MARQUETTE AUDIO LABS

* Since 1994 *

Buzz Audio A-Rack 8+1


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 MA-2.2 True Class A preamp. To this end, we have 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 we offer the MA-1.5 Mic Pre module.

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 Minimum Gain: +22dB (+2dB with pad in)
Bal Mode Maximum Gain: +70dB
Unbal Mode Minimum Gain: +16dB (-4dB with pad in)
Unbal Mode Maximum 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
Channel to Channel 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




Please call Dave at (510) 581-3817 for your price.