TS472 microphone preamp versus MAX9812

MAX9814  seems the best choice  it has AGC and jumpers for gain setting to max 60dB
 will test this one to when arrived. 


Received this low noise ST TS472  pre-amp  Diymore from eBay.
Main while the 3 transistor pre-amp with AVR earlier down in the blog works fine.
This TS472 IC is special designed for microphones  electret or magnetic and i was curious to find out how such integrated device performs.
With the magnetic  200 OHm Peiker element the signal is fine although not as sensitive as with an electret element. The maximum un-clipped output is about 2Vtt.
It did not match the low impedance mike input of the Condor as it is at first test.
Minimum drive load is 10k. 
An emitter or source driver is needed behind the TS472 and  low impedance tranceivers like the Condor. 
No documentation is supplied with it but the PCB looks similar to the 
ST  demo board TS472 PCB  well designed.  
The standby pad must be +    ,  minus = gnd  will switch to standby.
Left floating wil drift it uncontrolled standby.  
I guess the standby option is ment to use with a control or switch although there is no external pin .
At 3V3 the current is 1.5mA , including the LM317LZ 4.5mA  to high for 100% duty on a 3V Li cell
I choose gain max although that wil be too much for most applications. 
The bias pad provides 2V low noise on + input for condensator type mikes.
Do not know for what function  Vx pad is used it can be grounded i left it open.
Pity it does not feature AGC that seems a rare function?
Gain can be set by selecting pads or by connecting a 470kOhm potentiometer max gain is 0 Ohm.
Or ? by providing an AGC regulation controlled resistor to ground at max gain pad 
that resistor should be low  and regulating up for constant output.


With LM317LZ adapter for 5-37V onboard 1uF or more SMD sits close to power in.
No extra  output C is needed to prevent oscillating.

For safety I prefer 3V3 with the adjustable LM317LZ regulator to accept a wide supply range 5 to 37V
3V6 with LM317LZ  R1=560 R2=1k  divider 
Googling on the LM317LZ shows a lot but no real information about R1 R2 values or Vref 
But the ST TS472  device document  shows calculation  R1 R2.  
The formula in the application note below  must be + R2*Iadj
Iadj is  50uA typical in the ST specs
Vout=1.25V (1+R2/R1)  =3.48V   +  (R2*50E-6)=0.0625V   ( assuming 50uA Iadj  R1 560R R2 1k )
I measure 3.395V  at 4.55mA  using R1 510R R2 910R
using 560R and 910R will bring it pretty close to 3V3

Pro:  TS472  high sensitive microphone amplifier.
Con: It can not drive loads below 10k Ohm
PCB to big to integrate in existing microphones.

For amateur radio use a single transistor amplifier gain is high enough.
  

The MAX9812  PCB  
 a better choise  it can drive 1k load  small PCB fits into the Peiker 
includes power indicator LED  and condensor microfone
gain is fixed 20dB  excellent specs  
for 1€     
Pro:   very small
 microphone included
simple 3 wire connect  no settings needed.
LED power indication 
low price

con: fixed 20dB   no option to switch bias off
magnetic elements need DC separating capacitor
 
MAX9814  seems the best choice  it has AGC and jumpers for gain setting to max 60dB
 will test is as soon as arrived 

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