• WARNING: Tube/Valve amplifiers use potentially LETHAL HIGH VOLTAGES.
    Building, troubleshooting and testing of these amplifiers should only be
    performed by someone who is thoroughly familiar with
    the safety precautions around high voltages.

Millett Hybrid headphone amp.

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After trying it at work it seemed promising, but when I connected it with the source I would be using etc. It sounded wrong, was either too bright or lean on bass, changed C3 value and put some extra decoupling caps in place. But it still didn't drive the cans I am using, it was good don't get me wrong but not what I was expecting.

I have had Grado cans Sony MDR-V700s before and used them on a X-Cans V2 or on the mixer (Pioneer DJM600) and they were driven to the point where ears were buzzing....lots of headroom.

The NP-100v12 had no headroom sounded too bright and was lean with bass.

Just my opinion.
 
Question about impedance loading of amps.

I have never found a problem with it before as all items were of the shelf plug and play. Since I have started to play in DIY I have found out how important the matching is.

How do manufactures get around this? Do they have an impedance sensing circuit etc? If so, what could I look at? If not how do they ensure headphones work?
 
That was a little flip i guess.

There are a lot of approaches and most mainstream manufacturers don't care or try very hard.

Most headphone amp designers who design for headphone enthusiasts try for as close to 0 ohms as they can get.

I have a pro grade denon cd player with a headphone circuit that uses the impedance of the load to set the gain because it has no volume control.

I also have an old rotel integrated that sounds real good, and the headphone output is just a couple 120 ohm resistors coming off the speaker output

.:Sent by pneumatic tubes
 
That was a little flip i guess.

There are a lot of approaches and most mainstream manufacturers don't care or try very hard.

Most headphone amp designers who design for headphone enthusiasts try for as close to 0 ohms as they can get.

I have a pro grade denon cd player with a headphone circuit that uses the impedance of the load to set the gain because it has no volume control.

I also have an old rotel integrated that sounds real good, and the headphone output is just a couple 120 ohm resistors coming off the speaker output

.:Sent by pneumatic tubes

Good point Eric, think I am rusty on the theory side.

But was thinking along the lines or current sensing.

Eg, I can put some cans in the amp despite the "load" and they just work.
 
150 ohms for my old Pioneer. At least there's no issues with output power.;)

jeff

Yeah. My problem with the Rotel RA-820BX is that the design has wires going right from the output transistors to the binding posts (and the resistors) -- the owner's manual suggests disconnecting the speakers manually if you don't want to hear them while you are using headphones.

I have seen alleged here and there that 120 ohms or 150 ohms is the "ideal" or "preferred" output impedance for headphone amps, but that may be nothing more than extrapolation from how best to avoid having to build another output section in a power amp.
 
Care to share an example to a keen newcomer?

Sure, it's an old Pioneer SX-636 circa 1975, and I'm the second owner. I was a bit surprised how much better it sounded with the source going into the tape monitor, bypassing the selector switch.

Yeah. My problem with the Rotel RA-820BX is that the design has wires going right from the output transistors to the binding posts (and the resistors) -- the owner's manual suggests disconnecting the speakers manually if you don't want to hear them while you are using headphones.

Well that's slightly inconvenient isn't it.

jeff
 
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There was an old standard (IEC I think) that suggested 150 ohm source impedance for headphone outputs. That was just fine in the day of tubes and 600 ohm headphones. But with MP3 players and phones that can only output 3-4V P-P it doesn't work. So many modern headphones have 32 or even 16 ohm impedance and are designed to be driven with near zero source. So, there is no right answer. One could take this as a challenge...

Most commercial headphone amps compromise and give a fixed zout, somewhere between zero (opamps) and 100 ohms (cathode follower OTL). This is why a given headphone amp sounds so different with different headphones. Not to mention personal taste.
 
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