More Info:
FMR Audio RNP RNP8380 Preamp
From Mark McQuilken of FMR
Audio:
WHAT'S
COOL
Lots o' headroom. These days, the trend is for
microphones to increase their output signal levels while reducing their output
noise levels. This means either employing a front-end pad and/or increasing the
headroom of a mic pre. We decided to do the latter: at unity gain, the RNP 8380
has a clip point of +27.5dBu (almost 25Volts peak-to-peak)! Even with a hefty
microphone output, the RNP8380 should take what your mics have to give.
Fidelity. When designing a pre-amp, there are
many ways to balance the sometimes conflicting operating constraints.
Unfortunately, with the proliferation of integrated-circuit (IC) based mic pres
in recent years, one of the typical casualties has been fidelity. At this point,
I won't bore you with the geeky details, but I want to assure you that fidelity
was not sacrificed in the RNP8380. Even though there are many mic pres that are
quieter, there are very few that have the spurious-free (i.e., distortion-free)
spectrum of the RNP8380. Now, more than ever, what you put into a mic pre is
what you'll get out.
Ugly
box. If you look beyond the RNP8380's utilitarian ugliness, you'll see
that we opted to throw the money we saved in cosmetics into the quality of the
audio electronics. I like having nice-looking gear as much as the next guy, but
given the choice between something that sounds nice versus looks nice, the sound
wins out everytime.
Really Nice
Compressor (RNC) inserts. Each channel on the RNP8380 has an unbalanced
send/receive jack that allow you to connect an RNC1773 using a single
Tip-Ring-Sleeve (TRS) cable (per channel). With proper cabling, you could also
use this feature to balance any other unbalanced piece of gear. In addition,
with the right external configuration, the RNP can provide a separate +22dBu
unbalanced output and a +28dBu balanced output simultaneously to allow nifty
things like separate M/S decoding while tracking the M/S signal without
decoding.
Balanced/unbalanced operation. Both the mic
inputs and mic pre outputs are electronically balanced, differential signals.
Want to run to/from unbalanced sources? No problem, the RNP automatically
adjusts...no special cabling required.
Balancing an RNC. Using the above
features, you can allow/provide a balanced signal to/from an RNC/RNP set.
Hi-Z DI
inputs. These inputs are designed to take a source, such as a passive
bass, and not "suck the tone" away from the instrument. This input features a
high-impedance unbalanced 1/4" jack.
Slowly-ramping
48V supply. To reduce the chance of destroying mics connected to the
RNP that can't tolerate +48V applied to them, we ramp up the +48Volts slowly
just in case you accidently turn on the phantom supply with a phantom-intolerant
microphone attached to the RNP. In addition, this ramp helps reduce "settling
time" of the RNP's servos (see Geek Stuff below) and reduces the size of the
output pops/clicks.
EMI-resistant. The pre-amp's front end includes a
third-order EMI filter. It is specifically designed to attenuate RF while giving
a smooth audio performance up to 200kHz. This reduces the chances that you'll
have trouble with RF interfering with the RNP's operation even at high-gain
levels. When used with a nominal 150 Ohm balanced source, this filter yields
exceptional audio performance.
Output
mutes. During phantom engagement/disengagement and DI/mic switching, we
momentarily mute the output signals to reduce output pops & clicks that may
otherwise annoy you and others. This mute actually occurs before the
insert send signal, so even devices connected to the insert are
spared large pops & clicks.
Stepped gain
control. To allow precise gain-setting between multiple channels, we're
using a Grayhill 12 position switch to set the RNP's gain.
Phase
inversion control. This is fairly standard stuff to allow you to
accommodate any phase problems due to things like system cabling, etc.
Precision
metering. Three LEDs are provided for metering each channel (signal
presence, +18dBu and CLIP). In addition, the clip LED trips at 1dB below actual
clip and stays on for 3 seconds to make signal-chain troubleshooting easier. The
metering is digitally-calibrated and driven by the internal microprocessor.
