How to make an effect ready for DI recording?

[fuzzy645]

I know this is a very general/broad question, but is there some type of stage one can add to the output of an effect  to make it work for direct recording?

I would really love to have an effect that can be used for BOTH live and recording.  Thinking out loud here, would a solution be to have some kind of switchable output buffer to toggle between one buffer that provides the standard output impedance one would normally find in a stomp box (I guess in the 5K - 20K range) to send to an amp, and then a 2nd buffer to convert to a very low impedance (in the 100-200 ohms range) so that the effect can be plugged direct into a recording console.

Am I smokin' crack here???

[therecordingart]

Am I smokin' crack here???

Kind of.

You can do this a few ways ranging from cheap and simple to really expensive,  but some questions first:

-Do you want a balanced or unbalanced output?
-Do you want to plug into a mic level or line level input on the mixer or recording device?

You don't need to switch between a lower output impedance buffer and a higher impedance output buffer...you only need the lower output impedance buffer (and maybe a little gain) to drive the line input of your mixer or recording device. I throw this out there a lot, but it's all about the load loss calculation when it comes to signal level in relation to load/source impedances.

http://shure.custhelp.com/app/answers/detail/a_id/224/~/should-i-match-impedances-of-my-microphone-to-my-mixer%3F

EDIT: Now that I'm thinking about this a little more you probably only want to plug in to a line input, correct? If so, an IC buffer will provide the low output impedance, but you still MIGHT need some gain and the output will be unbalanced. Getting a little gain is easy (just a couple feedback resistors from the output of the IC to the inverting input). If you need a balanced output that can be done a few ways. You can use a transformer, a THAT Corp 1606/1646, or you can read this (section 2.4):

http://www.jensen-transformers.com/an/an003.pdf

[DavenPaget]

Why not ?

[tempus]

the standard output impedance one would normally find in a stomp box (I guess in the 5K - 20K range)

Are you sure that figure is accurate? I know the Boss page specs their pedals at only 1K output Z. May make a buffer unnecessary. I'd try one in a direct recording situation to see if the lower output Z is actually needed before getting too fancy. I suppose you could also just check the input Z of your recording interface/console.

[therecordingart]

The unbalanced input z (line level) on the Mackie Onyx is 15k ohms. A stompbox with an output z of 1k5 or less would be perfect if your signal level is a few hundred mv or higher.

Read that Jensen PDF tha I posted if you want both balanced and unbalanced outputs.

[fuzzy645]

 

EDIT: Now that I'm thinking about this a little more you probably only want to plug in to a line input, correct? If so, an IC buffer will provide the low output impedance, but you still MIGHT need some gain and the output will be unbalanced. Getting a little gain is easy (just a couple feedback resistors from the output of the IC to the inverting input). If you need a balanced output that can be done a few ways. You can use a transformer, a THAT Corp 1606/1646, or you can read this (section 2.4):

http://www.jensen-transformers.com/an/an003.pdf

Thanks all for your responses and info.

Yes, I'm looking to take the signal up to line level for recording purposes.  So maybe the pedal can have 2 outputs.  One output would be a standard unbalanced output to feed into an amp for live use, and the other output can go through this additional circuit w/transformer that converts to a balanced output.

[therecordingart]

This will do it for a few extra cents (pulled from the Jensen PDF). This is the cheapest option and it's simple...at least cheaper than a transformer. If we were allowed to do group buys it'd make orders from Edcor very attractive. Their prices are great, but to ship a single transformer in the US they charged me $14 (vs the $6 the transformer costs), and even using my UPS account the shipping would've only been $7, but I digress.

The other option if you want to avoid a transformer is to use a dual opamp (like a TL072) and make a splitter. One of the outputs can feed your amp while the other output can feed a THAT 1646 chip. You can even make a splitter from discrete components:

http://www.muzique.com/lab/splitter.htm

There are plenty of ways to do this and each one has it's own pros and cons. As I learn more about electronics I'm starting to find that you can do the same thing many different ways, but the devil is in the implementation. It's really easy to get carried away and over complicate things.

[tempus]

The Edcor transformers are a bit on the huge side as well. I use one for a balanced mic out from my pedalboard to the PA for my piezo bridge equipped electric. It sounds fine, and gives me an isolated, balanced out but it needs a fair amount of room. I think the Jensen and Sowter ones are about the size of a sugar cube by comparison.

This is one other thing to consider; using any of the non transformer balancing schemes doesn't give ground loop isolation, which may or may not be an issue. If the OP is using his box for either live or direct recording, it wouldn't be an issue. I needed the isolation, since my live shows require simultaneous connection to my guitar amp and the PA.

[therecordingart]

The Edcor transformers are a bit on the huge side as well. I use one for a balanced mic out from my pedalboard to the PA for my piezo bridge equipped electric. It sounds fine, and gives me an isolated, balanced out but it needs a fair amount of room. I think the Jensen and Sowter ones are about the size of a sugar cube by comparison.

This is one other thing to consider; using any of the non transformer balancing schemes doesn't give ground loop isolation, which may or may not be an issue. If the OP is using his box for either live or direct recording, it wouldn't be an issue. I needed the isolation, since my live shows require simultaneous connection to my guitar amp and the PA.

Very good point!