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PostPosted: 30 Nov 2016, 19:08 
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Hi Guys! Its been quite a number of years since I've been around. I started selling some kits locally at our Electronics Parts Outlet in Houston. I put a lot of work into the manuals and thought I would post them. They might be handy to explain to someone not only how to put this part here and solder it there but to explain how the amps work and why they work as well as why and how we choose certain components. I'll post all three but probably the other two tomorrow or the next day. Here is the Class AB 15 or so watt chip amp.
There are several guys smarter than me here so if you have a correction I would love to know.
I'll try to post the whole thing in several posts.


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PostPosted: 30 Nov 2016, 19:09 
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TDA2050 HiFi Audio Power Amplifier


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PostPosted: 30 Nov 2016, 19:10 
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The above circuit is a non-inverting power opamp with a gain of 34 times the input signal. This amplifier should give you between 20 and 25 watts if you are supplying it with the maximum power supply voltage of +/-25V. For most intents and purposes please expect closer to 15Watts of output power.
So let’s discuss the circuit. This one is pretty simple really as it IS just an opamp that can output many watts instead of milliwatts. First we’ll talk about a non-inverting opamp and how to set the gain, then we will move on to the various filters around the circuit.
Non-inverting means that the signal comes into the opamp and goes out of the opamp without changing phase. An inverting circuit (not this circuit) basically flips the signal on its head by changing the phase angle of the signal by 180 degrees.
Gain is set by the two resistors around the opamp. The 23k2 resistor that goes from the output to the inverting input (-) is called the Feedback Resistor, or Rf. The 680R resistor is the inverting input resistor and this resistor helps set the gain with the feedback resistor, so let’s call it Rfg. Gain is calculated, in non-inverting amplifiers, by the equation Gain=(Rfg+Rf)/Rfg. We can simplify that to Gain=1+(Rf/Rfg). In this circuit Gain=1+(23200/680)=1+(34.1)=35. This is a LOT of gain. If you were to feed it 1V it would try to spit out 35V and be unable to because the output signal would require a higher voltage power supply to support the higher output voltage. So, if your amplifier is way to loud at low volume settings you can change this gain equation easily by varying either Rf or Rfg. I suggest changing Rfg to 1k to start with and this will result in a gain of 24.2. The absolute minimum gain should be 10. If the chip/opamp gets hot then increase gain until the chip cools down (stops oscillating).
Lets start exploring the components in the above schematic from the left to the right:
The 1M resistor. This is a 1 million ohm resistor, or, 1 Megohm, or 1M. The value is not very important but it is important that its not a particularly low resistance resistor. Something high enough that it does not have much effect on the value of the 23k2 resistor to ground following it. These two are in parallel to each other and we don’t want the 23k2 to be much different than 23k2 when we put the 1M in parallel with it. Note, that its only in parallel when the signal is AC, and they are isolated from each other when the signal is DC which will be explained in the next paragraph. These two in parallel equal 22,700 ohms, or 22k7. A 2.2% difference. If 1M were actually 100,000, or 100k, the parallel value would be 18k8 so this is starting to make a significant difference, but you can see where in some cases exact values are not very important. What does the 1M resistor do? It simply drains stored power away from the capacitor next in line when power is off so that when we turn the amp on the power in the cap isn’t released all at once into the amp causing a loud pop in our speakers. That’s it. No big deal. Just about any value between 100k and 1M is okay. Higher than 1M might take a long time to drain off the capacitors stored energy so if we turned it on again a few minutes later we might actually get that loud pop.
The 1uf capacitor after the 1M resistor is to block DC. Via this cap AC is coupled (connected) to the input and DC is decoupled (disconnected) from the input. Capacitors store energy and allow frequency variations to pass through. They don’t allow DC, no frequency variation, to pass through but they do store that DC, thus the 1M drain resistor. Generally this cap is referred to as a DC blocking cap or an AC coupling cap. They mean the same thing.
The 220pf cap is only .00022uf. We would need one million picofarads to equal just one microfarad. Remember how capacitors allow AC frequencies to pass through them? Well the frequencies a cap allows or blocks depend on the value of the capacitor. There are other factors but we’ll not get that deep into it now. So what frequency will it allow to pass? Most AM and FM frequencies will see this capacitor as a great way to get to ground which is where all frequencies want to go as well as DC currents. All electricity wants to go to a place of lower potential, lower voltage, than it currently is at. So since these EMI (electro magnetic interference) and RFI (radio frequency interference) can find their way into your signal wires they will be INDUCED into your signal wires and will become an AC voltage transferred by wire rather than by air. Wire has a much lower resistance so the frequencies just love to travel by wire, just as lightning would much rather get to ground via a tree, rather than through the air. This induced signal will get to the 220pf cap and have a choice to get to ground through the cap or through the 23k2 resistor or through the positive input of the opamp or though the feedback resistor and then either the speaker or the Rfg. The signal wants to find the easiest way to get to ground because ground has a lower potential than the signal. The cap presents almost a short, close to zero ohm, impedance (resistance to AC) to high frequencies. Instead of a 23k2 resistor, a 500k input impedance of the opamp, or (23k2+680R) of the feedback path, or (23k2+8ohms) of feedback to speaker to ground the signal has an easy choice to make and shoots to ground via the cap rather than present itself to the opamp to be amplified. Voila! We have an output signal with less noise, more HiFi!
The 23k2 resistor to ground does two jobs. It presents an input impedance to the input signal. This is, for the signals we want to amplify, the lowest impedance path to ground. Some of the signal will go to ground via this resistor but it’s a very small amount and its not signal lost its signal amplitude lost. This simply means that a 1V signal might see this resistor and allow a few mV, millivolts, of signal to go through this resistor rather than be amplified. Still the integrity of the signal is kept. Every single variation of the signal still makes it to the amp, just slightly attenuated, but then gets amplified 30 some times so we never care about the lost signal at all. We’ll talk for a moment about this resistor’s other job in the next paragraph.
The opamp itself wants to keep the difference between the two inputs equal to zero. It has no control over this if it’s output is not able to have an effect on one of the opamp’s inputs. The feedback loop goes from output to inverting input via the Rf, feedback resistor. So, the opamp could output a copy of the input signal to the inverting input via the Rf resistor. If it does this then the positive input (non-inverting) is getting, lets say a positive 1V AC signal from your CD player, and the output of the opamp is replicating this signal and routing it to the negative input (inverting) so we have +1V at positive and +1V at negative. The negative input inverts anything at its input therefore making the +1V a -1V and making the sum of the two inputs equal to zero. So, when there is no signal at the inputs at all the opamp won’t know what to do. If we have the 23k2 resistor going from noninverting input to ground, which is tied to the inverting input via the 680R resistor then we basically have a 23,880 ohm loop between the two inputs. In other words they see each other as their own signal and thus are already at a zero difference between the two allowing there to be nothing at all on the output. If we had not allowed the noninverting input to see ground, or the inverting input, then the opamp would get confused and begin to oscillate.

