Search... ELectronics :

SAP15 use of the gallstone mixer amp

This paper describes the gallstone mixer, the use of high-frequency dual-triode 6 N3 do audio amplification, a distortion of small, high-frequency response, and high conversion rate, the advantages of large dynamic range.

Power output level by the Japanese company is willing to three audio supervisor SAP15N / P, which is two complementary Darlington on the internal diodes with a bias. The tube also known as high-speed thermal reaction transistors, TRAITR tube, has high thermal stability.
SAP15 use of the gallstone mixer ampSAP15N / P structure see Figure 1.

SAP15 use of the gallstone mixer ampThe Electrical and Mechanical Road shown in Figure 2.

Power output circuit for a typical OCL, and a constant current drive, SAP15N ② the first leg and foot SAP15P the ④ indirectly a 510 Ω potentiometers, for regulating the size of bias, thus adjusting the static-amp Current, the circuit of quiescent current 100 mA. Tube before class and after class between transistors by capacitive coupling.
Before a two-6 N3 respectively as voltage and power-driven zoom level, and then into SRPP circuit. To improve the performance of amplifiers, and the depth of the little negative feedback loop.
Using two power transformer power supply. A transformer capacity of 20 W, output DC 200 V, exchange of 6.3 V to 4 6 N3 tube power supply. Transformer can be used C-or E-core. Another transformer capacity should be more than 300 W, DC output voltage ± 45V, for transistor-level power amplifier.

Step by Step SMD Components Welding Process

1. first of all to a welding point of PCB map

2. Of course, this is the welding of the patch must be a tool

3. This is a preparation for welding of the DD (fainted, but will be a little careless)

4. First iron heating spot

5. Folder and then a patch immediately in the past

6. After the patch fixed, and so on the other side of the welding!

7. Welding of the IC, PCB in the first IC chip fixed on a foot

8. Then all the piles of large-scale feet! Become like this

9. And then look for thin copper wire with rosin and drawing as Apple

10. IC on the feet! With copper absorption tin

11. Finally, use of alcohol cleaning (with cotton)

12. You will find very rosin block and will not melt!

13. Do something at the end of the work

14. To complete the look

3.5 mm or 6.5 mm Mono Telephone plug

pinout

Used in various audio hardware

2 pin MONO jack male
2 pin MONO jack male connector at the cable
Name Description
SIGNALSignal
GROUNDGround

Universal Features TDA2030 Power Amplifiers

This chip amplifier NCH TDA2030A company ST Microelectronics enjoys well-deserved popularity among radio amateurs. It has a high electrical performance and low cost, which allows for the least cost to collect her high UNCH capacity of up to 18 Watts. But not everyone is aware of its hidden virtues: it turns out at the IMS can collect a number of other useful devices. TDA2030A chip is a 18 W Hi-Fi class AB power amplifier or a driver for UNCH capacity of up to 35 W (with strong external transistor) . It provides high output current, has a small harmonic and intermodulation distortion, wide bandwidth reinforced signal, a very low level of own noise, built protection against short circuits output, an automatic system for limiting the power dissipation, holding a working point of output transistors IMS in a safe area. This chip implemented in the shell Pentawatt and has a 5 findings. At first, a brief look at several standard charts IMS application - bass amplifiers. The model scheme to include TDA2030A shown in Figure 1.

The model scheme to include TDA2030A

This chip is included on the scheme neinvertiruyuschego amplifier. Gain is determined by the ratio of resistance resistors R2 and R3, forming a chain of OOS. It is calculated by the formula Gv = 1 + R3/R2 and can be easily changed by selecting the resistance of a resistor. Usually this is done through the resistor R2. As can be seen from the formula, reducing resistance of the resistance increasing the gain (sensitivity) UNCH. Capacity capacitor C2 light of the fact that its capacitance Hs = 1 / 2? FS at a lower operating frequency was lower than R2 for at least 5 times. In this case, at a frequency of 40 Hz Hs 2 = 1 / 6, 28 * 40 * 47 * 10 -6 = 85 ohms. Input resistance is determined by the resistors R1. As VD1, VD2 can use any silicon diodes with a current I OL 0.5 ... 1 A and U OBR more than 100, for example KD209, KD226, 1N4007. Hook-IMS in the case of a unipolar power source is illustrated in Figure 2.

