Royer Labs dBooster

Get the Microphone Boost You Need Without the Distortion from the Mic Preamp
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Royer Labs' Model R-DB2 dBooster is an in-line microphone signal booster for passive, low-output ribbon and dynamic microphones. It is connected between the microphone itself and a mic preamp's balanced input, and it's powered by 48-volt phantom power.

Royer Labs' Model R-DB2 dBooster

Royer Labs' Model R-DB2 dBooster

The dBooster will increase the output level of low-output ribbon and moving-coil dynamic microphones without adding significant noise, distortion or coloration. Switchable between 12 dB and 20 dB of super-clean gain boost, dBooster will increase the microphone's output signal to within the optimum gain range where most mic preamps operate and sound best.

When operated at or near maximum gain, microphone preamps tend to become unstable, noisy and not linear. Besides not accurately amplifying the microphone signal, their dynamic range becomes constrained where peak musical or vocal moments may distort. When recording quiet sources with dBooster, you will not have to run a mic preamp at or near maximum or add additional amplification to get a proper recording level.

Besides extra gain, the dBooster provides true electrical isolation and acts as a buffer stage for your preamp—especially good for the built-in (usually noisy) mic preamps within inexpensive USB DAW interfaces. Users are now able to record acoustic guitars using a Shure SM57 at full record level into their DAWs.

The full sound of certain dynamic and many vintage passive ribbon mics is compromised because of unwanted coloration of the mic preamp or long cable runs. Those long microphone cable runs (with unwanted distributed capacitance), microphone splitters and the low input impedance of vintage-style mic preamps can be difficult load impedances.

dBooster presents a relatively high-impedance balanced input (3.6 kohms) for the microphone's low-impedance output, thereby minimizing the effects of loading down and reducing the mic's sensitive output signal. And set to the 20 dB gain position, dBooster has an output impedance of 300 ohms and will maintain headroom and gain regardless of driving difficult load impedances.

What Is Inside?

Made in America, the dBooster is housed in a compact, one-piece anodized extruded aluminum box—measuring 3.62 x 2 x 1.62 inches. This enclosure is crush-proof and sturdy; that’s a good thing, as it will probably end up on studio floors most of the time.

Inside the dBooster is a thick, ruggedized circuit board using surface mount components. It has a single female mic input XLR connector with a 12/20 dB gain pushbutton at one end and a male XLR output connector at the other. Both connectors are Neutriks, have gold pins and are mounted to the unit's box.

To power the dBooster, incoming 48-volt phantom power is down-regulated to 16 volts, drawing up to 7.5mA at full output. However, phantom power is not passed through the unit so there is no danger of applying 48V to a ribbon microphone.

dBooster's input stage uses eight low-noise PNP transistors in a discrete Class-A bi-polar array amplifier circuit. This input stage then drives a Texas Instruments dual operational amplifier chip using separate amplifiers for the + and – of the balanced line output.

There are sufficient noise and RF filters to suppress contamination from spurious radio signals, cable, Wi-Fi routers and cell phones. The dBooster's circuit board ground plane and enclosure are all connected together to ground at Pin 1 on the XLR connectors.

In the Studio

In all my testing, I connected and placed the dBooster close to the microphone by using a short 0.5-meter XLR cable. (It would be a valuable addition for this kit to include a well-made XLR jumper cable for this purpose, as well as a way to "strap" the dBooster directly to the mic stand using a Velcro cable wrap.)

My first tests were for extreme usage. I set up a Royer R-10 ribbon mic that I normally use close in on loud guitar amps exactly 1 meter away from my acoustic guitar player. He plays a Taylor model 655-C 12-string guitar—mostly fingerpicking and light strumming. It will take a lot of mic preamp gain to record this guitar from that distance!

The schematic for the passive mic splitter built using a Jensen JT-MB-E transformer—it has three secondary windings, all with identical 150-ohm impedance.

The schematic for the passive mic splitter built using a Jensen JT-MB-E transformer—it has three secondary windings, all with identical 150-ohm impedance.

I wanted to hear any sonic differences with and without the dBooster by recording the same performance on two separate tracks at the same time in Pro Tools HDX at 96 kHz. To do this, I connected the R-10 to a passive mic splitter I built using a Jensen JT-MB-E transformer—it has three secondary windings all with identical 150-ohm impedance. (See Fig. 1 schematic.) This splitter has about 2.2 dB of insertion loss—gain that has to be made up by the mic preamps. I fed the splitter's two outputs to two channels of a transformerless Millennia Media HV-37 mic preamp. One channel went straight into Ch1 and then through the dBooster set to 20 dB to Ch2.

With the R-10 positioned that far away from the acoustic guitar, I had Ch1 of the HV-37 cranked "flat out" at its max 60 dB of gain (according to the spec sheet), and I could have still used much more record level to Pro Tools. It sounded fine, except it was too low in level. I applied a plug-in on playback and made up the level difference, but I was increasing the noise floor, as well.

Ch2 with the dBooster in line meant I could lower the gain on the HV-37 and still get a proper level. It took some experimentation to arrive at a new preamp setting—the HV-37 does not have any front-panel gain markings. After this first recording pass, I inspected the recording's waveform and found that I had clipped the HV-37's input with flat-topped peaks! To be conservative here, I went with 12 dB gain boost for the next pass.

Switching gain boost produces a "pop." Other than level, there were no sonic differences I could hear using either the 12 dB or 20 dB positions.

Just to verify, I repeated the entire 1 meter test using my Sunset S1P preamps. Unlike the HV-37, specific gain values in dB are silk-screened on the S1P front panels. Without the dBooster in line, I used more than 66 dB of gain to record into Pro Tools. The other S1P, with the dBooster set to 12 dB, used about 50 to 55 dB of gain for a similar recording level.

I removed the splitter and kept the R-10 and went for an acoustic guitar sound for a pop record. As a starting position, I would move the R-10 close in, maybe 10 inches out over the 12th fret and aimed back at the sound hole. With loud playing and the dBooster in line at 12 dB boost, I had the mic preamp cranked back down around its middle position—similar to a gain setting I would use for a small-diaphragm condenser.

Here with the dBooster, I noticed a difference in timbre, mostly in that the high frequencies sounded more open. Whatever change in sound apart from level is very subtle, and this will vary with every mic and/or preamp combination you use.

Rediscover Your Mic Collection

I definitely learned more about these preamps' unique character and nature when cranked to or near their maximum gain. I found using the 12 dB gain position on dBooster is effective for 80 percent of the microphone placements I used close in on sources. The 20 dB boost is great for more distant microphone techniques and/or helping out low-cost mic preamps/interfaces.

What was unexpected was rediscovering new uses for my collection of dynamic mics. dBooster is also useful for amplifying passive direct boxes connected to low-level piezoelectric pickups where clean gain is all that is desired! If you are looking for a great new tool to have in your kit, Royer's dBooster is a good choice.

PRODUCT SUMMARY

Company: Royer Labs

Product: Model R-DB20 dBooster

Website: www.royerlabs.com/dbooster/

Price: $179 MSRP

Pros: A great accessory to a mic collection

Cons: No option to attach it to the mic stand