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PostPosted: 30 Nov 2016, 19:13 
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Time to talk about Rf and Rfg. Lets look at them first without the rest of the circuit. Lets view the output of the opamp as the input to Rf, the meeting point between Rf and Rfg as the output of a circuit composed only of these two resistors and the bottom of Rfg as a ground reference then we can see where really Rf and Rfg create an attenuator. An attenuator is often also called a voltage divider. Let’s look up “voltage divider” on WikiPedia and you will see what I am talking about. So a voltage divider does just that, it divides voltage. You put X volts into the input and depending on the value of the two resistors you get Y voltage out. How do we figure out what Y volts value would be? Lets look at two things. The schematic and the equation (both are from Wikipedia's page on Voltage Dividers):


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PostPosted: 30 Nov 2016, 19:14 
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So we can see where if Vin was 10V and Z1 was 10k and Z2 was 1k then Vout = (1k/(10k+1k))*Vin. So Vout = (1k/11k)*Vin. So, Vout = .0909*10 or Vout = .909V.

Okay so now lets insert this voltage divider into our schematic where Vin is the voltage output from the opamp, Z1 is Rf, Vout goes to the inverting input and Z2 is Rfg which is still tied to ground. Pretty neat but what’s that do? Well from our understanding of how the output tries to effect the inputs to equal zero then we know that if we apply voltage to the non inverting input a larger copy of that voltage will come out of the output. This output voltage will enter the voltage divider and the voltage divider will send a smaller copy of the opamp’s output voltage to the inverting input. The opamp will keep increasing the value of its output voltage until the output voltage of the opamp is high enough that the output voltage of the voltage divider going to the inverting input of the opamp is equal to the input voltage at the non inverting input of the opamp. This is feedback.

