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Question about headphone amp and USB audio in

post #1 of 10
Thread Starter 

So I was looking into building a new headphone amp, my original just being a CMoy amp; this time I want to do a lot more of the work myself, not just following step by step directions...I probably will fail! but at least I'll have fun doing it! So my question, and I do apologize if this has been posted before I wasn't sure what to search for, but relatively speaking, is a 3.5mm in and a usb in interchangeable? I want to build an amp to hook up to my Galaxy Note 2 and I'm just looking for a way to avoid the built in amp and I'm not sure the best route to start. I've just been researching amps, comparing usb dac's and other amps and trying to determine if it's easy to toss on a usb or micro-usb in on whatever amp I build, or is the better route to just get something like a micro-usb to 3.5mm and an aux. Oh and as a side note, I'll mainly be using a pair of Monster Turbine Golds, so I probably don't even need an amp, but who knows!

Any and all help would be much appreciated!

Thanks, 

Arnold006287

post #2 of 10
Thread Starter 

Okay well now I did a bit more research and learned more about what I need...But now I guess I have a new question; for a headphone that with a relatively low impedance (16 ohms) and a sensitivity of 97db/mw @ 1kHz be okay with an amp at an impedance of 32 ohms? And if not, is there a way you can cut down the impedance of an amp...and I guess out of all of this, the last question would be...am I going to notice a difference if I amped these headphones?

Thanks, 

Arnold006287

post #3 of 10
Quote:
Originally Posted by arnold006287 View Post

Okay well now I did a bit more research and learned more about what I need...But now I guess I have a new question; for a headphone that with a relatively low impedance (16 ohms) and a sensitivity of 97db/mw @ 1kHz be okay with an amp at an impedance of 32 ohms? And if not, is there a way you can cut down the impedance of an amp...and I guess out of all of this, the last question would be...am I going to notice a difference if I amped these headphones?

Thanks, 

Arnold006287

First, USB is a different connector because it transmits different kinds of information.  A 3.5mm jack in our culture - if used as an input - transmits 2-channel analog signals to provide a stereo music signal.  A USB connector - if used as an input from a PC - is used to transmit both power (5VDC) and a digital signal.  That digital signal can be anything - programs, data files, a digital music signal, etc. - but you need hardware/software on the other side to know what to do with it.  IOW, the two connectors have nothing to do with each other.

 

Second, as for your second question above - there's not enough information to answer it.  You haven't even told us what headphones you're talking about.  32 ohms output impedance sounds like a tube amp.  That's not going to result in a very high damping factor, but depending on the headphone, it may or may not be OK.  It really depends on the inherent damping factor of the headphone and since those are not measurements that are ever published for headphones, you would have to rely on other peoples' reports on the traits of those headphones.  For instance, I have tube hybrids and tube amps that may have output impedances of 10 to 32 ohms and they may handle a 16 ohm pair of IEMs just fine.  For most very efficient IEM's, it depends more on the quietness of the amp not its output impedance.

 

I would suggest that you ask the same question - being specific as to headphones and amp - in the headphone section of Head-Fi.  There are more questions than one can count that begin with "Is Headphone X better with or without an amp?"  They all seem to get answered, though.wink.gif

post #4 of 10
Thread Starter 
Quote:
Originally Posted by arnold006287 View Post

 I want to build an amp to hook up to my Galaxy Note 2 and I'm just looking for a way to avoid the built in amp and I'm not sure the best route to start. I've just been researching amps, comparing usb dac's and other amps and trying to determine if it's easy to toss on a usb or micro-usb in on whatever amp I build, or is the better route to just get something like a micro-usb to 3.5mm and an aux. Oh and as a side note, I'll mainly be using a pair of Monster Turbine Golds, so I probably don't even need an amp, but who knows!

 

 

 

Tomb thanks for the reply, but I did specify the headphone I was primarily going to use, and it wasn't a question about if they need to be amped or not, I'm  building the amp regardless for fun, but I was trying to understand if I needed to do anything special for the input...I think I've found what I'm going to do though; I'm going to model my amp off of the skeleton DAC. From my understanding, I should be able to play music from my Note 2 with that amp. So you say that the 3.5mm and the micro usb in have nothing in common, but if I use the micro usb in, and run it through a DAC, the rest of the amp is fairly similar to if I used a 3.5mm to op-amp right? I really don't know what I'm doing but I'm in it for the fun, so if I crash and burn, hey it happens ;P lol

post #5 of 10
Quote:
Originally Posted by arnold006287 View Post

Tomb thanks for the reply, but I did specify the headphone I was primarily going to use, and it wasn't a question about if they need to be amped or not, I'm  building the amp regardless for fun, but I was trying to understand if I needed to do anything special for the input...I think I've found what I'm going to do though; I'm going to model my amp off of the skeleton DAC. From my understanding, I should be able to play music from my Note 2 with that amp. So you say that the 3.5mm and the micro usb in have nothing in common, but if I use the micro usb in, and run it through a DAC, the rest of the amp is fairly similar to if I used a 3.5mm to op-amp right? I really don't know what I'm doing but I'm in it for the fun, so if I crash and burn, hey it happens ;P lol

OK - sorry I missed the part where you stated the IEM's. wink.gif

 

The SkeletonDAC is not an amp.  It's a DAC with a DAC chip that has a small built-in headphone amplifier.  It's designed to be used with a PC running Windows or Linux.  The PC controls the OS, which negotiates the USB data connection.  Then music player software is needed to access the music storage on the PC, and transmit all of that in a digital stream over the USB output.

