Using computer audio output through effects?

[studiostud]

This has probably been covered before, but I was wondering what I need to do to run a line level signal from a computer through an effect pedal.  What I'd like to do is create some clean guitar sounds that I can run through a prototyping rig so I can see how the effect sounds with a guitar without either trying to play one while tweaking or having someone else there to play for me.  It would be sweet to just trigger an audio file on my computer.

Do I need some sort of impedance conversion circuit?

[Strategy]

Sometimes when I play live I will use a computer and I have an old MOTU 828 mark1 version. I use 828's additional audio outputs as aux send channels out to various FX pedals or synth modules -- and then back into the soundcard's inputs, using part of the software as a digital mixer. I have never used a Reamp style impedance converter; maybe I should do. Just make sure you can quickly adjust your computer's output volume so that you can compensate as different pedals have different gain stages and will respond differently. Unfortunately most soundcards that have knobs implement input gain control but not for the outputs, so output volume must be controlled in the software interface. or with your soundcard's master volume output knob.

Strategy

[studiostud]

hmm.  interesting idea.  I bet I could do that with my Digi002 and pro tools.  Would I have to do something different though if I wanted to output from the pedal into a guitar amp instead of back into the computer?

[ashcat_lt]

If you're working on something like a FuzzFace, which depends on the treble loss from loading a passive pickup, it won't work right without a pickup simulator.  For most other stuff, it should work just fine out from the computer into the pedals and then on to whereever you decide you want to go.  Back to the computer, into an amp, whatever.  The only real issue will be the output volume.  Line level is higher than standard guitar levels, but that was covered above.

[studiostud]

it won't work right without a pickup simulator. 

Is there such thing?  and if so, is there a schematic/layout for making one?

[.Mike]

it won't work right without a pickup simulator.  

Is there such thing?  and if so, is there a schematic/layout for making one?

Have a look over here: http://www.muzique.com/lab/pickups.htm

[jasperoosthoek]

@.Mika That's quite an interesting circuit! I'm quite bothered by a lot of mains hum when I roll back the guitar volume. Do you think it makes sense to build a mosfet booster followed by a pickup simulator?

This way my fuzz face still works normally, even at lower volume levels and I might get rid of the hum.

[studiostud]

Have a look over here: http://www.muzique.com/lab/pickups.htm

Sweet info, Mike!  Question:  The guide says to use a Mouser 42TL019 or 42TM019 transformer, but also said other small signal transformers would work.  I have a couple Mouser 41PG006 left over from an old project.  Would one of those work?  I know it's meant for small pedal board power supplies, but is there a difference between "small power transformers" and "small signal transformers"?

[alparent]

Not really using a computer..... but you might be interested in this?
http://www.geofex.com/FX_images/Fake%20Guitar%20Oscillator.pdf

[studiostud]

Interesting.  I might have to take a look at that soon.  Anyone have any feedback for my other transformer question?  Could I use a Mouser 41PG006 for the Muzique.com project?