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Foreplay as a headphone amplifier?

207.199.2.150
Posted on July 30, 1999 at 06:05:01
AlanC


 
Forgive me if this is a dumb question, but would it possible to build the Foreplay and use it as a headphone amplifier? Or better yet add two sets of outputs and a switch between them so I could use the Foreplay to feed either my headphones or my amplifier. This would be used at work and sometimes it just isn't appropriate to have my music blaring away.

Thanks
Alan Christiansen

 

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Re: Foreplay as a headphone amplifier?, posted on July 30, 1999 at 10:39:03
Paul Joppa


 
The current capability of the output is not enough to drive headphones. But with a small transformer on each output, it should work fine. I'd start with a cheap line transformer (like those used in the paraSEX, typically available for $5-10). Use the highest impedance tap on a "70.7-v" transformer to get the best performance. It makes the preamp into a sort of parafeed cathode follower. Choice of output coupling capacitor will become important, and depends on the headphone impedance at low frequencies, because the coupling cap interacts with the transformer to form a second-order highpass filter. You want the cap to be big enough that the filter Q is low so there's no bass peaking (unless you like some bass lift in your headphones!) Try it and see!

 

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