MFJ MFJ-651 User Manual

hamProAudio

Transmit Audio Conditioner

Model MFJ-651

VERSION 0A

INSTRUCTION MANUAL

CAUTION: Read All Instructions Before Operating Equipment

MFJ ENTERPRISES, INC.

300 Industrial Park Road

Starkville, MS 39759 USA

Tel: 662-323-5869 Fax: 662-323-6551

MFJ-651 hamProAudio

Transmit audio conditioner Instruction & Technical Manual

DISCLAIMER

Information in this manual is designed for user purposes only and is not intended to supersede information contained in customer regulations, technical manuals/documents, positional handbooks, or other official publications. The copy of this manual provided to the customer will not be updated to reflect current data.

Customers using this manual should report errors or omissions, recommendations for improvements, or other comments to MFJ Enterprises, 300 Industrial Park Road, Starkville, MS 39759. Phone: (662) 323-5869; FAX: (662) 323-6551. Business hours: M-F 8-4:30 CST.

MFJ-651 hamProAudio

Transmit audio conditioner Instruction & Technical Manual

TABLE OF CONTENTS

TOPIC PAGE

1. TABLE OF CONTENTS 2

2. LIST OF FIGURES AND TABLES 2

3. INTRODUCTION AND FEATURES 3

4. TYPICAL SPECIFICATIONS 4

5. SYSTEM CONTROLS AND INDICATORS 5 a. FRONT PANEL CONTROLS AND INDICATORS 5 b. REAR PANEL CONTROLS AND INDICATORS 7

6. SYSTEM SETUP 8 a. INTERNAL HEADERS 8 b. INTERNAL JUMPER BLOCKS 9 c. CABLES 17 d. POWER 17 e. HEADPHONES 17 f. RADIO AUDIO 17

7. THEORY OF OPERATION 18

8. MFJ-651 EASY-START INSTRUCTIONS 20

9. IN CASE OF DIFFICULTY 24

10.TECHNICAL ASSISTANCE 24

LIST OF FIGURES

Figure 1 Front Panel Jacks and Controls 5 Figure 2 Rear Panel Jacks and Controls 7 Figure 3 Internal Headers 8 Figure 4 Internal Jumper Blocks 9 Figure 5 Mic Jack Pinout 10 Figure 6-11 Internal Jumper Blocks 10 Figure 12 Yaesu Mic Jack Pinout, Front View 14 Figure 13 Functional Diagram 18 Figure 14 Compression and Gating Characteristics 19 Figure 15 Block Diagram 19 Figure 16 Schematic 25

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MFJ-651 hamProAudio

Transmit audio conditioner Instruction & Technical Manual

INTRODUCTION & FEATURES

INTRODUCTION

The MFJ-651 hamProAudio Transmit audio conditioner was designed with the serious operator in mind. Based on the Broadcast Industry Standard Speech Compression IC the SSM-2166 from Analog Devices, it allows the operator flexibility in the use of input sources and output methods.

FEATURES Choice of three Input Sources: In order to add versatility MFJ has included the

following input sources for the MFJ-651:

1. A standard RJ-45 input jack common to most new radios.

2. Standard 8 pin round chassis connector for the majority of the radios

produced in the last 25 years.

3. MFJ’s own input consisting of a 3.5 -mm jack that allows the user to choose from feeding audio, audio and a PTT function for use with the Heil series of Boom-Mic Headsets, or even provides phantom voltage on the tip for the MFJ-393 Boom-Mic Headphones or on the ring for use with a computer Boom-Mic or Boom-Mic headset.

These features are included along with allowing you to feed audio from a computer, TNC or Modem.

Fully Adjustable Gain Amplifier: You have control of the output level to bring weak microphones up to a useful level or provide over 1.2 volts peak to peak using the auxiliary output.

Wide Range Compression Settings: With an adjustable compression setting from 1:1 to 15:1 you control the amount of compression necessary to get your signal through the toughest of band conditions.

Adjustable Downward Expansion Level and Delay: No more feeding background noise into your signal. The MFJ-651 allows you to set the level of Downward Expansion to only pass audio when you are talking, and a delay to minimize cutting in and out between words.

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MFJ-651 hamProAudio

Transmit audio conditioner Instruction & Technical Manual

INTRODUCTION & FEATURES

Audio Pass Through from your Radio: No need to switch the headphones

from the MFJ-651 to the radio. At the push of a button you can instantly switch from normal operation to a test mode that allows you to adjust the settings without going on the air with the built in monitor amplifier.

