Hello. I am just finalizing mic preamp with ina217 datasheet schematic. Have a problem: when i switch phantom power have a hum and click noise.
Anyone can understand the problem with sound file ? Thanks
File with noise http://vocaroo.com/i/s08DHCvoJgDn
Anyone can understand the problem with sound file ? Thanks
File with noise http://vocaroo.com/i/s08DHCvoJgDn
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1. Too high gain.
2. 0.1ufs must be mounted near to pins 4&7.
3. Layout
4. Input screen
5. Voltage supply
Use the circuit diagram 4 at the datasheet, or else ?
Hi nec... thanks for your advice.
1. Too high gain.
I use gain step in datasheet
2. 0.1ufs must be mounted near to pins 4&7.
Are very close..
3. Layout
Certainly 🙂
4. Input screen
I'm using taskar 117 Divisible flat shielded cables: C117 - Tasker ELECTRONICS
5. Voltage supply
the schematic http://www.ka-electronics.com/images/jpg/Bipolar_Phantom_PSU.jpg
Yes nec... i'm using a relay set the phantom switch..
1. Too high gain.
I use gain step in datasheet
2. 0.1ufs must be mounted near to pins 4&7.
Are very close..
3. Layout
Certainly 🙂
4. Input screen
I'm using taskar 117 Divisible flat shielded cables: C117 - Tasker ELECTRONICS
5. Voltage supply
the schematic http://www.ka-electronics.com/images/jpg/Bipolar_Phantom_PSU.jpg
Yes nec... i'm using a relay set the phantom switch..
Hi Nec. Thanks for your advice.
My supply with LM7x15 http://www.ka-electronics.com/images/jpg/Bipolar_Phantom_PSU.jpg
Yes nec... i've only add a relay on phantom switch.
I'm using Gain-Set Resistor on datasheet
Are very close.
It is probable
Use taskar 117 Divisible flat shielded cables: C117 - Tasker ELECTRONICS
My supply with LM7x15 http://www.ka-electronics.com/images/jpg/Bipolar_Phantom_PSU.jpg
Yes nec... i've only add a relay on phantom switch.
-Just to isolate problem, remove the shielded mic cable from the points it is soldered at the IC input and see if hum stops.
-Remove phantom relay and check again.
-How is the gain set connected to the PCB? Discrete resistors soldered on the PCB ?
It is not a too complex circuit. and you have limited things to control. Soon or later it will work.
-Remove phantom relay and check again.
-How is the gain set connected to the PCB? Discrete resistors soldered on the PCB ?
It is not a too complex circuit. and you have limited things to control. Soon or later it will work.
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Things to check:
1. Input coupling capacitor polarity is correct?
2. Resistors R1/2/4/5 (as per Fig. 4) are all soldered correctly and well-matched? CMRR would suffer otherwise.
3. XLR pin 1 is routed correctly? It should have a dedicated ground return, ideally go straight to case (with as little inductance as possible) which later connects to star ground. Note that the INA217 output is ultimately referred to A2 +in, so if that is not exactly equal to output ground but rather polluted by phantom power return currents you may get hum or whatnot. In this case the volume of hum would be independent of gain setting, unlike for (2.).
Please note that the INA217 Fig. 4 circuit leaves room for improvement in several regards:
1. Practical CMRR should improve by about 8 dB when first connecting the R4/5 junction to about a 10 kOhm resistor and then to ground.
2. Input protection may not be sufficient, see the two publications on the "Phantom Menace".
3. Phantom power switching implementation is stupid. It neatly maximises turn-on/off common-mode pop noises. I would include another RC filter between switch and R1/2, with maybe 220-330 ohms series R and 22-47 µF parallel C.
1. Input coupling capacitor polarity is correct?
2. Resistors R1/2/4/5 (as per Fig. 4) are all soldered correctly and well-matched? CMRR would suffer otherwise.
3. XLR pin 1 is routed correctly? It should have a dedicated ground return, ideally go straight to case (with as little inductance as possible) which later connects to star ground. Note that the INA217 output is ultimately referred to A2 +in, so if that is not exactly equal to output ground but rather polluted by phantom power return currents you may get hum or whatnot. In this case the volume of hum would be independent of gain setting, unlike for (2.).
Please note that the INA217 Fig. 4 circuit leaves room for improvement in several regards:
1. Practical CMRR should improve by about 8 dB when first connecting the R4/5 junction to about a 10 kOhm resistor and then to ground.
2. Input protection may not be sufficient, see the two publications on the "Phantom Menace".
3. Phantom power switching implementation is stupid. It neatly maximises turn-on/off common-mode pop noises. I would include another RC filter between switch and R1/2, with maybe 220-330 ohms series R and 22-47 µF parallel C.
Hello boys!
Very kind and valuable tips.
Thaks sgrossklass. I tried to follow your advice.
Have a new clue. When unplug the microphone hear voltage noise.
Listen... Vocaroo | Voice message
Very kind and valuable tips.
The hum is active only with phantom on. With sm58 (cardiod mic) it's very silent.
With commutator switch in a pcb... i've tried to remove and solder one resistor. The hum don't stop.
Thaks for your support 🙂
Thaks sgrossklass. I tried to follow your advice.
Have a new clue. When unplug the microphone hear voltage noise.
Listen... Vocaroo | Voice message
Then, it must be some noise coming from phantom power circuit. Like Sgrossklass said, a low ESR capacitor around 1 uf soldered right at the joint of R1,2 to the ground will probably cut the hum.
This link also gives some good clues for click.
http://www.thatcorp.com/datashts/dn140.pdf
Yesssss nec! With a 1 uf soldered right at the joint of R1,2 to the ground noise decreases of ' 80 %!
Wow! I am sure that with right value i will solve the problem.
I do not know how to thank you. 🙂
Now, i try with sgrossklass value (220-330 ohms series R and 22-47 µF parallel C.)
Thank you so much.
Ciao 🙂
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