Divisor R1R2 and resistor R3 form a chain of shifting to get at the outlet of IMS (conclusion 4) voltage equal to half the supply. This is necessary to strengthen both symmetrical poluvoln input. The parameters of this scheme at Vs = +36 V correspond to the scheme shown in Figure 1, when the power source of ± 18 V. Example of chips as a driver for UNCH with powerful external transistor is shown on Fig.3.

When Vs = ± 18 V at 4 ohm load amplifier power 35 Watts. In the food chain IMS includes resistors R3 and R4, a drop which is opening for transistors VT1 and VT2, respectively. In a small output (input voltage) current consumed IMS, low and the voltage drop on resistor R3 and R4 not enough to open the transistors VT1 and VT2. As the input voltage increases output and consumption current of IMS. In pursuing its value 0.3 ... 0.4 A voltage drop on resistor R3 and R4 will be 0.45 ... 0.6 V. begin to open transistors VT1 and VT2, while they will be included alongside the internal transistors IMS. As VT1 and VT2 can use any pair of complementary transistors respective capacities, for example KT818, KT819. Square scheme incorporating IMS is illustrated in Figure 4.

The signal from a commercial IMS DA1 via divider R6R8 at inverting input DA2, which provides chips in the opposite. At the same time increasing the voltage at the load and, consequently, increased power output. When Vs = ± 16 V at 4 ohm load power output reaches 32 Watts. For fans of the two-, three-UNCH this IMS - an ideal solution, because it can directly collect active LPF and HPF. The scheme of three-UNCH shown on Fig.5.

Low channel (NCH) is made on the scheme with powerful output transistors. At the entrance IMS DA1 included LPF R3C4, R4C5, the first link LPF R3C4 included in the chain of OOS amplifier. Such designs allows simple control (without increasing the number of links) get high enough slope recession ACHH filter. Medium (SCH) and high-frequency (HF) channel amplifier assembled on a model scheme for IMS DA2 and DA3 respectively. At the entrance SCH channel includes FHP C12R13, C13R14 and LPF R11C14, R12C15, which together provide the bandwidth of 300 ... 5000 Hz. The filter frequency channel assembled in the cell C20R19, C21R20. The cutoff frequency of each link, or LPF HPF can be calculated by the formula f = 160/RC, where the frequency f expressed in Hz, R - in kiloohm, S - in mikrofarad. These examples do not exhaust the possible application of IMC TDA2030A as a bass amplifier. For example, instead of feeding dvuhpolyarnogo Products (Fig.3, 4), you can use a unipolar power. To do this, minus the power source should zazemlit at neinvertiruyuschy (output 1) input file offset, as shown in Figure 2 (elements R1-R3 and S2). Finally, the output IMS between 4 and load the conclusion should include electrolytic capacitor, a blokirovochnye capacitors on the chain-Vs from the scheme should be deleted.

TDA2030A IMS represents nothing more than an operational amplifier with a powerful weekend cascade and a very good performance. Based on this, have been designed and tested with several non-standard inclusion. Some schemes has been tested "live" on the breadboard, some - modeled in the Electronic Workbench.

Powerful repeater signal.

The signal at the output device Fig.6 repeats in shape and amplitude of the input, but has great power, that is scheme can work at low pressures. Repeater can be used, for example, umoschneniya power supplies, increasing the output of low-frequency generator (so you can immediately feel the head speaker or acoustic systems). The band working frequency repeater is linear from dc to 0.5 ... 1 MHz, more than enough for the generator NCH.

Umoschnenie power sources.

This chip is included as a repeater signal, output voltage (output 4) is the input (output 1), and the output current can reach values of 3.5 A. Thanks to the built-protection scheme is not afraid of short circuits in the load. The stability of output voltage stability is determined by reference, that is stabilitrona VD1 Fig.7 and integral stabilizer DA1 Fig.8. Naturally, the pattern shown in Fig.7 and Fig.8, you can collect stabilizers and other stress, just need to keep in mind that the total (full) power dissipated by the chip should not exceed 20 Watts. For example, you need to build a stabilizer at 12 V and current 3 A. There is a ready source of food (transformer, rectifier and filter capacitor), which gives U IP = 22 V, with the necessary current load. Then on the chip occurs voltage drop U IMS IP = U - U VYH = 22 -12 V = 10V and a current load 3 A dissipated power reaches values of R = U RAS IMS * I * N = 10B = 3A W 30, that exceeds the maximum value for TDA2030A. The maximum permissible voltage drop in the IMS can be calculated using the formula:

