Useful Arts BF-1 Tube Mic Preamp
MPN #UAA-BF1
All purpose Class A tube instrument preamp, with pickup to enhance clarity and dynamics - includes two-band EQ and dual outputs
The BF-1 is an all-purpose interface for any instrument with a pickup that enhances clarity, detail, audibility and dynamics whether used between the instrument and amp, the instrument and a PA or recording device or all of these at the same time. Whatever you plug into it just sounds better. This isn't because the BF-1 changes the sound of the instrument - it's because it preserves it in a way that the input stage of an amplifier or a console simply can't. Once you feed your amp, console or converters a strong representation of what's actually coming out of your instrument, you'll be amazed at how good it really sounds. (It's been sounding this good all along, but now you can finally hear it!)
So let's get nerdy. The BF-1 was built for musicians who care about the sound of their instruments. It's meant to be used by musicians with a minimum of fuss in any environment. Just plug the instrument in, plug the BF-1 into the amp, and be amazed.
We usually think of DIs as utility boxes designed to get an XLR-compatible signal out an instrument. Necessary, perhaps - but boring. The last thing anyone wants to spend money on. So what if we took the interface out of the realm of the boring and made it an indispensable part of the original sound The BF-1 does just that.
The signal generated by magnetic pickups is beautiful, nuanced, detailed and incredibly weak. That's even more true of piezoelectric pickups. It's not just a question of the level of the signal (a voltage concept), it's a question of the power of the signal (a current concept). All amplifiers make the signal do actual work to drive the input stage. The problem is that the most delicate parts of the signal aren't capable of doing that work, and are forever lost. It's a form of Heisenberg's "observer principle" - when we observe a phenomenon, we necessarily alter it. The goal in getting the best sound out of an instrument is to observe the sound while avoiding unintentional alteration of it.
It boils down to input impedance. The higher the input impedance, the less work the signal has to do before it is safely amplified. Consoles and recording devices usually have an input impedance of around 10,000 ohms - way too low for a pickup. Plug a guitar or bass directly in and it sounds lifeless, small and completely lacking in detail and low end. With a piezo pickup, it sounds thin, buzzy and grating - like you spent a few grand on a kazoo. Guitar and bass amps have an input impedance of several hundred thousand ohms - a big improvement. Instruments sound bigger, fuller and more detailed. This is why the traditional approach for recording or live gigs has been to run the instrument into a DI for the console and back out to the amp. The normal DI replicates the input impedance of the amp, converts it into a signal the console can use, and all is well. Boring, but fine.
What if we looked at this differently What if we made the pickup do even less work What if instead of a few hundred thousand ohms we created an interface with 20 million ohms input impedance Well, we did. And the results are astounding. Now we can observe even the tiniest details in the signal without ruining it, and pump the results out to an amp or console with the full detail in useable form. There's no reason to plug an instrument into anything else. The BF-1 can simultaneously drive an amp through its 1/4 ing output jack and a pro audio device via XLR. Everything sounds better.
It turns out that tubes are uniquely well-suited for this task, because they are inherently capable of creating ridiculously high input impedances. Passive DIs use transformers, which can't effectively create such high impedances. Active Dis use low-voltage FETs, which sound like .... transistors. And they usually offer input impedances far lower than a good tube stage anyway. But wait! You already have a tube amp - won't that do the trick Nope. Amps use tubes as high gain stages, and that drastically lowers their input impedance. They benefit hugely from the BF-1. The BF-1 uses the input tube the same way as a tube microphone - to convert impedances without the high gain.
There are other tube DIs out there, sure. But most of them resemble a traditional tube amp input and give you a nice low impedance output for the console. We took a different approach that offers better sound and way more flexibility - all for a ridiculously low price in a package that's small and rugged enough to put in a gig bag and use every day.
Instead of stopping at massive impedance conversion, the BF-1 also offers a Class A tube preamp, a two-band EQ and dual outputs that can be used simultaneously for your amp and console. But we didn't stop there. Bypass the EQ, and you have a choice of low gain (much like a traditional DI) or high gain, which gives you the ability to go straight to the converters for pure high-fidelity line level recording with no other amplification needed.
For bass players, the BF-1 can actually eliminate the need for an amp altogether. Feed a console with the tubes in the BF-1 and it will sound better than any bass amp output you've ever heard. Crank the low band of the EQ, and say goodbye to the windows and drywall in the venue.
Specifications
Just like the SFP-60, the SFP-30 features separate regulated DC power supplies for tube filaments, phantom power and high voltage. The high voltage soft start power supply puts out over 270 volts of clean, regulated power to ensure maximum headroom and the lowest noise possible.
Each gain stage is single-ended, inherently class A.
Audio Magnetics (Input and Output Transformers, Plate Inductor) custom wound by Cinemag
Output Transformer with 50% nickel core
Frequency response is flat within 2dB from 20Hz-30KHz:
Each channel of the SFP-30 features 4 switches:
High Pass FilterInput PadPhase ReversePhantom Power
Absolutely no signal passes through these switches, because we hate the noise that develops over time in even the most expensive switches. Instead, the front panel switches control sealed, gold-plated relays to ensure years of operation without pops and clicks.
The input and output levels of the triode stages of the SFP-30 are separately controllable by detented attenuators, and combined with the color control, the SFP-30 provides just over 55dB of useable gain.
The rear panel is simple: it offers a voltage selector for 115/230 volt operation in the IEC fuse block. The gold-plated XLR connectors are on the front panel.
The only active devices in the signal path are the three tube gain stages, consisting of 1 EF806 and 1 ECC82 per channel. We use new-manufacture JJ tubes for long life and easy replacement.
Each channel features an output level VU meter, which is op-amp buffered to ensure that the signal is not loaded by the meter.
The audio power supply features a toroidal dual-primary transformer and linear regulation for lowest noise.
Write a review about the Useful Arts BF-1 Tube Mic Preamp
View more products from
Useful Arts
