Inside the latest Benchmark DAC1 - Page 12

I returned the HOSA connectors and bought an HOSA headphone to RCA female adapter. I kept using GE ultra-pro unbalanced cable.

When I used the HOSA XLR->RCA connector with pin 3 connected to ground, I thought it sounded better than RCA output. Maybe it was just placebo effect.

I will try to do some blind testing to see of headphone output to integrated amplifier actually sounds better than RCA output.

I got my roomate to help me yesterday with some single blind testing.
I was comparing RCA output (1250 ohm) via cheapest radioshack 12 ft cable ($6) versus headphone output (0 ohm) via HOSA headphone->RCA adapter ($5) and GE ultra-prograde RCA 12 ft cable ($10).
The CD used was Harmonia Mundi/Bach Flute Sonatas vol 1.
This CD contains well-recorded harpsichord, very beautifully vibrant.
I tried to detect a difference by listening to the subtleties of string vibrations in the harpsichord. In my experience this is a very revealing test for hi-frequency extension.

I used the harpsichord solo in the beginning of track 3 (~30 s) to evaluate different connections. Headphone output is set to the same volume as the unattenuated RCA output. I used the input selector on my integrated amplifier to switch between the two.

I first did some non-blind testing myself. I was expecting the headphone output to sound better because of its lower output impedance. At first I did not discern any difference. After extended listening I thought I heard subtle differences in two particular notes. I thought with headphone output these two notes sounded more vibrant.

Then my friend came in to help me do the blind test. He designated the two outputs A and B and helped to switch them. On those two notes, again I heard some differences. B was more vibrant than A. And 80% of the time I was able to guess if it was A or B being played, when he randomly chose one or the other to play. My conclusion was that B sounded better because it carries more details. But the difference is so subtle I don't think it really matters. Much to my surprise though, B turned out to be the RCA output. Therefore my final conclusion is that headphone output is not as good as RCA output for connecting to amplifier. When I first expected headphone output to sound better due to low impedance, it did sound better in a non-blind test. However, blind test also revealed the same difference but in favor of RCA output.

I have learned several important lessons in this test:
1) Blind testing is extremely important. When I was psychologically biased, I heard a difference and the one I expexted to sound better sounded better. During blind test, I heard the same difference but the verdict for the better sound went to what I expected to be worse.
2) Even if there is a difference, the psychologically favored component is likely to sound better. If there is no difference, psycholgical effects can probably still create differences out of thin air.
3) These two outputs are drastically diffrent. Headphone output is NE5532/BUF634/0 ohm and RCA output is NE5532/1250 ohms. The differences are so subtle and could hardly be discerned on two particular notes on a very special recording. I don't think such differences have any relevance in real-life listening.
4) If extra IC in the signal path and huge discrepancies in impedance only affects audio signal so little, I wonder what difference can cables make except for better contact at the connectors?

Thanks for the lesson. I think if more blind testing are, many exotic cable manufacturers will go out of business.

I'm confused.
I've performed a blind test, too.
Opposite result, that's the problem.
My configuration:
Flac and MP3 --> RME --> Benchmark.
I've tried to calibrate the volume as good as possible by using a sine wave from a test tone CD and a multimeter.
I've used a cheap 1/4 " to RCA adapter and two identical Tech+Link RCA-RCA ICs, decent budget cables(about 30$ each) into a passive preamp.
The preamp should have a negligible effect.
In order to avoid subconscious influences this part of the rig was mounted onto the other side of the wall.This is the place where my PC is located most of the time since I don't want to listen to my computer fans, I've simply drilled a hole through the wall for the cables.
At my side of the wall an older Stax Lambda system (SRM-T1S/Lambda Nova)was connected to the preamp through the hole via an Oehlbach RCA IC (about 60$).
My girlfriend randomly switched (or not) 100 times.
In the morning, in the evening, next day, no listening session longer than 20 minutes to avoid fatigue.
My hit ratio was 79/21, that's more than significant.
What I don't want to tell you is that my hearing is superior.
I seem to have a lousy hearing, I can't hear a difference between a properly ripped and encoded 256 kbit MP3 and Flacs.
I can't hear a difference between a decent budget cable and an expensive high end cable in a blind test.
And so on.
Your probably superior hearing makes our differing results even more confusing.

