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[Matt]

I'm trying to find a way to plug two DACs into an A/B switch and quickly switch which plays out my headphones.

Something mechanical, as opposed to something I have to plug in and/or wonder if it's doing signal processing, would be best.  1/4" headphone plugs would be best.  Low cost would also be good.

Thanks for any tips.

[bobkatz]

I'm trying to find a way to plug two DACs into an A/B switch and quickly switch which plays out my headphones.

Something mechanical, as opposed to something I have to plug in and/or wonder if it's doing signal processing, would be best.  1/4" headphone plugs would be best.  Low cost would also be good.

Thanks for any tips.

Sorry to be the curmudgeon here, Matt, but I'd like to ask why you need this? Are you trying to objectively compare the sound of two different DACs as objectively as possible? I haven't seen any ready-made switch that does that. I could build something on a bench in an hour or so if you really need this. It's not a commonly-needed thing.

[Matt]

Sorry to be the curmudgeon here, Matt, but I'd like to ask why you need this? Are you trying to objectively compare the sound of two different DACs as objectively as possible?

Yes, exactly that.  I'm working in the propeller-head department again.

We have quite a few nice DACs here.  I thought it'd be fun to see if I could hear differences between them in a proper test.

I spent a little time trying this last night, and realized how hard it is to do a meaningful test.

It's a little tricky to level match headphones, although I think I got that right.

But then I know which DAC I've moved a headphone cable into, so it's not a blind test.  Then, it takes a few seconds to move the cable and our short term memory for sound isn't that good.

A way to instantly flip between two DACs would make doing a meaningful comparison easier.

With my insufficient testing method, all I could decide is that good DACs sound good (surprise!) and mostly the same

I haven't seen any ready-made switch that does that. I could build something on a bench in an hour or so if you really need this. It's not a commonly-needed thing.

Thanks for the offer.  I don't really need it, so let's see if anyone else turns up some little bit of hardware that would do the trick.

[mwillems]

I'm trying to find a way to plug two DACs into an A/B switch and quickly switch which plays out my headphones.

Something mechanical, as opposed to something I have to plug in and/or wonder if it's doing signal processing, would be best.  1/4" headphone plugs would be best.  Low cost would also be good.

Thanks for any tips.

Are your DACs intended to hook directly to the headphones (i.e. amplified output) or are they line-level outs?  

If you're passing an already amplified signal, a friend of mine wanted something similar, and spent a while looking.  He couldn't find one that was as simple as he wanted (all the commercial ones he found all had various unnecessary additional electronics in them, or were intended for line level signals).  Eventually he just wound up making himself one (like Bob said).  

If, instead, you want something to sit in between the DAC outputs and a headphone amp (i.e. switch between line level outputs), you might have an easier time finding a commercially made switch (because the connector type is irrelevant then). Something passive with a line out like this :http://www.amazon.com/Sima-SVS-14-Input-Manual-Selector/dp/B00005NCWK/ref=sr_1_13?s=electronics&ie=UTF8&qid=1372175275&sr=1-13&keywords=audio+selector+switch

[Matt]

Are your DACs intended to hook directly to the headphones (i.e. amplified output) or are they line-level outs?  

I'm testing headphone level outputs (ie. amplified already).

[6233638]

It's a little tricky to level match headphones, although I think I got that right.

I think you would normally use a multimeter on the headphone jacks for this?

[mojave]

The Behringer MiniAmp AMP800 lets you switch between two sources with one pair of headphones.

You've come a long way since some of your earlier critical listening efforts:

[mojave]

Since I own an SM Pro product I just checked out their website. The SM Pro M-Patch2 also allows you to switch between two sources with one headphone output. One source is balanced and one is unbalanced. Both the Behringer and the SM Pro allow one to level match both inputs.

[6233638]

Now that I think about it, I seem to recall FiiO making a product specifically for this purpose. I'll have a hunt around.

[6233638]

FiiO HS2:



$20 direct from the company: http://www.head-fi.org/t/662441/fiio-headphone-signal-switcher-hs2-open-to-retail-now

[Matt]

$20 direct from the company: http://www.head-fi.org/t/662441/fiio-headphone-signal-switcher-hs2-open-to-retail-now

Thanks.  I just ordered one.

It's supposed to take a few weeks to arrive, but I'll report back after it's here.

[bobkatz]

Yes, exactly that.  I'm working in the propeller-head department again.

We have quite a few nice DACs here.  I thought it'd be fun to see if I could hear differences between them in a proper test.