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PostPosted: 30 Nov 2016, 19:15 
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The 2R2 resistor and .47uf capacitor hanging off of the output going to ground create a high pass filter. This means that high frequencies will pass through it while lower frequencies won’t. When the opamp is presented with a light load (read high impedance) it has a tendency to oscillate. Loading the opamp, giving it some work to do, tames the tendency to oscillate. We don’t want to load it down at lower frequencies (lower being the frequencies in our hearing range) as it already has a decent load in the speaker. However, the inductance and capacitance of both the speaker wires and the speaker itself can create a high impedance at high frequencies. This means the amp has a light load at high frequencies and would love to oscillate. If we add a filter at the output that looks like a 2.2ohm load at those higher frequencies then we can keep the amp behaving rather than oscillating. If we google “high pass filter calculator” we can find several pages to plug our numbers (2R2 and .47uf) and we will find that the capacitor becomes transparent to frequencies above 153kHz so the amp, at those frequencies, sees a 2R2 resistor and would love to dump those frequencies to the resistor rather than run them in circles via the feedback loop, creating an oscillation.
The 220uf capacitors and .33uf capacitors decouple AC frequencies from entering the opamp at the power supply pins. While the opamp rejects power supply ripple at 45dB (basically noise from power supply ripple is attenuated by 45dB) we would still like to help it out by creating another high pass filter. You might be wondering where is the resistor in this high pass filter? Well its inherent to the capacitors. The caps have what is called ESR, or equivalent series resistance. So, while the capacitor will try to allow all frequencies to pass through it, some will make it through easier than others because of both the value of the capacitance and the value of the ESR. We have 3 capacitors in parallel on each power supply leg of the opamp. Each capacitor works independently and cooperatively from and with the other two capacitors. This small amount of capacitance will do a good job decoupling most frequencies from entering the opamp but they will not do much energy storage to help with extended bass notes.
The 220uf caps included in the kit are marked 25V. We need a 25% safety margin. This means that the DC voltage coming into the amplifier should be multiplied by 1.25 to come up with the value of capacitor voltage rating that is a minimum requirement. We know the amplifier can only handle a maximum of =/-25V and really shouldn’t have more than +/-22V. So if we start with the voltage of the caps, 25V, and divide by 1.25 we get 20V as the max DC voltage that these caps can handle. Since we also know that the AC out of the transformer goes through the rectifier bridge and is multiplied by 1.414 then we can divide our 20V by 1.414 to find out what is the max AC voltage that a power supply should have as its input voltage so that we end up getting only 20V coming to our amplifier. Dividing 20VDC by 1.414 gives us 14.14VAC as our maximum AC input to an AC to DC power supply. You can purchase a Linear AC to DC supply from EPO and you can buy a 24VAC center tapped transformer from them that will give you a 12V difference between its secondaries and its center tap. This would do nicely, giving you about +/-17VDC which is a good, safe voltage to put into the amp. You could look for a 28VAC center tapped transformer or a 14VAC dual secondary transformer to use but of course the transformer from EPO is quite easy to find and a reasonable price.
If you would like to increase the impact of the bass from your amp you will need a robust power supply with a large amount of capacitance available for the amplifier to draw instantaneous current from. My suggestion would be in the realm of 2200uf to 4700uf. There are diminishing returns to additional capacitance, however it couldn’t hurt.

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PostPosted: 30 Nov 2016, 19:16 
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Assembling the Kit
I will assume you know how to solder. It is a prerequisite for building this kit and really any kits I sell.
Begin with the smallest components first. All resistors (except for the 2R2) can be inserted and then soldered. I like to insert the resistors and bend the legs out a bit so they don’t fall back out.
Next solder in the film capacitors followed by the terminal blocks. Make sure all terminal blocks face the outside of the board.
Solder in place all electrolytics and then place and solder the opamp and 2R2 resistor. The 2R2 only needs one leg bent so that it can stand up vertically on the board.
NonPolar capacitors do not have negative and positive leads. Just pop them in their holes and solder. The 220uf capacitors are polarized and their short leg should point to the small filled in portion of silkscreen circle where they go. Each of these circles for the 220uf have a little plus sign near the top left of each circle. This is the side that the long leg of the cap goes to.
You MUST use the nylon shoulder washer and the T0-220 plastic insulating sheet when mounting the TDA2050 to the heatsink. Slather a little heatsink thermal paste (not included) onto the TDA2050 back. Then remove the excess so there is a thin coating. Do this also on the heatsink where the TDA will be. Put the washer in the hole in the tab with the washer collar on the front side. Place a bolt through the washer. Place the thermal insulating sheet on the back of the TDA (bolt also goes through insulating sheet) and screw the bolt into the heatsink. Bolt should be firmly tightened but not torqued down. The bolt must not make contact with the tab and the tab must not make contact with the heasink. This is why we have the insulating washer and insulating sheet. If contact is made the TDA will be instantly destroyed on power up.
None of these recommendations (other than insulating) are absolutely the way it must be done. They will just make assembly a bit easier.
Speaker wire should be a minimum of 20AWG. 18AWG or 16AWG are even better but there is no sense going to something like 12AWG.