Cosmopragma, so you heard that headphone output sounded better than RCA output, how is it different? Is it big?
I never thought I have a superior hearing, but I can only hope I have normal hearing.
Becuase I thought cables should not make a difference, so I used different cheap cables for each output. Maybe it is not so smart to do so.
Also, I did not do enough trials to allow a rigorous statistical analysis.
At last, I only used a very short music passage as comparison material.
Maybe I heard a slight difference, but "is different better?" is another issue.
I might very well be wrong about which sounds better. The main message I am trying to get across is that the differences between headphone and rca outputs are so tiny that I have decided to stop worrying about it.

If I got this correct, your setup was like this:
headphone jack of DAC1-->passive preamp-->Stax headamp-->Stax cans
RCA out put of DAC1-->passive preamp-->Stax headamp-->Stax cans

On the other hand, I was comparing using my speaker systems:
headphone jack of DAC1-->hybrid integrated amp-->speakers
RCA out put of DAC1-->hybrid integrated amp-->speakers

I heard that passive preamps have special impedance matching circuits inside them. My line level signal is going into a tube, on the other hand. The setup is really quite different. Maybe that is why we heard opposite things.

I am running my rig fully balanced, from the Benchmark DAC1 to the Accuphase E-211 integrated amp. What more can I wish for?

P.S. Actually I wish I had the money for a pair of B&W 805's.

cosmopragma,
i wouldn't worry about your ears - i would rather commend your pragmatism

there has been an mp3 test done by the german computer magazine c't in 2000 whose broad results still hold: while 128bit mp3 could be differentiated from cd under blind conditions, 256bit could not. interestingly, the only tester consistently (though not always) able to differentiate between cd and 256bit was somebody with a special hearing impairment. so if you don't hear a difference in blind test between cd and 256bit mp3, your ears are probably ok...

some would argue that if you don't hear differences between cables under blind condition, not only are your ears ok, but so is your resistance against self-deception (i hope i'm not out of line with that statement, if i am, i sincerely apologize. i have seen where blind test debates can lead, and the last thing i would want is some of that on head-fi)

short summary of the c't mp3 test (in german)
http://www.heise.de/ct/00/06/092/

come to think of it, doesn't fellow head-fier lini work for c't?

as a potential buyer of the benchmark i'm very interested in cosmopragma's and ferbose's tests and results - if you both hear differences but in different directions maybe it's simply a matter of preference? from all accounts i've read so far (some engineers among them) the benchmark dac is supposed to be clean and neutral in an almost absolute sense. this is studio gear for the recording engineers who depend on this neutrality and un-changed sound.

but maybe some of us prefer a little less resolution on some cds, and maybe the high impedance balanced output changes (degrades) the sound very slightly in that direction if used with an unbalanced amp? that's just a wild uneducated guess though, but if i understood correctly jsiau from benchmark has stated that there should be no sound degradation if the headphone out is used.

about the hpa2 intergrated headamp
<THD+N at headphone inputs: 0.0003% typical - under load! from the http://www.benchmarkmedia.com/interf...a2/default.asp > is it able to sustain this accurately across the entire spectrum constantly, which phones have you tested with it? Any cool test equipment you can tell us about?

thanx,

Sergio

Nice question.
I thought about an answer:
The difference is big enough for a good hit ratio in a blind test, that's enough for me to invest another 20$ in parts for XLR -->RCA cables.
The small but desirable difference I perceive is in the treble, I think it's a more coherently balanced overtone spectrum.
BTW, I never listened to an audio system, speakers or headphones, that was 100% capable of reproducing the overtones of a piano or violins, but some systems are closer to reality.
But I'm not sure, maybe I'm just rationalizing a statistically significant emotion based on something else.
Exactly.
Too many variables, but no problem at all since we both own a Benchmark DAC and are enjoying it.
What a wonderful world

I checked the manual but could not find a answer.
What are output pads?

TIA

Looking at the manual I just downloaded, it states:
"The output impedance at
the RCA jacks is 30 Ω and is low enough to allow for the use of high or low capacitance cable and the common
high capacitance of consumer receiver/amplifier inputs. Mono summing with a “Y” cable is not recommended as
this will cause high amounts of distortion."

This manaul is dated:
DAC1 - Manual - RevH-05-01-04 (2).doc Page 8 of 39 Ed. 1/4/2005

Has the product changed so that now the unbalanced output is 30 ohm (comparable to nonattenuated XLR)?

Thanks

edit: Nevermind, I see that this change was made with Rev F ofthe PCB. Have to make sure I get that one,