REVIEW (in progress) - Nuforce HDP 24/96 USB-Optical 24/192 Coax DAC Preamp and Headphone Amp - Page 11

It could be a ground loop issue or something?

Please bear with us on the availability of HDP. This thing is difficult to make and test so we didn't dare to commit to a large production for the pilot run. There is a digital daughter board that is isolated and snapped onto the main board. The factory in Taiwan won't open until 2/22 . The good news is that there will be 200 HDP available for shipping on 2/25, at least half of those will make it to the US.

Yes, but one thing you did not try is my ears

I've had many combos that hissed that no one else thought hissed. RA-1 into RS-1, HD497, all earbuds. XP-7 into RS-1, HF-1, HD497, all my earbuds.

The only amp I've tried that I've heard no hiss out of with any of my headphones is the Tomahawk. That is the one and only one. (of the ones I owned). I'm sure there are many others that have no detectable hiss, ones designed for IEMs especially. But I am usually a miss when it comes to finding something silent enough.

By the way, I can hear a little hiss out of the udac as well with the E4C (which means it will be even more pronounced with the se530) but it is at a much lower level than what I hear out of the HDP.

I'll give it some time, maybe some static has to dissipate (there is some warning about static dissipation on the box). But I mean, it hisses when the volume control is off and the power light turns off. I even had it connected to only power with nothing else (avoid any possible ground loops). The only time the hiss goes away is if I unplug the power.

comment #2. The 3.5mm analog line-in seems to be have it's channels reversed. I have not tried the RCA jacks yet. Larry, could you check on that with your unit?

Actually, I was wondering if it was some extraordinary hearing on my part. But I don't think so, as in all instances of my equipment hissing testing 2 of my other friends could hear the hiss as well when I let them try it. Unless by some odd luck, the people I chose to sample also have incredibly sensitive hearing.

I'm going to take the HDP home later so it's a completely different environment and try it out with many more headphones. There could be any number of factors contributing to hiss. Maybe impedance being low coupled with high sensitivity affects this amp more than straight high sensitivity like the es3x. Maybe I'm using it in a completely silent environment vs it being used in a more normal environment. Maybe there is some interference where it sits right now. Or maybe simply my unit is defective.

More investigation tonight once I take it home.

wrong thread

I need to get to the bottom of this hiss issue I have, more testing and a report later.

I've emailed nuforce about the channel swap, hopefully they'll be able to do something about it in time.

The ability to see through venetian blinds has its trade offs.

Yes, confirmed that 3.5mm analog L/R is swapped. Too many combination to test and we missed this one. Here's what we are offering:
1) recall all HDP (only a few went to end users) and we'll ship by express mail back.
2) offer free shipping and 20% discount via partial refund
I guess that's why we need to have a small 1st production run

Should we PM you here,send an e-mail to iconsupport@nuforce.com or use the help desk at Nuforce.com | Service & Refund regarding the options?

As you see, Nuforce has excellent customer service! Jason, it would be nice if you could clarify if it is (1 and 2), or (1 or 2).

When I got home and tested my HDP more, this is what I found:

-AKG K701 - no detectable hiss
-Grado RS1 - I could perceive a very light hiss, feels more like tension. I could survive with this level of hiss
-E4C - hisses noticeably
-JVC marsmallow - hisses louder than e4c
-SE530 - hisses like mad, music can't be enjoyed at all.

Now here's the part that has me thinking there is something wrong with my unit, it seems clearly defective. Most easily seen with my se530 (or any of my other IEMs), but I also notice it with my RS1.

1. With the volume at 9 o'clock (unit standing straight up), no inputs connected, the "D" (digital input) setting has a high pitched squeal. It gets louder as you raise the volume more. The "U" (usb) and "A" (analog) settings don't have this squeal. 9'oclock is where the sound usually becomes normal listening volume. This occurs with nothing connected to the unit but power.

2. With the analog RCA being fed I can hear the music at a low level when the switch is in the U or D settings. It is around the volume of the hiss. Trying to play music you hear a blend of both songs. If I turn off the amp, the bleed through goes away and the unit simply hisses.

3. The volume from off to when it starts raising the volume above the noise floor (hiss + bleed through) is almost 45 degrees of rotation. Yes, I'm saying the first 45 degrees don't seem to do anything with the volume. Then, once the music volume starts to raise, it is right first, then the next slightest rotation brings the left to balance, but at this point is is far too loud for my comfort with the SE530. From very low to very high volume in barely a touch. The K701 is my only headphone I can manage the volume ok.

4. The only way to get rid of the hiss is to unplug the unit. When it's plugged in and the amp switch is OFF I can still hear the same hiss.


Since I'm local I'm going to have nuforce take a look at my HDP sometime next week. I'll also bring in my SE530 and see if they have some test units I can plug into and see if the hiss exists there. I certainly hope it's a sample defect and not a design problem.