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2 much gain? DI vs line out


bear-foot-bass
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I play in 2 bands - one rock covers in pubs and clubs and another more mellow one in churches. For the rock band I use a Peavey Mark IV head and 1x15 Black Widow cab. I use a DHA for overdriven sounds on some songs. The sound is great, only challenge in smaller venues is keeping the volume down on the backline - rarely going past 1 on the master.

For the church band I use an old practice amp, its a bit ropy so I go through a Hartke VXL DI'd to the desk which gives a little extra definition to the sound and the option of some OD if needed (don't tempt me). Works well.

At a recent outdoors gig with the rock group we had a sound guy who was keen on taking a DI rather than the line out of my Peavey that I normally use. Whats the advantage of a DI feed rather than a line out?

Also as I already have a DI in the Hartke, which I'll take for future large PA gigs, should I be running through the DHA>Hartke>amp/PA in the pub band. Where I typically have more than enough volume and gain options.

Any ideas / thoughts welcome.

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The advantage of DI over line out is reasonably straight forward. There are many resources that can explain 'Direct Injection' better than I, but I'll try to simplify as much as possible.

DI is a low impedance 'balanced injection'. What this means is that your bass signal is split into 2 signals, one 180 degrees out of phase to the other. The 'transmitter' for want of a better word is designed to send this signal down longer cables with less effect on the signal (degredation etc). when the signal reaches the other end,at the 'balanced line receiver', the out of phase signal is flipped back 180 degrees and summed with the original signal.

Now what difference does this make, you ask?

Well, any noise that is pickups up along the cable on the 2 signal paths will be 'in phase' on both 'wires'. Now, when the receiver flips the signal over, the noise on the wires will now be 180 degrees out of phase with each other. When the receiver sums the 2 signals together the noise will be cancelled out leaving exactly what left the transmitter 'sent' in tact.

A line out signal does not have this ability, but you'll be ok with short cable runs on a line out. Also 'DI' is essentially a standard, so you can pretty much guarantee connectivity between all DI ins and outs, as they are all at line level and around 600 Ohms impedance. Line out signals can vary between instrumet level (bizarrely) and SERIOUSLY hot signals.. lol.

Hope this helps!

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What Dood said +1

When I was in my sound engineering days, if a bass amp didn't have a DI then we'd use a short cable run from the line out straight into a DI box before plugging that into the snake. If it wasn't from a mic or a DI box, it didn't go into the board.

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I don't get it... aren't the line outs of amps (XLR) doing all that phase stuff that DI boxes do? How else would you go to the mixer if not by a mic or a DI or a line out from the amp (which for what I know is the same as DI)?

I have an SWR 350x and 90% of the time the sound guy just takes a cable from the line out on the back and I usually flip the switch to have the preamp stage affecting it, so I get the valve warmth but I can also change EQ and volume to hear myself on stage without changing anything front-of-house ... Only a few times the engineer insists on taking the signal from my bass to a DI, which I hate, and it's usually coz he trusts that box and knows what to do with it and doesn't want anything added by the amp and doesn't want to take any chances (he'd rather have every1 sounding the same but control it). Very rarely a guy will prefer to mic it, which is fine with me as long as I don't change EQ and volume much during the gig...

[quote name='dood' post='39971' date='Aug 1 2007, 12:41 PM']The advantage of DI over line out is reasonably straight forward. There are many resources that can explain 'Direct Injection' better than I, but I'll try to simplify as much as possible.

DI is a low impedance 'balanced injection'. What this means is that your bass signal is split into 2 signals, one 180 degrees out of phase to the other. The 'transmitter' for want of a better word is designed to send this signal down longer cables with less effect on the signal (degredation etc). when the signal reaches the other end,at the 'balanced line receiver', the out of phase signal is flipped back 180 degrees and summed with the original signal.

Now what difference does this make, you ask?

Well, any noise that is pickups up along the cable on the 2 signal paths will be 'in phase' on both 'wires'. Now, when the receiver flips the signal over, the noise on the wires will now be 180 degrees out of phase with each other. When the receiver sums the 2 signals together the noise will be cancelled out leaving exactly what left the transmitter 'sent' in tact.

A line out signal does not have this ability, but you'll be ok with short cable runs on a line out. Also 'DI' is essentially a standard, so you can pretty much guarantee connectivity between all DI ins and outs, as they are all at line level and around 600 Ohms impedance. Line out signals can vary between instrumet level (bizarrely) and SERIOUSLY hot signals.. lol.

Hope this helps![/quote]

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[quote name='1976fenderhead' post='40879' date='Aug 3 2007, 01:02 PM']I don't get it... aren't the line outs of amps (XLR) doing all that phase stuff that DI boxes do? How else would you go to the mixer if not by a mic or a DI or a line out from the amp (which for what I know is the same as DI)?[/quote]

What don't you get mate? Yes, XLR DI outputs on amps are essentially the same as seperate DI boxes. Either will get the signal to the desk. I guess for an engineer an external box of his own is a known quantity.

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[quote name='dood' post='41248' date='Aug 4 2007, 12:59 PM']What don't you get mate? Yes, XLR DI outputs on amps are essentially the same as seperate DI boxes. Either will get the signal to the desk. I guess for an engineer an external box of his own is a known quantity.[/quote]

Well, I guess I don't understand what a line out is, since my amps always had balanced DIs, which I used to call line outs as well, but I suppose I shouldn't because that name applies to unbalanced outs? So some amps have unbalanced outs? What's the point of that???

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Unbalanced line-outs fall into the "useful" rather than "professional" category.

I use it for running my preamped signal into mixers without balanced inputs (most inexpensive home studios), running a line to a tuner to keep it out of the signal path and running a signal to a second backline amp. I use it a lot more than DI, which is just for "proper" recording and for our larger gigs. Line out gets used about 90% of the time my amp is on.

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[quote name='1976fenderhead' post='41301' date='Aug 4 2007, 04:31 PM']Well, I guess I don't understand what a line out is, since my amps always had balanced DIs, which I used to call line outs as well, but I suppose I shouldn't because that name applies to unbalanced outs? So some amps have unbalanced outs? What's the point of that???[/quote]

An unbalanced line out is usually just a 'pick off' of the amp/preamp/fx signal using a normal 1/4" / 6.3mm socket. The pick off point isn't always buffered either.

unbalanced 'line outs' can be used for slaving poweramps to drive additional cabinets for example. Thus the DI socket can still go to the PA. A line out socket sometimes appears after the volume control in the signal chain as well, so a DI wont be affected by changing your master volume control, whereas the line out can be.

Also, those who like chaining amp heads together could make use of this output. Take the Muse/Audioslave bass player thang of running one amp clean and an additional one dirty. Again, the line out is an option as you can add effects after the line out, feeding the second amp. You could send a line out to your stage monitors too. Again the FOH wont be affected by adjusting your stage volume.

Really, you can use the line out for whatever you want! In-ear monitoring output is another possibilty.

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Thanks for your help - I get it more now and will always take the VXL where we are in larger venues.

Having said that, have played 2 gigs last couple of days and left the DHA on full time cos I've fallen in love with the sound. I find the 'colour' options lose bottom end so I have on just straight gain 12 o'clock for a bit of beef. So I'm going to experiment with the VXL after the DHA as a futher boost / OD option for those songs where a bit more is needed.

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