[yourmando]

Quote:

Originally Posted by EliasGwinn /img/forum/go_quote.gif Well, you could test to see if this eliminates the hum by using a scrap of wire and just touching the rca sheild to a bare part of the chassis. If so, then you could try something more permenant. Thanks, Elias

Unfortunately, this did not work. I've been troubleshooting more with the help of the Linkwitz Orion user forum. The DAC1, ATI amplifier, and active crossover/asp all have properly designed chassis ground (I'm not ruling out that one of the pieces is defective). This is unusual in that if only those 3 components are connected to the same power strip/socket, I get ground loop hum. And there are others with identical components with no hum.

The only solution I could find was to float the ground in either the DAC1 or the ASP/crossover (I did not attempt to float the amp). This breaks the loop and kills the hum. So I am leaving the ASP floated with a two-prong plug. This solves the problem, but I do feel like I'm "cheating."

Everything is still grounded through the shield of the interconnect, so I should be ok (I hope

)

Thanks again,
Armando
P.S. I'd also be interested to see some more Audio Precision type measurements on a Jensen, just out of curiosity. I love how the DAC1 has tons of performance measurements.

 

[Bostonears]

Quote:

Originally Posted by yourmando /img/forum/go_quote.gif The only solution I could find was to float the ground in either the DAC1 or the ASP/crossover (I did not attempt to float the amp). This breaks the loop and kills the hum. So I am leaving the ASP floated with a two-prong plug. This solves the problem, but I do feel like I'm "cheating." Everything is still grounded through the shield of the interconnect, so I should be ok (I hope )

It is unsafe to use a cheater plug to float the ground. If a short were to develop inside the unit, unimpeded AC voltage could zap anyone who touches the chassis.

If floating the ground removes the hum, a better solution is to use a Hum-X from Ebtech, which is designed for the specific purpose of breaking an AC ground loop while still leaving the ground intact. It's available for about $60 at many online stores. I used one quite successfully when I had a nasty ground loop between a DAC and a tube amp. (I put the Hum-X on the DAC's AC line, and I didn't notice any audible degradation of signal besides killing the hum.)

 

[Crowbar]

Why pay $60 when there's an $2 way to defeat ground loops? Leave earth connected to the chassis, but between earth and the power supply ground use a heavy 10 ohm resistor, paralleled with two antiparallel diodes (opposite directions, in parallel) of a current rating higher than the equipment fuse to provide protection if the resistor burns, and a 100 nF cap to bypass RF.

 

[Bostonears]

Quote:

Originally Posted by Crowbar /img/forum/go_quote.gif Why pay $60 when there's an $2 way to defeat ground loops? Leave earth connected to the chassis, but between earth and the power supply ground use a heavy 10 ohm resistor, paralleled with two antiparallel diodes (opposite directions, in parallel) of a current rating higher than the equipment fuse to provide protection if the resistor burns, and a 100 nF cap to bypass RF.

That may in fact be what the Hum-X does, although your DIY solution would be beyond the skills of many users. (Not everyone is a DIYer.) Either way, the point is that a cheater plug is unsafe for devices intended to be grounded. Any solution that works without compromising the safety of the ground is fine.

 

[Bysheon]

Excellent thread. I've read most of it and the discussions in this thread was one of the reasons I decided to buy the dac1. I'm very satisfied with my dac1. Kudos to Benchmark for this great product.

A quick question - can changing the USB polling rate, for example changing the frequency to 1000Hz, affect the performance of dac1? I want to to this to improve my gaming experience, but my tech knowledge is kinda zero. Is it safe to do this?


Edit: Spelling

Thanks

 

[EliasGwinn]

Quote:

Originally Posted by Bysheon /img/forum/go_quote.gif Excellent thread. I've read most of it and the discussions in this thread was one of the reasons I decided to buy the dac1. I'm very satisfied with my dac1. Kudos to Benchmark for this great product. A quick question - can changing the USB polling rate, for example changing the frequency to 1000Hz, affect the performance of dac1? I want to to this to improve my gaming experience, but my tech knowledge is kinda zero. Is it safe to do this? Edit: Spelling Thanks

Hello Bysheon,

The DAC1 USB is not affected by the USB polling rate. Polling rate only affects items that use 'interrupt transfer mode', such as a mouse. It determines how often the computer 'asks' the device if there is a request for action.

The DAC1 USB uses 'isochronous transfer mode'. This means that it establishes a data-flow connection of a certain bandwidth with the computer, and then continues at delivering data as it becomes available. In this case, the data rate is similar to the polling rate, but it is determined by the sample-rate of the audio.

