Modifying the Zoom H6 for improved performance when using Primo EM172 based microphones
The Wildtronics Micro Mic PIP uses a Primo EM172 mic element. The Primo EM172 is an excellent element with good sensitivity and a low noise floor, which has made it a very popular element used in many products. Not many PIP recorders have the correct internal circuitry to obtain the full benefits and specifications of the Primo EM172, except for the Sony PCM-M10 and a few others. The Primo EM172 element requires a recording device to have a specific power supply voltage and resistor value. The microphone will still work, if the circuit is not optimized, but at reduced specifications. The general circuit found in most recorders will work with other PIP microphones just fine, but most of these have a much higher noise floor, >20dBA, and any optimization wouldn't be noticeable. From the factory, the Zoom H6 recorder is not optimized to work well with the popular Primo EM172 element. This article will describe how you can modify your Zoom H6 to get the most out of your PIP microphones, and reduce the noise floor by 5dBA when using an EM172 based microphone. We will also describe how to boost the gain of the XY microphone module, which only allows up to 46dB of gain from the factory, to 56dB, while also decreasing the equivalent input noise of the input amplifier. Wildtronics could provide the service of modifying your module for you. Please email us for details and cost.
The Zoom XY microphone module, XYH-6, has a 3.5mm connector that allows a mic or line input. The Zoom H6 can provide 2.5 volts to power PIP microphones. The issue is that the power is supplied through a 2K ohm resistor, which is too low to get the most out of the Primo EM172 element. The Primo EM172 can obtain a noise floor of 15dBA, but with that 2K ohm resistor in the circuit, it will only obtain 20dBA, resulting in a noisier recording than expected.
This mod is rather simple, but you will need to have skill and equipment to solder and handle 0402 surface mount resistors. 0402 parts are very small, just a millimeter in size. If you aren't skilled in handling small surface mount parts, you may destroy the pads on the pc board and ruin the entire XY microphone module. If you are skilled, you can do this mod in about an hour with very inexpensive parts, just a few resistors. It is highly recommended to use a good magnifying glass or magnifying goggles to work with the small parts, and to insure all the soldering is done without bridging to other parts.
Parts needed: quantity 2- 5.49K ohm surface mount resistors, size 0402; quanitity 2- 4.7K ohm surface mount resistors, size 0402 (for the gain mod). You can just use quantity 4- 4.99K ohm resistors if you would like to simplify. Buy at least 10 resistors, as it is very easy to lose the tiny parts.
First, take the XY mic module apart by unscrewing the 4 screws on the bottom, marked with the red arrows.
Separate the halves and unplug the connector.
Remove the screw holding in the preamp pc board, and carefully position the pc board in the open to work on.
Now comes the hard part. Remove the two, 2k ohm resistors that supply the PIP power shown with the arrows. They are located next to the 3.5mm connector, and near the two power supply regulators. Replace them with the 5.49K ohm resistors. This is not easy due to the tight location. If you want to further improve the circuit, you could replace the regulators with ones that will provide 4 volts, but that is a very involved project since Zoom used some very uncommon regulators with an odd pin out. The increased voltage would improve the circuit by just 1 to 2 dB at the most, so don't worry about it much. While inside the module, we noticed that Zoom used some pretty good parts. The input op amp has a noise rating of 3.3nV, which is a very good part capable of achieving a very low EIN, if designed properly. Seeing the power supply regulators is a big plus. Most consumer products would skip the regulators.
If you are happy with the 46dB max gain available in the module, you are now done. Check the unit for function then reassemble the module. Connecting a microphone that uses a Primo EM172 will now give you a 5dBA lower noise floor and about a 6dB increase in sensitivity. If you would like to increase the amount of gain available to 56dB, and lower the equivalent input noise to around -126dBA, turn the pc board over to see the op amp and related parts. By changing the gain, you will drop the max SPL rating from 136dB to 126dB, still really loud. Find the two 1K ohm resistors located in the feedback of the op amp, marked with the red arrows. Be very careful to replace the right resistors. Trace the circuit, if in doubt, the resistors are between pin 6 and 7, and between pin 1 and 2, of the op amp. Remove them and replace them with 4.7K ohm resistors. You are done. We recommend plugging in the mic module into the H6, and run a test to make sure everything is working before reassembling. The equivalent input noise of the preamp will now be about -126dBA because we are increasing the gain of the first amp stage which uses a lower noise op amp. The second stage amp in the module is not designed as well, using a lower cost op amp and very high resistor values. Increasing the gain of the first stage, allows the second stage to have larger signals and therefore the overall noise is less effected by the noise floor of the second amp.
Enjoy your new, improved Zoom H6 recorder!