[tylerfutrell]

Perhaps someone can answer this question. I was comparing NFB-11.28 to Atom, using the NFB's DAC to isolate differences in the amp sections only. I was listening to "Apostolo glorioso" by Dufay on Spotify (Lorelei Ensemble). 10 seconds in, only when Atom and NFB's DAC are both in high gain (NFB has variable DAC output for some reason), there is a static/distortion sound, first in the left ear, then the right. This does not happen when using the NFB's amp section, or when using Atom in low gain, or when using SDAC instead of NFB's DAC (in either high or low gain on Atom) - even when turning the low gain on Atom up so that it's much louder than the high gain, it still only makes the static noise on high gain. This is bizarre, isn't it? If it were clipping (or something else) in the DAC, it would happen on NFB's amp section too, and if it's clipping in the amp, it would still happen with SDAC, but it doesn't. Changing RCA cables didn't matter. Anyone have ideas what's going on? My only thought is that Atom outputs more power/current/whatever in high gain, even at lower volumes, but don't know if that makes sense.

Summarized:

NFB DAC (high) -- Atom (high) = static

NFB DAC (low) -- Atom (high or low) = no static

SDAC -- Atom (high or low) = no static

NFB only (high or low) = no static

 

[tomb]

It appears to me that the high gain on the NFB DAC is too much for the Atom. Not being familiar with the Atom, it could still have an input circuit that is more sensitive to the high gain from the NFB than the SDAC. The input circuitry of an amp can clip and yet the amp can still be louder with a lower-gain input. The two are often at distinctly different stages in the amplifier circuitry.

For instance, the volume pot on the O2 headphone amplifier is in-between the input stage and output stage on the O2. This has some advantages in reducing noise and distortion, but has the disadvantage in that the input stage can clip because the volume pot comes after the initial amplification. If the Atom is similar, that may be what's happening. The NFB DAC can have a stronger than normal source signal at high gain. Most headphone amplifiers have the volume pot as the first point in the circuit after the input connection. That means the volume pot is always able to attenuate without clipping the input signal, regardless of strength of signal. If the volume pot is later in the signal path, it's possible the signal can clip at certain components before the volume pot ever has a chance to attenuate the signal.

Not saying that's what's going on, but it could explain it.

 

[tylerfutrell]

Thanks, that certainly sounds possible. JDS does say they designed Atom using what they learned on the O2, so it's quite possible they kept the pot in the same chain-position, especially since they seem quite concerned with noise and distortion measurements. The NFB high gain DAC output is 2.5 VRMS (which I understand is uncommon), while the SDAC is 2.15 VRMS. It's a pity if that is the problem, since I ordered an Airist RDAC that also outputs at 2.5 VRMS.

 

[ProtegeManiac]

Perhaps someone can answer this question. I was comparing NFB-11.28 to Atom, using the NFB's DAC to isolate differences in the amp sections only. I was listening to "Apostolo glorioso" by Dufay on Spotify (Lorelei Ensemble). 10 seconds in, only when Atom and NFB's DAC are both in high gain (NFB has variable DAC output for some reason), there is a static/distortion sound, first in the left ear, then the right. This does not happen when using the NFB's amp section, or when using Atom in low gain, or when using SDAC instead of NFB's DAC (in either high or low gain on Atom) - even when turning the low gain on Atom up so that it's much louder than the high gain, it still only makes the static noise on high gain. This is bizarre, isn't it? If it were clipping (or something else) in the DAC, it would happen on NFB's amp section too, and if it's clipping in the amp, it would still happen with SDAC, but it doesn't. Changing RCA cables didn't matter. Anyone have ideas what's going on? My only thought is that Atom outputs more power/current/whatever in high gain, even at lower volumes, but don't know if that makes sense.

Summarized:

NFB DAC (high) -- Atom (high) = static

NFB DAC (low) -- Atom (high or low) = no static

SDAC -- Atom (high or low) = no static

NFB only (high or low) = no static

When you feed it into the Atom are you on fixed output line out mode or does the NFB-11's volume work? Does the gain change the output? Because it's not supposed to, normally.

AFAIK the switch itself doesn't really do that - there's some jumper inside that you need to disconnect to switch over to fixed line output.

If the gain switch and the volume control both work you're basically using two preamps and you're sending a higher voltage signal into the Atom instead of locking it to 2V.

