The NTL-1 is meant for load impedances of at least 10 kohm. The large winding resistances would cause excessive losses at lower load impedances.
OK! Feels more and more like
reverting to the earlier, single ended designs and get 5v from a step up converter…?
reverting to the earlier, single ended designs and get 5v from a step up converter…?
I know this sounds erratic, but have listened to the other recordings from the busy street with a lot of traffic.
There the bass does not sound distorted (though it must be).
The other clips sound like what I would expect from a decent mic preamp.
What triggered the distortion was a truck that stopped right in front of me,
with a hidden, loud device deeply humming, maybe for cooling.
So not an everyday solution. So I think I can leave it for now.
All the best,
Salar
There the bass does not sound distorted (though it must be).
The other clips sound like what I would expect from a decent mic preamp.
What triggered the distortion was a truck that stopped right in front of me,
with a hidden, loud device deeply humming, maybe for cooling.
So not an everyday solution. So I think I can leave it for now.
All the best,
Salar
For some reason the data for the LL1532 in that datasheet are inconsistent with the data in the LL1593 & LL1532 datasheet you linked to earlier. It can handle 10 dBu with 1 % distortion at 50 Hz with the primaries in series and 600 ohm source impedance in one datasheet and 12 dBu under the same conditions in the other datasheet.
The data for the NTE1 also seem inconsistent, on one page it can handle 1.2 V at 60 Hz and on another only -3 dBu at 50 Hz. One would expect about 1 V at 50 Hz, so about +2.22 dBu. Maybe they meant +3 dBu instead of -3 dBu?
I've tried to estimate down to what frequency the various transformers can handle 2 V RMS input (primary) voltage with at most 1 % distortion. My estimates are pessimistic, because I haven't accounted for the low driving impedance.
NTE1, only usable as a 1:1 transformer:
2 V down to either 100 Hz or 182.4 Hz, probably 100 Hz
LL1532 used as a 1:1 transformer:
2 V down to 40.8 Hz or 32.4 Hz
LL1593 used as a 1:1 transformer:
2 V down to 32.4 Hz
LL1532 used as a 1:2 transformer:
1 V down to 40.8 Hz or 32.4 Hz
2 V down to 81.6 Hz or 64.9 Hz
LL1593 used as a 1:2 transformer:
1 V down to 32.4 Hz
2 V down to 64.9 Hz
When you use the LL1532 or LL1593 as a 1:2 transformer, you can halve the op-amp gain to get the same overall gain. Looking at the maximum sound pressure level that can be handled, this makes things 6 dB better at high frequencies (> 64.9 Hz or > 81.6 Hz) than with an LL1532 or LL1593 used as a 1:1 transformer and the non-halved amplifier gain. The maximum SPL below 32.4 Hz or 40.8 Hz is the same as with an LL1532 or LL1593 used as a 1:1 transformer and non-halved op-amp gain. It's all better than with the NTE1.
The data for the NTE1 also seem inconsistent, on one page it can handle 1.2 V at 60 Hz and on another only -3 dBu at 50 Hz. One would expect about 1 V at 50 Hz, so about +2.22 dBu. Maybe they meant +3 dBu instead of -3 dBu?
I've tried to estimate down to what frequency the various transformers can handle 2 V RMS input (primary) voltage with at most 1 % distortion. My estimates are pessimistic, because I haven't accounted for the low driving impedance.
NTE1, only usable as a 1:1 transformer:
2 V down to either 100 Hz or 182.4 Hz, probably 100 Hz
LL1532 used as a 1:1 transformer:
2 V down to 40.8 Hz or 32.4 Hz
LL1593 used as a 1:1 transformer:
2 V down to 32.4 Hz
LL1532 used as a 1:2 transformer:
1 V down to 40.8 Hz or 32.4 Hz
2 V down to 81.6 Hz or 64.9 Hz
LL1593 used as a 1:2 transformer:
1 V down to 32.4 Hz
2 V down to 64.9 Hz
When you use the LL1532 or LL1593 as a 1:2 transformer, you can halve the op-amp gain to get the same overall gain. Looking at the maximum sound pressure level that can be handled, this makes things 6 dB better at high frequencies (> 64.9 Hz or > 81.6 Hz) than with an LL1532 or LL1593 used as a 1:1 transformer and the non-halved amplifier gain. The maximum SPL below 32.4 Hz or 40.8 Hz is the same as with an LL1532 or LL1593 used as a 1:1 transformer and non-halved op-amp gain. It's all better than with the NTE1.
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Whoah! And as always, much more work and thought put into the topic than expected!
Just came back from testing the drummers that gather in the park close to me.