U IMS = R RAS.MAH / I N. In our example, U IMS = 20 W / 3 A = 6.6 V, thus the maximum voltage rectifier must be U = U new IP + U IMS = 12V + 6.6 V = 18.6 B. The number of turns of the transformer secondary windings will diminish. Resistance ballast resistor R1 in the pattern shown in Fig.7, you can count on the formula:
R1 = (U IP - U CT) / I ST, where U ST and ST I - respectively voltage and current stabilization stabilitrona. The limits of the current stabilization can be found in the handbook, in practice for low stabilitronov his choosing within 7 ... 15 mA (typically 10 mA). If the current in the above formula to express in milliampere, the amount of resistance to get in kiloomah.

A simple laboratory power supply.

By varying the voltage at the entrance of IMS using potentiometer R1, produced a smooth adjustable output voltage. The maximum current, given a chip, depending on the output voltage and restricted the same maximum dissipated power at IMS. Calculate it could be the formula:

I MAX = R RAS.MAH / U IMS

For example, if the output voltage U billed VYH = 6, the chip is happening voltage drop U IMS IP = U - U VYH = 36 - 6 = 30, therefore, the maximum current is I MAX = 20 W / 30 = 0.66 A. When U VYH = 30 V maximum current can reach a maximum of 3.5 A, as well as a drop in the IMS slightly (6).

Stabilized laboratory power supply.

Source stabilized reference voltage - chip DA1 - powered by Parametric stabilizer at 15, collected at stabilitrone VD1 and resistor R1. Should IMS nurture DA1 directly from the source +36 V, it can be easily damaged (the maximum input voltage for IMS 7805 is 35 V). IMS DA2 included on the scheme neinvertiruyuschego amplifier gain which is defined as 1 + R4/R2 and is 6. Consequently, the output voltage adjustment potentiometer R3 can take the value from nearly zero to 5 * 6 = 30 V. With regard to the maximum output current, for this scheme true all this for a simple laboratory power supply (Fig.9). If it is less regulated output voltage (for example, from 0 to 20 in the U IP = 24), elements VD1, S1 can be excluded from the scheme, but instead R1 set the jumper. If necessary, the maximum output voltage can change the selection of resistance resistor R2 and R4.

An adjustable current source.

At the entrance inverting IMS DA2 (concludes 2), thanks to the OOS through resistance load, supported by tension U BX. As can be seen from the formula, load current does not depend on the resistance loads (of course, up to certain limits, due to end-voltage IMS). Therefore, changing the U BX from zero to 5 V using potentiometer R1, with the fixed value of resistance R4 = 10 ohms, can be controlled through the current strain of 0 ... 0.5 A. The device can be used for charging batteries and electroplating elements. Charging current stable throughout the cycle of charging and does not depend on the amount of discharge of the battery or the instability of the supply network. The maximum charging current, displayed using potentiometer R1, you can change, increasing or decreasing resistance resistor R4. For example, when R4 = 20 ohms, it has a value of 250 mA, and with R4 = 2 ohms reaches 2.5 A (see formula above). For the scheme are fair restrictions on the maximum output current, both for stabilizing voltage circuits. Another application of a powerful inhibitor of current - measuring small resistance through voltmetra on a linear scale. Indeed, if the value of a current exhibit, for example, 1 A, is connected to the scheme resistor 3 ohms resistance, Ohm's law to get the voltage drop its U = l * R = l A * 3 ohms = 3 V, and connecting, say, resistor resistance 7.5 ohms, we get a drop 7.5 V. Of course, this current can be measured only powerful Low resistors (3 V at 1 A - is 3 W, 7.5 V * 1 A = 7.5 W) But you can reduce the measured current and use the voltmeter to the lower limit of measurement.

A powerful generator of rectangular pulses.

