Understanding the FM3 output capabilities for stompbox replacement duty

[Chris Hurley]

Greetings folks-

I wanted to bounce this off of the community and see if anybody had any comments or suggestions. In addition to other more traditional applications, I'm trying to use my FM3 as a stomp box replacement in front of my tube amp. Ideally, I'd like to be able to boost the tube amp with an EQ pedal or drive block to get more of the amp's own overdrive.

Out of the box, this works fine but there is a noticable hiss from the FM3 in an application like this. From what I understand, this is inevitable D/A noise and is the reason for the boost/pad setting to exist.

Increasing Boost/Pad dramatically reduces the hiss, but it also seems to reduce your ability to drive the outputs without clipping which hits my application right in the nose.

I'm thinking that the answer really is: "Reduce Hiss, or Be able to drive the amp harder, pick one."

Any comments or thoughts?

Its a killer piece of gear. I thought I would fix it by simply putting an EQ pedal in front of the amp but after the FM3 to boost up its signal but as you might imagine, the EQ pedal is much noisier than the DA noise coming from the FM3. Maybe its just the case of pick between "low noise" and "output capability".

I don't remember having this same issue on my Axe-FX 3, so this may just be a difference on the FM3.

I appreciate any useful comments or suggestions.

 

[Smilzo]

Out of the box, this works fine but there is a noticable hiss from the FM3 in an application like this. From what I understand, this is inevitable D/A noise and is the reason for the boost/pad setting to exist.

No way DA noise is noticeable in front of an amp... there must be something else. AC coupling?

 

[Chris Hurley]

No way DA noise is noticeable in front of an amp... there must be something else. AC coupling?

heh- "no way?"

I'm not sure what it is, but I believe DA noise was what it was attributed to. I'll try to find the quote.

If you adjust the boost/pad setting up to 6db, the hiss gets significantly quieter. The overall level is the same unless you are clipping the output. At 12db or 18db, the noise is "gone" but with it the output headroom.

 

[ethomas1013]

I don’t have any hiss issues using the FM3 straight into an amp. It’s been a while since I did it. Don’t remember if I used a humbuster cable with output 2 for that, but I think I did. Of course that’s related to hum, not hiss, so take a look at your output levels too.

 

[Chris Hurley]

Here was the quote from FractalAudio from several years back: link

" Yes, it is very difficult to minimize the hiss when putting a digital processor in front of a high-gain amp due to the A/D and D/A conversions. The XL is probably one of the quietest processors made but there will still be some residual hiss when using high gain. The Output 2 Boost/Pad feature was specifically intended to minimize hiss in these scenarios by running the D/A converter as "hot" as possible and then reducing the signal level after the converter with an analog pad. "

Humbuster doesn't have any impact on hiss that I've seen. It can make HUGE improvements in hum and related noises though.

 

[Smilzo]

heh- "no way?"

I'm not sure what it is, but I believe DA noise was what it was attributed to. I'll try to find the quote.

If you adjust the boost/pad setting up to 6db, the hiss gets significantly quieter. The overall level is the same unless you are clipping the output. At 12db or 18db, the noise is "gone" but with it the output headroom.

The AD/DA conversion nowdays could replace a cable connection. Maybe hiss noise is due to other source or coupling. The higher the "gain" the louder the noise level. If the FM3 work at PA level in a mixer or monitor without audible hiss, than the culprit is the amp itself or the coupling.
You can minimize the noise by raising up digital level of eq or drive block. Than lower the FM3 Out level (I think it's the pad you mention...).

Let us now if this help: I have lots of amp, but I'm in the waiting list for FM3. With AX8 I have no prob with tube amp, other than different tones and levels when switching from real to block amp.