External Audio Connection

Have you ever had the need to record better quality audio on you DV camera than the built in mic provides? Sure, there are a number of purpose-built mixer solutions available, many costing hundreds of dollars. Here’s a way to achieve that same level of quality and performance for a fraction of the cost.

1. Hardware

First, you need a decent quality mixer. If you don’t already have one laying around, there are numerous high quality, low cost mixers available starting in the $50.00 price range and increasing in capability (and cost). Then, you need to construct a cable that will take the mixer level down to a level that is compatible with the external mic input on you camcorder. Some cameras are mono, but most are stereo so you want to determine what your camera is. If it’s mono, you only need mono connectors, and need to make one pad. If stereo, you need 2 pads and the appropriate stereo connectors.

2. Design Criteria & required materials

To interface a stereo external mixer into the external mic input of the camera keeping the size and weight at the camera to a minimum to reduce stress and strain on the camera’s connector.

Parts Needed: (All available at Radio Shack ® , or a similar electronics parts store)

• 3.5mm stereo microphone female jack to Stereo RCA male phono plug adaptor (short, maybe 6” in length).
• 3.5mm stereo microphone male to male extension cord (as long as you need to reach camcorder from mixer)
• 2 RCA male phono plugs to put pads in and replace plugs on adapter
• Soldering iron and electronic circuit board solder (60/40) NOT acid flux solder
• Resistors needed from circuit description below.
• Heat shrink tubing (if pad is to be put in line in the cord and not in the connector)
• Consumer audio line (-10dBu) level to microphone matching - "40 dB L-pad attenuator":
  R1 = 10 kohm, ¼ watt
  R2 = 100 ohm, ¼ watt
  OR
• Professional audio line (+4dBu) level to microphone matching - "50 dB L-pad attenuator":
  R1 = 33 kohm, ¼ watt
  R2 = 100 ohm, ¼ watt

3. Connection Diagram

Below is the connection diagram and the details of the circuit.

Most mixers have a “TAPE OUT” which is the same as the MAINS OUT, but at -10db. If you need to use the MAINS OUT, use the appropriate connector to mate with that output. Usually a ¼” TRS (tip, ring, sleeve) plug and the -50db pad. To make the adapter/pad, you want to either put the resistors inside the shell of the new RCA connectors, or just outside in the cable itself to keep the pad and the weight at the mixer.

PLEASE NOTE: All connections must be soldered properly, if you do not know how to make a good solder joint, PLEASE have someone who does make this adapter for you. The last thing you want is a bad connection causing the circuit to fail on a “one time only” event. Using the short RCA to 3.5mm adapter, build a pad into each RCA connector, replacing the RCA connector on the adapter. The + Line is the center conductor, the ground is the outside shell. If you put the pad in the cable instead of replacing the connector, be sure to appropriately insulate it using heat shrink tubing. Plug the newly created pad connector/adapter into the TAPE OUT of the mixer, and the extension cord from the adapter into the camera. If possible, dress the extension cord through/around the handle on the camera to help reduce strain on the cameras connector (very fragile). Now, when the camera is in record, the built-in mic will be disabled, and the mixer signal will be recorded. Remember to keep the mixer maximum output level at 0db on the mixer to prevent distortion.