want to establish a path around the diodes so that you don't get a sound made of a fundamental and its harmonics transformed into a sound waveform that contains the original waveform to a certain voltage then flatlines above and below that.  What sounds good with a guitar that has a frequency response starting at, say, 82 Hz, may not sound right at lower frequencies, and it is not a matter of tweaking the unit for more bass - it may require a fundamental rethink of what sound you want.  For example, a Tube Screamer may work fine because the non-inverting clipping stage has a gain of one for the input signal even when it is clipping whereas a DOD250 just clips flat and would sound more harsh.

[Jaicen_solo]

Don't forget that although the lowest frequency you can hear is 35hz, harmonics below that will still affect the sound if allowed to get into clipping stages for example.
A 35Hz signal when clipped heavily will give you a range of harmonics above, so it will become more apparent.

[auden100]

I'll definitely try to work in a Dry-blend. That seems like a great idea. I'll start breadboarding some things from here. Find out what happens with those various frequencies when clipped.

Thanks for the responses, folks. I hope I do ya proud.