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Moving from 9038Q2M to a 9028Pro board
Moving from 9038Q2M to a 9028Pro board
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Old 20th June 2018, 07:54 PM   #1
Mikett is offline Mikett  Canada
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Join Date: Aug 2003
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Default Moving from 9038Q2M to a 9028Pro board

During the modification of my 9038Q2M dac as on this thread ES9038Q2M Board

I accidentally killed my cheap DAC. This provided me an opportunity to decide whether to start all over again with the above DAC or start over with another kit but having perhaps less requirement for fabrication.

I looked at various DAC boards on Ebay and elected to not get something too costly because I could very well destroy it again and if I did. I would simply purchase something and be done with it.

Via the above thread I realized that substantial fabrication would be required and I did not wish to go to making boards again. With the cheap Es9038q2m mentioned, one needs to fabricate an op amp PS for AVCC as well as fabricate a new IV section for the DAC as the single op amp circuit on the board is simply not good despite putting on better op amps.

Then I saw a DAC board that looked interesting.
It has a proper IV converter section. I chose to stick with the 9028pro because the PS requirements were a lot less than a 9038Pro. Next, I wanted to get an DAC where I could easily insert improved PS sections that without too much trouble. I also desired a display.
The board I ended up with I think is a reasonable cost. It is a 9028pro board and the same design appears to be also used for the 9038pro. It can be found on numerous offerings on Ebay and AliExpress and appears to be a popular board. It uses 3 terminal regulators for the op amp supply...which easily allows me to insert improved PSs like a Sulzer which I already had or put in even a Super regulator for which I might still have some parts if I wanted to build one. It has one compromise. Left and Right AVCC is fed from a common regulator., has a display and a remote.

The project is not finished but this would be a project as it progresses I will report.

Warning, this thread will have a minimum of measurements as I don't have the equipment. So any reports of any improvement as I mod needs to be looked at as not fact but opinion. I state that up front.

After having received my DAC board, in stock form it had 5532/34 op amps. These provided a strong sense of midbass with a thick sound. High frequencies were slight muted. Changing these to LME49720 and LME49710 op amps removed the heavy midbass and provided more extended or more transparent sound. I had noted somewhat similar characteristics on the cheaper DAC but it was much more noticeable now.

The cheaper 9038q2M DAC before I killed it, had been modified. A lowZ low noise Sulzer Power supply was feeding the op amp and an LT3042 was feeding the DAC section. The LT3042 had 15uF of film caps for Cset. The DAC section had been modified by putting in 470uF OSCON sepc caps for decoupling.
The op amp IV section on the cheap DAC was in voltage mode with a single op amp section.

Now the stock 9028pro with the switch to the LME497xx op amps easily easily beat out the 9038q2m modded as above in the following areas. Lower octaves were more solid and defined. Separate voices were more distinct and transparent. This possibly points to the aspect that an ESS based DAC must have a proper IV section and the DAC must be operating in current mode for it to be good.

So as time progresses I will press forward by installing improved power supplies and possibly upgrading clocks and possibly upgrading on board components to better match ESS recommended circuits.

First I will install an improved power supply for the op amps.
Attached Images
File Type: jpg Setup 6_20_2018.JPG (678.8 KB, 424 views)
File Type: jpg IV section.JPG (709.4 KB, 400 views)
File Type: jpg OP AMP PS1.JPG (640.7 KB, 389 views)
File Type: jpg OP AMP PS2.JPG (600.6 KB, 384 views)
File Type: jpg AMS1117_1_2.JPG (677.4 KB, 369 views)
File Type: jpg 9028Pro.JPG (794.9 KB, 104 views)
File Type: jpg LT1963 Feed to AMS1117.JPG (746.9 KB, 97 views)
File Type: jpg Clock.JPG (671.9 KB, 95 views)
File Type: jpg LT1963s.JPG (629.2 KB, 98 views)
File Type: jpg AVCC divider.JPG (595.4 KB, 88 views)
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Old 20th June 2018, 08:10 PM   #2
Mikett is offline Mikett  Canada
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First mod, I will remove the three term regs and insert a superior PS I have on hand.
power supply sulzer-borbely

I have many of these power supplies in my box after the Super Regulators supplanted them. I just noticed, that I should be able to mod this to power AVCC as well if I just find a low enough component to replace the LM329Z....the LTC6655

http://www.analog.com/media/en/techn...ets/6655ff.pdf

Hey MarkW4, maybe I learnt something.
Attached Images
File Type: jpg OP AMP PS2.JPG (600.6 KB, 115 views)
File Type: jpg OP AMP PS1.JPG (640.7 KB, 93 views)
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Old 20th June 2018, 08:18 PM   #3
Markw4 is offline Markw4  United States
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Looks like you have a solder bridge on the dac chip. See the blue circle area in the attached pic.
Attached Images
File Type: jpg BRIDGE - LT1963 Feed to AMS1117.jpg (364.4 KB, 148 views)
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Old 20th June 2018, 08:21 PM   #4
Mikett is offline Mikett  Canada
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HA HA

Yes, I saw that when I rec'd it and inquired about it. It's meant to be there.
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Old 20th June 2018, 08:24 PM   #5
Markw4 is offline Markw4  United States
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Mikett, Do you know what under the other heat sinks? Looks like 5-terminal power ICs. Are those more voltage regulators?
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Old 20th June 2018, 08:33 PM   #6
Mikett is offline Mikett  Canada
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They are 2 - LT1963 1500ma Fast Trasient LDO regs. http://www.analog.com/media/en/techn...ets/1963fc.pdf

One feeds AVCC Left and R shared. The other provides the other 3.3V to clock and to 2x AMS1117 1.2V to the DAC etc.
I have 2 LT3042 to feed these now as soon as I mod them for 5V to 3.3 V.
The LT1963 is supposed to be protected from reverse voltages so I think I can tack on the feed from the external 3.3V sources whether it be from the LT3042 or Sulzer to be modded for 3.3V. I've ordered this board MLT - LTC6655 High Precision Voltage Reference Breakout Module | eBay to mod my Sulzer PS for AVCC
Attached Images
File Type: jpg LT1963s2.JPG (671.7 KB, 156 views)

Last edited by Mikett; 20th June 2018 at 08:42 PM.
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Old 20th June 2018, 08:35 PM   #7
Markw4 is offline Markw4  United States
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Probably the AVCC supply, then. Maybe roughly somewhere around 20 - 40 times worse noise than an LT3045 with 4.7uf Cset, which is worse again than if Cset=22uf.

Last edited by Markw4; 20th June 2018 at 08:46 PM.
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Old 20th June 2018, 08:38 PM   #8
Mikett is offline Mikett  Canada
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The left one is the AVCC supply
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Old 20th June 2018, 08:47 PM   #9
Markw4 is offline Markw4  United States
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Quote:
Originally Posted by Mikett View Post
The left one is the AVCC supply
For both channels? That's not good for stereo separation.
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Old 20th June 2018, 08:54 PM   #10
Mikett is offline Mikett  Canada
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I know. But I will accept that compromise unless I see a breakout where I can come back in. Like the traces to the AVCC divider. I will try and follow that back out and see.
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