Headphone amp for the DL 1608

[Sting]

Which radio shack adapters are you referring too? If you are not using the mono to L/R adapter then you will only get sound from one side. That's why you need the correct adapter. Me thinks you didn't have it.

After further checking, you are right on Jerry.  My radio shack adapters are mono to mono.  I had them on hand not in the package so I was unaware...thank you! 

[WK154]

Here are the measured impedance values for the various headphone output points.
DL Headphone output ----89 ohms
DL Aux-------------------139 ohms (specs say 120  ohms)
HA4700-------------------8.3 ohms (main input for source only)
The DL headphone output is not that great the Behringer is clearly better. It does verify my suspicions with the prior sound tests which of course leave a lot to interpretation (subjective). For total transparency the ratio of 1/8 (output/input) for impedance is used less than that produces coloration etc. You may be satisfied with less.

[WK154]

Now for the subjective test for 3 sources of IEM input plus a speaker.
To be a little scientific about this I adjusted the output of all 4 at 83 dbSPL or as close as I could with a 1K tone. This should avoid the old speaker sales trick of increasing loudness for the sale. I ran thru all 4 and still found the direct aux out light on the lows. The test source was Vocal  group a Capella the Alley Cats which should cover the vocal range. Instruments will of course increase the range. All off an iPod into channel 15 and 16 of the DL no processing. All output thru the aux's and phone output (L/R buss) of the DL. Since I was predisposed to evaluate this I called on my other set of ears and sometime A/B tester my wife. After being interrogated about the reason for this I asked her to pick out the best of the bunch. Here is the results:
The CA50A speaker was used as a baseline.
DL earphone out and the HA4700, she could not tell any real difference.
DL aux in her words sounded a little thin but not to bad.
Strangely similar to my take. This rarely happens around here.
The earphones were all Apex HP90's 50 ohms impedance.
No I won't test this at 90 dB SPL it hurts my ears and she complained about 83 dB SPL being too loud. YMMV is all I can say and your pocketbook may be the deciding factor. Ear-buds (16 ohm variety) may have a much different outcome. If I can find some I'll try it. Noise at this level was inaudible. I'm sure I can coax some out at higher amplification but that's not the point.
Just found some ear-buds of unknown origin and impedance but there was about the same results. Also tried my AKG K270 studio cans and no real change their 75 ohm impedance units.

[WK154]

Don't you want to know what you stick in your ear or what it's hooked to?
Well here goes more. I decided to change genre and include instruments. I thought Sarah Brightman would be a good start. The Symphony CD what a mistake. I've gone to her live concerts and the CD makes her out to be snake with a hoarse voice, definitely not her. Somebody needs to re due that album. So next stop were Barbara Streisand and Celine Dion and no problem as expected. Same basic conclusion as before. Country next. With  Garth Brooks the kick was light as was the low end so basically the same conclusion. It's not far off but noticeable if your picky like me. I've not done much critical listing except for my own stuff so this an eyeopener. I also don't use ear-buds only headphones and studio speakers.

[WK154]

One other thing about the aux outputs of the DL. The power is more than adequate to put a big hurt on your eardrums so power and sensitivity were never at issue here only tonality. That being said I highly recommend that you limit the aux out with the compressor and set realistic limits as to not cause any surprises. During my testing the DL lost sync but no sound was ever affected. I don't use the USB link for any sound play or record. I consider this broken until Mackie can come up with a fix. There is still no information of what would happen if the USB channel generates noise that the aux's won't be affected. All the more reason to limit the output with the compressor.

[RoadRanger]

One other thing about the aux outputs of the DL. The power is more than adequate to put a big hurt on your eardrums so power and sensitivity were never at issue here only tonality.

What about using series resistors? Seems to me you could select some to match up a given IEM powerwise and that would also help a lot with the impedance mismatch . The "no-clip" output comp preset could then be at a safe level and even if it glitched off you'd be OK. Of course the "right" option would be a small audio transformer.

