Line Level Output Mic's for Board Cameras
Dec 26 2015






I tell about my previous experience with two mic's on the 50H10PE-S Camera Mod's page and how I planned to buy more of the one that was best, but I published the page before ordering more which was likely a big mistake as the mic quickly sold out and has been "temporarily sold out" ever since. There's been no more of the mic's for 7 months now so I doubt they'll ever return, but I still have a few cameras that need mic's so I started over bought 5 different models to try this time with the hope that at least one was, or that one could be made, useable.

I ordered mic's from China again (as you can't beat the prices) although this made it next to impossible to know which may be better than others to try with the spec's and other information provided mostly wrong and misleading (as anyone that's ordered much from China quickly learns is often the case). And don't be fooled and think the spec's and other information on the box and/or the instruction sheet received with any mic's ordered is any better as it wasn't and was often even more misleading. Anyway, I was fairly lucky and able to make use of 4 out of the 5 models chosen after a few modifications.

The mic's may be ok as they are for some uses like with consumer equipment for which line-level is specified as 0.316Vrms (≈ 0.894Vp-p) as the output level of a typical electret mic. element is ≈ 5 mVp-p for someone speaking normally 3-5 ft. away and a mic with an amplifier gain of ≈178 would work. Many speak into a mic much closer however, so a gain of ≈100 would actually be enough and is about what of the mic's I ordered provide. Line-Level for professional equipment is 1.23Vrms (≈3.48Vp-p) which would require higher gain mic's

The IPC board cameras specify an audio input line-level signal of 2 Vp-p which means an electret mic with a higher amplifier gain of ≈400 is needed. Voices will never be closer than 10-20 ft. to the mic's used for my outdoor cameras and voices and other outdoor sounds will usually even softer so a bit more gain would likely be better and tests show a gain of 800 to 1000 works well and make a mic hear as good as I can.

Below are the 5 different mic models I bought with some basic information, a link to where it was purchased and a link to a PDF with a schematic, how it was modified and test results as components were changed to show the effect each change made. The Modified Max Gain is simply what it is now and it can easily be changed later if more or less gain is desired. Also my recommendation as to which I would get if you need a Mic to modify.

2 for $1.98 w/ free shipping from AliExpress Store: HK-VISION CCTV Technology Co., Ltd.

Do not get this one: It has a 2 Transistor Amplifier that can't be modified for more gain.
Luckily they were only 99 cents each.

See IMSD-JK26 PDF for details.

$2.95 w/ free shipping from AliExpress Store: Ton-Top

As is: Gain was ≈ 100                      Modified Gain is now ≈ 950
Least expensive & easy to modify, but no gain control & seller currently no longer selling.
See CS-04A Modification PDF for further details.

KZ-502B with a Gain Control
$2.95 + S&H (2 for $8.94 total or $4.47 ea.) from AliExpress Store: Ali NO.1 deals

As is: Gain was adjustable from ≈ 6 to 100          Modified Maximum Gain is now ≈ 1350
Very difficult to modify with needing to add a number of SMT and other tiny components.
Otherwise a great mic once modified.
See KZ-502B Modification PDF for further details.

MT-807A with a Gain Control
$4.99 w/ free shipping from AliExpress Store:CCTV Surveillance Provider

As is: Gain was adjustable from ≈ 16 to 540       Modified Max Gain is now ≈ 800
Easy to modify - just need to remove and jumper out a few SMT components.
See MT-807A Modification PDF for further details.

LY-901LS with a Gain Control
$3.23 (4 for $12.91 w/ free shipping) from AliExpress Store:CCTV Surveillance Provider

As is: Gain was adjustable from ≈ 5.6 to 90        Modified Max Gain is now ≈ 890
Easy to modify - just need to remove or change the value of a few SMT & thru-hole parts..
Least expensive of the mic's and what I recommend getting for an IPC camera mic.
See the following section below for additional information about this mic and
the LY-901LS Modification PDF for modification details.
And don't overlook reading "how to supply power to the mic's from the camera" (below) and seeing the Mic Supply Voltage Filter PDF

Additional Mic and Modification Information

The PDF files don't provide any real instructions as to how to perform the mod's other than what components to change or add as they are simply a PDF of my personal CAD drawings kept as a record of what I did in case I decide to make additional changes or get and modify another mic, however I'm sure most won't have any trouble figuring out what needs to be done and how to do it.

