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Topic: Help! Regarding capacitor upgrade. (DAC/Amp ELE EL D02) (Read 6047 times) previous topic - next topic
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Help! Regarding capacitor upgrade. (DAC/Amp ELE EL D02)

Well, from the beginning. It's been like 6 month since I bought said DAC/Amp, I just bought it to use it with a Motorola Moto G, and it does work perfectly, but all my plans ended up differently, and the Moto G ended belonging to my Sister. xD

Last week I realized that said DAC sounded better than my Xonar DG, basically I noticed that the bass performance is better on that DAC using my 681 Evos (And just those headphones are the ones where I noticed an improve) I even performed a Blind test between my D02 and my Xonar DG with Virtual audio cable and a RCA Splitter and confirmed that what I noticed is true. (I can't notice any difference when I use my 668B).

But there's a downside, I noticed a lot of hiss whe I use my Piston on the D02.

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Now, this is where things start to get odd, I know my Xonar DG output impedance (20 Ohm, measured by me) and I think that said improvemend that I heard on the Evos might be that the D02's output impedance is lower and the Xonar one.

But I cant measure it, the D02 has hiss and it seems that its hiss makes my DMM crazy, seriusly, when I get 1V and add the resistance, it goes to 0 and then to 3.54V and all kind of crazy readings. xD Even after unplugging the resistance the DMM keeps doing that, I have to switch back the DMM to AC to stabilized it.

And I tought it was DAC's fault, then I tried to measure my Motherboard's output impedance and I've got the same crazy behaviour. And same thing with every phone that I tried.

So, What am I doing wrong? Is there an alternative way to measure that? (By checking PCB and Opamp data?) The DMM I think is fine, I rechecked my Xonar's output impedance and everything went fine, and I´ve got exactly the same result.

My DMM is a Etekcity MSR-R500.

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Moving on, yesterday, I did some RMAA measurements comparing my Xonar DG, D02 and motherboard's audio, everything looked good until I repeat the test using my headphones as load and well...



... It starts rolling off the bass even with the 668B and it gets unbelievable on the Piston, -8 dB @30 Hz.

When I saw that (the first headphone that I tested were the Evos) I thought "damm, that is not any output impedance thing, it is the bass roll-off" but then, I went to audacity and I picked a music file (Diapason from Ace Combat Zero) and applied an EQ to compesate the Roll-off on the Evos, and then perform and ABX test on Foobar between the compesated and original file, and well my result was 5/8, so it seems that what I've heard is actuallly a lower output impedance and not the roll-off.

Anyway, I've read that kind of roll-off with low loads is because the caps capacitance is too low. So, how may I fix that? By putting a higher uF cap?? If so. How many uF should the new caps be? And would the caps upgrade also remove the hiss?

Picture of the DAC/Amp:

The ELNA ones (That I dont even know if they are true ELNA caps) are 50v 100uF. There are two on the line out and two on the headphone out. (I think I´ll just change the headphone out ones).


Sorry if this was too long, I'll really appreciate your help.

Help! Regarding capacitor upgrade. (DAC/Amp ELE EL D02)

Reply #1 –
Online Capacitive Reactance Calculator.    100uF is about 40 Ohms at 40Hz.

Quote
DMM keeps doing that, I have to switch back the DMM to AC to stabilized it.
Audio is AC, so you should be reading AC.  With a constant tone, your AC reading should be constant.

But, some inexpensive meters have trouble with low-voltage AC measurements because they have a diode in series with the input to rectify the AC, and the voltage drop across the diode (0.7V across a single diode and 1.4V across a full-wave bridge) makes low-voltage readings (below around 1V) unusable.    My meter at home has that problem...  It shows resolution  of 0.1V on the AC scale but it can't read voltages that low.

Quote
Last week I realized that said DAC sounded better than my Xonar DG,
Sometimes a higher impedance amp can sound "better" if there's an impedance bump in the headphone's mid-low range.  The response may not be flatter  but the boosted mid-bass might "sound better".

Help! Regarding capacitor upgrade. (DAC/Amp ELE EL D02)

Reply #2 –
Quote from: DVDdoug on
Online Capacitive Reactance Calculator.    100uF is about 40 Ohms at 40Hz.

Quote
DMM keeps doing that, I have to switch back the DMM to AC to stabilized it.
Audio is AC, so you should be reading AC.  With a constant tone, your AC reading should be constant.

But, some inexpensive meters have trouble with low-voltage AC measurements because they have a diode in series with the input to rectify the AC, and the voltage drop across the diode (0.7V across a single diode and 1.4V across a full-wave bridge) makes low-voltage readings (below around 1V) unusable.    My meter at home has that problem...  It shows resolution  of 0.1V on the AC scale but it can't read voltages that low.

