universal lav mic power supply

T

translumination

Active member
I've been purchasing lav mics of ebay but most do not come with a power supply that can convert 48v phantom to lav mic voltage
Does anyone make a universal converter that can run any lav so that I can use them wired as well as wireless?
 
I've got 2 mke 2, an at899 and probably getting a sanken cos 11 soon. The at899 I've got a power supply that gives me the otpion of battery or phantom power. I wasnt that happy with the at899, so much sibilance and noise pickup when compared to the sanken but you get what you pay for I guess. There are some great deals on ebay for second hand lavs but they never include the power supply.

I wonder if I could retrofit the other lavs to work of the at899's power unit ?
 
You will most likely need to get a power supply for each mic made by those manufacturers. There is no universal lav mic power supply because each mic requres different power.

-Dave
 
http://www.epanorama.net/circuits/microphone_powering.html





Phantom powering electret microphone from phantom power

Simplest circuit
This circuit is a very simple method of connecting an electret microphone capsule to the a balanced phantom powered (48V) mixer XLR input.


_____
HOT (2) ---------|_____|------+
47 kohm |+
MIC
COLD (3) ----+ CAPSULE
| |-
GROUND (1) ----+-----------------+


Note that this is a very simple "hack" to interface an electret microphone capsule to a mixer. This circuit works but has it's downsides like sensitivity to noise in phantom power, unblanced signal transmission (prone to interference) and high output impedance (can't properly drive long cables). This circuit can be used to test electret capsules connected to mixer using very short cable. This circuit makes very high level popping noise when it is connected/disconnected from the mixer or when the phantom power is turned or disconnected. Other downside is that this circuit loads the phantom power in very unbalanced way which can disturb some older mixers (in some mixers input transformer can saturate if such exists, in that case try adding 47 ohom resistor between pins 1 and 3).

In practice this circuit seems at least to work on modern mixers, but I don't recommend this circuit for any real recording or PA application For any real use you are much happier with a better quality balanced circuit. They are more complicated but perform much better.


Balanced electret microphone circuit
This circuit gives out balanced signals and has around 2 kohms output impedance which enables it to be used successfully with mic cables of several meters or tens of meters.


10u
+---------o-------------||------o----------------- HOT (2)
| | |
| |- |
| CAPSULE 22k
| |+ |
| | 10u |
| o-------------||------|------o---------- COLD (3)
2k2 | | |
| 2k2 | 22k
| | | |
| o--330R---o----o------o------+
| +| +| |+
| 10u 12V 10u
| -| -| |-
--o---------o---------o----o------------------------ GROUND (1)

The component "12V" is a 12 Volt zener diode
The 10u capacitors in the HOT and COLD signal leads should be high-quality plastic film types. The values of these may be reduced to 2u2 if the preamp input impedance is 10k or greater. If you for some reason use electrolytics for the capacitors which couple the audio signal then those these mutst have >50V working woltage and you must bypass them with 100n plastic film caps. The 10u capacitor in parallel with the zener should be a tantalum type, and can have a 10n plastic film cap in parallel if you wish.

The cable to the capsule should be twin+shield. The shield should be connected to ground near the zener diode, and left unconnected at the capsule. The pinout given is the standard for XLR3 mic connectors.

Source: PZM Modifications web page by Christopher Hicks.


Better electret microphone phantom powering circuit
This circuit provides lower impedance output than the circuit above:


+-----o---------------------330R--------+
| | |
| 2k2 +---10k----+ |
| | | | |
| | | E--o---|--------------- COLD
| o---------||----o--o-------B |
| | 1u0 | C |
| |+ +-100k-+ | |
| CAPSULE |---o------o
| |- +-100k-+ | |
| | | C |
|+ o---------||----o--o-------B |
10u | 1u0 | E--o---|--------------- HOT
|- | | | |
| | +---10k----+ |
| | o----+
| 2k2 +| |+
| | 12V 10u
| | -| |-
--o-----o---------------------------------o----o---------- GROUND

Component EBC is a PNP bipolar transistor (for example BC479). Ideally these should be hand-picked for low noise and matched gain. Bear in mind that VCE can be up to about 36V. The 1u0 capacitors should be high quality plastic film types. The circuit may benefit from the addition of 22pF capacitors in parallel with the two 100k resistors. For minimum hum pickup the two 2k2 capsule bias resistors should be accurately matched.
Source: PZM Modifications web page by Christopher Hicks.


Phantom power feeding unit for microphone
This is a schematic of external phantom power feeding circuit for those who don't have mixer with phantom power output.

Microphone Mixer
47 uF
HOT (2) ---------+---------||--------------- HOT (2)
|
6k8
|
+--------+------100 ohm---- +48V feed
| |
| === 100 uF
6k8 |
| GROUND (pin 1)
|
COLD (2) ---------+---------||--------------- COLD (2)
47 uF

GROUND (1) ----------------------------------- GROUND (1)

The +48V phantom power feed is grounded to signal ground (pin 1). +48V voltage can be generated using transformer+regulator, using batteries (5x9V=45V which is enough), or using a DC/DC converter circuit which makes well regulated +48V voltage from batteries.
There should be two 12V zener diodes (wired back to back) between audio wires (HOT and COLD) and the ground to prevent 48V voltage pulse passing through the capacitors going to the mixer microphone input.

Use 1% accurate resistors for those 6.8 kohm resistors for best hum and noise elimination.
 
Dave_Fisk said:
You will most likely need to get a power supply for each mic made by those manufacturers. There is no universal lav mic power supply because each mic requres different power.

-Dave
Click to expand...

if it was like that we have been buying allot of wierless tx :-)
 
Oleg the samson specs look very similar to the specs of the power unit I have with the at899. I'm not sure what performance characteristics are with different mics and their requirements are though. I might give it a try to rewire my mke2 to see if they will work with the at899's phantom unit.
thanks
 
oleg said:
if it was like that we have been buying allot of wierless tx :-)
Click to expand...


All I know is I spend every day trying to get a power supply from one manufacturer to work with the lav of another. I have tried "universal" power supplies that aren't universal at all, at least for the mics I deal with.


-Dave
 
Okay guys I just rewired a 3 pin lemo to the mke2 and it works with the at899's power supply! I will rewire the 3 pin lemo to a miniplug so I can use it with the sennheiser G2 wireless as well. Its good that means I wont have to get rid of my at899 as its power supply is useful.
 
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