 

I haven't kept up lately with how they're doing using smartphones as music storage devices for offboard DACs, but the last I read, it was pretty much cutting edge.  Phones are not designed to use their USB connection as an output. A phone has to specifically negotiate the USB connection using software similar to a PC in order to communicate as a source with a DAC's USB controller.  It may be that the Note 2 is one of those phones they're experimenting with over in the "Androids Phones and USB DACs" threads in the Portable Source Gear section:

http://www.head-fi.org/t/595071/android-phones-and-usb-dacs


Edited by tomb - 2/16/13 at 11:33pm
post #6 of 10
Thread Starter 

Thanks for that Tomb, really helped me understand a little bit better, since it is possible to use my phone for output, can you put on an op-amp from the DAC? like...run through the dac, and then an op-amp or is that just too much stuff going on - or not even possible. Thanks a ton for this info btw, I really appreciate it. 

post #7 of 10
Quote:
Originally Posted by arnold006287 View Post

Thanks for that Tomb, really helped me understand a little bit better, since it is possible to use my phone for output, can you put on an op-amp from the DAC? like...run through the dac, and then an op-amp or is that just too much stuff going on - or not even possible. Thanks a ton for this info btw, I really appreciate it. 

By itself, an opamp doesn't mean anything.  Either the DAC can provide enough of a signal to power headphones, or it can't.  Or, the "box" contains a headphone amplifier or it doesn't.  There are many DACs that use an opamp(s) for an output.  Practically speaking, that may mean they can operate as an amp a bit better than a DAC whose output is taken directly from the DAC chip, but that isn't necessarily true in every case.  Some DACs may have an output opamp simply because the DAC chip is not capable of connecting to any sort of line load.  In that case, perhaps the opamp is capable of a little bit of amplification, but probably only for efficient IEMs or earbuds.  Anything else and it clips from low voltage.  There are other DACs that may have very elaborate opamp or discrete buffers that are capable of driving many types of headphones.  You really have to know the topology of the particular DAC to determine its capabilities in that regard.  It's like anything else - unless you are looking for a combination product that can do everything (but no single thing "well"), you need to be aware of what components you need to make up the audio stream.  Fundamentally, if a product advertises itself as a "DAC," then it almost always means that it will operate as a conversion source for music, nothing more.  You would have to provide an amp to complete the audio string between the DAC and the headphone and in almost every case, provide the data source for the music (PC or CD transport).


Edited by tomb - 2/17/13 at 5:53pm
post #8 of 10
Thread Starter 

huh okay, I think I'm starting to understand a bit better here...so I mean, seeing as IEM don't really need much amplification, something like a SkeletonDAC may sound better, just due to the fact that it would avoid the built in amp, and potentially just bring out more of the natural headphone sound? Because from what I know, the Note doesn't have the best built in amp, so that's why I was trying to find a better way to listen to music from it. 

post #9 of 10
Quote:
Originally Posted by arnold006287 View Post

huh okay, I think I'm starting to understand a bit better here...so I mean, seeing as IEM don't really need much amplification, something like a SkeletonDAC may sound better, just due to the fact that it would avoid the built in amp, and potentially just bring out more of the natural headphone sound? Because from what I know, the Note doesn't have the best built in amp, so that's why I was trying to find a better way to listen to music from it. 

What you sound like you're looking for in this post is an LOD for your Note 2.  That's a Line Out Device - it turns your phone into a source that can directly feed an amp, becauses it bypasses the amplifier in the Note 2.  This is much less cutting edge.  In fact, there may be adapter connectors such as this for almost every phone on the market that can act as a music player.  The SkeletonDAC would not be in the equation in this scenario.

post #10 of 10
Thread Starter 

Well, I am and I am not, just because I don't believe there is such a thing for android phones, it has to use a USB OTG cable; I was able to use an LOD when I built the Cmoy and had an iPhone. But the LOD was generally what I was looking for, but since I can just use a OTG cable, that brings me back to my idea about building a DAC, because wouldn't  that allow the Note to be the host/source > otg cable > peripheral/usb dac > 3.5mm out and the dac would act similarly to how the op-amp works with the lod? And if that does sound good, then I guess I wouldn't know the best one to build, now I feel like the skeleton is a little underpowered? Maybe I just need to research more on that. 

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