Processing and Control for Professional AV Installations
Legacy Hardware

302 Dual Microphone Preamplifier

The 302 is an ultra-clean two channel dual mono preamp for use in critical digital and analog recording situations. The 302 delivers exceptional sonic performance even at extremely high input levels, making it the ideal mate to the newest transformerless condenser microphone designs.


There are two separate AC supplies coming out of the PS-3: 8.5 VAC @ 1A and 34.5 VAC CT @ 250mA. Pinout is as follows: 8.5 VAC on pins 6 and 1, 17 VAC on pins 7 and 3, center tap @ pins 4 and 5 are connected to earth ground. This is when viewed at the end of the PS-3 7-pin DIN plug.

View Image

How-to: More than three levels of paging with the Zone Mix 760
Within the offices of Symetrix, we often joke that our all-encompassing banner should actually read ‘Over-engineered by Symetrix’. We take great pride in the design of our products, so much so, that we often subconsciously overdo things — just a touch. It’s all for the better in the end, reinforcing our commitment to produce extremely high value, robust and affordable products for audio professionals.

As we’ve come to find out, the Zone Mix 760 is no exception. It is advertised as having three levels of paging plus emergency page and background music. However, it is possible to get four, and even five, levels of paging if you do not require the emergency page and/or wish to forego background music in a zone.

For up to four levels of priority paging plus one BGM (background music) source, you can use the Program 1 and Program 2 inputs for each zone as the lowest two paging levels (lowest of all is the BGM).

1. For a given zone, assign your BGM as the source for Program 1.
2. Select your lowest priority page mic as the source for Program 2.
3. Adjust the Ducker Threshold, Depth and Hold as necessary.
4. Set Page mics 2-4 as the sources for Page Stations 1-3.
5. Set the Page Station Priority to Low, Med and High, respectively, for Page Stations 1-3.
6. That’s it!

It is also possible to get five levels of paging. If you forego BGM in a zone, you can use the Program 1 source as your fifth paging source (lowest priority). Note that an external microphone preamplifier, such as the Symetrix 302 Dual Microphone Preamplifier, is required in order to connect microphones to the Audio Media inputs of the Zone Mix 760.

But why stop there? You can expand even further on this configuration because the Symetrix 302 is a dual microphone preamplifier, why not use that 2nd channel to feed the next Audio Media input on the 760 so you can have a unique lowest level paging source for another zone?

The 302 has significantly less noise and distortion. THD+Noise .007% (1kHz, 0dBu, 600 Ohms out) .01% (1kHz, +22dBu, 600 Ohms out) Signal to Noise Ratio 95 dB (-50 dBV, 150 Ohms in)

Check the level of the input signal on the 302’s LED display. Is the CLIP light on all the time? If so, reduce the incoming signal level by turning the INPUT level counterclockwise. Is the incoming signal already distorted? Make sure that your microphone is not broken, and that the mic is not distorting, sometimes vocalists get a little too close to the mic causing its capsule and/or internal electronics to distort. Most studio condensers have switchable -10dB and -20dB pads to reduce the level from the capsule before it goes to the electronics, these are almost always needed with drum over-heads and high hats.

If your computer has a sound card with line level inputs (NOT microphone level!!!), use the TRS line output jack connecting the tip as (+) and the sleeve as the common or ground. However, it is recommended to have a computer audio card or interface with professional +4 dBu balanced line level inputs.

The 302 is an ultra-clean two channel dual mono preamp for use in critical digital and analog recording situations. For optimum sonic performance and lowest possible noise, route the 302’s output(s) directly into the tape machine or recording device’s line input(s) as opposed to going through a mixing console. This approach eliminates unnecessary noise and coloration, also most built-in mic pre amps on the small portable recorders and computer sound cards are rather noisy, using the line input and a good clean mic-pre will almost always result in a cleaner sounding recording.

If you’re going directly to line level inputs of a recording device as suggested chances are it’s coming from the microphone’s internal capsule pre-amp, some of the older microphones sought after for their character and warmth especially the tube versions have rather noisy electronics. Check input signal level. The input signal may be too low. If so, boost the incoming signal (if possible) or move your mic closer to the signal source. Obviously drum over-heads will need a lot less gain than an acoustic guitar.

Yes and no, the CLIP LED lights when the signal reaches 3dB below clipping. This LED should never be on solidly. It is usually all right if the CLIP LED flashes occasionally, on peaks in the program material. If you see the CLIP LED light, monitor your final signal destination to be sure that you are not creating distortion by running audio levels that are too hot.

No, the only option would be to use a 12VDC to 117VAC inverter with the supplied PS-3 inline power supply.