m802 remote controlled microphone preamplifier with optional A/D converter

NEWS: Our m802 remote control preamplifiers are now shipping with RS485/RS422 serial control ports.
More information here (pdf)



m802

m802

Possibly the world’s most evolved mic preamplifier, the m802 delivers functionality and performance which simply doesn’t exist in any other mic amp design.

The core is a high fidelity 8 channel microphone preamplifier designed to be extremely transparent and musical. But that’s just the beginning. The m802 is fully remote controllable. With our full featured stand alone hardware RCU (optional), up to 64 channels (a system of 8 m802’s) can be addressed and controlled seamlessly from up to 1000’ away. All preamplifier functions, including gain, phase, 48V phantom are instantly accessible and adjustable. These settings can then all be stored into preset locations and instantly recalled.

The m802 can also be controlled directly from Digidesign® ProTools|HD® systems, compatible control surfaces and many other MIDI devices. Working with Digidesign®, we have adapted their control spec to directly address the m802 as an integrated part of a ProTools|HD® system. Additionally, the m802 can be controlled by a wide variety of MIDI mappable devices, making it easily integrated into a wide variety of remote recording situations.

Next, consider the optional 8 channel 24bit/192kHz A/D card option. Developed as the perfect complement to the m802 mic preamplifier design, this converter card provides pristine, musical A/D conversion to rival even the finest stand alone units available. Included is our proprietary unique s-Lock™ dual stage PLL for extremely low intrinsic jitter and rock solid digital performance.

The m802 now includes ribbon mic mode, which shifts the preamplifier’s entire gain range up 10dB, while deactivating 48V phantom power, optimizing input impedance and bypassing the decoupling capacitors.

While the m802 works beautifully as a stand alone mic preamplifier, the optional Remote Control Unit (RCU) provides fantastic ergonomics and enhanced system control. This updated RCU now offers dedicated individual channel select switches and a new highly visible blue LED numeric display for channel gain settings. Both the RCU and the m802 now come with a high contrast, neutral backlight LCD.

Whatever your application, we invite you to discover the remarkable sonic performance, functionality and reliability of the new m802. We’re confident that it will help you make the finest recordings of your career.


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PREAMPLIFIER FEATURES
  • fast, musical transimpedance amplifier architecturefully balanced, transformeless design
  • flexible digital metering with peak hold and reset
  • controllable from Digidesign® ProTools|HD® systems and compatible control surfaces (and many other MIDI devices)
  • dual high-current outputs (XLR+D-Sub) drive long cable runs and loads down to 50 Ohms
  • fast, efficient Philips I2C serial protocol to control preamplifiers from up to 1000 feet away
  • gain range of -7dB to +63dB in 1.5 dB steps
  • new selectable ribbon mic mode
  • channel group mode (perfect for stereo pairs, subgroups)
  • RCU able to address up to 8 units (64 channels)
  • front panel lockout mode
  • large neutral backlit LCD display
  • 15 User preset memory locations, for saving preamplifier settings (gain, phantom power, phase)
  • five year transferable warranty on parts and labor

 

A/D CONVERTER FEATURES
  • Absolute purist A/D converter performance: 24 bit, 44.1kHz – 192kHz sample rates
  • Outputs include 2x8ch AES3 on DB25, 1x8ch AES3-id on 4 BNC connectors (supports double wire mode)
  • Optional ADAT optical output module. Supports s/MUX for 88.2-96kHz sample rates
  • Multiple clock sources: Internal crystal, external word clock and Digidesign™ loop sync
  • wordclock in and out, clock output can be word clock in, recovered word clock or internal ref word clock
  • s-Lock™ dual stage PLL for extremely low jitter without sample rate conversion
  • Ultra pure high performance analog front end
  • Very low distortion conversion: 0.0002% THD+N
  • Low phase noise, wide lock PLL for external clock. Locks to Fs +/- 8%
  • Extremely low jitter s-Lock™ crystal based PLL
  • 8 channel AES3-id/IEC60958 (S/PDIF) outputs on BNC
  • Single wire and dual wire operation (8 channels on DB25, 4 channels on BNC)
  • All ADC parameters are adjustable from the m802RCU or m802 front panel
  • All data outputs are transformer coupled
  • five year transferable warranty on parts and labor

 

owner's manual Revision F (pdf)

m802 firmware update
(preamp Rev 2.2 / remote unit Rev 2.0)
This dowload is a.zip file which contains the firmware, the firmware upgrader programs and all the necessary documentation to properly ugrade the firmware in your m802 unit.

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A/D CONVERTER DESIGN

The m802 A/D converter card option provides m802 users with state of the art A/D conversion for the most demanding music recording applications. The purpose for this new card is to provide A/D conversion technology capable of matching the transparent, musical character of our mic preamplifiers, with the combination of the two creating a new level of true audio purity. To understand what makes our A/D converter unique, the following is a discussionof our design’s three basic functional blocks: the analog input stage, the A/D converter, and the clock generation (or regeneration).

ANALOG INPUT STAGE
Our converter’s analog input circuitry is simple and pure. This fully differential circuitry contains no electrolytic capacitors and utilizes precision 0.5% tolerance thin film resistors, to ensure that there will be no signal coloration from capacitor dielectric absorption and resistor thermal modulation. Careful attention to grounding and power supply layout eliminates any sonic aberrations caused from unwanted interference from digital circuitry. The analog input amplifiers are powered from their own dedicated Voltage regulators and each analog power supply rail is double regulated to provide extreme isolation from power line related noise. Driving the input of modern delta-sigma converters requires a low driving impedance and high current from the A/D input driver, and our experience from designing microphone amplifiers with precision line drivers translates very well to this task.

