Help! 4cm Hiss

ianx

ianx

Experienced
First I want to thank Mark Day for giving me some pointers.
I'm connecting my AxeFXII mk1 to a Friedman BE100 using 4cm. I made humbuster cables, so no hum, but have a loud hiss on the BE & HBE channels. An aggressive expander helps, but the hiss is still detectable underneath the notes & chords. The hiss appears to be after the fxl block.
I've already searched the forum and it appears that when the question of hiss is brought up, the thread gets hijacked by hum.
Has anyone been able to resolve the hiss.
 
place a gate next block after fxl, hiss is suppressed, block before the fxl hiss is still there.
 
That means the hiss is coming from the FX Loop block, which includes the Amp and perhaps the output stage of the Axe out 2, but nothing before it.
 
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The hiss is either the tubes in your amp's preamp section or the noise floor of the Axe FX II Mk 1 passing through your amp's preamp section.

Make sure you've optimized signal to noise ratio ("input level") on both Axe inputs, Output knobs are at 100%, and block/preset levels are all at 0db/unity. Once you've established unity gain with the Axe connected in 4CM, completely disconnect the Axe from the setup. If you don't hear the hiss, then you've confirmed you're hearing the noise floor of the Axe (passing through the high gain BE and HBE tube stages).

A post-preamp gate (so, after the FX Loop block) is your best bet. More recent Axe models (and especially the FX8) improved the overall SNR and usability of 4CM method.
 
Outputs are at 100%, the noise is gone when the box is disconnected, also no noise when amps loop has a cable patched between send & receive. I tried an expander/gate post fxl, but had to set it to hard clamp, however I can still faintly hear the hiss underneath. I thought I had read a thread that indicated the problem was an impedance mismatch. Can anyone confirm this? Will a buffer help?
 
The outputs are already buffered so that won't help. You could try the Output 1 and Output 2 Boost/Pad settings.

Do you get hiss running the Axe into the front of the amp only (no amp loop)? What about using the amp loop only (guitar straight into the front of the amp, Axe in amp loop only) - does that have the hiss?
 
it's clean in front of the amp and in the loop. I tried a preset with only the fxl and the hiss was present.
Cliff said this in a thread about 4cm hiss:
"Any time you do an A/D or D/A conversion you add noise, a minimum of 3 dB each time. With the 4CM you've got four conversions so you're going to add at least 12 dB of noise. Just the nature of the beast and why I'm not a big advocate."

With that I'm going to abandon the idea of 4cm.
 
No, I had to reconfigure my rack for upcoming dates. I'll give it a try when I get a break.
 
I have no idea whether Fractal rectified the problem. However, a few years back when I attempted the 4ch method, I too experienced the deadly hiss. I sent my Axe back to Fractal and they performed some "special" technique to output 2, returned my Axe the following week, and Voila - deadly hiss was dead. Again, I am completely ignorant about the whys and hows and whens (and the issue I had with an older model may have been subsequently corrected in newer models). Nevertheless, it is a question work asking.
 
I use almost the same setup. Noise is improved with the XL but with some tweaking you should be able to nail it. Hopefully this helps ya:

 
xprophet said:
Again, I am completely ignorant about the whys and hows and whens (and the issue I had with an older model may have been subsequently corrected in newer models).
Click to expand...

Cliff:

"The very early Axe-Fx II's had more bandwidth than necessary on Output 2. The frequency response extended to hundreds of kHz. When used with certain tube amps this would cause instability in the output drivers. The solution was to limit the bandwidth to a "normal" range of 20 to 20 kHz. We provided the update for free and all units shipped after the first 100 or so had this update included. The Axe-Fx II Mark II, XL and XL+ have a redesigned output circuit that is immune from any of these issues."

"That hasn't been an issue since the first 100 or so units that were made years ago. The XL+ shares the same amazing low-noise architecture of the FX-8. I regularly use my XL+ in 4CM as this is part of the modeling process. It's the quietest device I've ever tried in 4CM."
 
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