Weird waveform

[Cult_Status02]

I just got a Presonus Bluetube to mess around with and I've two questions.

1: When I use the balanced output to my Mackie Onyx 1640's line in on a channel, my mono track looks weird. When looking at the track it has a line down the middle, horizontally, the wave form though is all off balance and ghetto looking. There are is no waveform image below the line it's all above it. When I use the XLR output from te Bluetube and into a channel Mic input the waveform is centered and looks like all my other tracks. Is there any reason why this weird waveform is bad, or any reason why I should use one Bluetube output instead of another?

What does this weird waveform mean?

2: If I do use the XLR output from my Bluetube to a channel mic insert on my mixer, does it defeat the purpose of using an external preamp? Does doing this basically take characteristics from both preamps?

Thanks guys.

 

[danny.guitar]

What does it sound like?

Or could you at least post a picture of the WaveForm?

 

[dgatwood]

I just got a Presonus Bluetube to mess around with and I've two questions.

1: When I use the balanced output to my Mackie Onyx 1640's line in on a channel, my mono track looks weird. When looking at the track it has a line down the middle, horizontally, the wave form though is all off balance and ghetto looking. There are is no waveform image below the line it's all above it. When I use the XLR output from te Bluetube and into a channel Mic input the waveform is centered and looks like all my other tracks. Is there any reason why this weird waveform is bad, or any reason why I should use one Bluetube output instead of another?

What does this weird waveform mean?

That sounds like what we call a really freaking huge DC offset to me.... My guess is somebody omitted the filter caps that are required to remove the DC from the tube's output, and that they count on a balanced input on the other device to cancel out the DC offset. If so, that's rather sloppy design, IMHO.

If you're going into an unbalanced line input, you should use the unbalanced output of the Bluetube, since that presumably is transformer coupled or something to eliminate the DC offset problem. That said, AFAIK, the Mackie's line ins are all balanced, which means either:

1. Your cable has a TS 1/4" connector instead of a TRS 1/4" connector on one end (i.e. it's an unbalanced cable instead of a balanced cable).
2. Your cable isn't wired correctly and one of the two signal pins isn't actually making it to the TRS connector.
3. You're plugging it into one of the instrument preamp inputs (unbalanced) instead of a line input. I think the 1/4" jacks on the first two channels or so are instrument pres on that board, but I looked at an owner's manual for a different model, so that might not be quite right.
4. Something is wrong with that input and it isn't truly balanced as it should be.

2: If I do use the XLR output from my Bluetube to a channel mic insert on my mixer, does it defeat the purpose of using an external preamp? Does doing this basically take characteristics from both preamps?

If the secondary preamp's trim is all the way down, it won't affect the signal all that much... a little, but not a lot.

 

[Cult_Status02]

Thanks dgatwood. I'm plugging into channel 16's input, so it's not a hi-z input like channels one and two are. I'm using a Hosa balanced TRS cable I purchased recently, but as you said it could be wired incorrectly. Both the 1/4" output one the BlueTube and the 1/4" input on my Onyx are wired toa ccept both balanced and unbalanced signals, so I think I'm fine as far as that goes. I think this evening I will go ahead and try another input. Thanks again for the suggestions, I'll let you know what happens.

 

[Cult_Status02]

Well, I tried another line in, same problem I'm gonna keep trying stuff.