Something that may require a bit of explanation is how to supply power to the mic's from the camera. Next to the camera audio input pin on connector 5 is a special audio input signal ground pin that's provided to keep the "noise" on the camera power supply ground from affecting the audio signal. There's no problem when a mic is powered from a battery or a different power source than the one used to power the camera (like a separate wall wort that's only used to power the mic). But the mic only has a single ground connection for both, its supply voltage and audio output signal which means, when the mic is powered from the cameras power source, that the 2 camera grounds will no longer be isolated and noise on the camera ground will affect the audio. Note: The audio will be affected by noise even if just the supply voltage lead is connected to the mic (which would leave the 2 grounds unconnected) as the supply voltage ground noise is also present on the supply voltage and the noise will be coupled to the mic ground by the mic circuits supply voltage filter capacitor. The solution I came up with (and that works perfect) is to use the supply voltage filter shown in the Mic Supply Voltage Filter PDF in conjunction with replacing the mic circuits diode with a 270Ω resistor and adding a second mic circuit filter capacitor as shown in each of the Mic Modification PDF's.

I selected the LY-901LS mic based on the sellers web page image showing it with a PCB with thru-hole components and a NE5532 dual op-amp IC, but the image is wrong and obviously an older model as the received mic's had PCB's with SMT components like all the others. No big deal and actually better as it made the circuit board much smaller which I never planned on leaving inside the large enclosure the mic comes with and it was nice to see that the SMT IC identification markings hadn't been removed, like they had been on all the other mic's and even though it wasn't a NE5532, as it's always nice to know what you're actually working with when modifying circuits. And disregard the listed freq. response spec as, like for all the mic's, this spec isn't even close to being correct and what's listed on the sheet with the mic, even though it's quite different, is no better. (A simple freq. response spec., like 200Hz to 12KHz, can't actually be provided for the mic's with a gain control with how they are designed as the gain control affects the freq. response as well as the gain.)

One has to wonder where some of the spec's come from like the 12 to 60mA operating current spec provided for some of the mic's when the maximum current would never be more than 3 or 4 ma and it would never vary more than a mA for such mic's. Or the output level that's often spec'd as 0 to 5 or 6Vp-p (which had me hoping that some mic's may be ok as is). 5 to 6Vp-p is pretty close to what the output level could be and the level at which clipping would occur if these mic's had much more gain, but the output would never be even close to that for a mic with a gain of only ≈100. And don't believe any statements about a mic having a Noise Reduction Processing Circuit and/or Automatic Gain Control (AGC) as I've yet to find any that do and this is obviously simply an attempt to mislead buyers and increase sales.

I began by modifying the two KZ-502B shown in the KZ-502B PDF. Different values were used for several components in the second circuit for a bit more gain and wider freq response to hear the difference this made, but it wasn't enough to bother changing and making the first one the same (although I liked the second one a bit more for it's slightly higher gain). The mic element of circuit #2 was also separated from the circuit board using some 2 conductor shielded cable. Single conductor shielded cable would have likely worked as well for the short distance, but for longer distances and where the cable will lay close to AC and other wiring which could introduce noise it's best to use 2 conductor shielded cable and I planned to use this second mic where the cable would be close to AC and switching power supply wiring that often creates noise problems. As shown in the KZ-502B PDF, when using 2 conductor shielded cable the 2 conductors are used to connect the mic and the shield is only connected to the grounded mic conductor at the amplifier end.

Wind Noise can be a big problem outdoors, but there's lot of info about it and how to solve the problem on the web and I've had great success using open-cell foam. Sponges and the foam used to package items is often open-cell which means there's a meandering path for the air to move through it. This and a lot of other good information about curing wind noise was found on this web page which also says that the shape of the foam should be aerodynamic (no sharp corners) to eliminate turbulence noise as the wind moves over it, but I've never paid much attention to the shape of the foam as close by the cameras I've added a mic to there's always been a place to put the mic that's fairly sheltered from the direct blast of the wind.

To determine which pieces of open-cell foam may work best without affecting the sound I start by simply blowing through it and trying whichever are the easiest to blow through. The best so far has been some grey foam used to package items, but I just came across my box of sanding pads and discovered that they are very open and something I definitely plan to try using.

Right - My assortment of sanding pads

Anyway, I hope this and my modification PDF pages help some add mic's to their cameras.