 

[tylerfutrell]

When you feed it into the Atom are you on fixed output line out mode or does the NFB-11's volume work? Does the gain change the output? Because it's not supposed to, normally.

AFAIK the switch itself doesn't really do that - there's some jumper inside that you need to disconnect to switch over to fixed line output.

If the gain switch and the volume control both work you're basically using two preamps and you're sending a higher voltage signal into the Atom instead of locking it to 2V.

I was using fixed line out to maintain my volume matching (I think I remember needing to do something inside the unit to use that option), so volume pot is disabled but gain switch still has an effect (I believe the amp doesn't actually have variable gain, so it's always the DAC making the change, but that's just my theory). Also nfb DAC is 2.5 volts not 2 in high gain, if that matters.

 

[ProtegeManiac]

I was using fixed line out to maintain my volume matching (I think I remember needing to do something inside the unit to use that option), so volume pot is disabled but gain switch still has an effect (I believe the amp doesn't actually have variable gain, so it's always the DAC making the change, but that's just my theory). Also nfb DAC is 2.5 volts not 2 in high gain, if that matters.

Weird that the output doesn't bypass that but then again there's only so much they can cram in there.

2.5V is still a bit too high. 2V is Sony Redbook standard for single ended. 4V is for balanced ie long cable connections for pro applications.

While some car audio receivers including Sonys have 4V (and some Pioneers 6.5V, Eclipse at 8V), car amps have their own gain knobs to adjust. And these are always on preamp mode, which you never hit on sane listening levels - anything over 2V is only really used for SPL compatitions (or idiots who drive around like they're at an SPL drag race).

 

[PurpleAngel]

Perhaps someone can answer this question. I was comparing NFB-11.28 to Atom, using the NFB's DAC to isolate differences in the amp sections only. I was listening to "Apostolo glorioso" by Dufay on Spotify (Lorelei Ensemble). 10 seconds in, only when Atom and NFB's DAC are both in high gain (NFB has variable DAC output for some reason), there is a static/distortion sound, first in the left ear, then the right. This does not happen when using the NFB's amp section, or when using Atom in low gain, or when using SDAC instead of NFB's DAC (in either high or low gain on Atom) - even when turning the low gain on Atom up so that it's much louder than the high gain, it still only makes the static noise on high gain. This is bizarre, isn't it? If it were clipping (or something else) in the DAC, it would happen on NFB's amp section too, and if it's clipping in the amp, it would still happen with SDAC, but it doesn't. Changing RCA cables didn't matter. Anyone have ideas what's going on? My only thought is that Atom outputs more power/current/whatever in high gain, even at lower volumes, but don't know if that makes sense.
Summarized: NFB DAC (high) -- Atom (high) = static, NFB DAC (low) -- Atom (high or low) = no static, SDAC -- Atom (high or low) = no static, NFB only (high or low) = no static

Could there be a grounding loop?
Are the Atom and NFB-11.28 using the same surge protector/power strip?
Try making the Atom and NFB-11.28 have as separate as possible power feeds, like eash using a separate surge protector.

 

[tylerfutrell]

Could there be a grounding loop?
Are the Atom and NFB-11.28 using the same surge protector/power strip?
Try making the Atom and NFB-11.28 have as separate as possible power feeds, like eash using a separate surge protector.

No, they were plugged into different sockets.

 

[tomb]

Thanks, that certainly sounds possible. JDS does say they designed Atom using what they learned on the O2, so it's quite possible they kept the pot in the same chain-position, especially since they seem quite concerned with noise and distortion measurements. The NFB high gain DAC output is 2.5 VRMS (which I understand is uncommon), while the SDAC is 2.15 VRMS. It's a pity if that is the problem, since I ordered an Airist RDAC that also outputs at 2.5 VRMS.

I suspect that the variable gain in the NFB DAC is probably even higher than the 2.5VRMS specified. Still, you may want to check with JDS if the Atom places the volume pot in the same circuit position as the O2. If so, then this may be an issue that could continue.

All that said, is there any issue with simply using a lower gain? Choice is often there for a reason. If it doesn't work at high gain with some amps, then don't use it.

 

[tylerfutrell]

All that said, is there any issue with simply using a lower gain? Choice is often there for a reason. If it doesn't work at high gain with some amps, then don't use it.

Just power hungry cans, especially when EQ is being used on uncompressed classical... It's really not a problem that comes up much, more of a mystery that peaked my curiosity.