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Old 29th June 2015, 05:54 PM   #1
visar is offline visar  Poland
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Default Good low impedance headphone amp project

Hi
I'm looking for a simple headphone amplifier project for my Sansui SS-20. Headphones parameters:
Impedance 8 ohm
Maximum input 500 mW
Sensitivity 105 dB
I'm looking for a simple, small and well sounding amplifier project for them. Any suggestions? Thanks in advance.
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Old 29th June 2015, 09:06 PM   #2
Koifarm is offline Koifarm  Netherlands
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You are at the right place.
Here are several good designs.

Below the best i ever made and it is simple to.

Just for fun
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Old Yesterday, 03:45 AM   #3
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With this sensitivity you most likely will be satisfied with something around 10mW. If you want to have a good margin - set 50-100mW as a top limit. This way you will need no more than 100mArms. There are a lot project around that can provide this sort of current. There is even my fiddling with opamps on this topic - "The Crocodile"
If you really want to be able to pump a lot of current, just for sake of doing it, you can go with discrete output or full discrete design. Or you can use high power opamps, like LT1210. Here is my attempt - A composite with LT1210 - another way of doing it
I even made a proper PCB for it, just do no have time and motivation to finish it.
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Old Yesterday, 08:20 AM   #4
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so.. I will not be too original.. Here is my design turned into follower (think you need only current amplification). However such modification never tested in hardware, in case of problems with stability - there're few grayed elements that should help...
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Old Yesterday, 01:04 PM   #5
HotIce is offline HotIce  United States
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The Wire. Maybe with lowered rail voltages, given the low load impedance.
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Old Yesterday, 01:35 PM   #6
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Quote:
Originally Posted by visar View Post
Sensitivity 105 dB
Just to make sure. Could you be more specific, is it dB/mW or dB/V? Or even something else?
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Old Yesterday, 06:30 PM   #7
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With those old 8 ohm cans, it's not even certain whether they're best driven from a voltage or current source. Typical headphone outputs of the time certainly would have been in the latter camp, featuring output impedances in the hundreds of ohms. I'd say try them with a random integrated amp or receiver, and that's pretty much as good as they're going to get. I didn't find anyone raving about the sound quality of this model, so I assume it's not anything too spectacular. (Most dynamic cans of the 1970s certainly weren't. Measurements of K240 Sextetts are really respectable though.)

If you need an approximated current source output without having to provide ridiculous voltage swings, about 80 ohms of output series resistance should do (so maybe 68, 75, 82 or 100 ohms). As for the amp to add these to, maybe something cMoy-ish with 2x 9V and an NJM4556A and a gain of about 10.

A real current output gets a little more tricky, one would basically need some kind of OTA for that.

Last edited by sgrossklass; Yesterday at 06:35 PM.
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