By-pass Function: Switch the MFJ-651 in or out and you still have the radios audio in the headphones. This feature is useful when you want to Rag Chew and don’t need the Compression or Downward Expansion of the MFJ-651.

Multiple Outputs: The MFJ-651 has multiple outputs for both receive/test audio and Microphone audio. No need to have to hunt for an adapter to switch between 3.5 -mm or ¼-inch stereo phone jacks. Microphone audio is fed from the RJ-45 connector through the 3.5 mm Auxiliary Output or through a separate

3.5 mm jack that gives a truly balanced output if you need it. Rugged Construction: Attractive all-metal cabinet, conservative component

selection, space age SMD Circuitry and extensive RF filtering ensure solid performance for years to come. Fully covered by MFJ’s “No Matter What” one year limited warranty.

Before attempting to operate your MFJ-651, please read the manual thoroughly. It contains important detail about setting up your unit to obtain the best performance.

TYPICAL SPECIFICATIONS

Input source……………………Dynamic or electret microphone low or high Z

Stereo or Monaural radio audio. Sound card or Modem

Output ………………………….High or low Z. Adjustable signal level Bandwidth …………………….20 kHz Total harmonic distortion ….1% maximum, <0.2% typical.

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MFJ-651 hamProAudio

Transmit audio conditioner Instruction & Technical Manual

SYSTEM CONTROLS

MFJ-651 JACKS AND CONTROLS

MFJ hamProAudio Professional Microphone Conditioner™

MFJ-651

COMPRESSION

OUTPUT

DOWNWARD EXPANSION

MONITORLEVEL DELAY

Compressor

POWER

Max Min Max Min Max Min

OFF

MICROPHONE IN

Max

Min

Max Min

OUTPUT LEVEL POWER

1 2 3 54 6 8 9

10 11

Figure 1: MFJ-651 Front Panel Jacks and Controls

1. 8 pin Microphone Input Jack: Accepts input from any standard 8 pin microphone.

2. RJ-45 Microphone Input Jack: Accepts the input from a standard RJ-45 Microphone.

3. Compression Level Set: Controls the Compression function from no Compression to 15:1 maximum Compression.

4. Output Gain Level LED: A one time adjustment will allow this LED to monitor your output level and allow you to set the gain level for any input source easily.

5. Output Level Gain: Allows a wide range of output levels for various radios or other uses.

6. Downward Expansion Level Set: Allows adjustment of the required audio level to allow the unit to pass audio. Great for noisy conditions.

7. Downward Expansion Delay Set: Sets the amount of time that the internal amplifier will remain open with no audio. Great to hold the audio open between syllables and words.

8. Power On LED: Instant visual identification if you are using the MFJ-651 or just the standard microphone.

9. Monitor Gain: Control the audio level in the headphones when in the test position.

10. Compressor ON & OFF: Allows you to use your microphone through the MFJ-651’s built in preamp.

11. Power ON & OFF: Allows you to either use your Microphone direct or through the MFJ-651.

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MFJ-651 hamProAudio

Transmit audio conditioner Instruction & Technical Manual

SYSTEM CONTROLS

REAR PANEL

MFJ ENTERPRISES, INC.

STARK VILLE, M S USA

POWER

12VDC

HEADPHONE AUD IO

FROM RADIO

FROM MFJ-651

OUT

EXTERNAL

PTT

SWITCH

AUX.

AUDIO

OUTPUT

BALANCED

AUDIO

OUTPUT

LED

LEVEL

AUX. AUDIO INPUT

MICROPHONE

OUT

RECEIVED

AUDIO INPUT

1 2 3 4 5 8 7 6 1110 9

Figure 2: MFJ-651 Rear Panel Jacks and Controls

1. Power: Accepts 2.1 –mm power plug to supply 12-15 Vdc to the unit.

2. From Radio/From MFJ-651: This switch allows the audio to be fed from the radio to the headphones or in the test mode for the audio from the microphone to be fed to the headphones for setting up the MFJ-651. Additionally, in the test mode the PTT is disabled allowing you to key the microphone without keying the radio.

3. Headphones Out: Allows you to use a pair of 3.5 –mm stereo headphones. The mono test audio is fed into both sides of the phones. The radio audio is what your radio puts out. Handy if you have a Main and a Sub-receiver.

