Adapting Stompbox Circuts for use with Synths/Line Level

[plushterry]

Hi!  I like your forum, lots of cool info on here.  Thanks for having me.

I don't actually have a guitar these days, but I like to use stompboxes as FX on my synths and samplers and also as inserts/loops on my mixer.  Some work ok and others not so well, I know this is because all my kit puts out a line level output rather than the lower level that comes from a guitar.

I've done a bit of research and ordered a kit to build a reamp box and a pad box from DIYRE, I will try these, hopefully they should get things in the right sort of range. 

I know just enough about electronics to be dangerous, so it seemed to me that there would surely be a way to adapt a circuit with a few resistors to make it work with a line level, or would you need to completely redesign the circuit?  Does anyone know enough about it to explain to a simpleton like me?

Ideally my ultimate goal is to be able to make my own multi-fx unit/mixer using stompbox designs that I can use with all my studio kit.  Am I mad? (Obviously I will do a few smaller builds first)  Please tell me if I'm on the wrong track.

I have a soldering station that I know how to use, and I'm willing to learn haha.

[ashcat_lt]

Usually, there's a volume control on the source and you have the opportunity to get gain somewhere after the pedal.  If you really want to, you could build those things into your pedals. 

The other option in some cases might be to just use a larger power supply, but in practice in real circuits that often requires changing a bunch of other things.

[anotherjim]

The thing that breaks a lot of guitar FX pedals with synths isn't level as such  - you can always turn the synth down! That said, I suppose if its a patchpoint feed from a modular or semi-modular, it may not have a dedicated level control.

An electric guitar has certain tonal quirks - weak bass under 200Hz, strong mids, little or no output over 5Khz and inductive pickups that interact with the pedals input circuit.

Then it's heard through a guitar amp - High input impedance, funny tone controls (hard to find a "flat" setting) with a mid cut to counter the guitars strong mids, speaker cab with weak bass and next to no output over 5Khz.

Guitar fx often lean on these quirks to allow simpler circuits. Have a look at an MXR Distortion+ schematic for a stupidly simple distortion that relies heavily on being in a guitar rig. Played over full range speakers, I think you would find it the most horrible sound ever. Even Trent Reznor might baulk at it!

So the first thing I would do is get an amp-simulator/DI that can feed the guitar stuff into it's expected high impedance, craft the bandwidth into guitar cab limits and then feed to your normal amplifications low impedance line inputs.

At the synth end, if it has extra high pass and low pass filters, use them or an eq pedal to control the synths overall bandwidth, but something more sophisticated might be possible, so the synth looks like a guitar to the fx input. A Passive guitar pickup emulator.

So far, this article is the "bible" as far as I'm aware.
http://www.muzique.com/lab/pickups.htm

[robthequiet]

Here is a thread that might shed some light, although not exactly beginner level it does include a nice explanation and layout, http://www.diystompboxes.com/smfforum/index.php?topic=113994.msg1057002#msg1057002

[Pedalhead]

I dunno if this is any good. Synth Stompbox Adaptor. No stripboard layout, but looks simple enough.

https://cgs.synth.net/modules/cgs60_sba.html

[Strategy]

I use all my pedals with synths, no adaptor. Only with modular synths, which put out 10vpp signals - really hot (except Buchla circuits, which are line level too.) I just control the synth output volume so I'm not clipping the pedal.

Strategy

[plushterry]

Wow you guys rock!

Many many thanks for the suggestions, that's a nice bit of reading to be done there.

Thank you!

[plushterry]

I've had a brief read through, it looks like the info you kind gents provided is pretty much exactly what I need.   Thanks again so much. 

I'm not going in totally blind, i have a fair understanding of physics, i understand ohms law, induction, electricity etc. how to read circuits, i can solder fairly well already and I've been 'producing' "music" for about 12 years so I understand audio/hertz/dB/sample rates fairly well.   I was sort of hoping it would just be a case of filling in a few gaps in my knowledge but it looks like it will take a bit more than that.   

No problem, i like learning!  Best way is in the deep end right?