Grace Design m501 — 500-Series Microphone Preamplifier

The signature transparency and detail of Grace Design preamps comes to the 500 series

The m501 is a 500-series module version of Grace Design’s highly respected m101 mic preamplifier. The m501, like all Grace Design preamps, is for audiophile recording where the goal is ultra accurate capture of the sound source with as little coloration or distortion as possible. To achieve Grace Design’s signature transparency, the m501 preamp module is a fully balanced, transformerless design with 48V phantom power, a 75Hz HPF and a ¼" HI-Z instrument input. The 500-compatible m501 also features Grace Design’s exclusive ribbon mic mode, which raises the mic input impedance and deactivates phantom power to protect delicate ribbon mics from catastrophic damage. Whether you track with large-diaphragm condenser, vintage ribbon, or your workhorse dynamics, the m501 500-series preamp brings out the very best performance from your mics and gives you a dependable, high quality input chain. The sound quality and musicality of the Grace Design m501 is tangible proof that transparent does not mean sterile.

Grace Design m501 unique features:

• New Ribbon mic mode (also great for dynamic mics)
• Relay bypass of phantom power decoupling capacitors, increased input impedance, and 48V lockout

Grace Design m501 key features:

• Fast and musical trans-impedance architecture
• Precision audio path with 0.5% precision metal film resistors
• 12-position, gold-plated rotary gain switch
• High-performance output line driver amplifier and HPF amplifier
• Wide 10-75dB gain range
• Enhanced RFI interference suppression
• Three output connectors: XLR balanced, TRS balanced and ¼” unbalanced
• Bombproof laser-etched black anodized front panel
• Sealed gold contact relay for Hi-Z input switching
• LED indicators for +48V, Ribbon mode, and HPF
• Five-year warranty on parts and labor
• Made in the USA

Don’t forget to check out RSPE’s Rack Revolution, a virtual 500-series rack builder that lets you custom-configure the perfect 500-series lunchbox for your studio, DAW, or mobile recording rig. RSPE carries every 500-series module imaginable, including mic preamps, compressor-limiters, equalizers, and 500 power racks.

Inside The Box — Grace Design m501

While there are a lot of preamps, both rackmount and 500 series, that have character and color, the m501 is for those who believe in recording the sound source as close to reality as possible, or prefer the option of adding “color” down the road in a mix rather that as an irremovable part of the sound source.

The m501 circuit is for engineers confident with the quality of the source, mic section and placement, and wish to capture it with as little coloration or distortion as possible, hence the m501 module’s transformerless design.

Ribbon Mic Mode

Pushing the ribbon switch does three things: +48V phantom power is locked-out to prevent potential damage to ribbon microphones, the impedance of the mic input is raised from 8.1k ohm to 20k ohm, and the 48V DC blocking input capacitors are bypassed with sealed gold contact relays.

The maximum gain available on the m501 is 75dB, which is achieved by setting the gain control to 65dB and the trim to 10dB. For recording low-level sources with ribbon microphones, the m501 has ample available gain, sufficient for even the most demanding low-level recording scenarios. The ribbon mode on the m501 is also ideal for many dynamic mics.

Transformerless, trans-impedance design

The Grace Design m501 microphone preamp is fully balanced, with transformerless inputs and outputs. The input amplifiers are based on monolithic, low-noise instrumentation amplifiers. Gain core sections are trans-impedance, or “current feedback” amplifiers, which have many important advantages over traditional “voltage feedback” op-amps.

First, trans-impedance amplifiers have a nearly constant bandwidth over a wide gain range and are not prone to large-signal slew rate limiting, which results in improved dynamic performance. Compared to voltage feedback op-amps (which are found in most preamplifier designs), trans-impedance amplifiers have better dynamic performance and are able to track complex harmonics without adding any metallic or “solid-state” character to the sound. Also, trans-impedance amplifiers reveal greater detail and provide a more open, musical sound quality. Furthermore, trans-impedance amplifiers maintain the same sound quality all the way up to the highest gain levels, which makes them dramatically superior for use with low-output ribbon microphones.

Output Driver Stages - The balanced output stage of the m501 preamp module is capable of driving extremely long cable runs and load impedances down to 50 ohms. Transient performance is superb and is not compromised when operating in unbalanced modes.