Plans powerful generator of rectangular pulses are shown in Fig.12 (with bipolar diet) and Fig.13 (with unipolar meals). Plans can be used, for example, the device alarm. This chip includes a Schmitt trigger, and the whole scheme is a classic relaxation RC-oscillator. Consider the job figures. 12. Let's assume that at the time of the power output of IMS is moving towards a positive level of saturation (U VYH = + U IP). Capacitor C1 begins to be charged through resistor R3 with a constant time-Cl R3. When the voltage on C1 will reach half a positive voltage power source (+ U IP / 2), IMS DA1 switch to a negative saturation (U VYH =-U IP). Capacitor C1 will discharged through resistor R3 at the same time Cl R3 to the voltage (-U IP / 2) when the IMS again switches into a positive state of saturation. The cycle will be repeated with a 2,2 C1R3, regardless of the power supply voltages. Frequency pulses can count on the formula:

f = l / 2,2 * R3Cl. If the resistance to express kiloomah and capacity in mikrofaradah, the frequency will get in kilohertz.

A powerful low-frequency generator harmonic oscillations.

An electric circuit powerful low-frequency generator harmonic oscillations is shown in Fig.14. The generator gathered on a bridge Wines, formed by elements of DA1 and S1, R2, C2, R4, providing the necessary phase shift in the chain of PIC. Gain voltage IMS, with the same values of Cl, C2 and R2, R4 should be exactly equal to 3. With less importance Ku fluctuations fade, and an increased - dramatically increasing distortion of the output signal. Gain voltage determined resistance filament bulbs ELI, EL2 and resistors Rl, R3 and is Ky = R3 / Rl + R EL1, 2. Lamps ELI, EL2 serve as elements with variable resistance in the chain of OOS. When increasing the output voltage resistance of the filament lamp by heating increases, causing a decrease gain DA1. Thus, stabilizing the amplitude of the output signal generator, and minimize distortions of form sinusoidalnogo signal. Minimum distortion at the maximum possible output amplitude sought through podstroechnogo resistor R1. To exclude the impact of stress on the frequency and amplitude of the output signal at the output of the generator includes a chain R5C3, frequency oscillations generated can be determined by the formula:
f = 1/2piRC. Generator can be used, for example, in the repair and inspection heads speaker or speakers.

In conclusion, the chips must be installed on the radiator with ohlazhdaemoy surface area of not less than 200 cm 2. When razvodke agents of the printed circuit board for the amplifier must be Bass track to "earth" tires for input, as well as the power source and output summed with the different parties (conductors to these terminals should not be a continuation of one another, and assembled together to form stars "). This is necessary to minimize the background of the AC and eliminate possible self-amplifier with output power close to the maximum.

By the magazine Радіоаматор

Concise FET Audio Amplifiers

FET voltage control devices for its high-frequency characteristics, and as a tube amplifier tube-like sound. I have produced a partial negative feedback FET amplifier, the actual effect of listening is not satisfactory. Designed as a negative feedback loop amplifier, the sweet sounds markedly effective, treble detail, the intensity of the full bass, outstanding results.

Principles:

Circuit principle as shown below, for a typical OCL amp. IC1-A for the input stage; BG1, BG2 incentive for the class; BG3, BG4 is composed of complementary MOSFET output level; IC1-B for the DC Circuit 0.1 Servo.

IC1-A voltage from the amplification, because of limited supply voltage, the level output signal range of not more than ± 15V, if the after-use of the radio output, output power too small.

The circuit is designed to play Yun-simple, excellent performance characteristics, but also meet the appropriate output power. Therefore, the power circuit from the two groups (± 15V, ± 36V) power supply, regulators ± 15V supply Yun-use, ± 36V supply after-use. BG1, BG2 for a total emitter circuit, R8, R9 for the negative feedback resistor, R1, R5, D1, D2, R18, R19 for BG1, BG2 provide a stable DC bias, in order to ensure its on-state, in addition to the same level Voltage amplification, the more important is to achieve a different power supply circuit signal coupling. FET voltage amplifier is the case, although the current drive did not specifically require, but to consider FET input capacitance of the characteristics of high-frequency.

Therefore, the resistance of the drive signal should be small enough. BG3, BG4 signal the driver were taken from the BG2, BG1 load R4, R3. BG1, BG2 the collector load resistance was divided into two sections, as the source of FET gate drive voltage should be no larger than 20 volts. BG3, BG4 for MOSFET on the composition of the drain output stage. R11, R12 for the source of negative feedback resistor. IC1-B's role is stable at the end of the mid-point of DC voltage, in order to achieve the DC amplifier. R13, R7 is a negative feedback loop resistance. R20, R21 to prevent the MOS high frequency of self-designed; C2, R16 role is to prevent self-circuit.