Also, there are significant advantages by having the A/D converter circuit wired directly from the analog microphone amplifier outputs (opposed to having separate preamplifier and converter chassis’). First, by having the preamplifier and converter in the same electrical enclosure, EMI interference from external sources (i.e. RF interference and ground loop hum) is greatly reduced. Additionally there is no need for ESD protection circuitry, RFI filtering, and complex input level adjusting circuits. The result is the most simple and pure signal path attainable with an absolute minimum of signal coloration.

A/D CONVERTER
The A/D converter employs a fifth order delta-sigma modulator and a low pass filter that exhibits very wide dynamic range and low latency. With a more gentle slope digital filter than other A/D chips, it is the most musical of the high end converter ICs. It is capable of 120dB dynamic range with distortion and noise artifacts at less than -110dB. Separate power supplies for the analog and digital portions of the A/D converter ensures that the precision delta sigma modulator will not be affected by other surrounding circuitry. As well, the differential inputs provide additional input noise rejection.

CLOCKS
A perfectly executed analog input stage and the best performing A/D converter IC can only result in audio performance as good as the quality of the sampling clock. Even the smallest amounts of clock jitter will readily degrade the performance of the converter by introducing non-harmonically related noise and distortion.

When operating on an internal clock, the A/D converter sample clock is generated by a quartz oscillator which has very low jitter. However, many applications require that the A/D converter be synchronized to an external clock source, usually in the form of a word clock, which is where the greatest challenge arises.

There is a common misconception that using the word clock input on any piece of digital audio equipment will result in better sonic performance. In reality, the vast majority of word clock PLL circuits will have more intrinsic jitter than the word clock signal itself and usually more intrinsic jitter than the PLL within the AES/S/PDIF receiver chip. As well, these PLLs usually have no incoming jitter attenuation in the audio band.

Our A/D converters employ a two stage PLL system to provide practically jitter-free recovered clocks with extremely high incoming jitter attenuation. The first stage is a wide lock range ultra low noise analog PLL, which can lock to incoming word clocks and Digidesign Loop Sync signals with a +/-8% lock range. Rather than using standard CMOS based PLL chips for the first stage PLL, we use an extremely quiet, discrete VCO (voltage controlled oscillator). When using a quality external clock source, this PLL alone will provide a nearly crystal quality clock. The incoming jitter rejection of this PLL begins at 500Hz and increases at 12dB/octave with rising frequency. The wide lock range allows for the converter to operate in vari-speed applications without a sacrifice in audio performance, provided that the external clock source is relatively low jitter.

Then, when the incoming sample rate is within +/-200 ppm of the selected sample rate, the secondary (our proprietary s-LOCK™) crystal based PLL will lock to the first stage PLL, providing the quietest possible recovered sample clock to the A/D converters. The s-LOCK PLL is capable of extreme rejection of incoming jitter, which begins at less than 0.1Hz and is better than 60dB at 1000Hz.

The word clock output connector(s) can output the incoming word clock or the recovered word clock from one of the two on board PLLs. If the incoming clock is of dubious quality, the output can transmit the jitter free version. If several A/D converters are to be used simultaneously, the word clock output jack can output a buffered version of the input clock for a daisy-chain configuration.

While it would be very easy (and economical) to provide “jitter free” sample clocks by routing the audio data through an ASRC (asynchronous sample rate converter), we believe that the convenience of these circuits does not outweigh the potential sonic degradation caused by additional signal processing. The performance of the s-lock PLL renders even the worst case interface jitter problems to a level well below the noise floor of the A/D converter.

Whatever your application, the m802 preamplifier/ A/D converter provides perfectly pristine preamplifier and converter performance, combined in a single, powerful and elegant package.

 

OUTPUT OPTIONS

the m802 A/D converter option is available in two configurations:

Output option A (below) includes 2 sets of 8 channel AES3 outputs on DB25, Word Clock in and Out, and 1 set of AES3-id outputs on 4 BNC connectors.


Output option B (below) inculdes 2 sets of 8 channel AES3 outputs on DB25, Word Clock in and Out, and 2x 8 channel ADAT / Lightpipe outputs.

 

CONTROL

When the A/D converter is installed and activated, the system’s sample rate, clocksource, format, and transmission mode are displayed on the user interface LCD. In addition, the preamp metering automatically switches to monitor the digital output level of the converter using a dBFS scale. Latching digital over indicators are also provided independent of the bar meters.

Need more information? contact Grace Design service

“Virtually every recording I have presided over during the past dozen years has been made using Michael Grace’s preamps - and this includes the m802, practically from the day the unit was launched. I cannot imagine getting more musical nuance from any other product.” -Tim Martyn, Phoenix Audio

“We have been using Grace mic preamps for a long time and if you told me that the 802 could have eclipsed the incredible sonic performance of our 801, I would have thought you were crazy. When we got the new 802 in and auditioned them we were completely knocked out. Better in every way. The Grace Design 802 sets new standards for performance in microphone preamps.If you are looking for a mic pre that doesn’t get in the way of what your mics are capable of delivering, the 802 is it.”- Mike Pappas Chief Engineer KUVO Jazz

"model 801R- We own a second 801R - so the new registration address applies to this unit also. We did a AD converter test, including a DA/AD loop of an original soundfile. The new files were rerecorded through a Benchmark DAC1 into all 5 AD converters, and also 5 times with a Gracedesign 801R inserted. While some converters had only neglegible differences, NONE of them were able to show any difference between no 801R and an 801R inserted ! This must mean either no converter was transparant enough, or the 801R is transparant enough. While we did this test to check for differences in absolute transparancy of the ADs, it turned out to be another proof that we shouldn\'t bother to invest in another brand of mic pre. So we happily expanded our 801R with a second one and a 801RCU."