Hi everybody,
I'm trying to make a mono, phantom powered version of Elektrosluch with a balanced out. Elektrosluch is an open source design created by Jonas Gruska of LOM Audio, basically it's a stereo EMF detector with an OP amp preamplifier (schematics here).
The core of my idea is to use an OP amp chip like NE5532 and build a single-ended input to a differential output amplifier powered through the +48 phantom power provided by my recorder. I came up to this design, can I have a comment on that?
I'm trying to make a mono, phantom powered version of Elektrosluch with a balanced out. Elektrosluch is an open source design created by Jonas Gruska of LOM Audio, basically it's a stereo EMF detector with an OP amp preamplifier (schematics here).
The core of my idea is to use an OP amp chip like NE5532 and build a single-ended input to a differential output amplifier powered through the +48 phantom power provided by my recorder. I came up to this design, can I have a comment on that?
Schematics link doesn't work.
Opamp input pin 3 needs a reference voltage of 2.5V.
What kind of fields do you want to detect?
Opamp input pin 3 needs a reference voltage of 2.5V.
What kind of fields do you want to detect?
An NE5532 draws 8 mA typical, 16 mA maximum supply current without load and even more when it has to drive signal current into a load. It needs at least 10 V between its positive and negative supply pins.
A 48 V phantom supply has a 3.3 kohm to 3.405 kohm nominal internal resistance (6.8 kohm or 6.81 kohm per side). With 4.7 kohm/2 added to that, it's 5.65 kohm to 5.755 kohm. 8 mA causes 45.2 V of voltage drop across 5.65 kohm, so you would have 2.8 V left.
You need an op-amp that draws less current, and as was already pointed out, either one that needs less supply voltage or a higher Zener voltage, and something to properly bias the input of U1A.
A 48 V phantom supply has a 3.3 kohm to 3.405 kohm nominal internal resistance (6.8 kohm or 6.81 kohm per side). With 4.7 kohm/2 added to that, it's 5.65 kohm to 5.755 kohm. 8 mA causes 45.2 V of voltage drop across 5.65 kohm, so you would have 2.8 V left.
You need an op-amp that draws less current, and as was already pointed out, either one that needs less supply voltage or a higher Zener voltage, and something to properly bias the input of U1A.
Thank you for your replies. I want to use an OP amp with single power supply in order to use less components, will the NE5532 work?
I have upgraded the schematic with a 12 V Zener diode, and added some gain to the amp stage like it was in the original schematic. Also, added a couple of filter capacitors on the OP amp feeding inputs.
I have upgraded the schematic with a 12 V Zener diode, and added some gain to the amp stage like it was in the original schematic. Also, added a couple of filter capacitors on the OP amp feeding inputs.
obviously #3 and #4 did not help. Without basic understanding of operational amplifiers you are lost.
The amplifier schematic comes from a TI tech doc where a single supply OP amp is used to do the trick (originally designed for powering a 5V electret mic). Ok, the NE5532 requires too much current for the use with phantom power, I'll switch to a TL972 if needed. I know usually OP amps need dual supply, my question is, will the TL972 powered with a 12 V single supply be able to do the same? Otherwise I'll add those 2 resistors and 2 capacitors needed for the virtual ground.
Let me try to explain better. I tried to combine two different circuits. This is the Elektrosluch, which is a stereo EMF detector with stereo unbalanced outs, powered by a 9v battery:
This is the second circuit I've found, made for powering an electret mic capsule with a mono balanced output, powered through P48 phantom power:
Original link
What I want is to combine the two circuits above into a mono EMF detector with balanced output, phantom powered, possibly using a single power OP amp like in the second schematic: I suppose the 2.7K resistor connected to the electret is the one that provide the correct biasing to the IN+ of the first operational, halving the Vcc+ value provided to the operational (so it basically works with +Vcc 5V, -Vcc GND and IN+ 2,5V). Am I right?
I also understand that the same biasing is not needed in the Elektrosluch circuit, because the op amp is powered with +4,5V and -4,5V, with IN+ basically working at 0V.
Trying to work with single power, I added R11 to my last review of the circuit. Is that enough for the job? R1 and C1 should act like a high-pass filter, cutting out the 50 Hz hum.
Thank you for your patience,
Lorenzo
This is the second circuit I've found, made for powering an electret mic capsule with a mono balanced output, powered through P48 phantom power:
Original link
What I want is to combine the two circuits above into a mono EMF detector with balanced output, phantom powered, possibly using a single power OP amp like in the second schematic: I suppose the 2.7K resistor connected to the electret is the one that provide the correct biasing to the IN+ of the first operational, halving the Vcc+ value provided to the operational (so it basically works with +Vcc 5V, -Vcc GND and IN+ 2,5V). Am I right?
I also understand that the same biasing is not needed in the Elektrosluch circuit, because the op amp is powered with +4,5V and -4,5V, with IN+ basically working at 0V.
Trying to work with single power, I added R11 to my last review of the circuit. Is that enough for the job? R1 and C1 should act like a high-pass filter, cutting out the 50 Hz hum.
Thank you for your patience,
Lorenzo
Thank you for the contribution.
I tried to rearrange the schematic using two inverting op amps and adding the virtual ground circuit.
My goal was to keep the first amp with a high gain like in the original Elektrosluch and use the second one with Av = -1 only to invert the signal. Any feedback appreciated. Thank you.
I tried to rearrange the schematic using two inverting op amps and adding the virtual ground circuit.
My goal was to keep the first amp with a high gain like in the original Elektrosluch and use the second one with Av = -1 only to invert the signal. Any feedback appreciated. Thank you.
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Thank you for your patience. Op amps are just a very washed out memory from school days, it happened ages ago...
Now, if the circuit is more or less correct, can I have a comment about the TL972? Is it comparable to my original choice (NE5532) in matter of audio quality? On YouTube I've found test comparisons between TL072 and NE5532 used as audio pre, and the difference is dramatic. TL072 leaks in detail and high frequencies versus NE5532. TL072 was my first choice, because of its low power consumption, discarded when I could hear how it actually sounds.
Now, if the circuit is more or less correct, can I have a comment about the TL972? Is it comparable to my original choice (NE5532) in matter of audio quality? On YouTube I've found test comparisons between TL072 and NE5532 used as audio pre, and the difference is dramatic. TL072 leaks in detail and high frequencies versus NE5532. TL072 was my first choice, because of its low power consumption, discarded when I could hear how it actually sounds.
Anecdotical BS
What is your goal? An esoteric hi-end pre-amp or an em-detector?
Good to know.
My goal is to use them (I need to make two) as they were a couple of stereo mics for field recording. I'm also thinking to performance-related uses, like moving them around different EM sources. Let's say "experimental" "music", sort of.
My goal is to use them (I need to make two) as they were a couple of stereo mics for field recording. I'm also thinking to performance-related uses, like moving them around different EM sources. Let's say "experimental" "music", sort of.
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Luckily all these dual-opamps are interchangeable due to identical pinning.
for more universal applicadtions opa 1662 comes into mind
for more universal applicadtions opa 1662 comes into mind
Nope, not the case, some are 5V, some 36V, some rail-to-rail, some not, some bipolar, some FET, decoupling requirements vary (get this wrong and the thing oscillates), and some aren't unity-gain stable (pretty rare admittedly), and a few have phase-inversion, some allow the inputs to be at different voltages (i.e. can be comparators), others not... Any/all of these things can matter.