It only workks from distance and btw wind hitting the mic produces distortion
that cannot easily being filtered out.
The Lundahl-seller here in Germany (looks like he is Dutch btw, www.jacmusic.com )
warned about resonances in "micversth", the last schematic.
But I am a litte bit lost - impedance-wise, which Lundahl fits the design best?
Then, there is this one, much cheaper, but not 1:2:
https://www.monacor.de/media/FLE/LTR-110@BDA.pdf
https://paforum.de/forum/index.php?thread/18016-übertrager-monacor-ltr-110/
All the best, Salar
Just came back from testing the drummers that gather in the park close to me.
It only workks from distance and btw wind hitting the mic produces distortion
that cannot easily being filtered out.
The Lundahl-seller here in Germany (looks like he is Dutch btw, www.jacmusic.com )
warned about resonances in "micversth", the last schematic.
But I am a litte bit lost - impedance-wise, which Lundahl fits the design best?
Then, there is this one, much cheaper, but not 1:2:
https://www.monacor.de/media/FLE/LTR-110@BDA.pdf
https://paforum.de/forum/index.php?thread/18016-übertrager-monacor-ltr-110/
All the best, Salar
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According to the first Lundahl datasheet you found, the LL1532 and LL1593 are essentially the same, except that the LL1532 has a magnetic and an electric shield.
I think the LTR-110, connected as a 1:1.5 transformer, would be very interesting for your application.
I think the LTR-110, connected as a 1:1.5 transformer, would be very interesting for your application.
Many thanks!
With the Monacor: P1 is 0db=1:1.5 Ratio?
The Panasonic S5 provides h.264 and h.265 as video formats for 4 k, sound is 16bit PCM.
But I transfer the material to 2k for offline / proxy editing in Apple ProRes,
and go back to the original material for color correction.
Codec for the master is ProRes 422HQ.
Audio standard is 24/48, both for editing and delivery.
With the Monacor: P1 is 0db=1:1.5 Ratio?
The Panasonic S5 provides h.264 and h.265 as video formats for 4 k, sound is 16bit PCM.
But I transfer the material to 2k for offline / proxy editing in Apple ProRes,
and go back to the original material for color correction.
Codec for the master is ProRes 422HQ.
Audio standard is 24/48, both for editing and delivery.
Finally you got 15k (R1+R5) for feedback 🙂
Can R11+12 be also 10ohm? Some user wrote,
the Monacor can be used also 1:4...?
I do not see how, you?
Can R11+12 be also 10ohm? Some user wrote,
the Monacor can be used also 1:4...?
I do not see how, you?
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Monacor specifies a recommended driving impedance of 50 to 600 ohm, I just took resistors that cause the impedance driving the transformer to be at the bottom of this range. I have no idea why they specify a minimum value, though, normally the only effect of a very low driving impedance is somewhat less distortion.
You could use the small secondary coil as the primary and connect the other two coils in series and use that as the secondary. I would not recommend that for your amplifier, though. It halves the input voltage that the transformer can handle and the op-amp is then loaded by 1/16 times the camera input impedance plus some wiring resistance.
Dear Marcel,
deed is done, looks uglier than ever, but it works.
The LTR-110 transformer is in the breakout box beneath the camera now.
I did go for 1:1.5:
1&3 primary, 5+6 bridged, 8&4 secondary, unbalanced.
The op amp circuit:
11KΩ as feedback resistors, 27Ω as output resistors.
Tests with my fieldmixer that provides +4dBu:
The transformer is about 2dB "hotter" -
0dB on the scale of the fieldmixer equals -10dB on the camera with the -12dB setting.
With the mic and your opamp inserterted, almost no distortion at max level.
Many, many thanks for your kind and thorough help and aid,
all the best, Salar.
P.S.: One mishap during soldering: While looking for shorts with a multimeter,
I accidentally measured the primary winding for a second.
Made a test with 20hz at about 30dB, did not see distortions...
deed is done, looks uglier than ever, but it works.
The LTR-110 transformer is in the breakout box beneath the camera now.
I did go for 1:1.5:
1&3 primary, 5+6 bridged, 8&4 secondary, unbalanced.
The op amp circuit:
11KΩ as feedback resistors, 27Ω as output resistors.
Tests with my fieldmixer that provides +4dBu:
The transformer is about 2dB "hotter" -
0dB on the scale of the fieldmixer equals -10dB on the camera with the -12dB setting.
With the mic and your opamp inserterted, almost no distortion at max level.
Many, many thanks for your kind and thorough help and aid,
all the best, Salar.
