Gory details about the FM3's headphone output stage anyone?

M

MrBollie

Member
I admit, the FM3 made me make some expensive follow-up investions. Background: Since FM3's USB audio latency offset guessing game is still unacceptable and we're all waiting for FAS to fix it, I used to use the FM3 together with an RME Babyface Pro FS... until I noticed how poorly the BBF drove my DT1770 headphones and what a powerful and clean headphone output stage the FM3 seems to have. I assume it's due to bus-powered audio interfaces having a rather poor power budget for proper headphone operation, unlike the FM3, which is mains-powered. That made me upgrade to the expensive RME Fireface UCX II and that opened a whole new world to me.

Anyway, can anyone from FAS maybe give a couple of details about the headphone output stage design of the FM3? Like what DAC is being used, how high the ouput power @32 Ohms is and so forth?

Is there also a chance, that in some upcoming firmware versions, headphone output levesl can be (optionally) adjusted seperately from the OUTPUT1 hardware pot, like they do it at Kemper? I usually run OUTPUT1 level set to max when using SPDIF or XLR outs, but I'm afraid to loose my hearing on one of my weak days when I forget to turn down OUTPUT1 before plugging in my headphones into the FM3. ;)
 
MrBollie said:
Is there also a chance, that in some upcoming firmware versions, headphone output levesl can be (optionally) adjusted seperately from the OUTPUT1 hardware pot, like they do it at Kemper? I usually run OUTPUT1 level set to max when using SPDIF or XLR outs, but I'm afraid to loose my hearing on one of my weak days when I forget to turn down OUTPUT1 before plugging in my headphones into the FM3. ;)
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Unfortunately no. The headphone output is hardwired to Output 1 on all the 3rd gen Fractal units. It's a bad design decision that causes unnecessary headaches but nothing you can do about that besides running a separate headphone amp.

Axe-Fx 3 is more flexible for this where I use Out1 just for headphones and plug my studio monitors to Out2 instead. Fractal FM9 would also work for this as it has XLR on Out 2.

Of course nothing stops you from using the 1/4" out 2 on the FM3 like this too but then you give up the fx loop.
 
laxu said:
Of course nothing stops you from using the 1/4" out 2 on the FM3 like this too but then you give up the fx loop.
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Yeah, these are already being used to have the fm3 additionally in a loop of a morning star looper, which is connected to Friedman tube head. That way I have the option to use FM3 in front of an amp as well as using it for "direct in". :)

You mentioned headphone out is hardwired to OUTPUT1. Wonder if they could at least decouple SPDIF from the volume pot. That way I could use that one and keep the pot all the way down.
 
Plug one of these between your headphone and the FM3 and you can attenuate the volume all you want:

Amazon product ASIN B00001P4XHIt's passive, so it probably is a better solution than an external headphone amp because you won't be re-amplifying the signal a second time.
 
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