Why do my headphones distort when using a Mackie HM-4 headphone amplifier

[armans]

I use a Focusrite for recording into my macbook pro and recently upgraded my headphones to a pair of Beyerdynamic DT770 pro (250ohm). When listening to music the headphones sound fine and loud enough but when I use them for tracking a vocal my input levels are much lower than those in finished mastered music and I was finding my levels too low even with my headphone amp 100% up. So I decided to get a small headphone amplifier and now I can get some more volume but the headphones sound distorted. My output from my focusrite is fine and within a reasonable level so not sure what is causing this. Can anyone please help to figure it out? THe headphone amp is the HM-4 from Mackie and I have it plugged into my Focusrite claretts headphone output using a 0.5m balanced TRS cable. This goes into the back of my Mackie and there I can adjust the level of 4 independent outputs. They all give me some more volume but they all distort the signal as well.

[forumuser931182]

Certainly sounds like the Mackie is running out of puff. It’s 12v dc supply and 45 ohm output impedance may be a factor - someone may be able able to give requirements for driving 250 ohm headphones. Would probably need to know how the Mackie circuit is configured - are the levels pots passive attenuation or do they set the amps gain.
When the Mackie distorts disconnect its input from audio interface and plug the headphones into the audio interface headphone output without touching any level controls - is the output clean without distortion?
I think you need to track down the reason why your tracking levels are so low - it’s probably better to make sure your gain structure is right before trying to compensate with a hardware solution. Trying with a more powerful headphone amp is also another option however.
I did have a HMA4 at one stage but didn’t like it and now use a Lehmann headphone amp.

[MarkOne]

I think the HM4 is expecting a line level stereo input, and I suspect the Claret Headphone output may well exceed the maximum input level for the HM4, that will probably be where the distortion comes from.

[Wonks]

The Mackie is a very cheap headphone splitter amp, so you have really bought more of the same headphone output amp that's already in your interface rather than something more capable. Given the lack of technical info that Mackie normally provide (there isn't even a power output into x ohms value given), these seem to be a more consumer level product for low ohm value headphones e.g. 32 ohms.

You've chosen 250 ohm headphones (you could have gone for a lower ohm version) which really need a much more powerful headphone output to drive loudly. Any headphone amp that's better specified will really need to be driven from two line level outputs from your interface. Have you got two spare outputs? If so, then something like the Behringer HA6000 should do the job. There are better headphone amps out there and I don't think I'd use it for mixing, but it's a low-cost solution for tracking.

If not, maybe get some lower ohm headphones (say 80 ohms or less) for tracking. The sound quality isn't of ultimate importance for these, but you need to be able to hear yourself (e.g. singing or playing guitar) and especially for vocals, you need good isolation and low leakage.

You may also need to spend some time adjusting the level of the backing track to the direct recorded sound. I often have to drop the mix output level by 20dB or so to get the direct sound vocals loud enough, though the direct/mix adjustment knob that's on a most Focusrite interfaces should take care of that.

[armans]

THank you. I do have lower ohm headphones but I like the way the 250ohm headphones sound. I have 4 X line outputs on my Clarett. Please see the picture here. I only use two of these for my monitors so the other 2 are free



Can you recommend another headphone amp that I can buy that will work with my setup? I looked at the behringer but it has 6 channels and I wonder if money could be well spent on one channel only to get a better sound quality. If not I may consider returning my Beyerdynamics since it seems quite complicated getting enough volume to them with my current setup.

[Wonks]

What budget do you have for a headphone amp?

[ajay_m]

For the price of four resistors and a couple of plugs and sockets just about any standard amp e.g a stereo hifi amp can be coupled up to high impedance headphones. Modern transistor amps don't care if they drive a much higher impedance load than a speaker (that was more of a problem with valve amps) so if we took say a 40w per channel hifi amp of the kind not uncommon in charity shops then the voltage swing into 8 ohms is about 50V peak to peak. If we assume the headphones want to see a driving source impedance that's fairly low, say 25 ohms, then a 270 ohm resistor in series with the speaker out and then a 27 ohm resistor to ground gives you a 5v peak to peak signal approx to drive the headphones and you can obviously modify the 270 ohm resistor value for a higher or lower signal level if necessary. At full power the resistor would dissipate about 5W I think, so a 10W wirewound unit would suffice. These are just rough calculations but these consumer hifi amps (sansui, Sony etc) have pretty decent noise and distortion figures so there's no reason they can't be pressed into service in this manner. Headphones are just small speakers, after all

[Wonks]

I think Armans just want to buy a headphone amp, not make one!

[James Perrett]

I've never had any problems using the humble Behringer HA400 with high impedance headphones. There is possibly a very very slight change in the sound quality when using it but it is more than good enough for foldback monitoring. You can drive it from a headphone output or from a line output.

[forumuser931182]

Most “music”headphone amps have multiple outputs but there a huge number of “hifi” ones that have a single output: Zen, Topping, JDS labs etc.