Unfortunately no change, it clips at the same level without divider.
A new one with 1000Ω/750Ω is now inserted.
https://filetransfer.io/data-package/8ZHsMpCg#link
Is the power consumption of an op amp steady no matter the signal strength?
Then it could maybe tapped to 46.5V with a resistor?
A new one with 1000Ω/750Ω is now inserted.
https://filetransfer.io/data-package/8ZHsMpCg#link
Is the power consumption of an op amp steady no matter the signal strength?
Then it could maybe tapped to 46.5V with a resistor?
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What is the clipping level right now, with 22k Feedback resistors and 3.3V?
How far does it miss the theoretical clipping level? (I assume theroetically about 97dB)
How far does it miss the theoretical clipping level? (I assume theroetically about 97dB)
I finally start to understand that I misinterpreted what you wrote. I thought you meant that the microphone preamplifier clips at a sound pressure level 6 dB lower than the sound pressure level that made the camera clip in the old set-up with just the microphone, modified phantom supply and transformer. I now gather that what you mean is that when you have the microphone, preamplifier and camera connected, increase the sound pressure level until the microphone preamplifier clips, the camera indicates -6 dB when it is set to its least sensitive position.
If the latter interpretation is correct, I'm afraid it is perfectly normal. The level coming out of the microphone preamplifier can't go above about 1 V RMS due to the limited supply voltage and unbalanced line inputs are normally designed such that they can handle 2 V RMS, because a maximum unbalanced line level of 2 V RMS has become a defacto standard after the introduction of CD players. The difference between 1 V and 2 V is about 6 dB.
The gain of the microphone preamplifier is now about 38 dB. It will clip somewhere around 88 dB SPL. With the old set-up, the camera probably clipped at about 87 dB SPL without and 96 dB SPL with the 9 dB attenuator, assuming that the camera's microphone input can handle 45 dB less than 2 V RMS when set to minimum gain.
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Correct! And many thanks for the updated schematics! Are you sure it is 88db, as it was 100dB with 15k? Ignore this question, if 88dB are because of the 3.3V. What do you think? Are the 46.5V directly generated from 3.3V or is it „cascaded“, so that 5V might be tapped from somewhere? Tapping directly frommthe Lipo battery is not possible, it will drain.
With 22kohm, it should be something around 97dB SPL? Or does the first quote refer to the single ended design?
88dB because the limited voltage?
The voltage divider could be 1600Ω / 1500Ω, this will give me -9dB. I guess, still ok?
I made an incredibly stupid mistake. The latest microphone amplifier can produce about 2 V RMS, so the clipping levels are 6 dB higher and the story about CD players is complete crap.
So 96dB is the theoretical clipping level, but the amp clips at 88dB...?
What about the Zener diode? Would removing it with R3 save power?
What about the Zener diode? Would removing it with R3 save power?
Corrected for my mistake:
The clipping could still be normal. The level coming out of the microphone preamplifier can't go above about 2 V RMS. Unbalanced line inputs are normally designed such that they can at least handle 2 V RMS, but it could be that the camera is designed for somewhat higher levels than that. If it is designed to handle 4 V, the difference is still 6 dB. The camera's manual has no information about the maximum line level it can actually handle.
The gain of the microphone preamplifier is now about 38 dB (for a given feedback resistance, the balanced design has about 6 dB more gain than the earlier versions). It will clip somewhere around 94 dB SPL. With the old set-up, the camera probably clipped at about 93 dB SPL without and 102 dB SPL with the 9 dB attenuator, assuming that the camera's microphone input can handle 45 dB less than 4 V RMS when set to minimum gain.
I wouldn't recommend leaving out the Zener diode and R3, as it only saves a very small part of the power and might damage the circuitry running off the 3.3 V.
The clipping could still be normal. The level coming out of the microphone preamplifier can't go above about 2 V RMS. Unbalanced line inputs are normally designed such that they can at least handle 2 V RMS, but it could be that the camera is designed for somewhat higher levels than that. If it is designed to handle 4 V, the difference is still 6 dB. The camera's manual has no information about the maximum line level it can actually handle.
The gain of the microphone preamplifier is now about 38 dB (for a given feedback resistance, the balanced design has about 6 dB more gain than the earlier versions). It will clip somewhere around 94 dB SPL. With the old set-up, the camera probably clipped at about 93 dB SPL without and 102 dB SPL with the 9 dB attenuator, assuming that the camera's microphone input can handle 45 dB less than 4 V RMS when set to minimum gain.
I wouldn't recommend leaving out the Zener diode and R3, as it only saves a very small part of the power and might damage the circuitry running off the 3.3 V.
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OK. Maybe one day a step up converter but I assume they are noisy...
Put in a 1600Ω to 1500Ω voltage divider in the adapter box.
and leave the mic preamp for now.
BTW, the CD-story is not complete crap.
As far as I remember, about 1.55V was a standard in the pre-CD age.
But as the early D/A converters could deliver higher gains, they quickly settled
to 2V as "louder" is preceived "better" to our ears.
Many, many thanks for all,
Salar
Put in a 1600Ω to 1500Ω voltage divider in the adapter box.
and leave the mic preamp for now.
BTW, the CD-story is not complete crap.
As far as I remember, about 1.55V was a standard in the pre-CD age.
