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Old 20th December 2003, 09:25 AM   #1
Rookie is offline Rookie  Serbia
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Default Headphone amp with OPA561. Any thoughts?

Hi all!

I've been thinking about building a headphone amp in a gainclone fashion (unregulated power supply, small filter capacitors...). I searched and found the OPA561 as an interesting candidate for this. It's a high output current (1.2A) op-amp in a small package (HTSSOP20). I would use it as a non-inverted buffer, as I don't need any voltage gain so the number of parts would be minimal (2 1000uF filter capacitors, 2 0.1uF film caasitors close to the supply pins, input ptentiometer, maybe a zobel on the output...).

Anyone tryed something similar? Is this a good idea? It would be very cheap to implement... Have anyone experience with gainclones driving headphones
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Old 21st December 2003, 10:06 PM   #2
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Hi Rookie

1.2 amp is MUCH more than you will ever need for any headphone so be very carefull

or you will kill your headphones very fast.

Depending on the impedance of your headphone and the output level of your source you will most likely need some voltage gain.

If you really are a "rookie" don't start out with something in a SMD-pack like this. Work on a few normal packages to start with.

Thomas
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Old 21st December 2003, 10:28 PM   #3
joensd is offline joensd  Germany
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Indeed such an opamp would be overkill and not appropriate for a headphone amplifier regarding sound, distortion etc.
If you have high impedance headphones a simple opamp circuit with an OPA134 for example would be perfect.
For low impedance cans you can always add a buffer or class a output follower.

Best place for a big variety of headphone amplifiers : Headwize
In the library youŽll find all the different amps.
The "DIY workshop" is the forum where these circuits are discussed.
YouŽll find everything you ever wanted to know.

Cheers
Jens
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Old 23rd December 2003, 08:22 AM   #4
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Thanks for the replies

1.2A current capability is no danger with right voltage gain. Regarding the sound quality, I read somewhere that a gainclone sounded beautiful on headphones. Since this chip is from the same family as some other op-amps used in gainclones (OPA548, OPA549) but with some better characteristics, I have some gut feeling that this could be a great headphone amplifier. After I finish my current project, I will probably build it cause it is very cheap.
I know about Headwize, but it is too easy and boring to copy somebody elses design. It is much more interesting to come out with something your own.
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Old 23rd December 2003, 10:26 AM   #5
protos is offline protos  Greece
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Yeah , go ahead and do it.I have tried it with opa 548 and I have also connected my phones to my opa 549 gainclone.Not bad at all.In fact the 561 might be better since it is designed to work with lower voltages and you could probably pwer it from a 9v battery perhaps using a rail splitter.You could also try biasing it in class a with a jfet cascode such as in the meta 42/ppa head amps since you will have plenty of current to "throw away".Even low impedance phones only need a handful of ma to sound really loud.Is this going to be portable mainly?
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Old 23rd December 2003, 04:48 PM   #6
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I didn't plan to build it as a portable amp. A battery power supply is probably a good idea regarding the sound quality, but a little impracticle if using regular batteries and not accumulators. I don't think that the op-amp should be biased into class A, cause it is probably already working in class A on such a small power levels (quiscent current is 50 mA). Maybe a regulated power supply is better idea than unregulated, but those gainclones are really funny things...
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