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XLR out from amp or a DI box to the board?

Anthonyfranklin9000

Anthonyfranklin9000

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Nov 12, 2014
205
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43
South Carolina
#1
Questions about DI use....
I play thru a Hartke 1x15 kickback combo that my church owns; it provides stage volume and the house PA carries the bass signal as well. I run my bass (passive Jazz) into a PRO DI passive box, XLR output then goes to the board, and the "Thru" output from the DI box goes to the amp. Pretty standard I imagine.

This has generally worked for my bass sound but I am getting some noise lately with the "Lift" engaged, but not enough volume with the "Lift" disengaged. I am curious if it might be simpler to forego the DI box and just use the XLR output from the amp to run to the board. Any reason why this is inferior or would be a problem? I generally stay out of the sound guy's business and just ran with the existing set up as it was before I came along.
 
#2
The lift should have absolutely no effect on the output gain of that DI. That's a separate issue that needs to be investigated. You might have a bad mic cable that is what is know as "one-legged". That means that either positive, or Pin 2, or negative, or Pin 3, of the mic cable has become disconnected. Using the "Lift" switch could be having some goofy effect on the signal because of the one-legged-ness, if that's the case. The same thing could happen with the DI, although that's less likely. Bottom line here, try another mic cable on yer DI.

I'm going to skip all the pontificating for why it's good to do it one way or the other and say that you should be fine coming from the XLR out of the Hartke amp, should you decided to go that route. However, if you have a bad mic cable, going to the XLR out of the Hartke won't solve that problem, either. Check that mic cable!
 
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#5
Anthonyfranklin9000 said:
Thanks. Should the Lift button on the DI affect the signal going THRU it into the amp? I should have specified the amp is where I am noticing the noise when it is engaged, as well as a serious loss of volume when disengaged.
Click to expand...

The only effect you should notice is a decrease in noise, no change in noise, or the noise increases, depending on what the noise problem actually is (it could be from one or a few places. And it doesn't necessarily mean that something is wrong, only that there's some interaction with the ground potentials of the various pieces of gear connected together). A discussion of instrument noise and interaction is way too deep to get into here, but there should be NO effect on the gain or quality of your output signal going to both FOH and directly through to your amplifier.

Again, try another mic cable, if that's doesn't help, try another DI. And report back with the results...;)
 
#6
Geri O said:
The only effect you should notice is a decrease in noise, no change in noise, or the noise increases, depending on what the noise problem actually is (it could be from one or a few places. And it doesn't necessarily mean that something is wrong, only that there's some interaction with the ground potentials of the various pieces of gear connected together). A discussion of instrument noise and interaction is way too deep to get into here, but there should be NO effect on the gain or quality of your output signal going to both FOH and directly through to your amplifier.

Again, try another mic cable, if that's doesn't help, try another DI. And report back with the results...;)
Click to expand...

Thanks, good to know! I'll report back, we have a practice tomorrow night.
 
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#7
So at practice tonight we tried:
1) Ran XLR output from the amp to board, it hummed badly.
2) Swapped cables but same channel on the board. Still hummed badly.
3) Set up DI box again, bass running thru it into amp and the DI's XLR out to the board, this time with the swapped cable. Small bit of hum. Engaged the "pad" on DI and it was quiet.

Doesn't make sense to me but everyone's happy.
 
#10
Anthonyfranklin9000 said:
I didn't get the loss of volume with the "pad" engaged though, so it works for me. Just wish I understood it.
Click to expand...

My only explanation for this is insane. Insane, I say! But seriously, it's all I can come up with based on what you've posted...

The "Pad" switch and the "Lift" switch on yer DI are labeled backwards. Really, think about it. You engage the lift switch and the signal level drops (significantly, I presume. Read the first post on why I think this...) as though you engaged the pad. And you engage the pad switch and the hum goes away. Is that a Radial Pro DI?

Crazy, I know...

As for the hum you had when you connected the XLR output to the mixer, you can try a "shield lift" adapter. Think of it as a very short mic cable, I mean literally, 4-5 inches long and the Pin 1 connection inside the XLR is cut or disconnected. You plug it in to the output of your amp, then connect a regular mic cable to the adapter. You are accomplishing the same thing as a "Lift" switch on a normal DI (No idea if that's the case on YOUR DI, but I digress...). You sound guy should be able to make you one.

Man, I'm out of ideas past this. Good luck....:eyebrow:
 
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#11
OB-OX507_HEAD07_DV_20110727131527.jpg
 
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#13
Geri O said:
As for the hum you had when you connected the XLR output to the mixer, you can try a "shield lift" adapter. Think of it as a very short mic cable, I mean literally, 4-5 inches long and the Pin 1 connection inside the XLR is cut or disconnected. You plug it in to the output of your amp, then connect a regular mic cable to the adapter. You are accomplishing the same thing as a "Lift" switch on a normal DI (No idea if that's the case on YOUR DI, but I digress...). You sound guy should be able to make you one.

Man, I'm out of ideas past this. Good luck....:eyebrow:
Click to expand...
A lift cable should not only have pin 1 disconnected but have the shield separated from the connector shell on one end. If the shield is connected to the shells on both ends then the board may still be able to "see" the chassis of the amp though the shield and thereby still have a ground loop.
 
