Posted on - April 19, 2006 [at] 3:15 pm by Brad
Tagged in - gear, review
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Just got a really informative response back from Chad at Presonus support about my -6db clipping/low gain issue with the Presonus Firebox:
Yes, the FB pre’s are a bit on the low gain side, although they shouldn’t clip too easily.  Unfortunately, if they don’t provide enough gain with the digital boost engaged (and you may try disengaging it to help with clipping), you may want to couple them with the Blue Tube or use the Blue Tube with line in.  The BT has about 20db more analog gain than the FB. Sorry.  As I understand it, they had to make the FB in a way which was bus-powerable even under the most extreme conditions (daisy-chained w/ other FW devices, on laptops, etc.) which probably compromised the voltage that the preamps could run off of.  The BT gain circuit runs off of about 16v rather than the 6v or so that the FB runs from
That’s some good information for your ass right there. Awesome support from Presonus.
Unfortunately the goal was to replace my Bluetube and Delta66 with a portable firewire thang. The Presonus Firebox would handily replace the Delta66, but replacing the Bluetube with a quieter preamp that doesn’t go above -6db kinda blows. If I’m going to keep using the Bluetube, then I’m not sure why I’d pay a bunch of extra money for a device with preamps I never use on it. So much to think about.
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10 Comments on this post
johnsonic on Firebox gain update
April 23, 2006 at 1:45 am
Yeahman, presonus tech support rocks. Those guys get right back to you and stick with you till you figure it out, kinda rare…
That’s a bummer about your firebox though, my firepod sounds great (but is powered by an adapter). I’d rather a wall wart and more gain than the tiny bit of convenience bus powered offers.
jtheory on Firebox gain update
June 21, 2006 at 3:17 pm
I ran across this page after asking Presonus the same question about my new Firebox. The reply:
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The FireBox preamps were designed with a bit lower gain potential than our standard analogue preamps. This was done to ensure bus-power operation via 6-pin firewire in even the most demanding applications. For this reason, they operate on a bit lower rail voltage than, say, the preamps in the BlueTub, MP20, or FirePod.
They have about 35dB of analogue gain plus a 12 dB boost via the +12dB boost control in the FireBox Control Panel. This is generally more than enough to run any tube mic or condenser microphone and about 75% of the dynamic & ribbon microphones available in most applications.
In cases where a low sound source or output mic (RE20, SM7, RCA44, etc.) is being used or where a substantially hot signal is desired, it is advisable to use an external preamp via line inputs 3 or 4 or even in combination with the preamps in channels 1 & 2.
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Same thing. You’ve probably already returned yours by now; I’d comment to other users, though, to make sure you check the +12dB Input Level Boost in the control panel — with that, it’s not too bad (and I think I’m going to keep my Firebox in spite of this issue)… without it, it’s basically unusable.
Brad on Firebox gain update
June 21, 2006 at 5:04 pm
I believe I tried the level boost but it was still a bit low and I feel dirty using those boosts. I always assume they’re junking up the sound somehow.
Si on Firebox gain update
April 22, 2007 at 10:25 am
Just come across this page googling for the same issue. Not nearly enough gain for my dynamic mic I’ve got plugged into the mic input. I’m either going to have to get another interface of get a pre connected to the spdif as I’m using all the other IOs. Can you advise on what the level would be like connecting a preamp (thinking of focusrite trakmaster) to a spdif?
JD on Firebox gain update
September 29, 2007 at 11:00 pm
Unfortunately, what Presonus is telling people about the Firebox’s low preamp gain is a lie.
I’m an electrical engineer, and I’ve been designing audio circuitry for over 15 years. There’s absolutely no relation between preamp gain and power consumption. None. How many times have you seen a mic pre with only 35dB gain? Personally, never. That’s 20 to 100 times less than a typical mic pre, at 60 to 75dB gain. So why the deception? Well, 60dB of gain may not take any more power than 35dB, but it does take higher quality circuitry. I opened up my Firebox to have a look… it uses low-grade opamps, and a cheap switching power supply. Poorly designed, and not what I expected from a company with Presonus’ reputation. It takes a much cleaner design to deliver 60dB of gain without contaminating the signal. 35dB is probably as much as they could squeeze without exposing how bad their analog circuitry is.
Check out the markings on the front panel. Anything look fishy to you? The mic pre gain knobs (at least on mine) are labeled 0 to 60. Hmmm. I’d bet money that Presonus intended the Firebox to have respectable 60dB of mic gain, but knocked it back to 35dB when they discovered problems at high gain (rather than re-designing the circuits properly), and then threw in the 12dB software boost as a band-aid, knowing full well that 35dB would be insufficient for almost any microphone. Even my hottest condenser mic, at -32dB sensitivity, is generally too quiet on the Firebox. Ribbons and dynamic mics? Forget it. Not even worth the effort.
Brad is also right about the +12dB digital boost. You’re just throwing away dynamic range by boosting all the low-level noise and digital modulation garbage along with your signal. There’s no substitute for clean analog gain, which is why one always records at the highest possible signal level, without clipping, whether it’s to tape or into an AD converter / DAW.
One more thing: the Firebox does not meet the firewire (IEEE 1394) power specification at all. Not even close. Bus-powered firewire audio devices are notorious for violating the inrush current spec, often by a factor of 100 or more, simply because the manufacturers don’t want to spend the extra $0.50 to add a current limiter circuit.
Computers have protection circuitry to meet safety requirements, so that people don’t get hurt if a metal object accidentally goes into the firewire port. These safety limits are usually well above the firewire spec, but firewire devices which are out of spec can still malfunction if they run into these safely limits when they’re plugged in. Also, these safety circuits exist mainly to prevent injury to a person. They may or may not offer good overload protection to the computer itself. So out of spec devices such as the Firebox may draw so much initial power that they damage the motherboard.
Moral of the story is: always, I repeat ALWAYS, use the external power supply, and be certain to plug it in before you connect the firewire cable! I also recommend to use a firewire hub instead of plugging straight into your machine.
Presonus clearly went overboard on their cost-cutting. I’d much rather pay just a little bit more for something which works properly.
ryu on Firebox gain update
January 19, 2008 at 12:43 pm
thats a good review from you, JD. i wish i have seen this before i bought it. the gain is too terrible. i should have bought a 80 behringer audio interface. it might have been better…
Kyle on Firebox gain update
November 25, 2008 at 9:40 pm
JD, great post!
The firebox doesn’t even work on a Mac unless you start it up with the power supply… so annoying. But good advice to always use the external power.
Thanks
Kyle
Hmm on Firebox gain update
December 29, 2008 at 7:24 pm
“Brad is also right about the +12dB digital boost. You’re just throwing away dynamic range by boosting all the low-level noise and digital modulation garbage along with your signal.”
Do you have actual evidence that this is a digital software boost or are you just making assumptions?
PreBigBanger on Firebox gain update
May 11, 2010 at 8:50 am
After reading all these posts, I want to get something better than the Firebox. What can I use in a Firewire home studio to effectively pre-amp something like the Rode NT1-A?