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PostPosted: 30 Nov 2016, 19:17 
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I have to admit this portion needs expounding on but I'm not sure how to do so without typing another thousand words.

Testing
There are a few different ways you could test to see if you’ve completed the build correctly. Its going to be pretty hard to do this incorrectly so I don’t see you having any trouble. However, in the interest of safety, my safety, I will first absolve myself of any responsibility for your safety. Anything you do here is on your own and best judgement. I am simply giving my opinion and its up to you to either already know, or research, whether my description of the build, testing, and use of this device should be followed or if you even have the capability to proceed without hurting or killing yourself. You sure could kill yourself with the 120VAC that the input of your power supply will require and if you put any part of your body somehow in electrical contact with the positive and negative rail it will hurt quite a bit and I suppose its possible this could also kill you. Consider yourself warned and proceed if you agree to NOT hold me responsible for your inept or perfect build and any damages to yourself or anything that you connect to this device.
Really you should wait a day after your build and then come back and review your assembly. Any mistakes I make I can usually find if I leave it alone for a while and come back with a fresh mind and eyes. Backwards capacitors really will explode and really could take an eye out. So, review after a rest.
Test, with a multimeter, for resistance between the TDA bolt and the TDA tab while the TDA is mounted to the heatsink. If there is resistance then you have a problem with either the shoulder washer or the insulating sheet. Or, somehow one of the legs of the TDA is touching the heatsink.
You can test the amp with an easy test called the “dim bulb test.” It will show you if you have any shorts and can be used on many different projects to test. Google it up and use your best judgement. You can also use a variac. A variable voltage transformer. Of course this dim bulb tester and/or variac would supply your power supply with AC. Your power supply must supply the amplifier board with dual polarity DC. You can use very low voltages if you need to but I suggest, for best sound quality, to stay between +/-12VDC and +/-22VDC. +/-25VDC is the max and +/-4.5V is the minimum but I don’t recommend either extreme. When we say +/-12V, etc.. what we mean is you will need a supply that gives a positive 12VDC and a negative 12VDC. This must have a 0V point on the supply also. Maybe a more precise and detailed way to say it would be +12V/0V/-12V. I have used batteries to power this board but if plus and minus are not connected at the same exact time the chip will fail. Better to use a transformer into a AC to DC power supply and put an on/off switch on the primary of the transformer so that the whole circuit turns on at exactly the same time. At the end of the manual you will find how to hook up a power supply and transformer, both available from EPO as well as a diagram showing how to hook the same power supply up to the TDA board and how to hook up signals to and from the TDA board.

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PostPosted: 30 Nov 2016, 19:18 
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Parts List Per Board
1x TDA2050 – Amplifier
2x 2 position Terminal Block
1x 3 position Terminal Block
1x 220pf NonPolar Film Capacitor – Red Box with WIMA 220/630
1x .47uf NonPolar Film Capacitor
A few kits have a .47uf red resin covered capacitor 6mm wide
Most kits will have a white box marked .47J63
2x .33uf NonPolar Film Capacitor – White with .33J63 marking
1x 22uf 16V NonPolar Electrolytic Capacitor – Metallic Green
4x 220uf 25V Electrolytic Capacitor – Gold with Black Stripe(neg lead)
1x 1Megohm (really 976k) 1/4W Metal Film Resistor – Brown 9763F
1x 680 Ohm 1/4W Metal Film Resistor – Blue 2322
2x 23k2 Ohm 1/4W Metal Film Resistor – Blue 6800G
1x 2.2 Ohm 2W Metal Film Resistor – Gray with Red/Red/Gold/Gold stripes OR just Gray with 2.2Ω J

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PostPosted: 30 Nov 2016, 19:20 
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The two following pics show how to connect a power supply kit I sold to EPO to the TDA board. This manual referenced but did not delve into the power supply. I will post PSU info another day.


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