Second, installation and commissioning:

IC1, BG1 ~ BG4 principle of choice as shown in the device can also be optional parameters similar to the device. BG1, BG2 request β value greater than 100, Vceo greater than 100 V, Icm more than 1 A, Pcm more than 10 W; BG3, BG4 parameters for the VDSS = 140V; ID = 8A; PD = 100W. To the extent possible, all of the complementary pair. Resistance R2, R3, R4, R10, R16 optional 1 W Metal Film, R11, R12 optional 3 W resistance, resistance to other optional 1 / 4 W Wuhuan resistance. R20, R21 should be installed as close as possible to the MOS gate. You Zhipin capacitor selection.

Static accurate detection, connect the power to detect whether the midpoint voltage to zero volts; measurement BG3, BG4 gate-source voltage, usually about 1 V. To be pure A Larger, more R18, R19 resistance. To connect all the normal speakers, audio test machine.


Stereo 60W+60W RMS Power Amplifier using LM4780

Features
60W per channel into 8 ohms load at less than 0.5% THD+N from 20Hz-20KHz
Signal-to-Noise Ratio >= 97dB
Quiet fade-in/out mute mode
Click and Pop supression
SPiKe protection
Compact Stereo

Design Objectives

The idea is to design a compact power amplifier system. The design should be simple and cost effective while maintaining the sound quality at optimal performance. It should be built modular so that the same PCBs can be simply cascaded to provide additonal 4, 6 or more output channels. The selection of the components to be integrated into the final design are carefully picked to maintain the THD+N performance.

System Operation & Description
The LM4780 power stereo amplifier is configured as a non-inverting amplifier which has to a gain of 20V/V which is high enough to maintain stability and not too high untill increasing the noise and THD+N performance. The input is taken from the RCA jack which then feed to two high quality 1uF metallized polyester film capacifor with 100V rating. The power output socket provides easy push-release terminals for speaker cable connections (see snap-shots picture below).

Schematic diagram taken from NS referance PCB design schematic
Schematic diagram taken from NS referance PCB design schematic

The schematic diagram is taken straight out from the National Semiconductor's referance PCB design schematic. However I have omitted the muting switch and replaced it with the soft start circuit, as explaned in the LM4780 datasheet. I have also added the L//R network (L=0.7uH, R=10 ohms 2W) at both the outputs.


PCB Drawing (Not in Scale). The LM4870 power amp and the PSU (drawing left)
PCB Drawing (Not in Scale). The LM4870 power amp and the PSU (drawing left)

Circuit Description
Two 10,000uF capacitor provides sufficient buffer for the amplifier to pump and handles the bass response without distorting the output signal. A mica-sheet with heat sink compound is used in between the LM4780 and heatsink ensures proper heat transfer. A T0-3 type mica-sheet is being used because it is widely available. The heatsink is mounted vertically with its fins as shown on the snap shots below, allows heat to dissipate naturally, without the need of a cooling fan.

Full view of the power amplifier
Full view of the power amplifier


Angle View
Angle View


Abit closer
Abit closer


Complete side view of the power amplifier
Complete side view of the power amplifier


Top view - A 125VA 24V-0-24V transformer is used
Top view - A 125VA 24V-0-24V transformer is used


Two 10,000uF capacitor ensures there is enough buffer
Two 10,000uF capacitor ensures there is enough buffer



Upgrades & Comments
A speaker protection circuit which detects faulty DC level at speaker terminals should be added to ensure speaker protection. This amplifier can be linked with the stereo pre-amplifier project for full-functional amplifier systems with digital tone and volume control. You can add an additional mono-channel 120W RMS power amplifier to drive a subwoofer, giving a 2.1 channel amplifier system.

Basically the output sound quality, channel cross-talk, stability, channel gain matching are much much better than those constructed using discrete components. The overall PCB size has been reduced as more function has been integrated into the LM4780 chip. The basic protection features are also integrated, ensures total protection of the chip.

With its high PSRR rating, a simple power supply design can be constructed thus reducing cost of components used in designing a well regulated power supply.

