Impedance Question

[bharris22]

Hi Everyone,

I plan to use a Laney IRT Pulse to record my electric guitar into my DAW. The Laney sends both a processed and a clean signal to two different tracks in the DAW. I would like to "reamp" the clean signal out of the box using some of my guitar pedals. I found this product from Radial Engineering that seems intended to do just this: http://www.radialeng.com/extcsa.php. As I understand it, I would take the line level signal out of my audio interface (a Steinberg UR22), plug it into the Radial device, plug my pedals in to the Radial device and then send my pedal-processed guitar signal back into the Hi-Z input of the UR22. The issue, though, is that the Radial device is approximately $260. I already own an ART Tube MP Studio preamp that would accept a line level signal and output an unbalanced signal with an output impedance of 300 ohms. Although this output signal is not a high impedance signal, can I still use this as an input for my guitar pedals to achieve the same purpose? Using the usual rule that the input impedance of a device should be at least 10x the output impedance of the source, the guitar pedals should still be well over 10x the 300 ohm output impedance of the ART preamp. Would this signal sound okay? Would I do any damage to my pedals in this setup?

Thanks in advance for your assistance!

[BertKoor]

Would I do any damage to my pedals in this setup?

From both a theoretical and practical view: nope, no harm will be done. Most likely that is, and don't feed it full force at the first try

[khanyz]

Check out Orchid Electronics, it's what I use.

http://www.orchid-electronics.co.uk/Amp_Interface.htm

Then an isolator or DI (depending on pedals used) all for £100 or so. They can also do custom stuff for not much more and with the dollar being strong, it should be a bargain.

You can also use the Art Tube MP for the return, but I prefer to have some form of isolation. This stops any problem with earths, DC offsets (from asymmetric distortion) etc, etc.. This is why I wouldn't plug directly into the Hi-Z input of your interface. I don't think the Art has any isolation/transformers in the audio path. Personally, I wouldn't use the Art to send. I'm guessing it would workish, but with a purpose built box for ~£50, I haven't tried (I have the Studio V3 and a Levelar).

[sprnva]

While we're talking impedence... when using a laptop or iPad as a guitar effects processor, is it better to use the headphone out or a line-level out from an audio interface into the amp (or it's effects loop)?

In the case of the iPad it's much more convenient for me to just run the headphone jack into the amp as I don't have to disconnect my Scarlett from the computer to hook it up to the iPad. I have an iRig Pro to feed the guitar into the iPad.

[bharris22]

Thank you, everyone, for your input! Khanyz, that Orchid device looks perfect - if I understand correctly, it does the exact same thing as the Radial - in other words, takes a balanced line level signal from the audio interface and outputs a hi-z signal for further amping, pedals, etc. - is that correct? If so, it certainly is much less expensive than the Radial. I already sent an e-mail to them to see how much extra to put an isolator in the box, too. One additional question, though - if I plan to send the signal from the pedals back to my audio interface (and can use the hi-z input on the interface) why do you think I would I need a DI? Just trying to figure out if I would ever need this so as to have them include it in the box, too, if necessary.

Thanks!

[khanyz]

^Yes it takes a balanced signal and coverts it for amp/pedal use.

The reason I use an isolator for the return is to stop DC offset and solve earth issues. These may not be an issue for you, and they aren't always for me, but it saves time/hassle just to do it.

You can always just get the Amp Interface, then an Isolator/DI later on. I already had one of their Isolators (with a TRS one end and XLR the other) so just used Velcro pads to stick them together. Also, if they are busy (which is usual), custom jobs can take a while.

Please note that the output from the isolator/DI is balanced and can be mic or line level (depending on the padding, if any). I treat my isolator as line level.

[BertKoor]

While we're talking impedence... when using a laptop or iPad as a guitar effects processor, is it better to use the headphone out or a line-level out from an audio interface into the amp (or it's effects loop)?

In the case of the iPad it's much more convenient for me to just run the headphone jack into the amp as I don't have to disconnect my Scarlett from the computer to hook it up to the iPad. I have an iRig Pro to feed the guitar into the iPad.

I've done the maths, and you can plug a headphone out into something that expects line level signals without damage. Just be careful with the level you're feeding! If this amp has a low impedance input: better use that ofcourse. But a high impedance input should not really be an issue.

More choices means you can compare what gives best results in your situation.

[bharris22]

^Yes it takes a balanced signal and coverts it for amp/pedal use.

The reason I use an isolator for the return is to stop DC offset and solve earth issues. These may not be an issue for you, and they aren't always for me, but it saves time/hassle just to do it.

You can always just get the Amp Interface, then an Isolator/DI later on. I already had one of their Isolators (with a TRS one end and XLR the other) so just used Velcro pads to stick them together. Also, if they are busy (which is usual), custom jobs can take a while.

Please note that the output from the isolator/DI is balanced and can be mic or line level (depending on the padding, if any). I treat my isolator as line level.

I heard back from Orchid and the Amp Interface apparently does have transformer isolation . Thanks again for letting me know about this!