but I've been called worse.
Amazing Forum, I am looking forward to learning tons!
I poked around quite a bit and didn't see this answered but i may of missed it so here goes.
Is it possible to/how would one add a headphone out to a Class D board such as this one
https://www.parts-express.com/2x15w-at-4-ohm-ta2024-class-d-audio-amplifier-board-only--320-330
?
I realize (or at least I think I get it) that the rating for the board changes because its rated at 15W @ 4ohm so whatever the standard headphone impedance will just reduce the Watt rating which will not be enough to hear at some point.
I think I'm kind of answering my own question as I type but I'm not even sure I'm on the right track.
I am aiming to build my own amp (not design) so i am still reading everything I can find but there is a ton of info here so it's taking time to digest.
cheers!
Amazing Forum, I am looking forward to learning tons!
I poked around quite a bit and didn't see this answered but i may of missed it so here goes.
Is it possible to/how would one add a headphone out to a Class D board such as this one
https://www.parts-express.com/2x15w-at-4-ohm-ta2024-class-d-audio-amplifier-board-only--320-330
?
I realize (or at least I think I get it) that the rating for the board changes because its rated at 15W @ 4ohm so whatever the standard headphone impedance will just reduce the Watt rating which will not be enough to hear at some point.
I think I'm kind of answering my own question as I type but I'm not even sure I'm on the right track.
I am aiming to build my own amp (not design) so i am still reading everything I can find but there is a ton of info here so it's taking time to digest.
cheers!
Looks like a BTL based on the picture with four filter inductors.
Can't find a data sheet.
IF the modulation scheme is conventional (1 SPW mode) you could tap one of the outputs with a 100R resistor to feed your headphones. ( you might have to do the same thing to the other polarity output for balance)
If it is not conventional (BD mode) then the output will not sound correct without a differential speaker.
You could use a transformer to get the differential signal to a single ended.
Or you could run 4 wire headphones and (through attenuating resistors) connect them where the speakers connect.
Hope that helps.
🙂
Can't find a data sheet.
IF the modulation scheme is conventional (1 SPW mode) you could tap one of the outputs with a 100R resistor to feed your headphones. ( you might have to do the same thing to the other polarity output for balance)
If it is not conventional (BD mode) then the output will not sound correct without a differential speaker.
You could use a transformer to get the differential signal to a single ended.
Or you could run 4 wire headphones and (through attenuating resistors) connect them where the speakers connect.
Hope that helps.
🙂
+1 for the transformer suggestion. It'll also help you maximize the dynamic range of your amp because most headphones (lower impedance ones) will overload given the full voltage swing out of this amp.
To answer the original question; the '15W in 4 ohms' spec only says that the amp will put out about 7.8V audio. Most headphones need just a volt or two to split your head, so the amp will overdrive your headphones if you turn it up all the way.
Although the power in those headphones (32 ohms? 64 ohms? 300 ohms?) will be much less than those 15W, the sound will be loud enough and then some.
Hence the one suggestion to connect the headphone to the original speaker connection with some series resistance. You can determine that by trial and error if you don't know the impedance of your phones.
Note: if the amp is a balanced output one (many class D ones are), both original speaker connections carry signal so make sure you don't accidentally short the headphone 'ground' connection to any metal parts of the amp.
Jan
Although the power in those headphones (32 ohms? 64 ohms? 300 ohms?) will be much less than those 15W, the sound will be loud enough and then some.
Hence the one suggestion to connect the headphone to the original speaker connection with some series resistance. You can determine that by trial and error if you don't know the impedance of your phones.
Note: if the amp is a balanced output one (many class D ones are), both original speaker connections carry signal so make sure you don't accidentally short the headphone 'ground' connection to any metal parts of the amp.
Jan
OK, awesome guys thanks.
I found a few articles that mention adding a 2k Ohm resistor tot he positive speaker output, It sounds like that matches up with on of the scenario's DUG listed, is that the same as a "100R resistor" suggested?
I am still low on the learning curve here...
🙂
I found a few articles that mention adding a 2k Ohm resistor tot he positive speaker output, It sounds like that matches up with on of the scenario's DUG listed, is that the same as a "100R resistor" suggested?
I am still low on the learning curve here...
🙂
My Headphones are Sennheiser 205s 32Ohms
Amp board Schematic here:
http://www.sure-electronics.net/download/AA-AB32155V300 SCH.pdf
Amp board Schematic here:
http://www.sure-electronics.net/download/AA-AB32155V300 SCH.pdf
Start with 2K...try to operate the volume control at or lower than the normal levels and see what the level is in the headphones.
For a lower drive impedance ("damping factor") use a 1k in series and a 47R in parallel with the headphones.
See what the sound is like with that arrangement.
Adjust the series and shunt values until you get the sound you like.
You will probably not need to go either side of 100R and 2K.
And the shunt may be between 10R and 100R.(if you go that route)
Play and have fun.
🙂
For a lower drive impedance ("damping factor") use a 1k in series and a 47R in parallel with the headphones.
See what the sound is like with that arrangement.
Adjust the series and shunt values until you get the sound you like.
You will probably not need to go either side of 100R and 2K.
And the shunt may be between 10R and 100R.(if you go that route)
Play and have fun.
🙂
If you have no speaker connected but have high z headphones there is a chance the class d amp wont start up.
Some class d amps need a speaker to load the output and let it oscillate properly.
I got caught out with that on a irs2092 design.
Turned on a brand new amp only connected to a scope and all I got was 17VDC on the output. I couldn't work out what was wrong so connected a speaker to see what would happen and it burst into life.
Some class d amps need a speaker to load the output and let it oscillate properly.
I got caught out with that on a irs2092 design.
Turned on a brand new amp only connected to a scope and all I got was 17VDC on the output. I couldn't work out what was wrong so connected a speaker to see what would happen and it burst into life.
if you decide to go the transformer route, you can get inexpensive PA transformers on ebay. They are usually around $15 to $40 a pair. The step down ratio is usually 3.8:1 to 11:1, depends on which tab you use.
I would agree that it is not a good idea to run a class D without a load close to what is specified.
Good catch.
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