Carvin BX1200 DI Hiss

[dancrocker]

I normally play through the cabinet only but recently used the DI to go into the board so I could hear myself through our floor monitors. When I did this, I was surprised and disappointed to hear a pronounced hiss in the monitors. It's not a hum that would indicate a gnd loop (at least what I'm used to hearing). Any suggestions on what could be causing this?

[WingKL]

Noisy opamps in the signal path? Someone skilled with an oscilloscope and schematics can easily find out where the noise is coming from. You could probably have those opamps replaced with lower noise equivalents.

[dancrocker]

Originally Posted by WingKL

Noisy opamps in the signal path? Someone skilled with an oscilloscope and schematics can easily find out where the noise is coming from. You could probably have those opamps replaced with lower noise equivalents.

I suppose it could be something wrong with the amp, but the amp is only a year old. I was hoping there might be a connection problem that someone could clue me in to.

[5port]

The BX1200 has a Pre/Post switch and gain control. You could try varying the settings on these to reduce the hiss. If its already in the post setting and the gain control were set to a high output I would expect some hiss. Try setting it to Pre and increasing the gain on the board.

17. DIRECT OUT PRE/POST SWITCH AND GROUND LIFT SWITCH
The direct out PRE/POST switch allows the choice of either a simple buffered signal straight from
the input jack (PRE mode) or a processed signal including the Drive, Compressor, Tone, Graphic
EQ, and Effect Loop processing (POST mode).
If a hum occurs when connecting the XLR to a mixer, try using the GND LIFT switch. The GND
LIFT switch lifts the ground pin 1 of the XLR to 100 ohms above chassis groun

[dancrocker]

Originally Posted by 5port

The BX1200 has a Pre/Post switch and gain control. You could try varying the settings on these to reduce the hiss. If its already in the post setting and the gain control were set to a high output I would expect some hiss. Try setting it to Pre and increasing the gain on the board.

17. DIRECT OUT PRE/POST SWITCH AND GROUND LIFT SWITCH
The direct out PRE/POST switch allows the choice of either a simple buffered signal straight from
the input jack (PRE mode) or a processed signal including the Drive, Compressor, Tone, Graphic
EQ, and Effect Loop processing (POST mode).
If a hum occurs when connecting the XLR to a mixer, try using the GND LIFT switch. The GND
LIFT switch lifts the ground pin 1 of the XLR to 100 ohms above chassis groun

Thanks. Obviously for my monitoring purposes, "pre" is fine. But, if I were going to the mains, I assume I'd want post. But, playing with this switch is certainly worthwhile to try to figure out what's going on.

[Lync]

I have the same issue with the DI on my BX500 (straight signal before the pre amp). It sounds good, there is just hiss. Once the music kicks in, you don't notice. Maybe just the nature of Carvin amps?

[dancrocker]

Originally Posted by Lync

I have the same issue with the DI on my BX500 (straight signal before the pre amp). It sounds good, there is just hiss. Once the music kicks in, you don't notice. Maybe just the nature of Carvin amps?

Interesting. Maybe this is just the way these amps are. But, I still find it a little odd. I admit that the hiss is not horribly loud and I am standing right next to the monitor which lets me hear it very well. I'll still play with the pre/post switch to see what happens.

[WingKL]

Different people have different threshold for what they would consider objectionable hiss. I may have given the impression that there might be a bad opamp but in reality it could be normal or within the tolerance of the amplifiers design specs. The ubiquitous TL072 opamps for example, are decent opamps but a higher grade drop in replacement TLE2072 exist and they cost quite a bit more.