P.S.: One mishap during soldering: While looking for shorts with a multimeter,
I accidentally measured the primary winding for a second.
Made a test with 20hz at about 30dB, did not see distortions...
About 34 to 35 dB for the op-amp and transformer together.
(Ideally it should be 32.1 dB for the op-amp circuit and 3.52 dB for the transformer, so 35.62 dB overall, but that's neglecting losses due to the nonzero output impedance of the op-amp circuit, transformer winding resistance and things like that.)
(Ideally it should be 32.1 dB for the op-amp circuit and 3.52 dB for the transformer, so 35.62 dB overall, but that's neglecting losses due to the nonzero output impedance of the op-amp circuit, transformer winding resistance and things like that.)
I did reopen the preamp as 11k is technically perfect, but too low for daily use.
I did put in 22K..
Of cours there is clipping of the opamp as 3.3V are not enough power.
I would like to put in this boost converter:
https://www.ebay.com/itm/4013320116...=2047675&ssuid=&widget_ver=artemis&media=COPY
https://dzrmo.wordpress.com/2017/01/26/a-tiny-but-good-boost-converter/
I assume it is quite noisy, but do not know whether the noise will be drowned
by the mics noise anyway.
If not, any advice how "denoise" this step-up converter?
All the best,
Salar
I did put in 22K..
Of cours there is clipping of the opamp as 3.3V are not enough power.
I would like to put in this boost converter:
https://www.ebay.com/itm/4013320116...=2047675&ssuid=&widget_ver=artemis&media=COPY
https://dzrmo.wordpress.com/2017/01/26/a-tiny-but-good-boost-converter/
I assume it is quite noisy, but do not know whether the noise will be drowned
by the mics noise anyway.
If not, any advice how "denoise" this step-up converter?
All the best,
Salar
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Datasheet of the IC of the boost converter, ME2108:
https://archive.espec.ws/files/ME2108 Series.pdf
https://archive.espec.ws/files/ME2108 Series.pdf
The potential problem is whistles rather than noise (as in hiss).
The boost converter works in variable frequency mode (VFM). At light loads, and I think the microphone amplifier is a light load, its switching frequency might end up in the audible range. The slightest crosstalk to the output will then result in an audible whistle.
If it stays in the ultrasonic region, it may or may not still cause problems. If the anti-alias filtering of the camera is very poor, it could still alias to an audible frequency. Assuming the camera has good anti-alias filtering, harmonics of the boost converter frequency could still cause audible difference frequencies with the harmonics of the phantom supply switching frequency.
I can't predict whether any of these issues will actually occur to an audible degree.
In any case, you will only win about 3 to 3.6 dB of headroom when the supply is increased from 3.3 V to 5 V (above 5.5 V, you would blow up the op-amp, which could be solved by using another type of op-amp). Alternatives:
-Make some sort of script to conveniently batch normalize the audio levels after recording and reduce the microphone preamplifier gain to 28...29 dB, so you have 12 dB more headroom than you have now and 6 dB more than when the feedback resistors were 11 kohm. You then don't have to record soft sounds at -9 dB anymore, because you can easily correct it afterwards for a whole bunch of audio files by running the script. I have no idea how to do this, but maybe someone from the software tools subforum does.
-If you can fit a switch (single pole on/off switch) in the phantom amplifier somehow: make the gain switchable, with a high and a low setting.
The boost converter works in variable frequency mode (VFM). At light loads, and I think the microphone amplifier is a light load, its switching frequency might end up in the audible range. The slightest crosstalk to the output will then result in an audible whistle.
If it stays in the ultrasonic region, it may or may not still cause problems. If the anti-alias filtering of the camera is very poor, it could still alias to an audible frequency. Assuming the camera has good anti-alias filtering, harmonics of the boost converter frequency could still cause audible difference frequencies with the harmonics of the phantom supply switching frequency.
I can't predict whether any of these issues will actually occur to an audible degree.
In any case, you will only win about 3 to 3.6 dB of headroom when the supply is increased from 3.3 V to 5 V (above 5.5 V, you would blow up the op-amp, which could be solved by using another type of op-amp). Alternatives:
-Make some sort of script to conveniently batch normalize the audio levels after recording and reduce the microphone preamplifier gain to 28...29 dB, so you have 12 dB more headroom than you have now and 6 dB more than when the feedback resistors were 11 kohm. You then don't have to record soft sounds at -9 dB anymore, because you can easily correct it afterwards for a whole bunch of audio files by running the script. I have no idea how to do this, but maybe someone from the software tools subforum does.
-If you can fit a switch (single pole on/off switch) in the phantom amplifier somehow: make the gain switchable, with a high and a low setting.