A charitable organization has requested me to help them transmit a microphone signal (picking up ambient sounds) over a distance of nearly 600 metres.
The microphone is to be placed at the gate to their campus, which will then be monitored by security personnel located at that distance.
They have already purchased a condenser mic which the French manufacturer claims will transmit an unbalanced signal upto 300 metres.
My thoughts:
Use a dedicated supply for the condenser mic. Convert the signal to balanced using a circuit like this http://www.diyaudio.com/forums/soli...topologies-balanced-unbalanced-amplifier.html posted by Marcel in post #4.
Use a pair of the Elektor Class A preamp shown in this thread http://www.diyaudio.com/forums/elektor/41993-mat02-03-elektor-preamp-schematic.html
Again use Marcel's circuit above to covert back to unbalanced and feed this into a DVR already available with them.
Use one single run of Balanced Mic cable, silver-plated, drain-wire with shielding, foil wrapped, teflon insulated.
Use damping RC networks at both ends of the cable to counter reactance.
The output expected is not hi-end but listenable through the day and night.
Not an easy situation. Any foreseeable problems, precautions to be taken etc.,
Any information would be much valued and appreciated.
Thanks in advance,
The microphone is to be placed at the gate to their campus, which will then be monitored by security personnel located at that distance.
They have already purchased a condenser mic which the French manufacturer claims will transmit an unbalanced signal upto 300 metres.
My thoughts:
Use a dedicated supply for the condenser mic. Convert the signal to balanced using a circuit like this http://www.diyaudio.com/forums/soli...topologies-balanced-unbalanced-amplifier.html posted by Marcel in post #4.
Use a pair of the Elektor Class A preamp shown in this thread http://www.diyaudio.com/forums/elektor/41993-mat02-03-elektor-preamp-schematic.html
Again use Marcel's circuit above to covert back to unbalanced and feed this into a DVR already available with them.
Use one single run of Balanced Mic cable, silver-plated, drain-wire with shielding, foil wrapped, teflon insulated.
Use damping RC networks at both ends of the cable to counter reactance.
The output expected is not hi-end but listenable through the day and night.
Not an easy situation. Any foreseeable problems, precautions to be taken etc.,
Any information would be much valued and appreciated.
Thanks in advance,
Take a look at transmission lines......
High Current is the issue here. Use a line level amplifier with low output impedance (20-50 Ohms) and terminate the cable at the end with a resistor with the same value could be the right solution.....
High Current is the issue here. Use a line level amplifier with low output impedance (20-50 Ohms) and terminate the cable at the end with a resistor with the same value could be the right solution.....
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What about something like THS4130/OPA1632 driving a pair of BUF634T with an INA134/137 on the other end?
Thanks everyone for your inputs. A radio link seems nice but the organization's electrical department wants a line-level link.
Jan, I was also thinking of a relatively high current. That is why I thought of the Elektor Class A preamp I pointed to in my opening post. The preamp is set at an Iq of 40mA and has an output impedance of 10E.
Alternately, I am also brooding on using a pair of Mini-Alephs ( http://www.diyaudio.com/forums/pass-labs/2001-mini.html ); the reactive load should not matter for the mini Class A amp.
Jan, I was also thinking of a relatively high current. That is why I thought of the Elektor Class A preamp I pointed to in my opening post. The preamp is set at an Iq of 40mA and has an output impedance of 10E.
Alternately, I am also brooding on using a pair of Mini-Alephs ( http://www.diyaudio.com/forums/pass-labs/2001-mini.html ); the reactive load should not matter for the mini Class A amp.
No need for using class A here. You can use a class A/B amplifier. It's not the Iq thats important but the Current through the cable......
Does the cable provide a phantom supply back to the microphone end?
If so then that supply can power any tiny "follower" stage. This follower stage should be capable of driving that 500m of cable capacitance. That is not a particularly difficult task.
And keep the transmission impedance balanced. You must reject noise before it contaminates the signal.
If so then that supply can power any tiny "follower" stage. This follower stage should be capable of driving that 500m of cable capacitance. That is not a particularly difficult task.
And keep the transmission impedance balanced. You must reject noise before it contaminates the signal.
Attached herewith are the Microphone already in possession with the concerned party. It requires only +12VDC.
Andrew, are you saying 2 follower stages, driving a balanced signal?
I was also contemplating on using 2 Mini-Alephs ( http://www.diyaudio.com/forums/pass-labs/2001-mini.html ) to drive a balanced signal.
It does appear that line level stages may not be as suitable as a power stage.
Small power follower, Mini-Aleph or a small Class A/AB amp (2 for balanced drive)? Thanks in advance.
Andrew, are you saying 2 follower stages, driving a balanced signal?
I was also contemplating on using 2 Mini-Alephs ( http://www.diyaudio.com/forums/pass-labs/2001-mini.html ) to drive a balanced signal.
It does appear that line level stages may not be as suitable as a power stage.
Small power follower, Mini-Aleph or a small Class A/AB amp (2 for balanced drive)? Thanks in advance.
Why on earth would you need a power amp for this?????
Any decent mic preamp, with a low impedance balanced line driver will do the job.
Then terminate as appropriate at the receiving end and feed to mix/amp or whatever will be used to monitor this.
Use a decent cable - properly balanced and preferrably screened, depending on your RF environment. Depending on impedance, you may loose some treble, though.....
I run party-line intercoms, converted to balanced transformer drive, at distances above 1 km.....
Any decent mic preamp, with a low impedance balanced line driver will do the job.