Headphones would be one way to A/B the DACs but not the definitive way. That's because differences in depth and dimension are usually masked in headphones which tend to reduce the depth of the soundstage, and also bring the (false) inner details up to the eardrums. It's a bit like listening to a friend talking right into your ear, not very natural. There's no substitute for loudspeaker listening in a good listening room to make the final judgment.

BK

[6233638]

Well I had almost forgotten all about this, but I ordered one as well and it turned up today, so hopefully yours will be arriving shortly.

I don't have access to my Benchmark DAC2 right now, but I did do some testing with some of the devices I have at my disposal here - not DACs, mostly various portable devices, and a few other pieces of AV gear with headphone outputs, so it's maybe not a definitive test.

I level-matched them by ear as best as I could before doing any listening - I checked at 500/1000Hz, and with full bandwidth and narrowband pink noise so that there was no perceived difference between any of them when switching inputs. Most of the devices have fairly coarse volume controls anyway, so it wouldn't really have mattered if I had used a better method than adjusting by ear.

The hardest thing was syncing up any music being tested. I actually did the listening tests in two ways:
1. Synced playback by tapping the play/pause button until there was no perceived difference when switching inputs.
2. Delayed playback with a second or two between each device, so that I would hear the same short section played in quick succession for comparison. (as our auditory memory is so short)

While this may have been a "sighted" test rather than a "blind" listening test, I was randomly going back and forth between which device was out of sync etc. so I wasn't consciously aware of which one was behind, and I was switching the inputs they were going into at random without looking at the devices, so it was as fair as I could do without someone else controlling the test.


Maybe it's just because I was comparing lower-end devices, maybe I just have cloth ears, maybe it's because the listening conditions weren't ideal right now, or maybe there's some truth to "all DACs should sound the same" but my impression was that there was barely any difference between the devices I tried.

I'm really curious/concerned to see if my opinion changes when I get my DAC2 back. I feel like I heard a big improvement when I added it to my system, but maybe it was all in my head. Or maybe it really will show a big improvement, and it is that these devices all just happen to sound roughly the same.

The most obvious change by far was the noise floor when comparing them, especially when I left one input disconnected to be truly silent. That's one concrete improvement the DAC2 brings - it's silent at any volume level. But that's not really an issue at all when you are playing back music. The only time I really notice the noise floor is if I'm watching a quiet scene in a film that's being downmixed from 5.1/7.1 to stereo.

So maybe you really don't need to spend much on a DAC or headphone amplifier these days.
I don't know when I'll be getting my DAC2 back, so it might be a few weeks before I can report back on that - though I'm not sure that I want to test it, to be honest.

Now I'm really curious to see what the result of Matt's testing is.

[Matt]

6233638, thanks for posting your results.  They're interesting.

Please let us know how the DAC2 compares.

I'll do some tests and report back once my switcher shows up.

I agree with you about the noise floor.  This is especially important in a high gain situation like when using a power amplifier and digital volume like I do in my home theater.  Many DACs have an audible hiss all the time in cases like this.

[6233638]

Well my DAC2 turned up today without warning - they just sent out a new unit rather than them repair the first one.
I level matched everything using the line-in on my PC and a 1kHz tone, so that they were reading ~0.1dB of each other when running through the HS2.

As previously mentioned, the most obvious difference between anything by far is the noise floor.
I'm starting to see why there are a number of people that say DACs are basically a "perfected" technology where we are far beyond the limits of hearing, and differences on exist on paper now.

That said, maybe there is something else causing things to sound the same? Maybe there's a high enough level of crosstalk between the various inputs of the HS2 (not that I've noticed anything obvious) that it's impacting the results.
And when I have my headphones directly connected to the DAC2, they definitely sound better with the DAC2's 0-ohm output compared to anything else. Perhaps running through the HS2 is affecting the impedance and removing this advantage? I couldn't say.

There's a huge difference in sound between connecting my headphones directly to a portable device, and running a cable from it into the back of the DAC2, using its headphone amplifier instead, for example.
Because I'm not hearing this difference when running audio through the HS2, maybe it's impacting the test?

Or maybe doing a sighted test really is biasing things that much?

After spending the afternoon listening to my DAC2 again, I have no regrets about buying it.
If nothing else, that silent noise floor, excellent headphone output, and the connectivity options make it worthwhile.
And so does knowing that I never have to think about a DAC or headphone amplifier ever again, because it's not going to get any better. (OK, some people suggest there are better units above $5000, but I'm never going to be able to afford that)

But even though I'm not really hearing anything that stands out as being a dramatic difference with the HS2, maybe it's all in my head? Or maybe simply using an A/B switch when listening isn't really as good a test as you might think.
At the end of the day, if spending the money on the DAC2 can do that, even if it is all in my head (but I'm not sure that it is) then it's still worthwhile.

