I missed your comment earlier. Your point being? 47ohm gives with 300ohm headphones gives a damping factor of ~6.3, almost 1000 times smaller than the recommended damping factor.
Read the paper, it's short.
That's impossible. the data sheets for the LME49600 and the BUF634 are identical except for packaging. The circuits are the same as well. It's a moot point anyway since the LME49600 is NLA.
Recommend by whom? As I understand it, at least one school requires the Sony MDR7506, which has a flatter frequency response than the HD600. Likewise, the Sony MDRV6 is a classic choice. Both of these Sony's are far cheaper than the HD600 also. If you are going to EQ your headphones then you might as well start with some that are nearly flat to begin with. How are you going to EQ them anyway, by ear?
Yes, No Longer Available. TI has a last call order date of September 2016, but suppliers have long since run out. Unless you want to by 100's, then you are out of luck on the LME49600/10. As far as I can tell, they are identical to the still available BUF634 anyway, so it's not a huge problem. I'm guessing that the LME49600 was just a selected BUF634 anyway, but have not confirmed that with TI.
They have discontinued a process used to make some of their chips, so that means many of them are NLA now, including many from the LME series.
I use these buffers inside of a feedback loop for my headphone amps for Swetone Audio. They can drive anything (except HiFiMan). With a 300 ohm headphone, you may want some gain since 2Vrms (the consumer standard digital output voltage) may not be enough to drive them to full output. However, a buffer would be fine for a lower impedance headphone like the Sony's I mentioned.
Why is that important? I don't understand. The opposite is the case as far as I can tell for your application. You do not want to hear any background noise for mastering and recording purposes.
Look, it is a bad idea to just use a plain buffer with no feedback or op amp. The reason it's a bad idea is because the DC offset on the outputs of those buffers is uncontrolled and that is a big deal with headphones. Enclosing the buffer inside of a feedback loop with an op amp will insure that the DC offset is extremely low, depending on the skill of the designer of course. It's possible to screw up anything but running buffers without feedback is still a bad idea. Headphones are sensitive to DC so it's an important consideration.
I read the "white paper" describing the performance advantages of their 0-ohm headphone amplifier. Hmmmm.....this is the first measurement I've ever seen that proves that a 30 ohm resistor generates so much distortion!! I guess you have to take it at face value---their headphone amplifier does not like to drive resistive loads in series with headphones. I don't know why that is. I'm also not sure if that is true with every power amplifier extant.
That BUF634 board is running open loop. It looks to have 10-Ohm output resistors + the 10-Ohm output impedance of the BUF634 = ~20-Ohm total.
Perhaps OPA551 at unity gain would be a better option.
EDIT: There are also cheap BUF634 headphone amp boards on ebay. You could change out the resistors and op-amp for a unity-gain configuration.
Perhaps OPA551 at unity gain would be a better option.
EDIT: There are also cheap BUF634 headphone amp boards on ebay. You could change out the resistors and op-amp for a unity-gain configuration.
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It is important for a couple of reasons. The cases for open-back headphones are
- Improved, more natural stereo image (compared to non-existent in closed back headphones)
- Flatter frequency response
- Better, more realistic reproduction of bass
The production-related case for closed-back headphones, and probably the reason why a school would require them, is that open backs "bleed", ie. everyone within 20 meters can hear what you're listening to on the headphones. That is unacceptable when recording (laying down tracks, aka tracking), because any mic nearby would pickup the playback from an open-back set. A good set of closed-back headphones, however, eliminates this completely (imagine 20 students in a classroom with open-backs ...and headaches for all!). I hope that answers that for you 🙂
The feeding signal is the headphones output from the audio interface. Does it change anything?
Is the alternative solution below from Mooly a better idea?
For an opamp buffer all you really need is the output stage from the O2 amplifier... and its just classic opamp text book design. Two dual opamps and a few other resistors and a volume control. It would accept a line level input directly.
Anything in particular you recommend?
Where did you obtain the '10 ohm' figure for the BUF634's output impedance? I don't see it on the datasheet; perhaps I missed it.
Well, the one I see that I like is just a bare PCB. Includes a DC-servo in the design if you're into that.
LME49720HA LME49600 Headphone Amp Pre Amp Audio Signal Amplifier Buffer Board | eBay
Do you're headphones play loud enough for you from the amp as it is? If not, you might need some gain.
"I want to get headphones for mixing"
Well, I guess I'm just terribly old-school---NEVER in my 40 + years of working in high-end recording studios did I see a mixer use headphones to mix a record!
Well, I guess I'm just terribly old-school---NEVER in my 40 + years of working in high-end recording studios did I see a mixer use headphones to mix a record!
That's the whole point, though... I don't work at high-end recording studios, I'm producing music for my own pleasure at home 😉
@theAnonymous1 - what do you think about Mooly's idea I quoted in my post above?
Well, it's a simple design that will work. Would one option sound better over the over? Couldn't tell you. Different strokes for different folks.
Can you say which solution would yield the flattest frequency response, or color the signal the least?
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