How to forward external soundcard output to amp?

[Stealth]

Here's the deal: I recently got a Terratec DMX 6FIRE USB external soundcard, primarily for the fact it had (as I heard and later confirmed) extremely low latency and could support multichannel I/O (including a dedicated instrument input).

Along my uni course I decided, discussed, coded and finalized my B.Sc. final project, a real-time audio processor with the same general idea as the commercial Guitar Rig, but much simpler, of course. Still, the compressor/limiter, expander/noisegate, auto-tremolo/ring-modulator, nonlinear distortion and analog/digital fuzz seem to work rather well so far. Naturally, I used ASIO and tested at various sample rates, with 96 kHz still being rather fast and responsive.

Here's my question: the soundcard itself has, among the analog outputs, six RCA jacks (apparently with no preamplification) and a headphone 1/4" jack output with a headphone amp. Which of these outputs, if any, would be suitable for sending the signal through to my practice amp, and would I keep the active/passive switch on or off?

If someone can make sense of all the stats on the datasheet, I'd really appreciate it.

[debassr]

Use the 1/4" headphone out. Use whichever mode (active or passive) that sounds best to you and doesn't clip.

[Floridabwoy]

all of them... I would use a mono (one ring around tip) 1/4 cable from one of your analog outs.

[Stealth]

The reason I'm asking for this is because my last attempt at sending the bass signal through the onboard soundcard, then towards the amp resulted in much noise and no bass signal at all.

[Nick Kay]

You can use either the Headphone Out, or one of the line outs on the back (with the help of an RCA > 1/4" adapter). In either case, though, plug them into the Effects Return on your amp. Both outputs will put out consumer line-level or hotter, and the instrument input on your amp will (obviously) expect instrument-level signals. Line-level output into instrument-level input = distortion hell, which might not be correctable with the Active pad on your amp.

[Stealth]

Hmmm. I might have to toss the idea, then. My practice amp HAS no effect return - all I get is an input jack for the bass and an output jack for headphones. Am I pretty much SoL?

[LowDown Hal]

Just for the heck of it...
try using one of those ground isolator plugs for your Terratec.
You know, the thingies that let you plug a three prong device into a two prong receptacle. This will isolate the ground path into the Terratec. Your amp will still be grounded through it's power cord and when you plug in you get the reference for the sound card.

I know of several instances where the noise (like you describe, although it's hard to say for sure) was actually due to the ground references. I have personally experienced it with two different laptops using either the headphone output or using fire wire outputs.