Thanks,
Elias

 

[Bysheon]

Quote:

Originally Posted by EliasGwinn /img/forum/go_quote.gif Hello Bysheon, The DAC1 USB is not affected by the USB polling rate. Polling rate only affects items that use 'interrupt transfer mode', such as a mouse. It determines how often the computer 'asks' the device if there is a request for action. The DAC1 USB uses 'isochronous transfer mode'. This means that it establishes a data-flow connection of a certain bandwidth with the computer, and then continues at delivering data as it becomes available. In this case, the data rate is similar to the polling rate, but it is determined by the sample-rate of the audio. Thanks, Elias

Hi, Elias
Thanks for the guick answer! Good news.

 

[Terje]

If you type youtube.com in your url and Benchmark DAC1 USB in the search field....you can see an interview with director of technical engineering at Benchmark Jhon Siou...and a blip of DAC1.

 

[John Reeves]

Hi,

I am the owner of a DAC-1, and am very pleased with it. I did get eyestrain reading through all the posts although this was a little academic since I had already got the DAC-1.

I am contemplating new headphones for use with the headphone output. I do not want to use my UE10's, and want to improve on my Ultrasones.

I noted that the headphone out was designed for Senns HD650 and wished to know if anyone had tried these headphones and compared the sound with a dedicated headphone amp. It does seem that to get the best out of the Senns you need a Cardas or similar cable and a carefully matched head amp. Ditto for the HD600's.

Any comments would be much appreciated.

Regards

John

 

[EliasGwinn]

Quote:

Originally Posted by John Reeves /img/forum/go_quote.gif I noted that the headphone out was designed for Senns HD650 and wished to know if anyone had tried these headphones and compared the sound with a dedicated headphone amp. It does seem that to get the best out of the Senns you need a Cardas or similar cable and a carefully matched head amp. Ditto for the HD600's.

Hello John,

Thanks for joining our thread.

The headphone amp built into the DAC1 is not specifically designed for the Sennheiser HD650's. We simply recommend the 650's as a high-quality companion to our products.

The DAC1 contains a headphone amp design that was initially a stand-alone module that has become very highly regarded amond audio professionals. The amp built into the DAC1 is the HPA-2, which has been integrated into audio consoles used by television, radio, recording, and mastering studios around the world. They've replaced the console's stock headphone amp with the HPA-2 module to be used as a reference headphone amp. We put the exact same HPA-2 circuit in the DAC1 / USB / PRE.

Thanks,
Elias

 

[poo]

Hey Elias,

There is much debate regarding how to best drive/power the HD650s. For a long time, my HD650s have been my primary headphones, driven directly from the HPA-2 of my DAC1 USB. Sounds fantastic, but I often wonder if there is more to appreciate by adding an external headphone amp to the mix.

Most comments regarding this issue seem to relate to voltage, suggesting that (summarised) 'for the HD650, the more voltage the better'.

Can you comment on this? Does your experience suggest that I will or won't benifit from adding an amp in this case?

Thanks again for your help.

 

[EliasGwinn]

Quote:

Originally Posted by poo /img/forum/go_quote.gif Hey Elias, There is much debate regarding how to best drive/power the HD650s. For a long time, my HD650s have been my primary headphones, driven directly from the HPA-2 of my DAC1 USB. Sounds fantastic, but I often wonder if there is more to appreciate by adding an external headphone amp to the mix. Most comments regarding this issue seem to relate to voltage, suggesting that (summarised) 'for the HD650, the more voltage the better'. Can you comment on this? Does your experience suggest that I will or won't benifit from adding an amp in this case? Thanks again for your help.

I'm not sure I understand the idea about 'more voltage = better'. Higher voltage will only increase volume. Unless they are referring to voltage rails. In that case, higher voltage rails will get you more headroom...i.e., more output before clipping. The HPA-2 operates with 18V rails...about as much as you'll find anywher.

I don't think there is anything to gain from adding an external headphone amplifier. The HPA-2 in the DAC1 is our top-of-the-line, studio reference quality headphone amp. We didn't skimp at all when building into the DAC1. Its got 0-ohm output impedance, which will tame even the lowest-Z headphones on the market. It has enough headroom to drive a load at the end of 1000' of cable without struggling, and operates gracefully at lower gain settings as well.

I don't think there is another headphone amp on the market that can do what the HPA-2 does, as cleanly as it does it.

Now, with all that said, if you're looking for a headphone amp that will color the sound, add warmth, etc, then you may want to look for another headphone amp. The HPA-2 is designed for maximum transparency.

Thanks,
Elias

 

[poo]

Thanks Elias - fully answers my speculation... colour isn't my thing at this stage

 

[infinitesymphony]

I see a Benchmark DAC1 USB in my future.

Elias, you'd said earlier that Benchmark is constantly evaluating the performance of new DAC chips. Have there been any contenders to the Analog Devices AD1853, and is it still the best for this purpose/implementation? I'm always interested in reading more about the objective differences between DACs.

 

[nettokung]

I use it with my system (W2002+HA2002). the sound's great and better than my old soundcard.