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MPA685 Owner’s Manual 

 

 

3/2012 

 

 

 

4

 

 

 
INTRODUCTION 

 

The Ingram Engineering MPA685 is a dual channel audio preamplifier designed for recording 
amplified or instrument level signals with the highest quality and flexibility. 
 
Microphones of any type and with any output impedance may be used.  The preamplifier has 
variable input impedance that can be presented to microphones for maximum flexibility in 
capturing the audio accurately or in shaping the tones to taste.  Two ranges of impedances are 
possible, and the range is installed at the factory.  Your pre-amplifier has been configured at 
the factory for the high impedance range, and its model number is 110685-20, referred to as 
“Option 2” in this Owner’s Manual.  This range consists of 600, 1.5k and 2.5k Ohm 
impedances that may be presented to microphones.  This impedance range is particularly well 
suited to ribbon microphones, as they typically require higher impedance load for optimum 
performance.  However, the extremely accurate handling of transient signals, low noise, 
extended low and high frequency response and other features enable this preamplifier to be 
used with any microphone type and any audio signal with outstanding results.   
 
  

 
DESCRIPTION 

 

The MPA685 provides two channels of 100% discrete semiconductor-based amplification of 
microphone and instrument signals.  
 
Audio content can be input to the MPA685 via the balanced XLR input, pin 2 Hot, on the rear 
panel, or to the ¼” jack on the rear panel, labeled “Opt”, on your unit.  The 1/4” jack is fully 
balanced.  
 
The balanced microphone input uses an input transformer for high CMRR, optimum noise and 
impedance matching and smooth tonal character over a wide range of microphone types.  
Your pre-amplifier is configured with a custom Sowter transformer, designed for and exclusive 
to Ingram Engineering, The pre-amp is designed to provide the input transformer with constant 
impedance load, independent of pre-amp settings, therefore guaranteeing consistently 
excellent transformer transient, frequency and phase response, as well as impedance and 
noise matching. 
 
The impedance load presented to the microphone can be varied so that tonal and dynamic 
characteristics of the audio can be adjusted to taste.  Different impedances are selected using 
a front panel switch.  The impedance seen looking into the balanced microphone input is 
switched between 600, 1.5k and 2.5k Ohms. 
 

Содержание MPA685

Страница 1: ...MPA685 Dual Channel Microphone Preamplifier Owner s Manual INGRAMENGINEERING Option 201...

Страница 2: ...MPA685 Owner s Manual 3 2012 2...

Страница 3: ...ophone Impedance Selector 5 Adjusting the Audio Input Level Settings 6 Overload LED 7 48V Switch 8 Phase Invert 9 High Pass Filter 10 Adjusting the Output Level Audio Specifications AC Specifications...

Страница 4: ...le this preamplifier to be used with any microphone type and any audio signal with outstanding results DESCRIPTION The MPA685 provides two channels of 100 discrete semiconductor based amplification of...

Страница 5: ...ns 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 volta...

Страница 6: ...LOAD LED BUFFER BUFFER LOW FREQ RESPONSE SWITCH OUTPUT BUFFER OUTPUT LEVEL POT STEPPED SWITCH ATTN DIRECT LOOPTHRU GAIN STAGE GAIN STEPPED SWITCH MIC Z BLOCK DIAGRAM A block diagram of the MPA685 is s...

Страница 7: ...to a power supply only of the type described in these operation instructions or as marked on this product 8 Power Cord Protection Power supply cords should be routed so that they are not likely to be...

Страница 8: ...plug with an extension cord receptacle or other outlet unless the blades can be fully inserted to prevent blade exposure 13 Grounding or Polarization Precautions should be taken so that the grounding...

Страница 9: ...s are made with standard ITT Cannon XLR 3 31 and 3 32 types XLR audio input and output connections are balanced with pin 2 positive Pin 3 negative and Pin 1 ground A ground lift toggle switch is inclu...

Страница 10: ...p through may therefore dominate the instrument load if the loop through load is less than 1 Meg If excessive signal loading is experienced when using the loop through connection remove the loop throu...

Страница 11: ...t section stepped switch functions as a combined attenuator gain control When the switch is adjusted between 11 and 1 on the front panel the switch is attenuator mode and the pre amp gain stage operat...

Страница 12: ...Gain vs Stepped Switch Position 6 Overload LED The Overload LED is designed to illuminate at 1 THD The Overload detection circuitry accurately tracks the 1 THD threshold to frequencies higher than 30...

Страница 13: ...of the audio at the pre amplifier output is 180 relative to the input 9 Low Frequency Response Switch The Low Frequency Response filter applies a 6dB octave cut to low frequencies when activated To a...

Страница 14: ...ut High Setting 69 dB Direct Input Stepped Switch Gain Change vs Switch Position 4 dB Step Switch Positions 11 to 10 2 dB Step Switch Positions 10 to 4 3 dB Step Switch Positions 4 to 7 4 dB Step Swit...

Страница 15: ...otherwise noted Parameter Min Typ Max Unit Comments AC Voltage 115 230 V Selectable on rear panel AC Frequency 50 60 Hz Fuse 500 mA 250 V Slow Blow Size 0 25 x 1 25 3AG or 5x20mm GDC 213 depends on A...

Страница 16: ...crewdriver may be used to eject the fuse holder from the housing The fuse type is specified in the Specifications section 2 Power On Bulb Use only Chicago Miniature Type 756 bulb Other bulbs have the...

Страница 17: ...assembly and remove the bulb by pushing the bulb in and turning to the left Replace the bulb with the type listed in the Specifications section 3 Microphone Input Audio Sounds Distorted Decrease the...

Страница 18: ...ground In the event that the ground lift toggle switch does not eliminate hum Pin 1 of the cable connected to the pre amplifier output may be disconnected at the connection to the pre amplifier If hu...

Страница 19: ...ate and thus determine whether or not your Ingram Engineering product is still under warranty To obtain factory service 1 Call Ingram Engineering at 678 685 9838 9 AM to 5 PM Monday through Friday Eas...

Страница 20: ...sales receipt Final determination of warranty coverage lies solely with Ingram Engineering or its Authorized Service Centers Ingram Engineering products returned to Ingram Engineering and deemed eligi...

Страница 21: ...LY LIMITED IN DURATION TO THREE YEARS FROM THE DATE OF ORIGINAL PURCHASE FROM AN AUTHORIZED INGRAM ENGINEERING DEALER UPON EXPIRATION OF THE APPLICABLE WARRANTY PERIOD INGRAM ENGINEERING SHALL HAVE NO...

Страница 22: ...cts and or documents or to discontinue any product at any time without notice The product specifications contained herein are subject to change Ingram Engineering assumes no responsibility for inaccur...

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