Then terminate as appropriate at the receiving end and feed to mix/amp or whatever will be used to monitor this.
Use a decent cable - properly balanced and preferrably screened, depending on your RF environment. Depending on impedance, you may loose some treble, though.....
I run party-line intercoms, converted to balanced transformer drive, at distances above 1 km.....
....if the sound quality is not the #1 issue and cables already exist then this is very very easy
100v technology is the no1 solution when it comes to things like that ...
also CAT5 ( probably existing ) or simple telephone cables can be used
find any preamplifier fits your needs, and any simple amplifier like TDA 2002 will do . drive 100 v small existing anywhere transformer , use another transformer on the other side which probably have a 0-4-8 R secondary with a divider of a couple of resistors and you are done with no more than 10USD ...
offers also fully differential ground so no noises of any kind will insert the signal even if the distance is 1 klm
that is common practice .....
100v technology is the no1 solution when it comes to things like that ...
also CAT5 ( probably existing ) or simple telephone cables can be used
find any preamplifier fits your needs, and any simple amplifier like TDA 2002 will do . drive 100 v small existing anywhere transformer , use another transformer on the other side which probably have a 0-4-8 R secondary with a divider of a couple of resistors and you are done with no more than 10USD ...
offers also fully differential ground so no noises of any kind will insert the signal even if the distance is 1 klm
that is common practice .....
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in a way yes but the trick is that if you are looking for line level trafos that will be hard to find and expensive
on the other side speaker level transformers exist anywhere cost nothing and do the job with no problems except lower quality due to poor frequency response of the trafos .
kind regards
sakis
on the other side speaker level transformers exist anywhere cost nothing and do the job with no problems except lower quality due to poor frequency response of the trafos .
kind regards
sakis
IF you're not expecting "studio" signal quality 😎 , line transformers are available for 20-30$ each.... I use quite a number of them for voice++ (10kHz or so) quality distribution.
5W speaker level transformer audio grade will not cost more than 2-3 euros or usd in any electronics shop and yes it will not be studio quality ...just almost hifi expect a bandwidth from 100-120 HZ to almost 8.5K ....more than enough for such an intercom application
Thanks everyone for your responses. Absolute studio quality is not necessary.
A brief description of the application is as follows: The charitable organization is spread over a large area. The main gate is unmanned and the security personnel are stationed at the next gate which is a little more than 1/2 km away. The two points are connected by a winding road, so they are not in a straight, direct line of sight. They want to have a microphone pick up all ambient sound, synchronize this with their CCTV and make sense of what is going on in the vicinity of the main gate. The gates are shut at night and remain open during the day.
In such a situation, covering a wide band will convey more information; hence, restricting it to speech bandwidth may not be the best situation.
HDP pipe has been laid but no cable has been run as yet for this purpose.
Thanks again, for any further inputs.
A brief description of the application is as follows: The charitable organization is spread over a large area. The main gate is unmanned and the security personnel are stationed at the next gate which is a little more than 1/2 km away. The two points are connected by a winding road, so they are not in a straight, direct line of sight. They want to have a microphone pick up all ambient sound, synchronize this with their CCTV and make sense of what is going on in the vicinity of the main gate. The gates are shut at night and remain open during the day.
In such a situation, covering a wide band will convey more information; hence, restricting it to speech bandwidth may not be the best situation.
HDP pipe has been laid but no cable has been run as yet for this purpose.
Thanks again, for any further inputs.
If you have power at the gate, then I too would be thinking RF. Running 600M of cable is not cheap, and prone to damage. ( big expense if pipe was laid before working out these details.) Could you modulate the audio and piggy-back on the CCTV cable?
this is crazy. you can even pick up power line hum (magnetically induced50/60 Hz) with such lengths. my advice is to place an amplifier right at the microphone site, remotely power fed with a three wire cable and have at least one more repeater.
better yet. use a two wire twisted pair and treat it like a telephone system. send dc power over the wires for remote amplifier and superimpose the audio with a balanced system just like in telephony. since it works for several kilometres in telephony it will definitely work in your case.
is this really a Audio Forum?
no mention yet of phantom powered mics?
shielded twisted pair XLR cables, 48 Vdc power appled between the pair and the shield is a pro standard
active buffered phantom powered mics can have <100 Ohm output Z, will drive 1000 m of <100 pF/m cable with ~ 16 kHz -3 dB point
no mention yet of phantom powered mics?
shielded twisted pair XLR cables, 48 Vdc power appled between the pair and the shield is a pro standard
active buffered phantom powered mics can have <100 Ohm output Z, will drive 1000 m of <100 pF/m cable with ~ 16 kHz -3 dB point
The 50 ohm feed and coaxial cable is the right idea as suggested by Jan Dupont.
Cable TV uses DC and RF over the same line...30VDC and lots of TV channels.
If you need phantom power then transformer or inductor isolation of the AF and DC is another option. (see jpg's for ideas)
Make sure the Microphone side power requirements are less than 18 mA due to max 144H unbalanced current limitations.
Transformer-less dc coupled circuits can also be used with 50 ohm coax.
Try to amplify as much as possible at the microphone end.
Cable TV uses DC and RF over the same line...30VDC and lots of TV channels.
If you need phantom power then transformer or inductor isolation of the AF and DC is another option. (see jpg's for ideas)
Make sure the Microphone side power requirements are less than 18 mA due to max 144H unbalanced current limitations.
Transformer-less dc coupled circuits can also be used with 50 ohm coax.
Try to amplify as much as possible at the microphone end.
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