I'm left feeling that I need to devise a better test somehow, rather than this being definitive in any way.

[mwillems]

Well my DAC2 turned up today without warning - they just sent out a new unit rather than them repair the first one.
I level matched everything using the line-in on my PC and a 1kHz tone, so that they were reading ~0.1dB of each other when running through the HS2.

As previously mentioned, the most obvious difference between anything by far is the noise floor.
I'm starting to see why there are a number of people that say DACs are basically a "perfected" technology where we are far beyond the limits of hearing, and differences on exist on paper now.

That said, maybe there is something else causing things to sound the same? Maybe there's a high enough level of crosstalk between the various inputs of the HS2 (not that I've noticed anything obvious) that it's impacting the results.
And when I have my headphones directly connected to the DAC2, they definitely sound better with the DAC2's 0-ohm output compared to anything else. Perhaps running through the HS2 is affecting the impedance and removing this advantage? I couldn't say.

There's a huge difference in sound between connecting my headphones directly to a portable device, and running a cable from it into the back of the DAC2, using its headphone amplifier instead, for example.
Because I'm not hearing this difference when running audio through the HS2, maybe it's impacting the test?

Or maybe doing a sighted test really is biasing things that much?

After spending the afternoon listening to my DAC2 again, I have no regrets about buying it.
If nothing else, that silent noise floor, excellent headphone output, and the connectivity options make it worthwhile.
And so does knowing that I never have to think about a DAC or headphone amplifier ever again, because it's not going to get any better. (OK, some people suggest there are better units above $5000, but I'm never going to be able to afford that)

But even though I'm not really hearing anything that stands out as being a dramatic difference with the HS2, maybe it's all in my head? Or maybe simply using an A/B switch when listening isn't really as good a test as you might think.
At the end of the day, if spending the money on the DAC2 can do that, even if it is all in my head (but I'm not sure that it is) then it's still worthwhile.

I'm left feeling that I need to devise a better test somehow, rather than this being definitive in any way.

It's entirely possible that the output stage of the HS2 is causing a change; like you say it may have a higher output impedance than the Benchmark (some other Fiio products, such as the E09, have output impedances as high as 10 Ohms), which would sound different for sure.  You'd have reduced damping, and significant frequency response changes especially with low impedance headphones.  It would also account for why you don't hear differences between sources, but do hear a difference when not plugged into the HS2.

It's also not surprising that you'd hear a difference between the headphone out of the Benchmark and a direct connection to your portable player, although it is odd that they all sound similar when fed through the HS2.  The amps used in portable devices are often comparatively noisy and load-dependent (DACs may be close to perfected, amps are far from it).  It's not only a "power" issue, but also an issue that some amps are flaky with different or variable impedance loads, and a headphone amp really needs to be able to cope with that(but load-invariance is hard, costs money, etc.). 

If the HS2 has non-trivial impedances on the inputs or outputs, it could be having an "equalizing" effect by masking both problems, i.e. it could be hurting the damping of the Benchmark (making it sound more like the potentially underpowered portable sources) and also showing a more stable impedance to the portable player amps (helping stabilize a less load-invariant amp).

If you have a multimeter you could probably find out pretty quick if that's potentially what's going on, or if it really is just a sighted testing issue. 

[6233638]

It's entirely possible that the output stage of the HS2 is causing a change; like you say it may have a higher output impedance than the Benchmark (some other Fiio products, such as the E09, have output impedances as high as 10 Ohms), which would sound different for sure.  You'd have reduced damping, and significant frequency response changes especially with low impedance headphones.  It would also account for why you don't hear differences between sources, but do hear a difference when not plugged into the HS2.

The thing which makes me question that, is that I'm still hearing a difference in the noise floor. With my more sensitive headphones, if I add an in-line 75 ohm adapter the background noise disappears. (but everything also starts to sound terrible)
There's still a noticeable hiss from everything except the DAC2 when going through the HS2. But maybe it's adding enough to remove the DAC2's advantage in other areas, without silencing the background noise. I don't know. The headphones I was mainly testing with were 24 ohm, so it only needs to have more than 3 ohms of resistance to start hurting things.

