Do I need a DI box?

[algaib]

Originally Posted by mchalebk

Before trying adapters, try raising your gain controls. They're at 50% and may not be driving your inputs enough, which result in weak output and raised noise levels. The peak LEDs will let you know when you're overdriving the inputs.

The problem is if I turn the gain up, I just get loads of hiss. The other strange thing is that even if everything is full, the peak LED's only ever show a couple of green lights per row; I've never seen them go anywhere near the red ones...

[mchalebk]

Originally Posted by algaib

The problem is if I turn the gain up, I just get loads of hiss.

Is this true for both pickups/channels? It might indicate a problem with the pickup or cable (or channel, if only one). If raising the gain results in lots of hiss, I think it’s telling you that you’re inputting a noisy signal.

Originally Posted by algaib

The other strange thing is that even if everything is full, the peak LED's only ever show a couple of green lights per row; I've never seen them go anywhere near the red ones...

I think you’re talking about the master Level Indicator, which is a set of LEDs. I’m talking about the peak LEDs that are located next to the Pan knobs on your mono channels (single LED per channel). These will light when you’re overdriving the channel input section.

[algaib]

Originally Posted by mchalebk

Is this true for both pickups/channels? It might indicate a problem with the pickup or cable (or channel, if only one). If raising the gain results in lots of hiss, I think it’s telling you that you’re inputting a noisy signal.



I think you’re talking about the master Level Indicator, which is a set of LEDs. I’m talking about the peak LEDs that are located next to the Pan knobs on your mono channels (single LED per channel). These will light when you’re overdriving the channel input section.

They were like this from the beginning. This desk doesn't have peak LED's I don't think?

[lschwart]

Originally Posted by algaib

They were like this from the beginning. This desk doesn't have peak LED's I don't think?

According to this PDF of the specs, it has them on the two mic channels, but for some reason, as mchalebk noted, they're next to the pan knobs instead of next to the gain knobs where you'd expect them to be.

Louis

[lschwart]

Originally Posted by algaib

Thats right, two separate cables for each pickup. The cables are about 10ft. I'm inserting the effects into the FX loop of the UB1002 set at about 50% (then less on each channels individual FX control). The gain levels are at about 50%. Main slider is at about 75%. I have no idea what impedance the pickups are though. It doesn't seem to make a difference if I use channels 1&2 (both with XLR & 1/4" jack inputs, or any others which only have 1/4" jack inputs.

As others have noted and from what you've said, I'm guessing that both pickups are passive and that you need to set your gain structure correctly first to see if that resolves the issue with the hiss and the thin sound. To do that, follow the advice you've been more or less given (here are a few more details):

Plug one pickup into channel 1; start with the gain set at about 12:00, and the channel volume control at its "0" setting (12:00 on the channels, if I'm reading the images I've seen of your mixer correctly). You can set the master volume slider down all the way--you don't need it on for this--depending on what it's plugged into you'll have to find the right setting for it later.

Now play the guitar hard. If the "peak" light next to your "pan" control for that channel doesn't go on, turn the gain up a little and play hard again. Keep doing that until the light goes on when you play your hardest. Then back off on the knob from that point just a bit, so that the light only goes on--if at all--when you really hit the strings as hard as you're ever likely to do in performance.

Now do the same with the other pickup, plugged into channel two. If the light did not go on at the 12:00 setting, it should go on, ideally, somewhere between 12:00 and 3:00 or maybe a little higher than that. It's OK if the lights come on at different points--that just means that your two pickups are putting out signals of different strengths. What you're doing is setting the preamp section of your mixer. You're using this section of the mixer as a preamp for your passive pickups. If the peak lights don't go on at all, or if they only go on a bit when the gain knobs are turned all the way up, your pickups are not sending a signal strong enough for the preamps in the mixer to amplify them enough to be sent to whatever poweramp you're using without a lot of noise. This may be the case with one pikcup and not the other, or it may happen with both, and it may be because something is wrong with the pikcups or they might just need more robust preamplification than you mixer can provide.

