Designing a Headphone Amp for the Studio (Video) January 11, 2013 12:10 17 Comments

A diagram/schematics would be great! very difficult to see what’s going on in the video only.

What are the chances of ending up with this having balanced stereo inputs? I would be really into something with stereo balanced input and the ability to run off a 9v battery or AC, so that I could take it somewhere without power and still use it.

Hi, did I get anything wrong here? Headphones with high impedances like 600 ohms are normally in need of more power from the preamp, while a low impedance headphone can easily be driven by a portable MP3 player and it will be pretty loud. I cannot use my 600 ohms AKG K-240 DF on mobile devices or on the headphone out of a PC’s audio card, while low impedance headphones work great on these. In your video you tell it the other way around. Why?

Thanx & regards

Frank, great question. I misspoke-I should have said low-Z headphones need more current, not power. Low-z phones are often paired with portable devices because of the low (usually battery supplied) power rails. So low-z headphones draw much more current to reach higher volumes without running up against the amp’s power supply.

This is dandy at typical casual listening volumes, but in the studio we’re often asking for a lot of power from our headphone amps. If we want to keep supply voltages and hence costs low, we need more output current than your typical single-opamp design provides.

In short, everything you wrote is correct, except that we were both playing a little lose with the word ‘power’. All other things being equal, high and low-z headphones need the same amount of power. It’s rather that high-z phones need higher voltages while low-z phones draw more current.

The battery is definitely an option. Balanced inputs are a taller order simply because I’m already running out of space on the PCB. Maybe a small, optional balanced receiver board is what’s in order.

A feature that would be worth looking into is a “crossfeed” circuit. Jan Meir made a headphone amp kit a while ago that had the feature I am talking about.

I think a mixable aux in per channel (line level) would be a great addition. It would stop the “more me in the headphones” battle.

Interesting, there was another strong proponent of this idea on twitter. If I were aiming to make the ultimate amp for mixing and reference listening, I’d definitely be looking at cross feed. My project is more about creating a great monitoring amp for tracking. I don’t see cf as a key element in this, but perhaps you feel otherwise?

I maybe wrong, but wouldn’t the cf be necessary for stereo tracking (i.e. orchestra, room mics, etc.). I personally believe it would be helpful for determining mic placement. I maybe be wrong though it wouldn’t be the first time.

Ah gotcha. Very valid points. The ideal setup, I think, would be to offer things like balanced inputs and cross feed as optional add on boards. I will take a closer look at the cf circuit you mentioned.

Nice idea for a kit – a headphone amp for tracking. With that in mind, I think the usual setup has an input from an audio interface (stereo, balanced or un). This line level signal is run out of one room into another and plugs into the first box. Each headphone amp box should have 2 volume knobs: one for the output volume and one for an additional “more me” input that gets mixed in. The more me control can be a very small pot. Finally, the mix signal needs to be daisy-chained to other boxes in the tracking area.

Since you’re hoping to put them in a guitar stompbox and keep them cheap, I think that one headphone output per box is fine. That said, the unit should be able to drive a headphone splitter on the single output if the user needs more than one headphone plugged into a single box.

Thanks for working on this – I’ll buy a few of them when you’ve got it ready!

I would pay a little more for balanced inputs

would a mono switch be possible on this? I do remote diy recordings at people’s houses using 6 channel xlr multicores and would love it if i could send a return down it to the performer using xlr-trs or ts jumpers so they can get a mono mix of other musicians/click track etc

Looks promising!! Thanks for all the effort. What is the model of the Grado you where showing?

I have been looking for a small headphone amp to use with my IEM’s while playing on stage.
What I would love to see is a headphone amp with Volume Bass and Treble controls. Also Hi-z and Low-z inputs so it could be hooked up to mixers aux send.
And

Peterson,

Nice idea. Here are my requirements, might be a better idea to just buy something. What you are working on would be great for portable rigs. What about a modular design that we could add modules to add the features we need?
The output on my HD192 is pretty hot. (Line Level) so something that could handle +4 balanced would be sweet.
A switch for headphones/control room speakers
A volume control which would also control mains not just the headphones.
A mono/stereo switch
Maybe speaker A/B/C selection

Thoughts?

I love it. I really like that it could run off of DC power or a 9v battery. I do a little bit of field recording, and I’ve always found the headphone amps severly lacking in my pro-sumer field recording units.

I’d also be happy to have a rack of these as a headphone distribution amp. I have a small cheap behringer unit for bands, but it doesn’t get nearly loud enough, or provide proper drive for tracking phones.

I’m looking forward to seeing the final circuit.