Related Design Files & Materials
LM4780 Datasheet

Low-power amplifier APA4800 / APA480

Low-power amplifier APA4800 / APA480

Anpec APA4800/APA4801 is produced by SO-8 or DIP-8 Plastic Class A and B stereo audio amplifier IC, mainly used in portable digital audio, PC microphone and amplifier, and so on.
APA4800 drive with the stereo 290 mW, 8 Ω audio amplifier circuit as shown in Figure 1.
APA4800 built-in amplifier A and B, with its terminal phase (1 NA +, 1NB +) connected together and put 1 / 2 VDD reference voltage (VRFE). Power supply voltage range of 3 ~ 7 V, no-load supply current to 205 mA (VDD = 5V). Two input VINA, VINB the CiA, RiA and CiB, RiB separately applied to the amplifier A and B RP-INA-input and INB-, ① ⑦ feet and two feet of output respectively by the COA and capacitive coupling COB RLA applied to the load and RLB. Link IC ① ② feet and legs and feet and ⑥ ⑦ feet of the CCA, RCA, and CCB, RCB A and B respectively, the frequency compensation components. Signal to noise ratio (S / N) of 100 dB, total harmonic distortion plus noise and signal ratio [(THD + N) / S] is 0.15% (typical) slew rate to 5 V / μ s, power supply ripple suppression Than (PSRR) of 55 dB, working temperature range of -40 ~ +85 ℃.

APA4801 used as a driver of 280 mW, 8 Ω stereo audio amplifier circuit shown in Figure 2.
APA4800 compared with, APA4801 integrated resistor divider, eliminating the external resistance. At the same time, APA4801 also has excellent noise-free adjustment of the function, and flexible regulation and noise-free switching Kata without sound. IC's Mute feet (② feet) function is to control the importation of chips disability (disable). When Mute feet for the "H", the speaker movements for the "L", so that voices continue to weaken (Mute on). IC in the VDD = 5V and contained no power under the current IDD = 2.5mA, the standby current is only 150 μ A, Mute pin input voltage to 0.8 V, no noise attenuation adjustment (ATT) to 75 dB, (THD + N) S = 0. 1%, S / N = 100dB, slew rate to 5 V / μ s. In 10% (THD + N) into 8 Ω load on the output power of 280 mW; When RL = 16 Ω, the output power is 160 mW. Power supply ripple suppression (PSRR) = 76dB.
Amplifier input capacitance (CiA, CiB) circuit of the numerical impact of the low-frequency performance. If Ci and IC 130 k Ω resistance in the form of high-pass filter (HPF) inflection point for the frequency fc, while Ci = 1 / (2 π × 130k Ω × fC). In this circuit, Ci optional 1 μ F of the Ceramic capacitor.

Electronics Now

Your Ad Here
User Agreement

The creator of THIS PAGE or the ISP(s) hosting any content on this site take NO responsibility for the way you use the information provided on this site. These circuits here are for educational purposes only and SHOULD BE VIEWED ONLY. If you download any files to view them, you are agreeing to delete them within a 24 hour period. If you are affiliated with any government, or ANTI-Piracy group or any other related group or were formally a worker of one you CANNOT enter this web site, cannot access any of its files and you cannot view any of the HTML files. All the objects on this site are PRIVATE property and are meant for previewing only. If you enter this site without following these agreements you are not agreeing to these terms and you are violating code 431.322.12 of the Internet Privacy Act signed by Bill Clinton in 1995 and that means that you CANNOT threaten our ISP(s) or any person(s) or company storing these files, cannot prosecute any person(s) affiliated with this page which includes family, friends or individuals who run or enter this web site. IF YOU DO NOT AGREE TO THESE TERMS THEN LEAVE.

Disclaimer

All files are found using legitimate search engine techniques. This site does not and will not condone hacking into sites to create the links it list. We will and do assume that all links found on the search engines we use are obtained in a legal manner and the webmasters are aware of the links listed on the search engines. If you find a URL that belongs to you, and you did not realize that it was "open to the public", please use the report button to notify the blogmaster of your request to remove it. This is not an invitation for webblog haters to spam with requests to remove content they feel that is objectionable and or unacceptable. Proof of URL ownership is required.
NOTICE: This Blog Has Already Been Reviewed And Accepted By Blogger.com

© 2013. Another Electronics Circuit Schematics. Powered by Blogger.
 

blogger templates | Make Money Online