This might sound silly but i actually have no idea how i would do this? something id like to learn and nothing i search for on google seems to help me 😵 ive a 8002b and id like to add a headphone jack to it but it just seems to confuse me as ive no idea how to add it in 😵
Thanks!😀
Thanks!😀
You simply add a voltage divider. You might want to disconnect the speaker output though.
Headphone Adaptor for Power Amplifiers
Headphone Adaptor for Power Amplifiers
Since this is a "Class D" section, I'd be VERY careful about the intended "modification".
On that particular page, Rod Elliot says the following:
Warning: This unit is not designed to be used with bridged amplifiers! If there is a warning on your amp that states that the -ve speaker terminals must not be grounded, then you must not connect this adaptor, or the amplifier will be damaged. If in doubt, find out first from the manufacturer or distributor - assumptions can be very costly!
- and most of the usual ebay amps we discuss here are bridged, so any such proposed modification will result in the release of the magic smoke, and a pile of electronic rubbish that used to be an amplifier.
My advice: if you are thinking about adding a "headphone out" to an existing ebay class D amp (TPAxxxx), forget it - you'll most likely fry the amp.
It's better to find an existing amp module with a headphone out - those can be found on ebay (see e.g. http://www.diyaudio.com/forums/class-d/299007-modding-taobao-digital-amps.html - those amps have headphone out).
Or purchase a separate headphone amp board and use an audio input selector (can be a simple switch, or a more advanced relay board, also available on ebay) to switch between the "speaker amp" and "headphone amp".
On that particular page, Rod Elliot says the following:
Warning: This unit is not designed to be used with bridged amplifiers! If there is a warning on your amp that states that the -ve speaker terminals must not be grounded, then you must not connect this adaptor, or the amplifier will be damaged. If in doubt, find out first from the manufacturer or distributor - assumptions can be very costly!
- and most of the usual ebay amps we discuss here are bridged, so any such proposed modification will result in the release of the magic smoke, and a pile of electronic rubbish that used to be an amplifier.
My advice: if you are thinking about adding a "headphone out" to an existing ebay class D amp (TPAxxxx), forget it - you'll most likely fry the amp.
It's better to find an existing amp module with a headphone out - those can be found on ebay (see e.g. http://www.diyaudio.com/forums/class-d/299007-modding-taobao-digital-amps.html - those amps have headphone out).
Or purchase a separate headphone amp board and use an audio input selector (can be a simple switch, or a more advanced relay board, also available on ebay) to switch between the "speaker amp" and "headphone amp".
That's nonsense! Firstly: The amp won't be modified. Secondly: Each of the - of the amp gets the resistor in series, you can connect them after the resistors and there won't anything be fried at all.
BTW: I've posted the link for the values only.
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If the amp has full-bridge outputs then it won't work due to most headphones having a common ground. You could take the output from one side of each bridge, but then you need a DC blocking capacitor.
The other issue is the output filter being designed for loads <8-Ohms. There will be severe peaking with say 32-Ohm headphones.
The (-) of the amp is not ground - because it is bridged! And because of the headphone having a joined (-) I said the resistors are in the (-)s of the amp. That way the joined (-) of the headphone does not short the (-) because it's going over the (high) resistance of the resistor. That means, there is no need for a capacitor at all!
That depends on the amp (and from where and how the feedback works). And if you change the voltage divider to a lower impedance you can eliminate that problem completely anyway.
I've heard that some class D amps can be unstable without a load that is within a certain range of ohms. There's also the issue of the L and R circuits not having a common ground. There may also be an issue with the output impedance affecting the potential resonance of the headphone transducer. Any resistive divider could throw the amplifiers damping effect way off. This can be a big deal with speakers. Actual values for a resistive divider would depend on the impedance of the particular headphones.
do you happen to know what would be the optimal values for a 32 ohm impedance headphone? I would like to test using a tpa3116 module
Based on what I've heard and read (I haven't actually done this), I would always want the tpa3116 to see 8 ohms, or whatever it's output reconstruction filter is optimized for. So the resistive voltage divider would have a total resistance of about 8 ohms. I'd try putting an 8 ohm R in series with a 1 or 2 ohm R, put the headphones across the 1 or 2 ohm R and see if I like the level I get. I'd take it from there. If there's a switch involved to turn off the speakers when the headphones are used, I'd make sure the tpa3116 is never driving infinite ohms, even for milliseconds. I may be too paranoid there, but until I verified that the amp is OK with that, I'd worry about it blowing up my expensive speakers.
Well, if you are worried about blowing up your expensive speakers by disconnecting the amp from them, you should probably look for a more permanent solution, i.e. connecting them to the mains outlet.
I can see why you'd wonder about that. My experience with Class D amps is limited. I've read that some class D amps can go unstable and blow themselves up if the load is removed. If there was a switch that switched between a headphone out vs a speaker out, there might be a millisecond when there is no load on the amp while the switch is changing connections. It seems highly unlikely that this would ever be a problem, but I've read somewhere that it seemed to be for someone. It's part of why I'm dragging my feet on getting invested in class D amps. From what I've read though, the TPA3116 is allegedly one of the better ones. People say it has no turn-on or turn-off glitch. If I wasn't so busy with other projects I'd get a few and see how they react to various issues, such as no load.
No matter what amp you are using, once you're disconnect it, there's no way it can dmg any speakers. If you are worried, there are protection circuits you can use, which protect you from DC, over-current, over-voltage on- and off-pop noise. If that's not good enough for you, then you'd better stay off of diy-amps at all.
Yea, by the time you include protection circuitry and relays, you need a bigger chassis and more money. I know that a disconnected amp can't blow a speaker. I'm talking about the condition where the amp has been temporarily disconnected, but will then be re connected. I'm probably being too paranoid about this, but I have read that some class D circuits have stability problems with no load. That may be obsolete info.
That's still no issue. Wire a parallel 20W 33-47 Ohm resistor to the output. One problem solved. These protection modules are in wide ranges interchangable and therefore well reusable. They protect your speakers among other things from DC - which is the most dangerous fault for your speakers. And since they are below 15 bucks, I'd say, that's not a very expensive 'insurance'. Sign here please. 😀
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