Quote
Last week I realized that said DAC sounded better than my Xonar DG,
Sometimes a higher impedance amp can sound "better" if there's an impedance bump in the headphone's mid-low range.  The response may not be flatter  but the boosted mid-bass might "sound better".


I know audio is AC and the DMM it's been always set AC, what I mean to switch back to AC is that I basically had to set another option and then switch it back AC to reset the DMM.

If my DMM had that trouble, that wouldnt explain how I could measured my Xonars output impedance. (And the D02 is capable to go way over 1.3 Vrms that was the maximum that I could get on the Xonar). Anyway, if you know a DMM that does not do that, please tell me.

681 Evos impedance is fairly flat. (Supposing that they use the same driver of the original 681).


And Here 40 Hz hits 39 ohm, and 1KHz hits 34 Ohm, with that diference I would need a 300 Ohm output impedance to get +1.1 dB @ 40 Hz.



Now, sorry for this question that is gonna be dumb, what should I do with that page? Does that mean that I should go with say, 400 uF caps to get 10 Ohm on 40 Hz?






Help! Regarding capacitor upgrade. (DAC/Amp ELE EL D02)

Reply #3 –
Looking at it a little differently, the 100 microfarad capacitor into a 39 ohm load will roll off 3 dB at about 100 Hz. 3 dB roll off should be noticeable.

If you increase the capacitance to 200 microfarads, by adding another 100 microfarad capacitor in parallel, the 3 dB point will be 50 Hz instead of 100.

If you add a 300 microfarad capacitor for a total of 400, the 3 dB point will be 25 Hz.

You just need to decide how low you want your bass response to go.

Help! Regarding capacitor upgrade. (DAC/Amp ELE EL D02)

Reply #4 –
Quote
If my DMM had that trouble, that wouldnt explain how I could measured my Xonars output impedance. (And the D02 is capable to go way over 1.3 Vrms that was the maximum that I could get on the Xonar). Anyway, if you know a DMM that does not do that, please tell me.
Maybe your  meter...    And, for some reason you have to "reset" your meter.  Mine reads essentially nothing with "line level" signals.  I don't know if mine would read 1.3VRMS or not, but I wouldn't trust it to be accurate at that voltage. 

DC offset/bias can cause strange readings, but that would be leakage through the capacitors and it should ONLY  show-up with a high impedance load (such as the meter only) or when you first connect the meter with no other load.  With the resistors connected, the output should be sitting at ground when there's no signal, and the signal should have no DC component.

Help! Regarding capacitor upgrade. (DAC/Amp ELE EL D02)

Reply #5 –
Quote from: pdq on
Looking at it a little differently, the 100 microfarad capacitor into a 39 ohm load will roll off 3 dB at about 100 Hz. 3 dB roll off should be noticeable.

If you increase the capacitance to 200 microfarads, by adding another 100 microfarad capacitor in parallel, the 3 dB point will be 50 Hz instead of 100.

If you add a 300 microfarad capacitor for a total of 400, the 3 dB point will be 25 Hz.

You just need to decide how low you want your bass response to go.


Thanks a lot!

Help! Regarding capacitor upgrade. (DAC/Amp ELE EL D02)

Reply #6 –
Luckily, I found three of 16V 470uF caps inside of a old speaker amp that is no longer working.

Unfortunately, there were only three of them, so I had to change just the Headphone out caps, maybe in the future I´ll put the old headphone-out caps with the line-out ones in parallel.

Anyway, thank you so much guys for you help, I just measured everything again and now there's a huge improvement on the frequency response, a slightly improvement on the distortions and there's also a slightly reduction of hiss on the Piston.




Wow, the Piston went from -8 dB @30 Hz to -2 dB. Again, thank you so much guys for your help.

Help! Regarding capacitor upgrade. (DAC/Amp ELE EL D02)

Reply #7 –
Do NOT add a capacitor to the line out. It would be pointless.

Also, 16 volts is probably adequate, but without seeing the circuit diagram I can't be sure.

Help! Regarding capacitor upgrade. (DAC/Amp ELE EL D02)

Reply #8 –
Quote from: pdq on
Do NOT add a capacitor to the line out. It would be pointless.

Also, 16 volts is probably adequate, but without seeing the circuit diagram I can't be sure.


It reduces the hiss. And really, I couldn't find better capacitors. (The rest that I've found with higher voltage where too big to fit inside the case).

Help! Regarding capacitor upgrade. (DAC/Amp ELE EL D02)

Reply #9 –
Sadly there is a very simple circuit trick that eliminates the roll off, even with a fairly modest capacitor, and also makes the output impedance very low. Unfortunately many manufacturers seem to be ignorant of this.

