Box that allows guitar pedals to interface with mixer. A couple of questions...

[Tillmann]

I'm trying to find an elegant way of interfacing some relatively high quality effects pedals meant mainly for guitars with mixers.  The idea is to be able to use the pedals as effects either on an insert or on an aux or group bus for delays and reverbs and the like.  I am by no means a designer, but after a bit of a search here, I've not discovered anything here relating to this.  It all seems to be an issue of impedance to me unless there is something that I don't understand.  I want to take a moderately low impedance signal at line level and turn it into a high impedance signal at instrument level.  Then run it through the pedals, and then turn it back into a line level signal to go back into the mixer.  If I am not mistaken, mixer standards dictate that inserts are usually done unbalanced and aux and group busses are usually balanced, so that would have to be taken into consideration in the design of my proposed box.  Perhaps this is a taller order than I understand, but below were my ideas in regards to features and signal flow:


The Pedal Master

-Line In (¼” TRS or TS)  ---> 3-way selectable attenuation switch ---> transformer (raises impedance to instrument level) ---> Hi-Z Out (1/4” TS)

signal goes into desired pedals and comes out and then into:

Hi-Z In (1/4” TS) ---> Gain control (variable make up gain circuit) ---> transformer (drops impedance to line level) ---> Line Out (1/4” TRS or TS)


First off, is there a product out there already that I don't know of that does this already?  if not...
Does this path seem feasible or am I way off?  If I'm not way off:
Should the attenuation circuit be pre or post transformer?
Should the gain control circuit be pre or post transformer? Or:
Is the gain control circuit a bad idea?  Am I better of with only a transformer that drops the impedance to mic level and then I just send it out an XLR and use an external mic pre for gain control?  Basically this would turn it into a DI on the back end.

Note:
Line Inputs and Outputs of box should accept TRS or TS connectors for use on group (TRS), aux (TRS), or insert busses (TS).

 

[gemini86]

You're looking for a "re-amp" device to send line out to the pedals and then a DI to get back into the mixer, both of those things are well covered here. JLM audio also has some nice designs.

 

[Tillmann]

Yes, reamp would be a much better keyword for my search.  Thank you.

 

[abbey road d enfer]

The kind of circuits involved in your quest are really "Electronics 101".
Basically, you need a de-balancer (typically an opamp with 4 resistors or a dedicated THAT or SSM chip) and an attenuator (just a 10 cent-pot) to go from line level to guitar level. Then on the way back from your pedals, you need a balancer with some gain (a 3-opamp job or another SSM/THAT chip) preceded by another 10-cent pot.
Some manufacturers just do that, some do their utmost to load their stuff with all sorts of bells and whistles in order to charge you more.
There's a couple of DIY jobbers that offer just what you want at honest prices.

 

[joshco]

take a look at Ken Stone´s circuit. They are for Modular Synth but will work with Line Level

http://cgs.synth.net/modules/cgs46_sba.html
http://cgs.synth.net/modules/cgs60_sba.html

Its pretty much for what you are looking for.

 

[JohnRoberts]

Are you sure? 

Most TRS insert points are unbalanced so you can just use a TRS to dual TS "Y" cable.

I am not sure the sound quality of pedals justifies all the effort, but with the modest investment of a Y cable you can start using them on inserts and see what you get.

A friend of mine has a new business making pedals so he might have some input on the general topic. www.amptweaker.com

JR

PS: Something like an old -10dBv to +4 dBm bump box might help for interfacing into line level balanced inputs, a cheap bump box may not work well into unbalanced inserts.

 

[Tillmann]

Thank you for the help, ladies and gentlemen.  As to the issue of sound quality, although I own some mighty fine effects pedals, they're probably not an elegant solution when extremely high fidelity and transparency are the desired outcome.  That said, it's often the case that this is not necessarily the desired outcome for me and their coloration is nice.  They are an effect.  Also, just inserting a guitar effects pedal on a channel without some reworking of the signal will not do.  I own insert cables and the result's rarely anything but hum, buzzes, or oscillating tones.

The more I think about this, the only thing that I don't like about my original idea is that I would like to do this in a way where the box is passive.  I think gemini86 is right, a re amping box to get the signal down to instrument level, and then a DI to get it back to mic level and then use an external mic pre, which I have plenty of.  They'll handle "makeup gain" just fine.  Returning it to the mixer on an insert would require an adapter cable to unbalance the line unless returning it on an insert return on a patchbay, which should be prewired to do so already.

 

[dandeurloo]

The MW1 works really well for this kind of thing.  Pretty handy box!

http://www.creationaudiolabs.com/mw1studiotool

 

[gemini86]

Don't get me wrong, that's a nice looking piece of gear, but you're paying 800 bucks for bells and whistles and a producer's endorsement. This is DIY, just build a box, this is like a beginners project.

 

[zebra50]

Are you sure?  Most TRS insert points are unbalanced so you can just use a TRS to dual TS "Y" cable.

That's mostly what we've done over the years. Just use the insert or aux or group (or even headphone) sends straight to the pedal, then back to the insert, or DI box or line level in. No right or wrong here, just plug things in until you get the sound you're after. Guitar leads mostly take care of de-balancing! This usually gives something fun and usable for your 'science experiment'.

BTW, a couple of 1:1 transformers wired to jack plugs in boxes for balancing / debalancing duties are handy things to have kicking around.

 

[Tillmann]

Don't get me wrong, that's a nice looking piece of gear, but you're paying 800 bucks for bells and whistles and a producer's endorsement. This is DIY, just build a box, this is like a beginners project.

Once again, we are in agreement.

 

[gemini86]

To do this on the REAL cheap, you might grab some of those ground loop isolation boxes from radio shack that PRR suggested for his vari-mu design, there's two 1:1 transformers in there that would have a freq response that may be suitable for guitar use.

 

[pucho812]

depending on the pedal  just plug the fucker right in.  pedals can be loud enough. blanced to unblanced cable then unblanced to balanced on the way out. it may not be elegant but chances are if your using a guitar pedal on mixdown you don't want elegant.

 

[Nick Franklin]

If it was me, I'd be building a couple of re-amps and and a couple of DI boxes in a 1u rack using some cheap 600:10K or so mic transformers and forget about the switchable attenuators etc. You can always adjust the levels somewhere your DAW, on your mixer, or on the pedal itself. You could knock the whole project over for 150 bucks or so and get on with rocking  8)

 

[sodderboy]

This box does two channels I/O for $44, and you get volume control, albeit stereo, in both directions.
Mike

 

[Tillmann]

which box do you speak of, Mike?

Aaron

 

[sodderboy]

Sorry, forgot to copy the LINK to the BOX.  Rolls makes the exact same thing.  Based on 5532 chips inside and very moddable.
Good for a studio to have one or 2 on hand.  When I design a room, I recommend to have them wired to the bay, so the pedal can plug right into TRS tielines with guitar cables and be used wherever in the control room.
You really only need level matching with FX pedals.
Mike

 

[squib]

Putting my Broadcast hat on, I make a product perfect for your requirements

see here : http://www.broadcastproaudio.com/missing_link.htm

essentially a reamp and DI in one box, with interacting level / gain control, this enables you to set a suitable level into your pedals and have the level loss exactly made up in the DI stage back to your original line level.

 

[Hank Dussen]

... $450!!

if it's only levels adjustment, you can check out the adjusticator http://www.groupdiy.com/index.php?topic=35757.0

 

[Tillmann]

The missing link is great for all my requirements but one... my pocketbook.  Looks like a cool piece of kit however.