Showing posts with label microphone. Show all posts
Showing posts with label microphone. Show all posts
Sunday, December 22, 2013
Ultra Simple Microphone Preamplifier
This little project came about as a result of a design job for a client. One of the items needed was a mic preamp, and the project didnt warrant a design such as the P66 preamp, since it is intended for basic PA only. Since mic preamps are needed by people for all manner of projects, this little board may be just whats needed for interfacing a balanced microphone with PC sound cards or other gear. Unlike most of my boards, this one is double-sided. I normally avoid double-sided PCBs for projects because rework by those inexperienced in working with them will almost certainly damage the board beyond repair.
I consider this not to be an issue with this preamp, because it is so simple. It is extremely difficult to make a mistake because of the simplicity. As you can see, the board uses a PCB mounted XLR connector and pot, so is a complete mic preamp, ready to go. Feel free to ignore the terminals marked SW1 (centred between the two electrolytic supply caps), as they are specific to my clients needs and are not useful for most applications. The original use was to use them for a push-button switch that activated an audio switch via a PIC micro-controller. They are not shown on the schematic.
Ultra-Simple Microphone Preamplifier Image Project :
The DC, GND and output terminals may be hard wired to the board, you may use PCB pins or a 10-way IDC (Insulation Displacement Connector) and ribbon cable. Power can be anything between +/-9V and +/-18V with an NE5532 opamp. The mic input is electronically balanced, and noise is quite low if you use the suggested opamp. Gain range is from about 12dB to 37dB as shown. It can be increased by reducing the value of R6, but this should not be necessary. Because anti-log pots are not available, the gain control is not especially linear, but unfortunately in this respect there is almost no alternative and the same problem occurs with all mic preamps using a similar variable gain control system.
Ultra-Simple Microphone Preamplifier Circuit diagram:
The circuit is quite conventional, and if 1% metal film resistors are used throughout it will have at least 40dB of common mode rejection with worst-case values. The input capacitors give a low frequency rolloff of -3dB at about 104Hz. If better low frequency response is required, these caps may be increased to 4.7uF or 10uF bipolar electrolytics. These will give response to well below 10Hz if you think youll ever need to go that low. The project PCB measures 77 x 24mm, and the mounting centers for the pot and XLR connector are spaced at 57mm. If preferred, a traditional chassis mounted female XLR can be used, and wired to the board with heavy tinned copper wire. The PCB pads for the connector are in the correct order for a female chassis mount socket mounted with the "Push" tab at the top.
source: http://www.ecircuitslab.com/2011/08/ultra-simple-microphone-preamplifier.html
Wednesday, December 18, 2013
Quality Stereo Wireless Microphone or Audio Link
This stereo FM wireless microphone also makes a great quality audio link. We tested it to beyond 50 meters and it was rock solid. It’s certainly not the first wireless microphone we’ve ever published but this one is a little different. It’s stereo, providing surprisingly good quality sound. Second, it has a really good range. We tested it at well over 50m and it was still performing very well – noise-free, in fact – but at the time we couldn’t get our receiver any further away. So it’s likely to have even better range than that.
Its easy to build, requires very little setup... and its cheap! In fact, the low price might turn some people off, thinking its low quality. Try it - and be pleasantly surprised!
Third, it really is simple to build – the hard work (the transmitter module) is already done for you. It’s just a matter of assembling the microphone module, which contains the electret mics themselves, preamp and level controls, and soldering the transmitter module onto it, "piggy back" style.
FM Transmitter:
Finally, the transmitter module is crystal-locked, so you won’t have the drift probles of some earlier wireless microphones. And just in case you were wondering, that doesn’t mean the output is locked to one particular frequency – it has a nifty synthesis circuit built in to give you the choice of seven different frequencies between 106.7MHz and 107.7MHz.
On-board preset pots adjust the sensitivity of each channel to take into account mic differences or if you require different levels in each channel.
By the way, the transmitter module is quite capable of operating at line level if you want just a line level transmitter (eg, to feed an audio program around your home). Sensitivity is about 100mV. Oatley Electronics, who designed the kit, have the transmitter module available by itself if that’s what you’re after. But more on that anon.
Parts Layout:
You also have the choice of two power supply levels – 3-6V or 7-15V DC. The latter results in a lower current drain. The transmitter module also has a "5V out" rail to supply power to the preamp module.
Circuit Diagram:
Two electret microphone inserts are supplied in the kit. These can be soldered direct to the PC board to make it a fully self-contained project or they can be attached to the board via suitable lengths of mini shielded coax cable. A third option is to use "proper" microphones – they can be electret or dynamic types – but no provision has been made for plugging these in.
Audio response:.....................20Hz-15kHz.
