Connecting Balanced External SCA Preamp to Unbalanced Insert Jacks

[mdmitch2]

I just built an SCA T15 (transformerless) preamp, and I'll be using it for the first time this weekend to record vocals. My interface is an Alesis io26, which has 8 XLR/TRS combo jacks with inserts for each. According to the manual, to bypass the Alesis preamps, I need to connect via the 1/4 inch unbalanced insert jack. However, the T15 has only a balanced XLR output.

So, can I simply use an XLR to TS cable? I found a thread on the SCA forum suggesting wiring your own cables for this, but I'm wondering If I can't save myself the trouble and use an XLR to TS cable such as this one from EWI: http://www.audiopile.net/products/Mi...C_cutsheet.asp

Also, am I sacrificing any quality by connecting this way?

(Fyi, I posted this on the SCA forums yesterday, but no responses yet, and I need to get this working asap since the singer is coming in 2 days.)

Thanks!!

[roadsweeper]

you should ideally use an XLR to TRS cable to keep it balanced. However, if you are only going to be travelling a short distance with the cable a TS should probably be fine. If you're going to be buying a cable anyway though you may as well get a balanced one.

[Singinto Th'Can]

Search around here for threads on connecting to mbox 1 inserts (the threads often include the brick preamp). Should be the same deal. Basically you need an XLR to 1/4 in cable and a polarity reversal adapter (also sometimes called a phase inverter - such as those made by Shure and Hosa).

I don't know the exact specifics of your situation, but this is likely to do the trick. Good luck!

[mdmitch2]

Originally Posted by roadsweeper

you should ideally use an XLR to TRS cable to keep it balanced. However, if you are only going to be travelling a short distance with the cable a TS should probably be fine. If you're going to be buying a cable anyway though you may as well get a balanced one.

So it's not a problem connecting the balanced TRS cable to the unbalanced insert jack? For some reason, I was thinking that was a bad idea. (obviously I'm not up on my "cable science" )

Thanks for the reply!

[skatingbasser]

How is an insert jack unbalanced?

[roadsweeper]

Sorry, didn't see that the input is unbalanced. Why are you using the insert points rather than the line inputs? I'm afraid I'm not familiar with the Alesis interface but I assume that it has balanced line inputs? If the signal going into the line inputs has already been pre-amplified then it shouldn't need any additional amplification therefore bypassing the pre-amps (from my experience with interfaces). Also, surely the insert points are balanced as they need to both send and return a signal therefore requiring both hot and cold wires. If that it the case with your interface then you would have to use a TS however you will need to refer to the manual as to which wire (hot or cold) is connected to return.

All in all though I would avoid using the insert points for pre-amps, it seems like a strange way around it.

[mdmitch2]

Originally Posted by skatingbasser

How is an insert jack unbalanced?

I believer you're correct -- I think I was just misinterpreting the manual. The insert jack probably is balanced. It suggests connecting to the preamp with an insert cable which has one TRS end and two unbalanced TS ends... that threw me off. Thanks for pointing that out.

[mdmitch2]

Originally Posted by roadsweeper

Sorry, didn't see that the input is unbalanced. Why are you using the insert points rather than the line inputs? I'm afraid I'm not familiar with the Alesis interface but I assume that it has balanced line inputs? If the signal going into the line inputs has already been pre-amplified then it shouldn't need any additional amplification therefore bypassing the pre-amps (from my experience with interfaces). Also, surely the insert points are balanced as they need to both send and return a signal therefore requiring both hot and cold wires. If that it the case with your interface then you would have to use a TS however you will need to refer to the manual as to which wire (hot or cold) is connected to return.

All in all though I would avoid using the insert points for pre-amps, it seems like a strange way around it.

You're right, the inserts are balanced -- I misread the manual. The io26 does have balanced line inputs as well, but they're the neutrik combo type, and they run through the preamp circuitry, which is what I was trying to avoid since the T15 is high end in comparison to the onboard pre's (much like a DAV BG-1).

Thanks again for the quick replies!! I'll be buying an XLR - TRS cable

[filthyrich]

I have a rack of sca pre's as well (5 A-12's and 3 C-84's). I run the SCA's balanced outs into the back of my 1/4 balanced nuetrik patchbay. i use a patch to connect the top and bottom on the front and then out the back they go to my motu 24 i/o.

I would like to insert my RNC sometimes while I am actually recording. Can I run the RNC in the middle of the chain by just using balanced trs 1/4 patch cables?

I'm able to use the rnc's after I record because the line outs on the MOTU can send balanced or unbalanced.

Could I hurt anything by just trying it? OR..if it doesn't work..will the RNC just not pass signal (which i'd see/not see on the gain reduction led's)??

thanks-
-Rich

[mdmitch2]

I remembered seeing something on FMR's site, and sure enough, they have a pretty detailed write up with regard to connections (links below), and it seems like the TRS - TRS cable would probably work. However, they do offer the following caveat:

"If you're hooking up the RNC inputs to a balanced source, we strongly recommend that you get the source equipment manufacturer's to advise you on the best way to do this. There are some output circuit and hook-up combinations that could damage your source equipment if you're not careful. "

FMR Audio - Home of the Really Nice Compressor and Preamp (512) 280-6557

FMR Audio - Home of the Really Nice Compressor and Preamp (512) 280-6557