Balanced 1/4" inputs on interface have too low volume?

dem466

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Currently I own a MOTU 828mk3 firewire interface.

I have multiple inputs going, namely a guitar & dynamic mic among others. I used to run the guitar & mic directly into the two front inputs (the mic as an XLR, the guitar as a 1/4" TS input with the instrument switch flipped). Both inputs gave me a good input gain.

However, to simplify my live setup, i'm running all my inputs for everything into the back of the 828. The rear contains 1/4" balanced/unbalanced analog inputs.

My chain is this: Guitar > passive DI > rear 1/4" input via an XLR-TRS cable (XLR coming out of the DI, TRS going into the Motu).

The problem is that the input level using this method is much much lower than plugging into the front panel. Even using the same chain but a dynamic mic instead of a guitar, the input level is still significantly low.

My understanding is that regardless of whether it's an XLR input or TRS, as long as it's balanced, it should carry the same level of signal through it. However it seems that unless it's going through the two front panel inputs, the input is way too low.

Any ideas what's going on here?
 
Currently I own a MOTU 828mk3 firewire interface.

I have multiple inputs going, namely a guitar & dynamic mic among others. I used to run the guitar & mic directly into the two front inputs (the mic as an XLR, the guitar as a 1/4" TS input with the instrument switch flipped). Both inputs gave me a good input gain.

However, to simplify my live setup, i'm running all my inputs for everything into the back of the 828. The rear contains 1/4" balanced/unbalanced analog inputs.

My chain is this: Guitar > passive DI > rear 1/4" input via an XLR-TRS cable (XLR coming out of the DI, TRS going into the Motu).

The problem is that the input level using this method is much much lower than plugging into the front panel. Even using the same chain but a dynamic mic instead of a guitar, the input level is still significantly low.

My understanding is that regardless of whether it's an XLR input or TRS, as long as it's balanced, it should carry the same level of signal through it. However it seems that unless it's going through the two front panel inputs, the input is way too low.

Any ideas what's going on here?

No, the rear panel contains only LINE inputs. There are only 2 mic/combi XLRs on the front. If you want to feed guitar into the rear TRS jack you will need a pre amp but you could probably use a decent (NOT f&&%G! 'true' bypass) pedal. The Boss GE-7 EQ would suit as it gives about 10dB of lift plus it sorts the impedance error.

There are probably ways to set gains to get around the issue but I am NOT wading thru' 108 pages of manual for you! In any case I understand MOTUs 'Quemix' system has defeated much better men than I?

FYI Passive DI boxes are almost all pretty low in level.

Dave.
 
The clue is the fact that the socket ion the front is labelled as instrument capable - balanced and unbalanced are just different type of feeds, they have nothing to do with level. Line level is either just over or just under a volt - microphones tend to be over a hundred, sometimes even more less. Guitars tend to come in between - perhaps between a tenth of a volt and half of a volt if you thrash them.

So in practice there are 3 levels - mic - instrument - line, but if you wanted to be accurate, you have to cope with this from smallest to biggest

dynamic mic at a distance
mic close up
guitar pickups
keyboard and synth outputs
line level from domestic kit
line level from professional kit
This takes you from .001V to about 2V, peak to peak from a quiet signal to the loudest.
 
It could be even worse. He says the signal out of his passive DI is an XLR. Usually, if there's an XLR output, the DI is adjusting the impedance, balancing, and attenuating the signal so it can go into a mic input of a mixer or, in this case, audio interface.

Frankly, unless you are forced into a long cable run, I'd just go straight into the instrument socket on the MOTU.
 
It could be even worse. He says the signal out of his passive DI is an XLR. Usually, if there's an XLR output, the DI is adjusting the impedance, balancing, and attenuating the signal so it can go into a mic input...
Actually, ALWAYS, a passive DI uses a transformer to balance the signal and provide more current (look like a lower impedance source), and that necessarily means a step down in voltage (what we call level). It has to and it will, and that's without any pad switch that might be attached.

The passive DI is the main problem. ecc83 is right on with the suggestion to use a pedal. If you can get a little gain out of it (the Boss EQ is a great idea there, though I've heard they can be a little noisy), that's great, but just the buffer should be enough.

Keep in mind, though, that the Instrument switch adds gain as well as increasing impedance, so the line input is still going to be quieter. From what I've seen, the difference is usually be around 9db. Adjust for that in your DAW somewhere.

Edit to add - You don't need to "wade through manuals". Record through one input, then the other. Try to play about the same thing each time. Eyeball the difference in level and remember it or write it down somewhere or something. Turn up the input gain on the first plugin in your signal chain that much every time. If that plug doesn't have an input gain knob, drop a clean/flat gain plug before it.
 
Ok. So people are telling me I need to get a separate preamp.

Thing is, this isn't just for guitar. I have a bunch of inputs I need going in at line level - guitar, vocal, cello, violin. All direct.

How about an active DI? I was looking at the Behringer DI800 - it's an 8 channel active DI that also has an option for +20dB. I'm assuming it's not the same as a preamp but might do the trick?
 
"I have a bunch of inputs I need going in at line level - guitar, vocal, cello, violin. All direct."

Then, ^ you have a bit of a problem. If all of those are passive devices, i.e. no powered amps on the instruments, you will need high to very high impedance inputs. For cello especially a Z in of 5, better 10 meg Ohms is needed to get a good bass response. The GOOD news is that just one V high Z pre amp (Z converter*) will do for all three instruments and the MOTU already has mic pres. Mind you, there are various ways to do this and some might suit your M.O. better than others?

Personally I would look for a small mixer. The A&H ZED10 has 10 meg line ins and 4 mic pres. Other, 'lesser' mixers have just the usual 10k Ohm line ins but you could buffer the guitar with a pedal and then just buy one V high Z pre for the fiddle etc. Go ask at a company called 'Orchid Electronics' excellent kit at sensible prices.

*You see the pickups need to 'see' a very high impedance but you rarely need much voltage gain so the pre really just converts high to low Z.

Oh! And avoid Berry active DIs, not one of their best products (many ARE good) and tend to be noisy.

Dave.
 
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I don't quite get why you are thinking about DI boxes? They MUST go to mic inputs. Getting your instrument level instruments up to line level is going to be a pain. probably simplest would be a mixer with enough channels, and then use the insert sends to connect to the MOTU line level inputs?
 
I don't quite get why you are thinking about DI boxes? They MUST go to mic inputs. Getting your instrument level instruments up to line level is going to be a pain. probably simplest would be a mixer with enough channels, and then use the insert sends to connect to the MOTU line level inputs?

Hi Rob. I have found people tend to use the term 'DI' box for almost anything that goes between an electronic instrument and a mixer/interface/amp! The input and output levels can be all over the shop.

To me, a DI box (unless otherwise stated) is a device that take a passive guitar signal and delivers it as a mic level, balanced signal at lowish impedance (Z will depend on the transformer ratio and the guitar for a passive box) The 'classic' DI box will also to my mind, provide a means to isolate the XLR ground from the input circuitry and a 'pass thru' signal to feed a guitar amplifier.

Maybe OP is thinking "DI box" but expecting it to deliver line levels?

Dave.
 
Yep - I wondered this too - I always think it's kind of backwards - A device that reduces a signal in level, or a device that amplifies it? One of those strange things I guess.
 
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