[joeexp]

Hi. Bimby owner here and I just got a Gumby (gen 2) a week ago. My son, also a headphone audiophile, is visiting and we set up the Mac to output two USB ports at the same time (with drift correction), and set up a well made RCA switchbox with RCA cables running from both DACs into my Black Widow 2. We tried lots of headphones and for the most part cannot tell the difference between the DACs. I think, maybe, I can hear a difference in some female vocals. To me, the bimby might sound a tad smoother on some Female vocals.

I guess I was hoping for larger difference between the DACs...

Thanks

The Gumby needs a few days to warm up properly, to sound its best.

 

[Allanmarcus]

The Gumby needs a few days to warm up properly, to sound its best.

Yes. Thanks. I knew that. They have both been on for over a week.

 

[TK16]

Mine is due for delivery Tuesday.

 

[Don Quichotte]

Mine is due for delivery Tuesday.

Don't forget to check the DC offset of the dac while playing music. I suspect there might be a batch of defective units (see the recent discussion in this thread). And please post your results. Thx.

 

[nicoch46]

for real value the offset must test with no music ie before the relay in this case

 

[Ableza]

Don't forget to check the DC offset of the dac while playing music. I suspect there might be a batch of defective units (see the recent discussion in this thread). And please post your results. Thx.

There is nothing to be gained by this exercise. If a unit produces a large enough DC offset to be an issue you will hear it. If you don't hear it, it's not a problem. Simple.

 

[Don Quichotte]

for real value the offset must test with no music ie before the relay in this case

Why, would you expect a different value? How come?
FWIW, I also did a little experiment. I took a music track, I inverted the waveform in a wave editor and combined the two, resulting in a track of total silence. I played the track, the relays reacted as if it was some real music to be played and, upon measuring the DC offset, I've got exactly the same values as when real music was playing, namely 84mV left and 4.05V right.

There is nothing to be gained by this exercise. If a unit produces a large enough DC offset to be an issue you will hear it. If you don't hear it, it's not a problem. Simple.

Sorry, but I have to disagree. I think it's not so simple. Even if you don't hear a detrimental effect, you could have at least several problems:
1. The dac and the downstream equipment (at least until the signal meets a cap, if there is any to be met) are not working within the intended parameters. It is my understanding that some active components such as transistors will have a worse performance under these conditions - higher distortion and I suppose their thermal behavior might be different too, which I assume could also reduce their life expectancy. As a rather extreme example, a diy tube amp I have heard in my system, that was working perfectly fine with other sources, misbehaved badly when connected to my Gumby - noise, bass distortion, one channel dropped in volume after a few minutes etc. I don't know if it was the DC offset causing this, but I fail to see what else could have been (granted, the preamp might have had a problem as well). This potential for creating trouble was not apparent when I used the dac with other equipment (apart from the already mentioned pops on the right channel).
2. If the DC is amplified in a DC coupled amplified and passed further to the loudspeakers or headphones, the resting position of the cone will be moved from the center of it's excursion range - in other words, it will permanently be "pushed in" or "pulled out" a bit. This will result in uneven forces during the cone movement, as well as not only lower excursion to one side of it's real, correct center position but also higher excursion to the other side - and higher excursion correlates with higher distortion.
3. I've been told that up to 50mV DC offset should be certainly safe for my ex headphones AKG K1000. One can assume therefore that higher than 50mV might not be 100% safe. I had 84mV on the left channel which would be further amplified before reaching a phone such as the K1000, so I would definitely exceed the stated safe zone. My point is that this would happen in spite of the fact that I have not heard anything obviously wrong, such as pops or static, on the left channel and if not for the much higher offset on the right I wouldn't have known something is wrong.

The above sound and reliability issues might be or might be not noticeable at the moment, but might become audible or cause trouble in the future, for example when upgrading partnering equipment (more revealing speakers could make amp distortion more obvious, a DC coupled amp instead of the current AC couple one would start passing the offset to the speakers and so on), if the life of the partnering equipment has been shortened because of operating out of parameters (and you won't even have a clue about it) or when comparing your DC offset afflicted Gumby to a "healthy" one etc. Not to mention a possible drop in resale value.

Given all the above, I think it's reasonable to expect a perfectly functioning unit if I payed perfectly usable money for it, without any "if" or "maybe" regarding sound and reliability, and the same is true for all of you fellow Gumby owners. So, even if you are not convinced or wouldn't bother for your own sake, would it be too much from me to ask you: please, measure and report in order to help me?!

Actually, if this is not an isolated phenomenon, you would also help Schiit, other potential buyers and other current owners too...

 

[KeithEmo]

I'm afraid you're incorrect.

DC itself is totally inaudible.
Things like crackling on the volume control are actually side effects of there being DC present where it should not be.
However, excessive DC can cause problems ranging from none at all to permanently damaged equipment.
Some equipment, by the nature of its circuitry, ignores or is immune to DC offset altogether.
However, it can cause some equipment to temporarily malfunction, and can totally destroy other equipment.
You cannot safely make any sort of generalization about that sort of thing.

Specifically, applying DC to a potentiometer will often cause noises when moving the control - but is unlikely to cause permanent damage.
Applying DC to a speaker or headphone can cause problems ranging from slight distortion to completely burning out the driver elements (and such damage, being abuse, may not be covered under your warranty).
Applying DC to the input of an amplifier may do nothing, or it may cause distortion or even signal dropouts, or may damage the amplifier.
The DC may also be amplified, and passed on to the next component in the signal chain, where it may cause damage.

The precise amount of DC offset which is dangerous will depend on the equipment involved - and where in the signal chain you're looking.
4V DC is absolutely not typical for the output of a DAC (whose normal signal level is around 2V).

