GT The Brick and Excessive Distortion

[Zthom]

Hello all,

A quick question for someone who knows more than I do: I recently purchased a GT brick at a local music chain for a really great deal. I plugged it into my MOTU 828 mic input making sure that the mic/line switch was set to the line setting so as not to engage the phantom power on the motu itself. The preamp distorted like crazy even with the gain knob set to "0." I checked everything and it seemed to be working ok. As a test, I took the mic output cable, attached a XLR Male to 1/4" Male Mono Microphone Mic Adapter and plugged it into a standard 1/4 inch input on the MOTU and it worked perfectly.

Does anyone know why this is? I am a little confused. In both instances, the only phantom power was coming from the Brick itself and I don't see why it would make a difference if I use the 1/4 adapter or the XLR from the mic cable.

As a point of reference my chain went like this: BLUE baby bottle, Blue kiwi cable, GT brick, MOTU 828

Any input would be really helpful

Zach

 

[kojdogg]

was the 1/4" adapter TS (one stripe) or TRS (two stripes)?

 

[Zthom]

I think it's a TS (one stripe). Some cheap radio shack thing

 

[kojdogg]

It's not about phantom power, it's about signal level and balanced to unbalanced connections. Going from XLR to 1/4" TS most likely dropped the level of and unbalanced the signal level from your preamp output.
Await a more technically sound explanation from another poster or consult this link:
http://www.vandenhul.com/artpap/wiring4.htm

 

[notCardio]

So let me get this straight

You took the XLR output of the Brick into the XLR input of the MOTU, setting the MOTU for line input, correct? To me, it almost sounds like the MOTU is taking that XLR in as a mic level signal. When you say the gain knob, you mean the one on the Brick, or the one on the MOTU?

This sounds like it should be easy to solve, but give me a while to look up the literature.

If anyone else has an idea, jump in.

 

[Zthom]

Correct..

Yes, I took the mic output from the Brick and initially inserted directly into the mic input on the MOTU with the switch set to Line. I'm not sure if the MOTU bypasses this switch if an XLR is put into it but it doesn't seem like it should. I was addressing the gain knob on the Brick.

Zach

 

[notCardio]

OK, for starters, if your unit's like what I just read on MOTU's site, do NOT hook it up that way. I didn't get into the specifics enough to see if you could bypass the mic pre through the XLRs, but if you don't have to use them, don't. You don't want the Brick to go into a mic pre, so use one of the other 1/4" inputs. Also, as was mentioned earlier, you need a different cable. You need an XLR (is that the only out offered on the Brick?) to TRS cable. This will take your balnced out from the Brick to a balanced in on the MOTU. I guess I should look up the Brick because I can't believe it would only have an XLR out. It should have a TRS out, which would then allow you to just use a TRS to TRS cable (easier to find then an XLR to TRS, especially if you're in a smaller town).

 

[Zthom]

Thanks..

Ok...got it. The Brick does not have a TRS output just the balanced XLR output. I will go out and get an XLR to TRS cable.

Thanks

 

[notCardio]

Hmmm

the Brick only shows the one XLR out, so I guess you need the XLR to TRS cable. According to the Brick literature, when you are using the mic input (not true of the instrument input), even when you set the gain to zero, you're still automatically getting 25dB of gain, so that explains why it was still noisy.

I would think there would be something in your MOTU documentation about using an external pre with the unit. I'm fairly certain though, that you need that cable and to plug it into one of the non-mic pre 1/4" inputs on the MOTU. If you can, you probably also need to set up the MOTU input to accept +4 as opposed to -10, as the Brick outputs at +4.

I'm hoping some other MOTU people jump in here to help you with setting gain, etc. And to tell us if I'm way off base (I don't think so, though).

Good luck. I'll try to keep an eye on this thread for awhile, but I'm hoping to get to leave for GC soon. (I hear my credit cards scurrying in panic)

 

[mattamatta]

Yeah, you're gonna want to go into a TRS input on the MOTU. I dont believe that is a mic/line switch, just a phantom power on/off toggle, so you're still running into the other preamp.

 

[notCardio]

And, not getting pissy or anything, but in the future, questions about mic pres really belong in the Rack forum, unless it somehow involves a mic-specific problem or question.

Good luck.

 

[Zthom]

Thanks For the Help

Thanks for all the input.

Sorry about the wrong posting site.

Zach

 

[notCardio]

No prob.

You'll have more questions, I'm sure. Someone in the Rack forum surely will be able to help. You've made it to the limit of my abilities.

 

[Supercreep]

I had the same issue with my BG-1 into my 896HD. MOTU tech support swore, by the way, that there was no difference in using either XLR or 1/4 inch - once they actually got around to calling me back. The guy at DAV told me I could only use 1/4 inch - knowing more about MOTUs product apparently than MOTU tech support does, since he was right. It's a MOTU thing.


I do love my 896HD, by the way.


Oh, and I have an enormous pile of chinese condenser microphones.