Help with headphone Amp Plans
Mar 27, 2006 at 6:31 AM Thread Starter Post #1 of 2

SnooP_WiggleS

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I've got audio technica a500 headphones, which are low impedence (64ohm). So i thought i'd build an apheared 47 amp instead of a cmoy, since its made for low impedence headphones which the cmoy aint so good for. I don't have the time or money to build a pimeta (in particular the cost of the buf634's), and going off performance graphs cmoy is too compromising when used with low impedence phones. Current source is av-710, which provides enough plenty of volume, but I know I should be using an amp or buffer. I'm going off:

http://benfeist.com/a47/default.asp

However they use the uber expensive buf634 in the power circuit, and i'm building for a budget, so I've substituted an VPB opamp power circuit from tangeant, since a cheap 741 opamp can be used. Or can it?

http://tangentsoft.net/elec/vgrounds.html

To end up with the following circuit (only one of the two channels shown):
modifieda470sb.png


So now for the questions:
Any problems with changing the power circuit from the original?
With the given power circuit, how importent is the power supply choice?
Any problems with using this headphone amp (designed for 32ohm grados) with 64ohm audio technica?
The circuit doesn't have an output cap, so I should add one?
I'm guessing i should tie the input ground to -Ve of battery, and output ground to virtual ground?

Thanks for any help in advance
smily_headphones1.gif
 
Mar 28, 2006 at 3:19 AM Post #2 of 2

Garbz

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Your phones aren't that low, try using 18ohm phones
rolleyes.gif


In the powersupply you need an Opamp which is low noise and high current, otherwise it's no better then putting a TLE2426 in there driving the amp directly. Incidently a TLE2426 would would be a great replacement for the 10k resistors in there.

Any problems with changing the power circuit from the original?
- Probably not. THere's many different ways to do the power.

With the given power circuit, how importent is the power supply choice?
- If you look in the datasheet for the OPA2227 they have different characteristics for different Vs. Higher is normally better.

Any problems with using this headphone amp (designed for 32ohm grados) with 64ohm audio technica?
- No, infact it'll perform better with higher impedance loads.

The circuit doesn't have an output cap, so I should add one?
- It has an input cap. Providing the output offset of the opamps is low when you first try it there's not much to worry about as any source offset will be nulled. Output caps generally badly effect the sound since they are normally very large.

I'm guessing i should tie the input ground to -Ve of battery, and output ground to virtual ground?
- NO. Keep virtual ground virtual ground. Do not tie anything to before the Opamp. Input ground = output ground = psu virtual ground.
 

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