If there's nothing wrong with your pickups, and they simply have weak signals, you can solve this problem by adding an external preamp for both--or for only one if only one is giving you this problem. This may also solve your "thinness" problem. As many have found, a good external preamp can give some considerable body to the sound of a pickup. Most external preamp "boxes" will also function as DI boxes (a separate function, but one that often gets bundled together in a preamp). If your problem also has something to do with your running unbalanced cords and/or with an impedance mismatch, this will solve that by converting the pickup signal or signals to balanced, low impedance signals that you can then send to the mixer with XLR cords. A blending preamp would also do the mixing work of the little mixer and could replace it, altogether depedning on how you're using it, and assuming you can spend the money.

Now, if it turns out that you CAN set the gain knobs on yur mixer so that the peak lights go on with your loudest playing, you may find that whatever you hook the mixer up to works without much noise and with a decent sound. If so, no problem , of course.

But if you get the gain set right, and still have the noise, you'll have to figure out whether the problem is in your pickups or in your mixer or in a mismatch between them. Try using only one first to see if one is causing the problem. If the problems persist with both, you could try using a passive DI box on one and then on the other to see if the problem is with an impedance mismatch. If that isn't it, try plugging your pickups into another mixer that you know is working perfectly (maybe a friend has one?). If the pickups are working fine with the other mixer, and the gain there is also set right, you'll at least know that you have to trouble shoot with your mixer to see what's wrong and if the problem can be fixed. Unless, of course, the porblem is with whatever poweramp, or powered speaker, or combo amp you're plugging the mixer into....

Hope that helps.

Louis

[briggleman]

Louis,

Great instruction and explanation of what is happening and troubleshooting techniques. Only thing we could add would be video..... no don't go there.

Now if the above instructions still do not give enough volume, from looking at the specs on the UB1002, if he were to use the adapters on his unbalanced output from the guitar to go into the XLR mic inputs, it looks like from the ohm rating he can get a 10 to 20db boost. Am I looking at that correctly???

Brad

[lschwart]

Originally Posted by briggleman

Louis,

Great instruction and explanation of what is happening and troubleshooting techniques. Only thing we could add would be video..... no don't go there.

Now if the above instructions still do not give enough volume, from looking at the specs on the UB1002, if he were to use the adapters on his unbalanced output from the guitar to go into the XLR mic inputs, it looks like from the ohm rating he can get a 10 to 20db boost. Am I looking at that correctly???

Brad

It does look like he'll get more gain if he goes into the XLR mic inputs, or at least those inputs (or their preamps) provide more gain when the right kind of signal is sent into them, but the impedance for those is even lower than for the 1/4" inputs, so if impedance is his problem, as I understand it, this might make it worse. The impedance on the 1/4" inputs when unblanced is 10k (and 20k when balanced). The impedance on the XLR ins is only 2.6k. He doesn't know the impedance of his pickups, so who knows what effect this will have? The rule of thumb I learned from some very well-informed people on this and some other lists is that the load impedance of the mixer's or preamp's input should be higher than the source impedance of the device sending the signal, ideally about 10x higher. Again, as I understand it, most magnetic pickups have an impedance of about 5k to 15k ohms, and therefore should be plugged into devices with load impedances between 50k and 150k at the least. Piezo pickups require even higher impedance. If those numbers are correct, it may be that he does need a DI box to get the best sound out of this combination. The safest bet would be to use a DI box to ensure that there's no problem--but it's also possible that the match is close enough (at least for the mag pickup), even if it's not ideal, and I don't understand the details about how various mismatches actually affect sound differently (and not always, I gather, negatively) to comment on what he's likely to expect. Someone else with more experience and electronics knowledge will have to comment about that--and of course we don't know that impedance IS the problem in this case--although it does seem to me likely that the piezo and the mixer's imputs are indeed mismatched.

My comments were designed to suggest, first, how he might figure out if he needs preamps for one or both pickups (not an unusual need). If he does need one or two, whatever impedance problems he has, if he has any, will be solved by the DI function of the preamps anyway.

One other thing does occur to me, though, about the adaptor idea: if he uses an adaptor, he'll be able, as I understand it, to go into the balanced XLR ins, instead of the 1/4" ones, but the signal will still be unbalanced. I don't know how that will effect the impedance matching or the gain (I simply don't know enough about how the electronics work to say). I don't think it would do any harm to experiment, though, if the usual gain-setting techniques don't solve the problem. Maybe someone else can say with more certainty?

Louis

[algaib]

There is certainly plenty here for me to stick my teeth into. Thank you everyone for the advice. I'll see what happens, then let you know!