Handmade in New Zealand
Buzz Audio A-RACK 8+1
Modular Recording System
The A-RACK 8+1 is the result of many requests for a multi channel mic preamplifier system with the same specification as the venerable Buzz MA-2.2 True Class A preamp. To this end, Buzz Audio has designed a system that not only carries mic preamps, but can fitted with other modules when they come available. Planned additional modules include a Class A Compressor and Stereo Direct Box, initially Buzz Audio offers the MA-1.5 Mic Pre module.
Applications live, studio
Classical music recording
Remote recording trucks
Sound scoring stages
Professional recording studios

A-RACK 8+1 shown fitted with 8 MA1.5 modules

John Whitmer, an A-RACK 8+1 user

The standard rack bin is 3 units high and includes the power supply regulator and monitor module on the right. Due to the high amounts of heat generated by the True Class A circuitry utilized in this design, adequate ventilation should be provided and it is suggested that 1/2U rack space is provided above and below the A-RACK if the unit will be covered with other equipment. Alternatively, the system can be supplied in a 4 unit high frame with built in 1/2 unit ventilation areas front and rear. In addition to the rack mount chassis, the A-RACK can also be supplied in an attractive 4U ventilated desk top enclosure.
To ensure best noise performance the power transformer is external, housed in a robust diecast box with carry handle and fixing points enabling it to be mounted elsewhere in an equipment rack. The standard power transformer supplies one A-RACK with a larger version available to power two A-RACKS. All power cables are fully detachable with heavy duty diecast body "Ceep" connectors being used for the connection to the frame.

The system includes a Solo buss that can be linked via 1/4" jack leads to other A-RACKs in a multi rack setup. The Solo monitor section has a high output headphone amplifier and 43dB range PPM (peak program meter) for monitoring module output levels. The Solo buss audio is also available on a balanced XLR output on the rear panel.

As well as direct XLR's, the line output of the first 8 module positions are internally connected to a DB25 connector at the rear of the monitor section, wired in accordance to the Protools-HD and DA88 style.

Fully modular, all modules including the associated rear connector panel can be easily fitted to or removed from the frame only requiring a small flat blade screw driver. The handle attached to the front of every module provides a convenient place for the user to label channel use


The first module available for the A-RACK 8+1 is the MA-1.5 True Class A Microphone Amplifier. All circuitry is real Class A discrete transistor using the Buzz Audio BE40 module. There are no transformers in the signal path, high quality film coupling capacitors are used for DC isolation. The circuitry is very similar to the MA-2.2 with the addition of the Solo feature and a Direct Drive Balanced Output circuit (the DDBO).

There are two main advantages to the DDBO over conventional "transformer acting" electronic balanced outputs. The first is near perfect common mode performance on balanced lines ensuring accurate audio signal transmission over long cables as may be found in remote live recording situations. The second advantage is an increase of output headroom by 6dB allowing the MA-1.5 to deliver a staggering +32dBu before the onset of clipping. The only disadvantage of the DDBO is that when driving an unbalanced load, one of the output amplifiers will be shorted to ground, which is not desirable. To enable the MA-1.5 to work with unbalanced loads, the MODE switch converts the output to a pin 2 hot unbalanced output, which also results in 6dB less gain.

The MA-1.5 provides real "straight wire with gain" performance in a modular format, and modules can be purchased as budget permits, perfect for all multi channel recording situations.

Fully discrete hi-bias wide bandwidth differential Class A amplifiers.
Matched and selected semiconductors.
Transformerless input and output with hi-grade film coupling capacitors.
2 stages of power supply regulation.
Individual discrete regulators for each stage of the 2 stage amplifier.
Single Point Ground pcb layout.
41 position max trimmed GAIN control.
Trimmed common mode noise rejection.
Optimized "grunty" Class A amplifiers for the input/output functions.
Output Mute and Hi/Lo input impedance switches.
Exceptional clarity, "straight wire with gain" performance

Bal Mode Min Gain = +22dB (+2dB with pad in)
Bal Mode Max Gain = +70dB
Unbal Mode Min Gain = +16dB (-4dB with pad in)
Unbal Mode Max Gain = +64dB
Maximum Output Level = +32dBu in Bal Mode, +24dBu Unbal Mode.
Frequency Response = 2Hz to 250kHz @ 20dB gain (-3dB).
= 20Hz to 250kHz @ 65dB gain (-3dB).
Harmonic Distortion = less than 0.008%100Hz to 10kHz.
Slew Rate = typically 140 V/uS, @ +20dBu output level.
EIN = -133.5dB A wtg, 150ohm source Z.
Signal to Noise Ratio = -74dB A wtg, input shorted.
CMNR = 100Hz-80dB, 1kHz -80dB, 10kHz-70dB internal trims.
Module to Module Crosstalk = below noise.
Input Impedance = 3k ohms/1k2 ohms switchable.
Controls = Gain, Solo, Mode, Mute, Input Impedance, 20dB Pad, Phase Reverse, Phantom pwr.
Indicators = Peak Level @ +18dBu (internally adjustable)
Connectors = In-XLR3F, Out-XLR3M.
Size = DIN 41612 standard 8 HP wide.
Power requirements = Must be fitted into A-RACK module rack bin.

0dBu reference = 0.775 volts RMS

designer of the Buzz Audio products:
Tim Farrant

Buzz Audio
77 Kent Terrace
Wellington 6001
New Zealand

tel/fax +64+4+385-2478

PO Box 6677
Wellington 6035
New Zealand


Studio Fuoriporta
Riccardo Corbari
via Brambilla, 2.
27010 San Zenone al Po (Pavia)
Tel. (+39) 0382.72.96.77 , eMail

advanced technologic sound magazine
2005 October issue 142

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