4. Headphones Out: Same function as number 3 but for ¼ inch stereo headphones.

5. External PTT Input: This ¼ inch jack allows PTT from a Hand Switch or Foot Switch.

6. Auxiliary Output: This 3.5 –mm jack allows direct audio to be fed from the unit. Useful when high levels of audio are required, as up to 1.2 volts peak to peak are available.

7. Balanced Output: This 3.5 –mm stereo jack give a balanced output.

8. Output LED Level Set: This trim pot is used to adjust the point at which the LED illuminates.

9. Auxiliary Input: This multifunction input allows just about anything to be used with the MFJ-651 by setting the appropriate input jumpers.

10. RJ-45 Output: This is where the MFJ-5398 or the MFJ-5397MX radio interface cable is attached.

11. Received Audio Input: This jack allows either stereo or mono (if wired properly) audio input from your radio

Bottom of MFJ-654 (not shown)

1. Bypass Gain Control: Sets the gain of the internal MFJ-654 bypass

gain amplifier to be equal to the mic level when the MFJ-654 is turned off.

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MFJ-651 hamProAudio

Transmit audio conditioner Instruction & Technical Manual

SYSTEM SETUP

Internal Headers Main Board View

Figure 3: Internal Headers

1. Header 1: This sets the input impedance of the unit to your specific microphone. Default 1-2 is set to 680 ohms, the standard impedance setting for most stock microphones. If you need low impedance, move the jumper to position 3-4. Remove the strap for high impedance microphones.

2. Header 3: This allows the PTT line to be placed on the ring of the 3.5 –mm auxiliary input jack. Default is off.

3. Header 4: This header allows phantom voltage to be fed to electret microphones Default is 0 volts pins 1-2 shorted. Move this jumper to pins 3-4 for 1.5 volts, 5-6 for 5 volts or 7-8 for 8 volts.

4. Header 5: High impedance output. Default is shorted for low impedance output. Remove this jumper for approximately 50K output impedance.

5. Header 6: This header allows the phantom voltage set by header 4 to be passed to the ring of the Auxiliary input jack. Default is off. If used with standard computer microphone/headphones, set to 5 volts.

6. Header 7: This header ties the CT of the output transformer allowing a balance output to be available at the 3.5 –mm jack. Default is off.

7. Header 8: This header allows the PTT line to be placed on the Auxiliary Output ring terminal of the 3.5 –mm jack. Default is off.

8. Header 9: This Header places phantom voltage on the microphone input line and the tip of the 3.5 mm input jack. It must be shorted when using a microphone requiring phantom voltage.

9. Header 10: This header allows the transformer to be bypassed to increase the low frequency response. Default is 3-4 bypassed.

10. Header 11: This header allows the transformer to be bypassed to increase the low frequency response. Default is 3-4 bypassed.

11. Header 12: This header grounds the Mic Ground to the radio and must be shorted if the transformer is being bypassed. Default is on.

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MFJ-651 hamProAudio

Transmit audio conditioner Instruction & Technical Manual

SYSTEM SETUP

Internal Jumper Blocks Main Board View

Figure 4: Internal Jumper Blocks

The default jumper settings from the factory are set for ICOM 8Pin Round Microphone. (SEE FIGURE 6)

Refer to Table 1 for common microphones. Consult your owner’s manual to determine your specific microphone pinout.

1. Jumper 2: PTT from the Microphone. Place a jumper on the pin number that corresponds to the pin of your microphone that supplies the PTT line to the radio.

2. Jumper 3: Microphone Audio Ground. Place a jumper on the pin number that corresponds to the pin that supplies the shielded ground from the microphone.

3. Jumper 4: Microphone Audio Input. Place a jumper on the pin number that corresponds to the pin that supplies microphone audio.

4. Jumper 6: Pass/Thru. This allows you to pas any other lines from the microphone for feature such as up/down/fast. Normally all lines that are not being used for the Mic Audio, Mic Ground and PTT line will be jumpered.

5. Jumper 7: Microphone Audio to Radio. Place a jumper on the pin that corresponds to the pin on your radio that feeds microphone audio to the radio.

6. Jumper 8: Microphone Audio Ground to Radio. Place a jumper on the pin that corresponds to the pin that your radio requires for the shielded ground.

7. Jumper 9: PTT to Radio. Place a jumper on the pin corresponding to the pin that your radio requires for PTT

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