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iBasso D42 "Mamba" with dual dacs! !! Hey Hey! Improved Starting on Page 76 . - Page 54

post #796 of 1153
Does anyone know if the recently shipped D4s have the same distortion problem in the DAC when setting the volume on the computer to 100%? Do they need the 2.2k mod?

Is there a way that I can check my early feb one?
post #797 of 1153
Myself and others here haven't had any distortion issues at all with the D4. It makes me think that there must be other factors involved other than 100% volume.
post #798 of 1153
Quote:
Originally Posted by dongringo View Post
Myself and others here haven't had any distortion issues at all with the D4. It makes me think that there must be other factors involved other than 100% volume.
Yes, there are other factors involved. The distortion threshold is determined by the input voltage. Not all source inputs are the same. Many of these distortion issues can be caused by incorrect mastering of the music source. One notable example can be found on some of the Norah Jones albums.

Input distortion can also be caused by the use of opamps that have a low input voltage range. This can be checked on in the datasheet specs for the selected device.

Distortion can also be caused by setting the source volume too high if using the source headphone output rather than a true line-out.

There should not be audible distortion when using a true line-out as the source for your D4 unless the music was incorrectly mastered at the studio.
post #799 of 1153
Quote:
Originally Posted by HiFlight View Post
Yes, there are other factors involved. The distortion threshold is determined by the input voltage. Not all source inputs are the same. Many of these distortion issues can be caused by incorrect mastering of the music source. One notable example can be found on some of the Norah Jones albums.

Input distortion can also be caused by the use of opamps that have a low input voltage range. This can be checked on in the datasheet specs for the selected device.

Distortion can also be caused by setting the source volume too high if using the source headphone output rather than a true line-out.

There should not be audible distortion when using a true line-out as the source for your D4 unless the music was incorrectly mastered at the studio.
I think it was distortion from the DAC portion of the D4 itself, when using it as a DAC for a computer. Word was that if you set the volume on the computer volume to 100%, it would distort the signal, and you should therefore set it to 80%. Not the master volume slider bar, but the slider in the app you're using. The issue as I understand it is for the internal DAC, not for a line in connection from an external source.
post #800 of 1153

D4 Distortion

I am struggling with this issue even with the volume on Itunes set at 80%. I have sent the unit back to the retailer who was very helpful but ultimately could only say that they replicated the problem on another one of their D4's.

On big choral music or jazz with very closely miked instruments I am still getting quite severe distortion on peaks.

My source is a macbook pro 2008 vintage.

I am beginning to think that there is a real problem with the D4 design.

I have seen the following "solutions" mentioned and I would be really grateful if someone could point me in the right direction for details so that I can have a go at sorting the problem out.

1. Inserting some attenuators to reduce signal levels.

2. The "2.2k" solution

3. The use of a "true line out" from my computer.

I am not very technical so may need some hand holding.

I am very frustrated and disappointed so I would be very grateful for any help.

Thanks in advance.
post #801 of 1153
Although I have heard some clipping a few times on my D4, I feel certain it is in the mix, as it is repeatable even with reduced volume on the source. I did the 2.2k mod and since heard no clipping, but I can't say for sure whether it is the result of the mod or not.

FWIW, I have never heard clipping when listening to streaming music from my computer.

I do believe that the design of the D4 is sound, and the DAC simply translates what it is fed, good or bad. I have not discovered any circuit glitches or shortcomings in the last several iBasso amps that have reached production.
post #802 of 1153
Thread Starter 
I did the change to the gain of the op amp with the resistor but I am not sure I like the sound. It is more etched and while sounding more detailed it may be do to the etched sound but not more musical detail.
post #803 of 1153
Quote:
Originally Posted by HiFlight View Post
Although I have heard some clipping a few times on my D4, I feel certain it is in the mix, as it is repeatable even with reduced volume on the source. I did the 2.2k mod and since heard no clipping, but I can't say for sure whether it is the result of the mod or not.

FWIW, I have never heard clipping when listening to streaming music from my computer.

I do believe that the design of the D4 is sound, and the DAC simply translates what it is fed, good or bad. I have not discovered any circuit glitches or shortcomings in the last several iBasso amps that have reached production.
I too believe the problem to be with recording quality. There is section of one Dream Theater song I listen to a lot (The Count of Tuscany) that has a very slow, atmospheric guitar solo where I get some audible distortion in the treble peaks using the D4 dac. I tried the D10 and it sounded exactly the same. Then I plugged straight into my Turtle Beach soundcard and it still had the distortion. There are a few other instances of distortion that takes place at specific peaks. I tried the same test and the results were the same.
post #804 of 1153
When an amplifier clip harmonics are added to the sound. The frequencies are in multiple of the original, many of which would not be audible to the human ear. It is not easy to know just by listening if the amp is clipping, but if the sound do crack it is very serious.

Many people like the sound of clipping actually. Especially if you are into Metal music. The added harmonics gives the sound more body and some air around it.

In fact, many guitar amplifier comes with this clipping feature some even modify their amp to clip Add Diode-Clipping Distortion to your Guitar Amp. In the url there is a video where you could hear the effects of clipping.

On the D4, clipping happened on the DAC section, Clipping will only occur if you used the USB input, with audio signal from the source at more than about 80% of the max.