Flexible power
supply requirements. The RNP will run off of either AC or DC as long as
the voltage range is within 9-12V (and has a current capacity of at least
1.5Amps). Polarity of the wallwart connection is unimportant so that you don't
have to worry about that detail either. In addition, if you happen to connect a
wallwart that doesn't have enough oomph to power the RNP (like the RNC's
wallwart), the RNP will tell you by periodically flashing it's front panel LEDs.
Geek
stuff. An internal microprocessor provides control and monitoring of
many RNP internal activities: power supply operation, source (mic/DI) selection,
precision metering, push button control and phantom voltage control. The preamp
itself is a unique, full Class A self-biasing-fully differential-DC
servoed-transimpedance-100MHz GBP-instrumentation amp with an input impedance of
5k. The RNP's maximum level is +28dBu (differential mode) with an EIN of -120dB.
High common-mode impedances help reduce the effect of interfering noise sources.
Both phantom coupling caps and gain port voltages are independently servoed.
WHAT
SUCKS
Now I will violate a very important marketing rule by telling you
what I think sucks about the RNP. Why? Because nothing is perfect and
compromises always have to be made. By giving you some perspective on the RNP's
shortcomings, at least you'll have some insights into the whys about my choices.
Let your ears and application requirements be the ultimate guides.
The RNP uses a wallwart. As I
explain on our website for the RNC, the RNP also uses a wallwart to: (a) reduce
internal noise induction, (b) to make the national/international regulatory
compliance less costly, and, (c) to permit easy adaptation of the RNP to
countries other than the U.S. The upside is that we've designed the RNP to use a
range of wallwarts (see what's cool, above) instead of the pain-in-the-ass one
used on the RNC.
The RNP is relatively noisy when
evaluated by lab measurement. Many mic pres these days (including the really
cheap ones) have very low noise floors (EINs of -127dB or better). The RNP's EIN
of -120dB is obviously not as "good" as these others.
I decided that the sonic character
(or lack thereof) and a decent price point were more important than the absolute
noise floor. Why? First, many of the sought-after vintage mic pre noise levels
are much worse than the RNPs. So in actual use, I concluded, many folks
(particularly those "in-the-know") prefer good tone, even if it's slightly
noisier. Second, even though we have internal versions of the RNP with a lower
EIN, we'd have to charge at least $100 more for the privilege of meeting lab
measurements that few actual applications would challenge. Third, the trend in
microphone development has been to raise the output level of microphones,
thereby reducing overall gain requirements of external mic pres. Are there some
applications using the RNP that may be problematic? Yes. Will most of us
encounter them? No.
The RNP has coarse gain steps of
6dB/step. Under ideal circumstances, when gain staging your signal path, you
want to only use as much gain as necessary to do the job. Too much gain and you
possibly run out of headroom. Too much or too little gain and you possibly get
more noise than you'd like for a given application. So, why not use a gain pot
or a switch with more positions to allow finer gain steps?
First, pots are notoriously
inconsistent and imprecise for gain setting (see John Hardy's discussion of this) without using a two stage pot...one stage for low
gains and the other for high gains. That's OK, but I personally don't like to
have a "gain range" switch that can cause the gain to jump 30dB or more. This is
primarily 'cause I've been known to inadvertently push the button at an
inopportune time (don't tell anyone)! Second, 16 and more positions make for a
very expensive switch. In an ideal world, I'd have a switch with an infinite
number of steps to allow us to smoothly and precisely maximize the mic pre's
dynamic range...allowing us to exactly dial-in the gain we need without too much
noise or too low of a clip point.
Given these trade-offs, we've made
the RNP with a twelve step switch. The lowest gain setting is 0 dB with a clip
point of almost +28dBu. Each step then adds 6 dB of signal gain. Even though
this requires that we (the users) are more careful in setting the maximum gain
before clipping, its gain setting is a little less critical given the high
pre-amp clip point. So, a user is likely to be more concerned with the signal
being too hot further down the signal chain, at which point the signal can
usually be attenuated to the appropriate level.
Of course, you can always get
finer amplitude control by using an RNC in conjunction to your RNP.
