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Old 19th July 2019, 04:49 PM   #181
ishizeno is offline ishizeno
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Join Date: Mar 2015
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Originally Posted by Markw4 View Post
I would really suggest to get the eval board first. It is designed so you can try alternate voltage regulators. You can get an LT3045 module and see if it makes any difference to dac performance. if not, maybe you don't need it. Or then again, depending on incoming power quality, it may need some cleaning up. Maybe LT3045 can do part of that. In other words, I think you are jumping the gun here. You should first figure out what matters a lot and what matters very little, then expend effort and board space where it is useful.
I think you are absolutely right, I am really champing at the bit here... I really wish that I could have a board right now, but it won't be available for another month. In the meantime, all I can do is study as much as I can.

That being said, I like to believe that some of this work will be useful, especially because of the desire to put so many components directly on the DAC board, instead of a separate board like is done by AKM for their evaluation board. And because I am dealing with pretty severe space constraints, I want to make sure that the overall design is feasible. In other words, if the NJM78M05 is enough and the LT3045 does not make any difference, I'll take that as a great piece of news (simpler design, cheaper BoM). But if we realize that using an LT3045 is the way to go, I want to make sure that the overall brick configuration can accommodate it, otherwise the whole stack falls apart.

Also, I really like the idea of having options that are not necessary but make the stack better, and the drop-in replacement of the NJM78M05 by the LT3045-78XX is a perfect example of such an upgradeable design, much like the fact that the Sitara SoM will be optional. Or the fact that the two mono DAC boards could be replaced by a single 4-channel DAC board, without changing much at all. In fact, I'll make sure that we design a single DAC board that can be used in both configurations by setting the right jumpers (assuming that we can do that without any degradation of our critical signals).

Finally, this exercise, while certainly premature, remains a good way for me to learn about many different components.
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Old 19th July 2019, 05:08 PM   #182
Markw4 is offline Markw4  United States
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Quote:
Originally Posted by ishizeno View Post
In the meantime, all I can do is study as much as I can.
In that case I would suggest to study things such as:
https://www.diyaudio.com/archive/blo...pre-g-word.pdf

Henry Ott's, Electromagnetic Compatibility Engineering



https://www.electronics-tutorials.ws...k-systems.html
https://www.electronics-tutorials.ws...-feedback.html
https://linearaudio.net/sites/linear.../volume1bp.pdf

The latter stuff is to clearly understand why amplifiers and voltage regulators can turn into oscillators, and how their regulator error amps interact with capacitors in the regulation loop. If you are going to be designing with parts like LT3045, you should have some familiarity with such topics. For a more through treatment a text on control systems engineering might be useful to study, at least to start with.

Last edited by Markw4; 19th July 2019 at 05:13 PM.
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Old 19th July 2019, 05:13 PM   #183
ishizeno is offline ishizeno
diyAudio Member
 
Join Date: Mar 2015
Quote:
Originally Posted by Markw4 View Post
In that case I would suggest to study things such as:
https://www.diyaudio.com/archive/blo...pre-g-word.pdf

Henry Ott's, Electromagnetic Compatibility Engineering



https://www.electronics-tutorials.ws...k-systems.html
https://www.electronics-tutorials.ws...-feedback.html
https://linearaudio.net/sites/linear.../volume1bp.pdf

The latter stuff is to clearly understand why amplifiers and voltage regulators can turn into oscillators, and how their regulator error amps interact with capacitors in the regulation loop. If you are going to be designing with parts like LT3045, you should have some familiarity with such topics. For a more through treatment a text on control systems engineering might be useful to study, at least to start with.
Thank you Mark! Much appreciated. I will dive in right away.
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Old 19th July 2019, 07:36 PM   #184
chris719 is offline chris719  United States
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Join Date: Jun 2004
Location: Connecticut
The LT3045 is overkill for the supplies other than VREF and clock it would seem. I would use something relatively simple to replace the 7805s, like ADP7112 for example.
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Old 19th July 2019, 09:34 PM   #185
ishizeno is offline ishizeno
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Originally Posted by chris719 View Post
The LT3045 is overkill for the supplies other than VREF and clock it would seem. I would use something relatively simple to replace the 7805s, like ADP7112 for example.
I'm starting to understand your point (and Mark's) better: the NJM78M05s are used for the VDD supplies, and as such are not as critical. The VREFs are handled by the Jung-Didden circuits, which we should not mess with. Therefore, we should not need the LT3045.

Sorry that it took me so long to understand that.
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Old 19th July 2019, 09:46 PM   #186
chris719 is offline chris719  United States
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Quote:
Originally Posted by ishizeno View Post
I'm starting to understand your point (and Mark's) better: the NJM78M05s are used for the VDD supplies, and as such are not as critical. The VREFs are handled by the Jung-Didden circuits, which we should not mess with. Therefore, we should not need the LT3045.

Sorry that it took me so long to understand that.
No problem .

I actually think the LT3045 could be higher performance than the Jung variant regulator that AKM is using because of their choice of AD817 as the error amplifier. AD817 has some pros and cons, but it is noisier than LT3045 (LT3045 is 2 nV/rtHz at 1 kHz, while AD817 is 15 nV/rtHz. Would need to see complete measurements of that regulator, which don't exist.