Controls - The gain control used in Grace Design’s m501 500-series preamplifier consists of a precision switch wired with 1% metal film resistors. The advantages of a fixed resistor switch over a potentiometer for gain setting is substantial: as music signal flows through a potentiometer, the potentiometer’s temperature modulates, causing its resistance to modulate. As the value of resistance changes, so does the amplifier gain, resulting in unwanted dynamic distortion. Most conductive plastic potentiometers have temperature coefficients of +/-1000ppm/oC, which can cause considerable signal degradation at high amplifier gains. By comparison, a metal film resistor has a typical temperature coefficient of +/-50ppm/oC, which represents more than an order of magnitude improvement in thermal stability.

Relays - To keep signal paths as short as possible, relays are used to perform phase reverse, input selection, and input attenuator functions. Sealed, gold contact relays offer no signal degradation and are completely reliable (rated for over 50 million operations without significant change in contact resistance).

Outside The Box — Grace Design m501

The laser-etched black anodized front panel of the m501 preamp module hosts the following controls:

Peak Indicator — The LED peak indicator, which monitors the signal at the output of the preamplifier, illuminates green at -14dBu and red at +16dB (10dB before clipping).

Gain Control — The gain control has 12 positions and adjusts the voltage gain on the micro- phone input from 10dB to 65dB in 5dB steps. When using the instrument input, the gain range is –10dB to 45dB in 5dB steps.

48v Phantom Power — This switch provides 48 Volts to power condenser microphones. LED indicator illuminates red when active.

Ribbon Switch — Pushing this switch activates ribbon mic mode which optimizes the signal path for non-active ribbon mics. LED indicator illuminates white when activated.

High-Pass Filter — (labeled HPF) 75Hz, 12dB/Octave high pass filter.

Trim Control — The trim control provides zero to +10dB of continuously variable output trim.

¼" TRS Hi-Z instrument input

The front panel of the Grace Design m501 preamp module also has a balanced ¼" Hi-Z instrument input for line level or instrument input. When a plug is inserted into the instrument input, a sealed gold contact relay switches the preamplifier input source from the rear panel mic input connector to the front panel TRS jack. The input impedance of the instrument input is 2.5M ohm unbalanced and 5M ohm balanced, which is ideal for inserting high impedance sources such as guitars with passive pickups, as well as any instrument with a high level output. The gain range of the m501 when using the instrument input is –10dB to +55dB. Using the instrument input with an unbalanced source is simple. When a mono 1⁄4" jack is used, the sleeve will automatically ground the inverting input (ring) when plugged in.

Who’s using Grace Design

Here’s a partial list of Grace Design clients who share one need common: uncompromising audio quality.

Bob Ludwig, Gateway Mastering and DVD
The Metropolitan Opera
Berklee College of Music
Chicago Symphony Orchestra
Tanglewood / Tanglewood Music Center
Nashville Symphony Orchestra
Tim Martyn, Phoenix Audio
Music Mix Mobile
Capitol Mastering
Leslie Anne Jones, Skywalker Sound
Shawn Murphy, Todd AO
New York Metropolitan Opera House
Warner Bros.
DPA microphones
Oberlin College and Conservatory
Shure Microphones
Patrick Leonard
MTV New York
CBS New York
NBC New York
Jazz at Lincoln Center, New York
Steve Boeddeker, Skywalker Sound
Chris Boyes, Skywalker Sound
Jerry Harrison, Talking Heads
Airshow Mastering
Mastermix, Nashville
Stevie Wonder
Jackson Browne, Dennis Scrimo
Kitaro
The Hollywood Bowl
Sarah McLachlan
Phish, Paul Languedoc
Trey Anastasio
Bill Frisell
Bela Fleck

About Grace Design

In 1990, Michael Grace began building single order custom audio products for a small, devout following of recording engineers and artists. Before long, the word had spread about these custom microphone preamplifier designs, which were said to outperform anything else that was commercially available. In 1994, Michael partnered with his brother Eben and Grace Design was founded and began production of the model 801 microphone preamplifier. Not only did the model 801 provide a new level of audio performance and functionality, it helped to establish outboard the outboard microphone preamplifier as a new keystone in professional audio production.

Over the years, Grace Design has maintained a steady, methodical pace to developing new products and technologies. The Grace product line has evolved into a definitive collection of microphone preamplifiers, monitor controllers and other unique hardware. Grace Design prides itself on providing audio professionals and enthusiasts with some of the finest tools imaginable. And above all, Grace Design remains driven by the original passions that founded the company—the love of music and the art of recording it.

Regardless of the style of music you record, certain sound sources require accurate, transparent audio capture, and nothing does it quite like the Grace Design m501 modular preamp. For more information, call or chat with an RSPE representative today.

This product is also available as part of the RSPE Demo 4 Free & Rental Program, click here to see the rental product page.