MPA685 Owner’s Manual
3/2012
5
Amplification is provided by a two-stage all-discrete JFET input / Class-A Output circuit. Rather
than use a 20dB input pad, a combined variable-attenuator / gain stepped switch control by
Goldpoint provides the ability, unique among most pre-amp designs, of optimizing signal to
noise, dynamic range and transient response for any audio signal level and any pre-amp
setting.
A high impedance JFET buffered instrument input provides full Direct Box capability.
Maximum flexibility is realized for working with DI signals, as the pre-amplifier has a DI loop-
through so that the signal may be routed to amplifier/speaker cabinets or processing
equipment while simultaneously tracking or monitoring the DI signal.
An electrically balanced, buffered output stage provides isolation of the amplifier stage from
output cable effects. The pre-amp is configured with a Jensen output transformer. A fully
floating, ¼” output is provided for routing unbalanced signals from the output. This output
provides an ideal tool for re-amplifying previously recorded tracks. For additional information,
refer to Application Note “App Note AN6851_A Re-Amping”. This Application Note provides
detailed information about how to re-amplify a recorded track for additional recording options.
Extremely tight gain matching between channels, along with the transformer usage and
discrete circuit design, also makes the MPA685 an excellent choice for stereo make-up gain
applications.
High voltage rails enable excellent headroom and provide high output level. A reg48V
power supply provides reliable power for phantom power mics. Overload indicator LED
accurately detects distortion to ultrasonic frequencies.
Top quality electronic components include long life Panasonic HE Series and Nichicon Fine
Gold Electrolytic Capacitors, polypropylene and metalized polyester non-electrolytic
capacitors, low noise 1% Vishay/Dale RN55/RN60 Resistors, gold-plated stepped switch by
Goldpoint for recalling exact pre-amp settings, and continuously variable output level control
using long life State Electronics noiseless level control pots with high rotational life expectancy.
MPA685 part number is defined by the options installed, as described below:
Part number 110685-ABCD
“A” refers to the input impedance range option
“B” refers to the output transformer option
A = 1 is used for 60, 200, 600 Ohms
B = 0 is used for the standard transformer
A = 2 is used for 600, 1.5k and 2.5k Ohms
B = 1 is used for customer transformer 1
B = 2 is used for customer transformer 2
“C” refers to the power supply installed
“D” refers to special options
C = 0 or no character is used for fixed 115V
D = E is used for any special options
C = 1 is used for 115V/230V selectable power supply
as defined in this manual