Using the line in to D4 only uses the Amplifier hence no clipping, it does not matter what the volume setting on the D4.
post #805 of 1153
I'am feeling I should stop using alkaline and get some rechargeables,I know most of you mention a few different types but most of them are not readily available down under.
I came across these
Maha PowerEx 96V230 9.6V 230mAh Rechargeable NiMH Battery

jamato, hiflight and other masters care to advise
post #806 of 1153

D4 Distortion

Thanks so far everyone. I always find it difficult to really isolate problems and worry that my methodology is not sound. However in light of the above comments I would make the following points

1. The distortion occurs on numerous recordings which would suggest an unlikely plague of bad recordings. Two examples are on Cyrus Chesnuts "You are my sunshine" and Claudio Abbado's recent Stabat Mater.

2. The distortion is not audible on my main home (admittedly very expensive) main system.

3. The distortion is not audible using line in from my Ipod via the D4 amp.

4. It only occurs via the USB input from my Apple and occurs with my macbook pro and strangely to a worse extent with my wife's macbook G4.

5. It is helped but not eliminated by putting the Itunes volume at 80%.

6. It happens on a number of different headphones but is worse with my HD650's. I am still considering whether this bit of data illuminates the problem or not.

My overall conclusion is that the DAC is somehow being overloaded by the laptop and positively that it is not the recording (all files are apple lossless).
However,the problem is repeatable with other D4's according to my retailer.

Their suggestion is that I buy a Graham Slee solo and use it as a more powerful amp stage.I am not convinced as I think the problem is the DAC. (To be fair that have offered me a reduced price on the Solo as they are concerned about me being disappointed so I really don't think it is a sales effort!).

I have already bought your topkit Ron but don't want to introduce it to the situation until I have sorted this problem out.

I have not discussed this with the manufacturer pending further comments from forum members.

Overall I still reckon there is a design problem with the DAC stage but would appreciate further comment from more technically minded members.

Any further thoughts on the problem and/or my methodology would be most welcome. Also any further guidance on the solutions mentioned above would be appreciated.

Thanks in advance.
post #807 of 1153
Maybe you should just contact ibasso. It can't hurt. It could be a defect in your dac. Let us know what they say.

Sorry if that's not technically minded enough.
post #808 of 1153

Block diagram of ibasso D4 Mamba

The supply voltage of the AD8616 is insufficient to handle the output of the WM8740.



Possible solution is
1) Redesign the power supply so that the supply to the Ad8616 is at least 5v or more

2) Reduce the gain of the AD8616 so that the output is within the supply limit
(the so called 2.2K resistor mod)

3) Reduce the signal feeding the WM8740 DAC so that the output is below clipping level. Setting iTune, (Windows media player or VLC) volume to 80% or lower.

If you are using line in, you are not affected.
post #809 of 1153

beating a dead horse?

Quote:
Originally Posted by jamato8 View Post
If you are using the amp section of the D4 you can use it in the 5V position and it will draw from the USB for the power. If you have the switch on the back set to 9 volt then it will only (the amp) use the 9 volt battery, it can't use both at the same time. The dac section is powered only by the 5 volt USB and will not work unless connected to the USB getting both the power and digital signal.
When you say "it can't use both at the same time." you mean the amp using 5v and 9v (or 14v combined) at the same time?

Not "it (D4 Mamba) can't use both at the same time." meaning the amp using 5v and the dac using 5v (both drawing off of the USB) at the same time?

I can have the D4 connected via USB and run the amp and the dac at the same time, at 5v, correct? And if I have a 9v battery installed (with amp switch set to "5v") the amp and DAC still both operate simultaneously off the 5v USB power supply.

But if I want an "amp boost" for a song (and I have a 9v installed) all I have to do is set the amp switch to "9v" and BAM! boosted amp operation, right?

.
post #810 of 1153
Quote:
Originally Posted by talleywho View Post
I can have the D4 connected via USB and run the amp and the dac at the same time, at 5v, correct?
Yes.

Quote:
And if I have a 9v battery installed (with amp switch set to "5v") the amp and DAC still both operate simultaneously off the 5v USB power supply.
Yes.

Quote:
But if I want an "amp boost" for a song (and I have a 9v installed) all I have to do is set the amp switch to "9v" and BAM! boosted amp operation, right?
Yes.

It's really this simple. There is a switch on the back labeled USB and Battery. This controls ONLY the amp, and is completely independent of the DAC. All it does it change where the amp gets it's power supply. If you want the amp running at 5V, switch it to USB and make sure the usb is plugged in. If you want the amp running at 9V for some more juice or portability, install a battery and switch it to 9V. That's what this switch does.

Now, if you have USB plugged into your computer and no line input connected to the aux in, the D4 will be using the DAC as the source, playing songs from your computer. If you have the USB plugged in (but not playing songs on your computer), AND you have an auxiliary source connected to the aux in, like your ipod, the D4 will use the aux in as the source. I don't want to confuse you, but if you have the USB connected, playing songs from your computer, AND you have something plugged into the aux in, it will actually play both at the same time, mixing the two. Though, the songs from your computer, from the DAC, will be much quieter to the point that they are hard to hear over the aux in input. When you remove the aux in, the songs from the DAC/computer get louder again. I don't think it's intended to be used this way ever, with both feeding it a signal simultaneously, so I wouldn't recommend it, just telling you what happens.

Again, regardless of using the USB DAC as the source or the aux input as the source, or even both, the switch in the back for USB or Battery will only control which source is providing power to the amp.

At least, this is how my early February model works.
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