[WK154]

One other thing about the aux outputs of the DL. The power is more than adequate to put a big hurt on your eardrums so power and sensitivity were never at issue here only tonality.

What about using series resistors? Seems to me you could select some to match up a given IEM powerwise and that would also help a lot with the impedance mismatch . The "no-clip" output comp preset could then be at a safe level and even if it glitched off you'd be OK. Of course the "right" option would be a small audio transformer.

Let me first list a concern that hasn't really been brought up before specific to the DL. Normally the aux and L/R outputs where meant to drive a high impedance input such as an amp input. The rule of thumb in audio voltage interfaces is to have at least a 10:1 or higher ratio. The DL has a spec'd output of 120 ohms (600 for L/R) and should drive an input of at least 1200 ohms which in most cases it does some as high as 30K. My concern about driving lower impedance headphones is that the thermal overload will eventually cook the DL's non-vented analog section. We also both know that the impedance oversimplification does not really deal with what is a speaker design (IEM). It's just a coarse rule of thumb with all the pitfalls that Mfg.'s can create. Here is a more formal explanation from the designer of the O2.  http://nwavguy.blogspot.com/2011/09/more-power.html
My recommendation for someone wanting to use aux outs as a wired IEM is to get a reasonably priced headphone amp such as the Behringer P1. Unfortunately you will have to wait a bit since none have been spotted on this planet ( per Starin). Millenium in Europe has a similar unit called a HA100 (34 euros) but reviews point out some issues such as turn on pops and of course no limiter. I haven't found any comparable unit specifically with balanced inputs. Does anyone know of any? Please post.

[Sting]

WK154 does raise a legitimate concern regarding impedance mismatch here.   We need to learn more from Mackie on potential damage to the DL using headphones directly from aux sends. 

[Jerrylee]

I have been doing this for over a year now & hundreds of times. There has been absolutely no issues and the dl shows no signs of damage. There are others here who have done the same thing as well with no issues. Consider this a field test we have done for Mackie. And it passed.

[WK154]

I ran across this product on another forum. OK Uli what's going on???
http://fischer-amps.de/uploads/media/Fischer-Amps-In_Ear_Hardware-2013.pdf
P1 a clone??
Here's another headphone amp as well.
https://elitecoreaudio.com/product/retail/elite-core-pma-personal-monitor-amplifier
with a MAP of $79

[Greg C.]

People here are going to say not to do this because the auxes are no meant to bee used like this. Greg might give some technical reason. Ignore them all. It works and has been overly tested.

There are valid technical reasons to not do this as I had said a year ago on the Mackie forums, unless someone knows for a fact that the driver circuit in the aux sends are designed to handle low impedance loads. I'm not going to bother going into anymore since people are going to do what they're going to do even if there's potential to cause damage at some point.

[Wynnd]

I agree.  You won't find me using headphones directly plugged into the mixer anywhere except the headphone jack.  (I really don't care if it works, it doesn't look like it was designed for that use.) 

[WK154]

The new QSC Touchmix actually was designed to deal with headphones on aux's. Low impedance outputs.

[Wynnd]

If I had waited to go digital, that might make a difference in my life.  By the time I go after a different mixer I'll probably be collecting Social Security.  Anyway, that's good to know if anyone else is starting to look for a digital mixer now.  Thanks for the heads up.

[Greg C.]

This is the last I'll post on the topic of using a line output to drive headphones. The "official" word from Mackie support delivered to my inbox this morning:

Hey Greg,

So here's what we think: It's not supported, it's not recommended, it's probably not the best quality of sound you can get.

The output circuit can get damaged with improper use, and that is what we're concerned about. The aux sends have a 240Ω output impedance.

By plugging in such a low resistance headphone into the jack you are actually maxing out the output circuit of the aux send. Again I don't think it would hurt the mixer, it still isn't recommended.

I would suggest picking up a very cheap headphone amp and using that instead. There are 4 channel headphone amps for as cheap as 30 dollars.

Hope this helps,


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