Channel separation: ........................40dB
Total Harmonic Distortion: ...............0.1%
Output Frequency:...........106.7-107.2MHz
Pre Emphasis: ..................................50μS
DC supply voltage range: ................3-15V
Supply Current: .......................30mA @ 9V
Source: http://www.ecircuitslab.com/2011/06/quality-stereo-wireless-microphone-or.html
Thursday, October 3, 2013
FM Wireless Microphone
Here is a very simple, inexpensive and interesting project which provides lot of fun to a home experimenter or hobbyist. This simple transmitter can transmit speech over a short range. It can be used as a simple cordless microphone. The circuit uses two integrated circuits from Maxim. IC1 a MAX4467, is an amplifier raising the microphone signal to a level suitable for frequency modulation (FM). IC2 is a voltage-controlled oscillator (VCO) with integrated varactor (a.k.a. varicap diode). Its nominal frequency of oscillation is set by inductor L1. The inductor value 390 nH provides an oscillation frequency of about 100 MHz. For best performance, L1 should be a high-Q component. L1 may consist of 4 turns of silver-plated wire wound around a 10-mm drill bit, and stretched to a length of about 1.5 cm.
The wire diameter can be anything between 26 SWG (0.5 mm) and 20 SWG (1 mm). No core is used. The MAX4467 is a micro-power opamp for low voltage operation and providing 200-kHz gain bandwidth at a supply current of just 24 µA. When used with an electret microphone, some form of DC bias for the microphone capsule is necessary. The MAX4467 has the ability to turn off the bias to the microphone when the device is in shutdown mode. This can save several hundred micro-amps of supply current, which can be significant in low power applications particularly for battery powered applications like cordless microphones. The MIC-Bias pin provides a switched version of Vcc to the bias components.
Resistor R1 resistor limits the current to the microphone element. The output impedance of the MAX4467 is low and well suited to driving cables over distances up to 50 m. The MAX2606 intermediate-frequency (IF) voltage-controlled oscillators (VCO) has been designed specifically for portable wireless communication systems. The IC comes in a tiny 6-pin SOT23 package. The low-noise VCO features an on-chip varactor and feedback capacitors that eliminate the need for external tuning elements. Only an external inductor (here, L1) is required to set the oscillation frequency and produce a properly operating VCO. To minimize the effects of parasitic elements, which degrade circuit performance, place L1 and C5 close to their respective pins.
Specifically, place C5 directly across pins 2 (GND) and 3 (TUNE). Potentiometer P2 then lets you select a free channel by tuning over the FM band of 88 MHz to 108 MHz. Output power is about –21dBm (approx. 10µW) into 50 Ω. P1 serves as a volume control by modulating the RF frequency. Signals above 60mV introduce distortion, so the pot attenuates from that level. To decrease stray capacitance, minimize trace lengths by placing external components close to IC1’s pins. Using a wire antenna of about 75 cm the transmitter should have a range of about 35 m. Try to keep all leads as short as possible to prevent stray capacitance. The transmitter operates on a single supply voltage in the range 4.5 V to 5.5 V from any standard battery source. The transmitter must be housed in a metal case, with shielding installed between the two stages (AF and RF). Try to keep all leads as short as possible to prevent stray capacitance.
Continue reading...
The wire diameter can be anything between 26 SWG (0.5 mm) and 20 SWG (1 mm). No core is used. The MAX4467 is a micro-power opamp for low voltage operation and providing 200-kHz gain bandwidth at a supply current of just 24 µA. When used with an electret microphone, some form of DC bias for the microphone capsule is necessary. The MAX4467 has the ability to turn off the bias to the microphone when the device is in shutdown mode. This can save several hundred micro-amps of supply current, which can be significant in low power applications particularly for battery powered applications like cordless microphones. The MIC-Bias pin provides a switched version of Vcc to the bias components.
Resistor R1 resistor limits the current to the microphone element. The output impedance of the MAX4467 is low and well suited to driving cables over distances up to 50 m. The MAX2606 intermediate-frequency (IF) voltage-controlled oscillators (VCO) has been designed specifically for portable wireless communication systems. The IC comes in a tiny 6-pin SOT23 package. The low-noise VCO features an on-chip varactor and feedback capacitors that eliminate the need for external tuning elements. Only an external inductor (here, L1) is required to set the oscillation frequency and produce a properly operating VCO. To minimize the effects of parasitic elements, which degrade circuit performance, place L1 and C5 close to their respective pins.
Specifically, place C5 directly across pins 2 (GND) and 3 (TUNE). Potentiometer P2 then lets you select a free channel by tuning over the FM band of 88 MHz to 108 MHz. Output power is about –21dBm (approx. 10µW) into 50 Ω. P1 serves as a volume control by modulating the RF frequency. Signals above 60mV introduce distortion, so the pot attenuates from that level. To decrease stray capacitance, minimize trace lengths by placing external components close to IC1’s pins. Using a wire antenna of about 75 cm the transmitter should have a range of about 35 m. Try to keep all leads as short as possible to prevent stray capacitance. The transmitter operates on a single supply voltage in the range 4.5 V to 5.5 V from any standard battery source. The transmitter must be housed in a metal case, with shielding installed between the two stages (AF and RF). Try to keep all leads as short as possible to prevent stray capacitance.
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