Showing posts with label circuits. Show all posts
Showing posts with label circuits. Show all posts
Thursday, October 16, 2014
Electret Mic Booster Circuits Diagram
Anyone who’s spent much time searching the web for interesting circuits is likely to have found at least one TL431 based audio amplifier, the circuit being based on the principle that any comparator can be used in linear mode if it’s rolled off with enough negative feedback. Although the TL431 is often referred to as a programmable or adjustable zener, it is in fact a comparator with it’s own 2.5 V reference all neatly wrapped up in a TO92 package.
The problem with the TL431 amplifiers to be found on the web is that they simply roll it back with large nfb and leave it at that, which results in ver y low gain, to make mat ter s worse some such circuits make a bit of a hash of biasing the control input.
The problem with the TL431 amplifiers to be found on the web is that they simply roll it back with large nfb and leave it at that, which results in ver y low gain, to make mat ter s worse some such circuits make a bit of a hash of biasing the control input.
Electret Mic Booster Circuit Diagram
The circuit presented here takes care of the low gain by adding an AC shunt to the feed-back path and using an electret mic for the input the 2.5 V set on the control input at stable operating condition suits an electret mic per fectly. The first prototype had a 35 ohms loudspeaker as a load (RL), this gave good results although the TL431 ran a bit warm with a Vccof 12 V. An old 130 ohm telephone earpiece is likely to present a less stressful load. AC shunt C2 (100 µF) has to be a quality component in terms of its ESR specification don’t just use a scruffy capacitor lying about as you may experience RF sensitivity. It was necessary to add a series resistor (R3; about 100 ohms) or in extreme cases an inductor (L1; 100 – 220 µH).
Components C1 & R1 are entirely optional to selectively feed some unshunted feedback to reduce noise; 1.5 k? & 5.6 nF are as good a place as any to start off with.Initial set-up depends on the current drawn by the electret mic and the value for RL any-where between 200 and 2,000 ohms is good. R2 allows the TL431 cathode to swing despite the AC shunt, 1.2 k? was found to be satisfactory, P1 can be a 47 k? trimpot and is used to set the voltage drop on RL. In the case of moving coil speakers a compromise between volt-age swing and prebiasing the cone should be sought, with a resistive load adjust for 0.5 Vcc, once the operating point is determined P1 can be measured and replaced by an equivalent fixed resistor.
The circuit has a couple of handy features, firstly it wor k s ver y well on the end of a twisted-pair the output can be tapped off at the wiper if RLis a pot at the power supply end, secondly by salvaging the JFET from an old electret mic (some common types of JFET will work but not quite as well), just about any piezo electric element can be used as the transducer. Brass disc sounders give a good output (handy as vibration sensors if glued to a structure); even the quartz discs from clock crystals give some output, a phono crystal cartridge gives a high output and the piezo-ceramic pellet from a flintless cigarette lighter gives a huge output... the range of possible applications is awesome!
A surprising application is the ability to test the microphonic sensitivity of ordinary capacitors! Disc ceramic types don’t need to be tapped very hard to produce an output but rolled metalised foil types produce some out-put too.
The circuit has a couple of handy features, firstly it wor k s ver y well on the end of a twisted-pair the output can be tapped off at the wiper if RLis a pot at the power supply end, secondly by salvaging the JFET from an old electret mic (some common types of JFET will work but not quite as well), just about any piezo electric element can be used as the transducer. Brass disc sounders give a good output (handy as vibration sensors if glued to a structure); even the quartz discs from clock crystals give some output, a phono crystal cartridge gives a high output and the piezo-ceramic pellet from a flintless cigarette lighter gives a huge output... the range of possible applications is awesome!
A surprising application is the ability to test the microphonic sensitivity of ordinary capacitors! Disc ceramic types don’t need to be tapped very hard to produce an output but rolled metalised foil types produce some out-put too.
Sunday, August 24, 2014
25 Watt Audio Amplifier Circuits Wiring diagram
25 Watt Audio Amplifier Circuits Diagram
Parts:
R1,R4_________47K1/4W ResistorsR2____________4K71/4W ResistorR3____________1K51/4W ResistorR5__________390R1/4W Resistor
R6__________470R1/4W Resistor
R7___________33K1/4W Resistor
R8__________150K1/4W Resistor
R9___________15K 1/4W Resistor
R10__________27R1/4W Resistor
R11_________500R1/2W Trimmer CermetR12,R13,R16__10R1/4W ResistorsR14,R15_____220R1/4W ResistorsR17___________8R22W Resistor
R18____________R224W Resistor (wirewound)C1___________470nF63V Polyester CapacitorC2___________330pF63V Polystyrene CapacitorC3,C5________470µF63V Electrolytic CapacitorsC4,C6,C8,C11_100nF63V Polyester CapacitorsC7___________100µF25V Electrolytic CapacitorC9____________10pF63V Polystyrene CapacitorC10____________1µF63V Polyester CapacitorQ1-Q5______BC560C45V 100mA Low noise High gain PNP Transistors
Q6_________BD14080V 1.5A PNP Transistor
Q7_________BD13980V 1.5A NPN Transistor
Q8_________IRF530100V 14A N-Channel Hexfet Transistor
Q9_________IRF9530 100V 12A P-Channel Hexfet TransistorPower supply schema diagram
Parts:
R1____________3K31/2W Resistor C1___________10nF 1000V Polyester CapacitorC2,C3______4700µF50V Electrolytic CapacitorsC4,C5_______100nF63V Polyester Capacitors D1__________200V 8A Diode bridgeD2__________5mm. Red LED F1,F2_______3.15A Fuses with sockets T1__________220V Primary, 25 + 25V Secondary 120VA Mains transformerPL1_________Male Mains plug SW1_________SPST Mains switchNotes:
- Can be directly connected to CD players, tuners and tape recorders. Simply add a 10K Log potentiometer (dual gang for stereo) and a switch to cope with the various sources you need.
- Q6 & Q7 must have a small U-shaped heatsink.
- Q8 & Q9 must be mounted on heatsink.
- Adjust R11 to set quiescent current at 100mA (best measured with an Avo-meter connected in series to Q8 Drain) with no input signal.
- A correct grounding is very important to eliminate hum and ground loops. Connect to the same point the ground sides of R1, R4, R9, C3 to C8. Connect C11 to output ground. Then connect separately the input and output grounds to power supply ground.
- An earlier prototype of this amplifier was recently inspected and tested again after 15 years of use.
Technical data:
Output power:
well in excess of 25 Watt RMS @ 8 Ohm (1KHz sine wave)
Sensitivity:
200mV input for 25W output
Frequency response:
30Hz to 20KHz-1dB
Total harmonic distortion @ 1KHz:
0.1W 0.014% 1W 0.006% 10W 0.006% 20W0.007% 25W 0.01%
Total harmonic distortion @10KHz:
0.1W 0.024% 1W 0.016% 10W 0.02% 20W0.045% 25W 0.07%
Unconditionally stable on capacitive loads
Saturday, August 23, 2014
Mini and simple power amplifier circuits
What is the meaning of the picture above? The above picture is a miniature audio amplifier and very simple. Here I will give an audio amplifier schematic is very simple which only requires a few components only, can be seen under this scheme.
Read more
Subscribe to:
Posts (Atom)
