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Thank you! My guess is to reduce the risk of failure due to cheap contacts.
Hi, I am not sure what kind of help you are asking for.
Looking forward. Be careful when you solder. Good luck!
You need two supplies that can deliver at least 12V each. Even if you get the MacBook supply to work, you still need another one, so my recommendation is still to buy two low cost supplies. The 3886 requires at least +-9 V , but at such a low voltage the amp will not be usable in any practical sense.
I am sorry, but I can't help you with the MacBook thing. I suggest that you buy the 12$ power supply at Amazon (link above), strip the cables and use your voltmeter to find "Ground" and "18V" If that works out, buy another one and use those two as the +- 18 V power supply. Or build the amplifier and use whatever you have to provide +-10 - +-12V (four USB chargers will provide +- 10V). Not much power but you will know if the amp works.
No, you certainly do not need +-35 V. The 3886 works from +-9 volts. In the data sheet page 17 fig. 37 (http://www.ti.com/lit/ds/symlink/lm3886.pdf) you can see that you get about 15 W in 4 ohms with a supply voltage of +- 12 V. The easiest way to get power maybe is to buy two laptop power supplies (18-19 V 3-4 A) e.g. https://www.amazon.com/Replacement-Satellite-L875D-S7332-PA3097U-1ACA-PA3714U-1ACA/dp/B07RL5K812/ref=sr_1_3?keywords=laptop+power+supply&qid=1573897066&sr=8-3 (or look in the scrap heap)The you will get nearly 40W in 4ohm output. Good luck!
Sorry, I do not think that the power supply is usable. The Apple Power supplies are maybe be usable. What do the labels say? Outputvoltage? Power? Amps?
The fan sucks air into the housing and forces the cool air to pass between all the thin metal sheets of the heat sink and out thru the four slits under the heat sink. I would not say that it is unnecessary. Whitout fan I would have to have a heat sink outside the housing.
Hi, I would use the non-inverting side (the upper amp) because of the higher input impedance. You an also get higher gain, so that you can plug in you guitar directly. In that case increase the values of the volume pot and the 47k resistor so that you reduce the load of the guitar mics. A stomp box after the guitar will also take care of the load issue. Increase the value of the feedback resistor (132,8k) for higher gain. The power supply must be the same, but you should decide how much output power you want, that decides the voltage and the effect (VA= VoltAmpere) of the transformer. To make it even simpler I would remove the fan and use a big heatsink. Or have a 12 V fan with a separate 12V adapter. I designed my step down and fan control just for the fun of it.Good Luck!
Thank you for your good comments. Good tools for woodwork and a little training is all that is needed (and somewhere to be). Try it. Yes you are of course completely right about the circuit improvement. I think a 4PDT switch is required, although if you just don't use input B when in "bridge" you could always have it connected to the positive input. I think I will change my amp, I don't like the low input impedance of the inverting input. I made a quick sketch. Note that SW2A must switch between ground and input A.
Haha, I had to look up "scrounged". Thanks a lot!/Håkan
I am really sorry for the oh so late reply. R7/R8 corresponds to e.g. R215 in the photo. It is very difficult to see the colors, but the third marking ought to be gold, which is the 0.1 multiplicator, so my guess is around 1 ohm for each resistor. If the first marking is red, then 2 ohms. Best regard and again - Sorry/Håkan
LM3886 Power Amplifier (dual/bridge)View Instructable »
Dear Brandon,sorry about the late reply.Since I posted the instructable I replaced the battery jack and soldered the cable directly on the +5 and ground pins. The reason was that the connector was unreliable. So if you do that you only need to get yourself an old USB cable and strip the red and black wires and solder them.RegardsHåkan
Hi JoshuaThe amplifier is in my summer cottage, so I can not measure the value, but on the photo it looks like the value could be 2,7 ohm, which seems reasonable to me, since the function is just to reduce the load/increase the impedance of the small right and left channel speakers. The value is not critical and depending on the impedance of your speakers you could choose to replace the resistor with a wire. The amplifier itself handles overload and short circuit so it is zero risk. Good LuckHåkan
Thank you so much! I was actually surprised myself. The first attempt was an ugly five LED construction with the only purpose of eliminating the need for 230 V AC. When I saw the stars in the ceiling and on the walls I decided to make something that could be used every christmas.
Swedish Christmas Star 2.0View Instructable »
Hi Vinsu,Please notice that my doorbell actually is wireless. Maximum distance from the pushbutton unit to the Bell unit is said to be 100 meters. I am sure that you can find a similar doorbell kit. Good luck!
Power Failure Alarm for Freezer
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I will copy the comment of Kevanf1 - Simple but brilliant, Well done and thank you
Thanks for the nice comment Alex. It made my evening!
Dual-Band Guitar/Bass Compressor
Charging Stand for Mobiles Etc.View Instructable »
Convert a Labtec 2+1 PC Speaker System to TV 3+1 AudioView Instructable »
Thank you Sean! Yes, I was really happy when I had that idea and when I found the software for "mirror converting" the photo. That really made it possible to RE the design to a standard electronics drawing on paper(if that is the English name). It is so time consuming and difficult to look at the board from both sides and then try to draw the connections and the components.
good design, I have the same need for a power load. I har planned to design something like this with a PowerMOS, now I don't need to. Thank you. Good choice of op-amp. Not all can handle inputs down to the negative (ground) rail. I liked your text. It is always interesting to read about design discussions etc. Ambitious - to make a PCB board!
The idea was nice, but the capacitor solution would require additional controls for bass and mid, and the tone control with only one pot that is used now, can not be redesigned for a capacitor solution. So the capacitor goes to the museum. But thanks for the interest anyhow!
Thank you Jfieldcap!But the truth is that the tuning capacitor had to be replaced by a 50k pot.The large surface area of the cap was a too good antenna for all hum and noise present int the amplifier. Yes the looks is almost as in 1953, only one tele input and one gain control.