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Old 16th April 2018, 01:13 PM   #701
freezebox is offline freezebox  Germany
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Hello Markw4,


I understood madds1 circuit as an easy to apply i/v output which sets the DAC to current mode. But if I understand correctly, this above circuit in my post #697 does not include the LP filter and is just i/v and single-end "transformer" and so it cannot be used as direct connection to my DAC outputs -/+?
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Old 16th April 2018, 02:03 PM   #702
MrSlim is offline MrSlim  Canada
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Quote:
Originally Posted by Markw4 View Post
Attached below is the full circuit as recommended by ESS. Anybody recognize the differential output part? Obviously, the parts values are different from the other proposed circuit and have been scaled for optimal SQ in its intended role.
It could be an LM4562. Twisted Pear uses it on their IVY III to sum the balanced signals

Last edited by MrSlim; 16th April 2018 at 02:06 PM.
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Old 16th April 2018, 02:11 PM   #703
Markw4 is online now Markw4  United States
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Hi freezebox, I would say the madds1 circuit sorta kinda does that, but so far as I am aware nobody has measured it, compared to other outputs for SQ, or done a full and careful analysis of it. Using a 100uf cap to average out the AC component of the inverted output phase (short the audio to ground) and use it to get a very marginally filtered 1/2AVCC isn't very good IMHO compared to a number of other possibilities. As is, a cap would be adversely affecting sound quality, just not in the way everybody seems to be thinking about.

BIG EDIT: Okay, I am just going to say that using the circuit below as is would be expected to give better sound quality than any so-far-seen simple cap removal circuit. If you want easy and good SQ just use it, would be my recommendation.

If you really want to make it even better, and you think getting rid of the cap will help, then you need a more complex circuit. Sorry.
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File Type: jpg ESS2.jpg (49.7 KB, 273 views)

Last edited by Markw4; 16th April 2018 at 02:21 PM.
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Old 16th April 2018, 02:53 PM   #704
freezebox is offline freezebox  Germany
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Hello Markw4,


you mean like this?
Attached Images
File Type: jpg SE output 9038.JPG (39.1 KB, 264 views)

Last edited by freezebox; 16th April 2018 at 02:57 PM.
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Old 16th April 2018, 03:16 PM   #705
Markw4 is online now Markw4  United States
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freezebox, No, sorry. I was trying to think of something quick like that when I realized ESS only said that circuit works well if both opamp inputs and both DAC outputs are held at AVCC, not 1/2 AVCC.

Not clear how it would work the way I was first thinking of and that you drew. Probably not as well as the circuit ESS recommended otherwise they would have recommended this one.

Thing is, the DAC outputs are a given. They work they way they do and nothing we can do about that. Apparently they like to both be connected to a 1/2 AVCC IV, one DAC output phase at a time, or they like to both go to AVCC sort of together as in the last schematic I posted.

That is what we have to work with. It means there will be an offset unless we want to remove it with some additional circuitry.

Again, it is silly to worry about the sound of one cap, the distortion it gives is probably down around -110dB or -120dB. It is something like that, maybe lower, and if you tried really hard maybe you might just ever so barely be able to hear it, but it is completely negligible unless all the DAC mods and those we haven't done yet are completed. It takes all that to make the DAC really, really clean to the point removing a cap might actually be worthwhile.

Otherwise, as-is now it is a useless distraction, IMHO. People seem to have some kind of fixation on it like it is more important than it is, at least right now.

In the meantime, if the cap is 220uf or more it should be fine. The important thing about electrolytics to remember is that DC voltage on them is not a problem, but to keep distortion really low it can help a lot to keep the AC voltage on the cap very small. Maybe less than 80mV. That means that we want the impedance of the capacitor to be much lower than the impedance of the load that follows it. If you connect the output to a line level preamp or a power amp, the input impedance is probably 10k or maybe a few times greater than that. The electrolytic cap and the load make a voltage divider and we want the AC voltage across the cap to a few millivolts.

So, say the preamp or power amp input is 10k. Say, we are concerned that we want less than 80mV AC on the cap at 10Hz. If the DAC output is 10 volts (peak), then the AC output current will be approximately 1mA. That means there will be 1mA AC current through the cap. If the cap is 220uf, then it's impedance at 10Hz is 72 ohms. With 1mA peak current, the peak AC voltage on the cap will be 72mV. So, we're good!

Last edited by Markw4; 16th April 2018 at 03:30 PM.
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Old 16th April 2018, 06:05 PM   #706
freezebox is offline freezebox  Germany
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Thank you for the explanation. I will think about trying the simple ess recommended circuit. Wonder why the board is not designed like this as it might be same or even less complex and similar costs as the orig. design of the board...
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Old 16th April 2018, 06:28 PM   #707
tubesguy is offline tubesguy  United States
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In the interest of saving someone a bit of troubleshooting time, along with the busting up of furniture and the swearing, let me point out that on version 1.07, or at least on mine, the Toslink input jumper is on J1. So not J3. Or any of the others.
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Old 16th April 2018, 06:33 PM   #708
Markw4 is online now Markw4  United States
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Moving along, while I am waiting to hear back from an ESS distributor to inquire about non-disclosure and a datasheet, I decided to go ahead a try a couple of other things I have been thinking about. However, I did make multiple changes at once, so can't say for sure how much effect each one has. Sorry.

Attached below is yet another photo. After some thought, I decided it might make the most sense to treat the oscillator clock as HF analog, rather than digital. Therefore, it got its own 3.3v low noise regulator. Also added some 1,000uf caps where the power comes into the board. Some film caps were added previously while experimenting with and otherwise working on power supply noise issues.

It turned out that the silent switcher did not like the big 1,000uf capacitive loads and it started causing some odd noises in the DAC output even with the volume all the way down. So, the SS is gone and the DAC and headphone amp are both on the linear power supply.

It sounds very good, but not quite as much of the most subtle details as the reference system which includes a Benchmark DAC-3 and Benchmark ABH2 power amp. The reference system is extremely detailed, probably not wrong to say state-of-the-art detailed. It makes a pretty challenging comparison.

Having made the comparison, the Chinese DAC is still quite good. IMHO, it is definitely a keeper as it is now. It is dynamic, has good well-defined deep bass, detailed and realistic cymbal sounds (one of the hardest things to reproduce accurately in a DAC and amp, it seems), and so forth.

Next steps will be to see if I can get a datasheet here and start testing what can be done to get master mode I2S working.

In parallel with I2S, and as I have time, my notch filter is now working, I need to do some calibration and testing on that. Hopefully, before too long I will be able to post some basic DAC measurements.
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File Type: jpg Osc3.3vSupply+Incoming3.jpg (176.4 KB, 239 views)

Last edited by Markw4; 16th April 2018 at 06:44 PM.
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Old 16th April 2018, 06:35 PM   #709
Markw4 is online now Markw4  United States
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@tubesguy, My Toslink is on J1, and Coaxial on J2. J3 is the slow transition minimum phase reconstruction filter that sounds so good if upsampling is used. 1.06 board.
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Old 17th April 2018, 05:08 PM   #710
Markw4 is online now Markw4  United States
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May I ask if anyone else is using or planning on using an SRC4392?

How about an LME49600 headphone amp?
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