But as the early D/A converters could deliver higher gains, they quickly settled
to 2V as "louder" is preceived "better" to our ears.
Many, many thanks for all,
Salar
I would say in the real world pretty much o.k. with its limitations.
I hear a very slight distortion in the bass when the truck is approaching,
could be the transformer - or even the AAC Codec:
Image and sound:
https://filetransfer.io/data-package/rBi8dIdE#link
The wav sounds cleaner to my ears:
Sound only:
https://filetransfer.io/data-package/HUPdoq8m#link
Recorded at-12dB.
BTW, again, the transformer distorts in bass before the opamp clips at 22k feeback,
38dB gain, about 94dB SPL, Voltage divider after transformer R1 1600 R2 1500 ohm.
I hear a very slight distortion in the bass when the truck is approaching,
could be the transformer - or even the AAC Codec:
Image and sound:
https://filetransfer.io/data-package/rBi8dIdE#link
The wav sounds cleaner to my ears:
Sound only:
https://filetransfer.io/data-package/HUPdoq8m#link
Recorded at-12dB.
BTW, again, the transformer distorts in bass before the opamp clips at 22k feeback,
38dB gain, about 94dB SPL, Voltage divider after transformer R1 1600 R2 1500 ohm.
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Below 100 Hz...120 Hz, the transformer distorts before the op-amp clips no matter how you set the gain.
That is, when you reduce the gain, the transformer and the op-amp will both start distorting at higher sound pressure levels, but the transformer will still be the first to distort at frequencies below 100 Hz...120 Hz and the op-amp at higher frequencies.
That is, when you reduce the gain, the transformer and the op-amp will both start distorting at higher sound pressure levels, but the transformer will still be the first to distort at frequencies below 100 Hz...120 Hz and the op-amp at higher frequencies.
Hmmm... In the meantime I rechecked on my earphones that have a very deep bass -
yes, the distortion is audible.
As the resistance of the voltage divider is higher now (1600Ω/1500Ω @2200Ω impedance),
any chance to leave out the transformer?
All the best, Salar
yes, the distortion is audible.
As the resistance of the voltage divider is higher now (1600Ω/1500Ω @2200Ω impedance),
any chance to leave out the transformer?
All the best, Salar
No, not with this circuit and this camera.
Theoretically, you could double the output voltage clipping level and solve the transformer distortion by halving the feedback resistors, using a 1:2 transformer that can handle 2 V RMS of primary voltage down to the lowest frequencies of interest, and maybe further increasing the divider impedance. I'm afraid that such a transformer would be too large, though. It would also be expensive.
Theoretically, you could double the output voltage clipping level and solve the transformer distortion by halving the feedback resistors, using a 1:2 transformer that can handle 2 V RMS of primary voltage down to the lowest frequencies of interest, and maybe further increasing the divider impedance. I'm afraid that such a transformer would be too large, though. It would also be expensive.
Many thanks! I will look for a better transformer. It could be put into the adaper box beneath the camera. Space there is limited as well, bit bigger than in the Xvive.
When the transformer is removed from the circuit, any changes? Second capacitor for the negatice output?
When the transformer is removed from the circuit, any changes? Second capacitor for the negatice output?
Would the Lundahl LL1593 work?
It would fit. But +6dBU - 1.55V = 1VRMS...?
https://www.lundahltransformers.com/wp-content/uploads/datasheets/1532_1593.pdf
It would fit. But +6dBU - 1.55V = 1VRMS...?
https://www.lundahltransformers.com/wp-content/uploads/datasheets/1532_1593.pdf
With the primaries in parallel, it would distort 1 % at 1.55 V, 50 Hz, proportionally less at lower frequencies. Not quite the 2 V at 40 Hz that you want. Then again, that's at 600 ohm/4 = 150 ohm source impedance, it will distort less when driven from the low impedance of the op-amp circuit.
All in all, I don't know.
All in all, I don't know.
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If you have enough space, I would recommend something like this:
R5 and R1 have half their previous value, because of the factor of two gain that you get from a 1:2 transformer. The total gain is then still about 37 dB...38 dB, like it is now, but with a 6 dB higher maximum SPL for high frequencies (and with an improvement of more than 6 dB at low frequencies because of the better transformer).
The new components C2, C3, R11 and R12 are meant to keep the amplifier stable no matter how long the cable between the amplifier and the transformer may be. I hope you have space for C2 and C3. They could be fairly small, for example 0805 or 1206 ceramic SMD capacitors or through-hole ceramic capacitors with 2.54 mm pitch.
The circuit at the bottom left shows how transformers with a split primary winding are normally connected when you want them to work as a 1:2 transformer. If the secondary also happens to have a split winding, you could make a -6 dB output without even needing a resistive divider.
Many Thanks! Up to now, for 1:2 I only found Jensen or Lundahl, too big or not enough headroom for distortion
Looks like the Neutrik NTL-1 could be a better solution against distortion in bass , but is only 1:1. As far as I understand, the NTL-1 does not distort at the given levels. Maybe I can get C2 and C3 in but would likely not change the feedback resistor.
Looks like the Neutrik NTL-1 could be a better solution against distortion in bass , but is only 1:1. As far as I understand, the NTL-1 does not distort at the given levels. Maybe I can get C2 and C3 in but would likely not change the feedback resistor.
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