LME49600/LME49740 Headphome Amp

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I haven't seen any LME49600 headphone amps built around here so I figured I would post mine. It's the basic circuit from the datasheet with minor adjustments for parts on hand.

It sounds great with an absolutely pure black background. It's impossible to tell it's even on with the pot turned all the way down.

I built it small for portable battery powered use, but the idle current is ~47ma so I'm not so sure how good that's going to work out.

When I have the time I plan on building the regulators in the datasheet as well.

An externally hosted image should be here but it was not working when we last tested it.


An externally hosted image should be here but it was not working when we last tested it.
 
TzeYang said:
I think this amplifier is incredible.

How did you split the rails? Are those two huge ICs BUF634?

EDIT: Did you etch the board yourself? The boards looks very nice.

Thank you.

I was using a +/-15v test supply I have; there isn't any rail splitting or buffered ground stuff happening on the board.

The two huge ICs are the LME49600 buffers. I think I read somewhere they are very close if not the same as BUF634.

I etched the board, but to be honest I think it turned out like c**p. I had already been up for 22hrs when I started on it and it shows. Then my dremel tools bearings decided to go bad making the drilling a PITA with little bits of carbide flying everywhere, so most of the holes are off center.

Oh well, I guess it's function not form that really matters, and it definitely functions.
 
TzeYang said:
^Self-etched double layer boards tend to have HIGH failure rate. I'm surprised it turned out so reasonably well for your case.

I do it all the time, it's not so hard to get both layers lined up with each other after getting a process down. The tedious part is drilling all the holes and soldering all the little wire "vias".

The only thing that surprises me is when it actually works the very first time without even double checking any of the connections. I either have a lot of confidence in my building process or I just get lucky a lot.
 
theAnonymous1 said:


The two huge ICs are the LME49600 buffers. I think I read somewhere they are very close if not the same as BUF634

Sound like the LME49600 are better. I made a tweeter amp with the BUF634s. The music sounded fine, but during quite periods there was more hiss than I wanted. (barely audible at listen position, but quite noticeable near field).
 
I guess it is something like this you use.
This is the circuit for the special
LME49600 HeadPhone Amplifier Evaluation Board.
A board that can ordered.
Almost same circuit is in the LME47600 datasheet.

Power supply is from +-2.5V to +-17.0V.
Supply current may be a bit lower for lower Voltage supply.

Supply current will be like 50% when using lower BW.
But of course only for the LME49600 chips.
Not for the opamps.
The LME49600 offers a pin-selectable bandwidth: a low current,
110MHz bandwidth mode that consumes 8mA and a
wide 180MHz bandwidth mode that consumes 15mA.

LME49600 is rated +-250 mA output. ( +- 0.25 Ampere )
But shortcircuit Current is like +-500 mA
At higher voltage Supply we should be more careful not to put out too much current.

LME49600 datasheet:
http://www.national.com/ds/LM/LME49600.pdf
App. Note. AN-1768, LME49600 Headphone Amplifier Evaluation Board User's Guide
http://www.national.com/an/AN/AN-1768.pdf
 

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headphone buffers

theAnonymous1 said:


I hooked this up to a pair of 3-ways and it actually sounded good and played at a listenable level. Try doing that with an iPod.

I am not surprised. I am planning on build a power amp using the 49600s. For extended home speaker use, one would need to parallel a number of buffers and pay attention to heat sinking.

For headphone use (of which I know little), I am surprised that headphone amps have so much current capability. I have listened to a AD811 on headphones and found that 0.1 amp output was more than enough. Using just a LME49713 (C.F. amp with .1 amp out) for the gain and output would drop your quiescent current to around 20 mAmps for both channels.

Can anyone fill me in on why headphone amps need .25 amps? Are there some low impedance or low sensitivity headphones out there or do I listen at wimpy SPLs?
 
Re: headphone buffers

benchtester said:
Can anyone fill me in on why headphone amps need .25 amps? Are there some low impedance or low sensitivity headphones out there or do I listen at wimpy SPLs?

Head-fiers are superstitious. They think more current = more and better bass, biasing opamps to class A is better (even though they're buffered), using ridiculous large rail-to-rail caps give more and better bass, using fancy cables and connectors significantly improves performance, expensive lead, audio grade fuses etc etc. Placebo is a strong medicine, especially red and/or expensive pills. This has been prooved in medical trials.
 
We also have to consider how much HeadPhones can take.

Some smaller, freestyle, in-ear phones will burn already at like 50 mw (0.05 Watt)
Others will not garantuee to survive more than 100 mW (0.1 Watt).
A few large Phones will survive 200 mW or even 500 mW.

But before Your HeadPhones reach such level as 50-100 mW
and those tiny, very thin voicecoil copper wires are burnt & destroyed,
you will Have gotten you self Serious Hearing Damages.

For rest of your Life
:D Congratulations!!!
Have a good listening to to music, with those bad ears of yours.
You fool!!!!



I mentioned the absolute upper Current Limitis of LME49600
only because there was a mention they can drive small SPEAKERS.
At normal listening levels.
And probably LME49600 can drive 8 Ohm speakers, with high/normal SPL.
But what is the use?

We do not build headphones amplifiers to drive LoudSpeakers.
There are better ideas for this.
At the least buffering your op-amps
with a one or two POWER Transistors as followers.
 
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