Presonus TubePre v1. buzzing when both outputs connected

[Jason Grosser]

Hello,

I have a presonus tubepre v1 and recently I have had a problem.
So I am trying to use the Tubepre as a DI for my bass player while we record. So the hookup is like this: Bass into 'instrument' input, unbalanced 1/4" output into his bass amp, and balanced XLR output into Audiobox 1818VSL.

The problem is whenever I have both outputs connected I get a nasty buzz on both ends. If I take the xlr out, the bass sounds fine through the amp but when I plug it back in the interface... Buzz again (and vice versa). I have tried MANY other configurations. ie, different cords, different outlets, different interfaces, etc. The drive and gain are both all the way down so its not coming from that. It actually still does it even when there is no input connected at all...

Is this some sort of grounding problem? Ground loop?

 

[ido1957]

Hello,

I have a presonus tubepre v1 and recently I have had a problem.
So I am trying to use the Tubepre as a DI for my bass player while we record. So the hookup is like this: Bass into 'instrument' input, unbalanced 1/4" output into his bass amp, and balanced XLR output into Audiobox 1818VSL.

The problem is whenever I have both outputs connected I get a nasty buzz on both ends. If I take the xlr out, the bass sounds fine through the amp but when I plug it back in the interface... Buzz again (and vice versa). I have tried MANY other configurations. ie, different cords, different outlets, different interfaces, etc. The drive and gain are both all the way down so its not coming from that. It actually still does it even when there is no input connected at all...

Is this some sort of grounding problem? Ground loop?

You are trying to put a line level output from the amp to the mic input on the interface. It's probably too hot a signal or the cable is faulty.
A line out of the pre into the bass amp is probably too hot too as it's expecting an instrument level.

 

[Steenamaroo]

You are trying to put a line level output from the amp to the mic input on the interface. It's probably too hot a signal or the cable is faulty.
A line out of the pre into the bass amp is probably too hot too as it's expecting an instrument level.

Agreed. You want a DI box rather than a preamp.
A DI box takes your instrument level input and gives you a mic level and instrument level output.

One goes to a mic input on your audio interface for recording and the other goes to the amp for live playback.

 

[witzendoz]

The way to do this is to split the signal from the bass before the Tubepre. Use a simple Y connector Bass to both the bass amp and the Tubepre. Then use the XLR to the audibox.

The way you have it plugged in at present you are probably shorting the XLR balanced out (Pin 1 & 3) when you plug the unbalanced jack into the output as well.

Alan.

 

[Jason Grosser]

Guys, thanks for the responses.

The thing is this used to work fine for me and is a new problem. This is from the TubePre owners manual..

"Direct Box
The 1/4” and XLR outputs can always be used simultaneously. The
instrument should be plugged into the 1/4” instrument input. The 1/4”
output can be connected to an amplifier on stage and the XLR output
could be connected to the PA system or monitoring mixer."



And like I said, it works fine when I have the bass plugged in and ONLY the XLR into the interface OR ONLY the TS cable going to the amp. But when both outputs are connected is when i get the loud hum/static sound..

 

[witzendoz]

Guys, thanks for the responses.

The thing is this used to work fine for me and is a new problem. This is from the TubePre owners manual..

"Direct Box
The 1/4” and XLR outputs can always be used simultaneously. The
instrument should be plugged into the 1/4” instrument input. The 1/4”
output can be connected to an amplifier on stage and the XLR output
could be connected to the PA system or monitoring mixer."



And like I said, it works fine when I have the bass plugged in and ONLY the XLR into the interface OR ONLY the TS cable going to the amp. But when both outputs are connected is when i get the loud hum/static sound..

OK, I did not realise this, in this case what you have is a ground loop between the bass amp the preamp and the audiobox (more likely the computer connected to the audiobox). You could try lifting the shield on pin 1 of the XLR at the Audiobox input (see diagram). This does the same as the ground lift switch that is on a DI box. If you don't want to do the wiring thing, there are cheap XLR ground lift connectors you can use.

This problem could have appeared where is was not there in the past due to:

Different room
Different power outlets being used
different bass amps
different computer
different interface

Cheers
Alan