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Use as a guitar pedal.

e14 Contributor

I was hoping to use the Cirrus board as a digital effects guitar pedal. I was planning on using line in and line out since the connections make things very simple. However, I have run into some problems with the line out to guitar amplifier connection. First of all, though, I tried recording through line in. When I played what I recorded through my computer speakers it sounded pretty good. When I connected the line out to my guitar amps (Vox AC15C1 / Marshall MG15FX) it had a significant amount of noise coming from the board. I then thought it might be the cord. I tested this by connecting my laptop to my amp with the same cord and playing the same file from my laptop, but this time there was no noise. I checked and the output impedance of the RPi and the Vox are both 15 ohms. One thing I was thinking might be a problem was the max capacitive load for the line out, which was 2 nF, but I haven't been able to find anything about that related to the Vox.

 

So does anyone know what could be causing noise from the line out only when it is connected to a guitar amplifier? And has anyone tried to use the Cirrus board with the RPi as a guitar pedal?

 

Thanks

  • 0 in reply to e14 Contributor

    the power supply you are using is a switching(switch mode), while they are typically more efficient, and cheaper(smaller parts) than a linear type, but they follow the two out of three rule, they are going to be noisy compared to linear supplies. you can put a ferrite core around the end of the power supply cable, this may reduce some of the noise from the wall wart. http://www.newark.com/ferrites-split-core?searchRef=SearchLookAhead

     

    most all transformers do not have electrical connection between the primary and secondary windings. this is where the isolation comes from. as long as the two grounds are not connected together external to the transformer.

     

    can you tell what frequency the noise is?

  • 0

    I tinkered a lot while in college, my grades suffered a bit image  I kept getting in trouble with girls so I instead took some time to build an MP3 player for my car, this is when a 32MB mp3 player was like $200.   I was of course a Jr by then.

     

    Back in the day (1998) there was this guy with a small effects box, it had tons of effects.  I always wanted one of those, but they seem to be phased out.  Now you can use a phone as an effects box.  I have one for my IPAD and it works very well, can record etc..

     

    Odd, most guitar amps these days have noise filters for us not so good players.  Allows me to be sloppy on the stings.

     

    You could try a battery, I can show you a cheap setup if you want.

    Did you try powering the PI from a USB port on a PC?  That may provide an alternative just for testing.

  • 0

    Hi all, sorry I just moved back to college (junior year) and was without internet for a while.

     

    When I first was trying out the RPi it was powered from a PC and that was really noisy.

     

    Are there any suggestions for an audio isolating transformer? One of my friends has a Voodoo lab pedal power 2 plus for his

    pedal board (which I think includes the audio isolating transformer), but I don't have enough pedals to justify buying something like that (for now at least).

     

    Also, there is virtually no noise when I plug the RPi into the same power strip as my amp, so the noise isn't too much of a problem,

    I'm just nervous after hearing how potentially bad not having an audio isolating transformer can be.