I did open it up, and it seemed to be very simple inside. I can post photos of that if anyone wants. (I also managed to do some cosmetic damage to the outside because the switch wouldn't come off easily, oops)
FiiO did initially produce these for their product demonstrations, and offered them up to the Head-Fi community if anyone wanted them (which is why you have to order them direct) so it shouldn't be doing anything detrimental, but I can't explain what I'm hearing.

Maybe doing an A/B test with the tracks synced like this just isn't a good way to approach it.

If you have a multimeter you could probably find out pretty quick if that's potentially what's going on, or if it really is just a sighted testing issue.

I don't, unfortunately. (I probably should buy one, one of these days)

[mwillems]

The thing which makes me question that, is that I'm still hearing a difference in the noise floor. With my more sensitive headphones, if I add an in-line 75 ohm adapter the background noise disappears. (but everything also starts to sound terrible)
There's still a noticeable hiss from everything except the DAC2 when going through the HS2. But maybe it's adding enough to remove the DAC2's advantage in other areas, without silencing the background noise. I don't know. The headphones I was mainly testing with were 24 ohm, so it only needs to have more than 3 ohms of resistance to start hurting things.

The absolute Ohmage isn't really the issue.  The output impedance won't start siphoning off significant volume until the output impedance starts to become significant with respect to the impedance of the headphones.  I'd suspect that the reason your noise goes away with 75 Ohms in series with 24 Ohm cans is that 3/4 of the power output is burning up in heat (so the hum is much less loud).  But you don't need 75 Ohms of output impedance to get strange frequency response fluctuations (as you note).

For example, let's say it's a 6 Ohm output impedance (hardly uncommon).  It's unlikely to affect the noise floor dramatically as it's only consuming about a fifth of the power.  But that's not why high output impedances are pernicious. It's because headphone load impedances (and speaker impedances generally) aren't linear across the frequency band, the 6 Ohm output impedance would be sucking up a different amount of power at 1Khz than at 10 Khz, etc.  This would cause the headphones to exhibit more non-linear frequency response than they otherwise would.  That's why the "rule of 8" exists, to try to minimize disturbances in frequency response from the output impedance of the amp.

I did open it up, and it seemed to be very simple inside. I can post photos of that if anyone wants. (I also managed to do some cosmetic damage to the outside because the switch wouldn't come off easily, oops)
FiiO did initially produce these for their product demonstrations, and offered them up to the Head-Fi community if anyone wanted them (which is why you have to order them direct) so it shouldn't be doing anything detrimental, but I can't explain what I'm hearing.

Maybe doing an A/B test with the tracks synced like this just isn't a good way to approach it.

I'd try finding a way to measure the device before giving up on A/B testing.  It's possible that these devices all sound the same, but it's also possible that the HS2 is affecting the sound.  If you can take a picture of the guts, I might be able to see if there are obvious resistors in series with the outputs, but I might not be able to tell anything from here if they're small, hidden, or integrated.

[6233638]

As I said, there's nothing obvious to me that should be significantly impacting the impedance - it seems to be a direct connection, but I really wouldn't know.



Maybe there really isn't a difference, or maybe something else is causing it. (bad testing procedure etc.)

[mwillems]

As I said, there's nothing obvious to me that should be significantly impacting the impedance - it seems to be a direct connection, but I really wouldn't know.



Maybe there really isn't a difference, or maybe something else is causing it. (bad testing procedure etc.)

Yeah that looks pretty sparse, unless there's something inside the switch or the jack assembly.  No way to know without measurement, but thanks for the nice photos.

Maybe I'll order one and test it, the price is right, and I had a friend who wound up building something to do this because he couldn't find something like the HS2 (and he might want a more compact version). 

[6233638]

Yeah that looks pretty sparse, unless there's something inside the switch or the jack assembly.  No way to know without measurement, but thanks for the nice photos.
Maybe I'll order one and test it, the price is right, and I had a friend who wound up building something to do this because he couldn't find something like the HS2 (and he might want a more compact version).

As it was designed to be used for FiiO to demo their products, I have to imagine that it is properly designed for this task.
So I think there must either be something else in my setup causing problems (thinking about it now, I don't know what the quality is like on the 1/4 to 1/8 adapter I needed, for example) the DACs/Amplifiers really do sound the same,  my hearing is terrible, or the testing methodology is flawed. Maybe I just need to spend some more time with it.

I'm looking forward to reading Matt's impressions are once his turns up.
To be honest though, I just thought it would be an interesting project, and as I said in my post, I'm not that concerned about the results as I'm happy with the DAC2.
I am definitely hearing a big improvement when I use it on its own, whatever the reason for that is.