Help! Regarding capacitor upgrade. (DAC/Amp ELE EL D02)

Reply #10 –
Quote from: pdq on
Sadly there is a very simple circuit trick that eliminates the roll off, even with a fairly modest capacitor, and also makes the output impedance very low. Unfortunately many manufacturers seem to be ignorant of this.


By the way, I´ve checked the TDA1308's data sheet and it says that it has a 0.25 Ohm output resistance.

I checked the D02's PCB very carfully and put the Ohmniometer on everywhere, and I couldn't spot any resistor on anywhere. Could that mean that the D02's output impedance is close to the Opamp output resistance?

Help! Regarding capacitor upgrade. (DAC/Amp ELE EL D02)

Reply #11 –
TDA1308 is just the bare opamp. What effective output impedance you get will depend on the surrounding circuitry.

I notice that the application shown in the data sheet suffers from the same problem that you were seeing, a 100 microfarad capacitor to the output. Apparently someone took this literally and reproduced the same poor circuit design presented by the manufacturer.

Help! Regarding capacitor upgrade. (DAC/Amp ELE EL D02)

Reply #12 –
I think I've finally managed to measure the output impedance. I added a 5 Ohm resistance in serie to the output to clean some of the Hiss, the whole cable + resistance + adapters impedance was 10.1 Ohm. (It is a pretty long cable by the way).

First, I tested the Xonar to make sure, the result with the Xonar was 32 Ohm (- 10.1 Ohm of the cables, resistances, etc) = 21.9 Ohm Which is close to the 20.17 Ohm of the last time.

Using that setup. I've got stable results on the ELE EL D02, but not perfect. My readings at 1 Vrms without load vary between 1.0 and 1.1 Vrms. And the results with the 48 Ohm resistance as load were 0.8 and 0.9 Vrms.

So, the best result could be 1.0 V no load and 0.9 V load, but that is not possible because the result after taking off 10.1 Ohm would be -4.74 Ohm

Now the second best case could be 1.1 V no load and 0.9 V load, which gives a Zout  = 0.57 Ohm

The third best possible result could be 1.0 V no load and 0.8 V load which gives a Zout of 1.9 Ohm.

And the worst result could be 1.1 V no load and 0.8 V load which gives a Zout of 7.9 Ohm.


So, in other words the output impedance of the D02 is less than 8 Ohm. Although dont take these results seriusly, because I also tried this setup with my motherboard and well, the voltage drops from 1 V to 0.1 V. 

Help! Regarding capacitor upgrade. (DAC/Amp ELE EL D02)

Reply #13 –
Output impedance is calculated like this: Zout = (Rload * (Vnoload - Vload)) / Vload

Where Vnoload is the "unloaded" output voltage and Vload the voltage when there is a load, e.g. a parallel Rload=30 ohm resistor.

If you measure with a digital multimeter then be aware that they may not be very accurate measuring above 50/60 Hz sinusoidal signals.
"I hear it when I see it."

Help! Regarding capacitor upgrade. (DAC/Amp ELE EL D02)

Reply #14 –
Quote from: xnor on
Output impedance is calculated like this: Zout = (Rload * (Vnoload - Vload)) / Vload

Where Vnoload is the "unloaded" output voltage and Vload the voltage when there is a load, e.g. a parallel Rload=30 ohm resistor.

If you measure with a digital multimeter then be aware that they may not be very accurate measuring above 50/60 Hz sinusoidal signals.


I used a 60 Hz sine wave created with audacity and this

Where R2 is the 48 Ohm resistance that I used as load in parallel, input voltage is the voltage without the 48 Ohm load and output voltage, the voltage with it.

And R1 is the Zout, but I had to take off 10.1 Ohm of each result because I also added a 5 Ohm resistance in serie to R1 to clean hiss. (And the impedance with the cable and the 5 Ohm resistance was 10.1 Ohm)

Help! Regarding capacitor upgrade. (DAC/Amp ELE EL D02)

Reply #15 –
Ok that seems right, I didn't follow the thread. Are there any problems left?

Btw, high output impedance does not result in bass roll-off. DC-blocking caps on the inputs or outputs will however cause roll-off. You should be able to measure that as an increase in impedance with decreasing frequency.
"I hear it when I see it."

Help! Regarding capacitor upgrade. (DAC/Amp ELE EL D02)

Reply #16 –
Quote from: xnor on
Ok that seems right, I didn't follow the thread. Are there any problems left?

Btw, high output impedance does not result in bass roll-off. DC-blocking caps on the inputs or outputs will however cause roll-off. You should be able to measure that as an increase in impedance with decreasing frequency.


Where did I say that? xD

The only problem left is the Hiss. I really dont have any idea of what could be the problem there.

By the way, I realized that if I plug my Piston to the D02 using the 10.7 Ohm "cable" the hiss gets close to the Xonar's hiss (Which is almost inaudible) that might explain why the DG has that output impedance.