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#14
ggunn said:
A lift cable should not only have pin 1 disconnected but have the shield separated from the connector shell on one end. If the shield is connected to the shells on both ends then the board may still be able to "see" the chassis of the amp though the shield and thereby still have a ground loop.
Click to expand...

The pro audio community hasn't connected the shells for many, many years now, but some cheaper and/or "import" cables still connect the shield for some reason. In my entire life, I've never connected the shell of mic cables.

I'd still like to figure out what the level change when the lift is engaged is about. Unless it's wired improperly and it's lifting pin 2 or pin 3, making the line one-legged and losing the obligatory 6db in the process. But that's so unlike Radial.
 
#15
Geri O said:
The pro audio community hasn't connected the shells for many, many years now, but some cheaper and/or "import" cables still connect the shield for some reason. In my entire life, I've never connected the shell of mic cables.
Click to expand...
There is an organization here in Austin that has a lot of mic cables that need fixing, and I am repairing them. Every single one of them has the shell connected to the shield and they are of many different makes. Every XLR connector I have opened up (and that's a lot of them) have a shell terminal, usually a ring.

I don't know whether what you say is true or not, but I know that there are a lot of mic cables out there with shells connected to the shield.
 
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#16
Oh, it's true, alright. I'd say to ask around the Live-Audio Board or SoundForums Dot Net, but those guys aren't terribly smooth when presented with that sort of question.

The answer would go something like "Hell Yes it's true and what 20th century numnuts is asking?". I never understood the inability of a group of otherwise really sharp guys to answer a simple question with a straightforward answer without the insults and condescension.

And yes, there are a lot of shell-connected mic cables out there, no doubt. It's like a mission...:D
 
#17
Other than that it might defeat ground lifting, is there any other reason to separate the shield from the shell? If you run and solder the shield through the ring that's tied to the shell before connecting it to pin 1 it provides strain relief for the rest of the connections.
 
#18
I'd have to go and look for the electrical reason for disconnecting the shell, I think it has to do with the shell actually becoming part of the equipment chassis, which is (or is supposed to be) connected to the shield. Now that I think about it, it was part of the whole Pin 1 thing going on in the 90s. And I've solved several hum problems by removing the shell connection when nothing else worked.

Way back in Soldering 101, we were taught to make the shield wire slightly shorter than the hot and cold wires for strain relief reasons.
 
#19
Geri O said:
I'd have to go and look for the electrical reason for disconnecting the shell, I think it has to do with the shell actually becoming part of the equipment chassis, which is (or is supposed to be) connected to the shield. Now that I think about it, it was part of the whole Pin 1 thing going on in the 90s. And I've solved several hum problems by removing the shell connection when nothing else worked.

Way back in Soldering 101, we were taught to make the shield wire slightly shorter than the hot and cold wires for strain relief reasons.
Click to expand...
But of course, in a balanced line, both pins 2 and 3 are "hot". If you loop the shield through the ring on the connector before soldering it to pin 1 (and putting some slack in the signal lines, as you say) you can just about tow your car with it.

I am hip to the shell often being connected to the chassis, hence my earlier comments. In my gig bag I carry a couple of very short "mic" cables (~3" long) with the shield completely disconnected at one end.

Whatever works.
 
#20
Yes, I send out show manifests with a dozen Pin 1 lifts, among other adapters. Quite valuable. I have 4 in my bass gear kit, as well...

It's true that both pin 2 and pin 3 are hot, but one is 180 degrees electrically reversed polarity. That's part of the "noise-canceling" thing, although that's a discussion beyond the scope of this post (and admittedly, probably out of my pay grade to competently get into...). That's why the Pin 2 hot thing got really wackadoodle way back when (did I just say "wackadoodle"??). Finally, the AES Standards committee settled on Pin 2 Hot as being the spec, although there's no law that requires a manufacturer to adhere to it.

Bizzarely enough, the beloved Countryman Type 85 DIs have always been and still are wired Pin 3 hot. Now, bassists that read that last sentence, forget about it. In the grand scheme of things, it won't affect your set-up, unless somehow the amp's mic'ed signal and the Countryman DI got 180 degrees out of polarity, and the chances of that aren't even calculable. Having said that, I've been known to use a measurement program to delay a bass DI's signal to the mic signal, something that's possible now with digital consoles with delay on every channel. Again, there's another sentence that should be forgotten...:D. That's a bad sign of OCD on the sound guy's part. The amount of delay used is in the .5- to 1-millisecond range. When I A/Bed the results, it was debatable that there was any difference to speak of, except in a couple of cases (which was an indication of MUCH bigger problems somewhere upstream from me).

Hey, all this to say, if you are getting along fine with the shields connected to the shells, then carry on. I'm not a torch-carrier for one case or the other, especially when the case I'd choose to work against is working for someone else. No point in that.

And geez, I just finished up 4 straight days of concert production when we ran short of engineers and if this is what I want to write about on a forum for bass players. then I need stop that crap! Now!....:roflmao:

Hope everyone had a great weekend!
 

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