There is nothing to be gained by this exercise. If a unit produces a large enough DC offset to be an issue you will hear it. If you don't hear it, it's not a problem. Simple.

 

[Ableza]

I'm afraid you're incorrect.

DC itself is totally inaudible.
Things like crackling on the volume control are actually side effects of there being DC present where it should not be.
However, excessive DC can cause problems ranging from none at all to permanently damaged equipment.
Some equipment, by the nature of its circuitry, ignores or is immune to DC offset altogether.
However, it can cause some equipment to temporarily malfunction, and can totally destroy other equipment.
You cannot safely make any sort of generalization about that sort of thing.

Specifically, applying DC to a potentiometer will often cause noises when moving the control - but is unlikely to cause permanent damage.
Applying DC to a speaker or headphone can cause problems ranging from slight distortion to completely burning out the driver elements (and such damage, being abuse, may not be covered under your warranty).
Applying DC to the input of an amplifier may do nothing, or it may cause distortion or even signal dropouts, or may damage the amplifier.
The DC may also be amplified, and passed on to the next component in the signal chain, where it may cause damage.

The precise amount of DC offset which is dangerous will depend on the equipment involved - and where in the signal chain you're looking.
4V DC is absolutely not typical for the output of a DAC (whose normal signal level is around 2V).

Of course you don't "hear" DC - and if you want to get technical about it you don't "hear" AC either, you only hear the result of a signal after it's been applied to some transducer. DC offset will shift the null of the signal and drive the circuit to operate in unpredictable ways for which it was not designed, causing distortion including often audible hum or clipping. So the simple presence of DC may or may not be audible, depending on what it does to the rest of the system - which was my point. It really doesn't matter if it is there or not if you can't hear the effect.

 

[KeithEmo]

I disagree.

If you don't hear it, but it makes your headphones smoke, then it probably matters.
Likewise, if everything works fine today, but it makes the next amplifier you plug into it smoke, then it's probably not OK either.
Excessive DC on the signal is a potentially destructive condition - and one which should never be present with equipment that's functioning properly.
It is neither harmless nor normal; it is an unusual condition which can reasonably be expected to cause audible problems or actual damage with MANY systems.

Of course you don't "hear" DC - and if you want to get technical about it you don't "hear" AC either, you only hear the result of a signal after it's been applied to some transducer. DC offset will shift the null of the signal and drive the circuit to operate in unpredictable ways for which it was not designed, causing distortion including often audible hum or clipping. So the simple presence of DC may or may not be audible, depending on what it does to the rest of the system - which was my point. It really doesn't matter if it is there or not if you can't hear the effect.

 

[Ableza]

Understood and agree, and unless it is damaged or defective none of that will happen with the types of DC offsets normally found in consumer or pro audio equipment. Which is what this discussion is about. And you'd likely hear an issue if that was the case.

 

[SilverEars]

We hear AC, the humm you hear from a dirty outlet is 60hz, but there maybe overtone as well. The music is mix of AC of various frequencies.

Yeah, DC alone you can't hear(it's 0 frequency. it's not a wave, or cannot cause a mechanical wave). It will push your cone outside the non-biased point and keep it there(if you look, DC is a straight line), and depending on severity, it can cause damage. This is for just strictly DC. DC is a straight line, whereas AC is alternating. The speaker is moving back in forth due to alternation. This back and forth creates movement of air, or sound.

Adding DC is like adding the same value everywhere on the sound signal, which means the sound signal will either shift up or down depending on the DC value(positive or negative). And this shift can be too much that, it can cause distortion since the sound signal has reach and went beyond the supply's voltage limit for the amp. Once again, DC is still is still there as it's added to the music signal, therefore depending on the severity, can damage the driver just like a strictly a DC signal.

 

[Don Quichotte]

Understood and agree, and unless it is damaged or defective none of that will happen with the types of DC offsets normally found in consumer or pro audio equipment. Which is what this discussion is about. And you'd likely hear an issue if that was the case.

This is very black and white. What if the issue consists of higher (but not much higher, not easily identifiable as "bad sound") distortion and you don't know your gear is supposed to sound better? What if you hear nothing wrong because you have an AC coupled amp - and later on replace it with a DC coupled one and have an unpleasant surprise? And so on...

All this discussion only to argue whether it makes sense or not to do a very simple measurement with a voltmeter!?

@KeithEmo: According to your knowledge, what is the highest DC offset you would deem acceptable (so would not see as a malfunction) in a dac or CD player? Thanks!

 

[Allanmarcus]

Folks, how about you move the DC offset discussion to a different thread and keep this discussion about the Gungnir?

 

[KeithEmo]

I'm going to answer this one last question - since it does relate to this particular thread - then I'm not going to talk about DC offset any more in this thread.
In a line level device like the Gungnir, I would consider anything over 50 mV - 100 mV to be a lot of offset.
Even that is a bit high by today's standards (it probably isn't dangerous - but I would ask the manufacturer if it's normal.)
(While the offset on a power amp might drift slightly higher, and would be difficult to measure under signal conditions, I would expect to see a similar number when no music is playing and it's warmed up.)

This is very black and white. What if the issue consists of higher (but not much higher, not easily identifiable as "bad sound") distortion and you don't know your gear is supposed to sound better? What if you hear nothing wrong because you have an AC coupled amp - and later on replace it with a DC coupled one and have an unpleasant surprise? And so on...

All this discussion only to argue whether it makes sense or not to do a very simple measurement with a voltmeter!?

@KeithEmo: According to your knowledge, what is the highest DC offset you would deem acceptable (so would not see as a malfunction) in a dac or CD player? Thanks!