Using their Jung style regulators is the safest bet still, if only because they have done it on the eval board. I would say that you do need to pay attention to their layout - it's not going to be any easier than LT3045.
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Old 20th July 2019, 07:32 AM   #187
ishizeno is offline ishizeno
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Join Date: Mar 2015
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Originally Posted by chris719 View Post
No problem .

I actually think the LT3045 could be higher performance than the Jung variant regulator that AKM is using because of their choice of AD817 as the error amplifier. AD817 has some pros and cons, but it is noisier than LT3045 (LT3045 is 2 nV/rtHz at 1 kHz, while AD817 is 15 nV/rtHz. Would need to see complete measurements of that regulator, which don't exist.

Using their Jung style regulators is the safest bet still, if only because they have done it on the eval board. I would say that you do need to pay attention to their layout - it's not going to be any easier than LT3045.
I totally agree.

A few questions:

1. Can I use the LM7805 as a replacement for the NJM78M05 without changing anything else to the circuit?

2. If so, is there any downside in using the SOT-223 form factor vs. the TO-263 form factor (besides the fact that DIY soldering would be harder)?

3. Is there any math that I can use to figure out the minimum ESR for C352, C357, C358, C361, or is testing the only option? The T59EE477M016C0020 gives us 20mΩ, while the T523H477M016APE070 gives us 70mΩ. Both are roughly the same price and have comparable footprints.

4. The NJM78M00 datasheet indicates that "the capacitance and the equivalent series resistance (ESR) influence [the] stable operation of the regulator," but this is related to Co, not Cin, which is 0.1μF in both the datasheet and the evaluation board. What would be an acceptable ESR value for this small capacitor?
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Old 20th July 2019, 07:36 AM   #188
ishizeno is offline ishizeno
diyAudio Member
 
Join Date: Mar 2015
Quote:
Originally Posted by Markw4 View Post
In that case I would suggest to study things such as:
https://www.diyaudio.com/archive/blo...pre-g-word.pdf

Henry Ott's, Electromagnetic Compatibility Engineering



https://www.electronics-tutorials.ws...k-systems.html
https://www.electronics-tutorials.ws...-feedback.html
https://linearaudio.net/sites/linear.../volume1bp.pdf

The latter stuff is to clearly understand why amplifiers and voltage regulators can turn into oscillators, and how their regulator error amps interact with capacitors in the regulation loop. If you are going to be designing with parts like LT3045, you should have some familiarity with such topics. For a more through treatment a text on control systems engineering might be useful to study, at least to start with.
Mark,

These articles are absolutely awesome. I love Bruno Putzeys' no bs. tone! And his overall approach to grounding, differential circuits, and feedback loops make a lot of sense. Instead of the arcane wizardry of HiFi propellerheads, it just seems like solid engineering to me. I still have a long way to go before I can understand everything, and an even longer before I can really make his of this knowledge in any practical sense, but this will help me understand many pieces of documentation a lot better.

Thank you very much.
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Old 20th July 2019, 07:42 AM   #189
chris719 is offline chris719  United States
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Join Date: Jun 2004
Location: Connecticut
Quote:
Originally Posted by ishizeno View Post
I totally agree.

A few questions:

1. Can I use the LM7805 as a replacement for the NJM78M05 without changing anything else to the circuit?

2. If so, is there any downside in using the SOT-223 form factor vs. the TO-263 form factor (besides the fact that DIY soldering would be harder)?

3. Is there any math that I can use to figure out the minimum ESR for C352, C357, C358, C361, or is testing the only option? The T59EE477M016C0020 gives us 20mΩ, while the T523H477M016APE070 gives us 70mΩ. Both are roughly the same price and have comparable footprints.

4. The NJM78M00 datasheet indicates that "the capacitance and the equivalent series resistance (ESR) influence [the] stable operation of the regulator," but this is related to Co, not Cin, which is 0.1μF in both the datasheet and the evaluation board. What would be an acceptable ESR value for this small capacitor?
I would just use something other than a 7805, they are ancient and low performance. The only advantage is cost.

There are 100s of parts that would meet your needs and be better probably, even if it they aren't necessarily going to compromise the performance. If you are going to make a statement design you might as well. Why did AKM use them? Probably to save a few cents and because NJM is a Japanese company. I've noticed Japanese companies love to use local stuff when they can.

Depending on how much current you need, you can look at simple fixed regulators like TPS7A80, LP5907, LP2992. There are lots of options that are designed to be stable with low ESR caps on the output because of the ubiquity of ceramic caps.
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Old 20th July 2019, 07:47 AM   #190
ishizeno is offline ishizeno
diyAudio Member
 
Join Date: Mar 2015
Quote:
Originally Posted by chris719 View Post
I would just use something other than a 7805, they are ancient and low performance. The only advantage is cost.

There are 100s of parts that would meet your needs and be better probably, even if it they aren't necessarily going to compromise the performance. If you are going to make a statement design you might as well. Why did AKM use them? Probably to save a few cents and because NJM is a Japanese company. I've noticed Japanese companies love to use local stuff when they can.

Depending on how much current you need, you can look at simple fixed regulators like TPS7A80, LP5907, LP2992. There are lots of options that are designed to be stable with low ESR caps on the output because of the ubiquity of ceramic caps.
Sounds good! I'll go out and look for some options. The NJM78M05 has a 500mA guaranteed output current, so I must assume that we won't need more, and I'll look for something that can deliver at least that.

Last edited by ishizeno; 20th July 2019 at 08:09 AM.
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