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Moving from 9038Q2M to a 9028Pro board
Moving from 9038Q2M to a 9028Pro board
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Old 30th September 2018, 10:46 AM   #141
carlmart is offline carlmart  Brazil
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Mikett,

Just curious: have you compared or tried the LT3042 regulator versus the Super Regulator?

Which LT3042 board or kit are you using?

Markw4,

Isn't there a way to cure that LT3042 LF noise? A different or larger cap perhaps?
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Old 30th September 2018, 01:09 PM   #142
Markw4 is offline Markw4  United States
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Quote:
Originally Posted by carlmart View Post

Markw4,

Isn't there a way to cure that LT3042 LF noise? A different or larger cap perhaps?
There are a couple of things. Best way is probably given in one of the LT3042 or LT3045 data sheets. See diagram below. Main problem I have found with using LT6655 is that it requires a physically big 10uf film cap for best performance, but I think Mikett found a prebuild LT6655 module that looks like it would work. Mike?

The usual way people try is less effective, and can be hard to retrofit. It involves increasing Cset in the LT3042 data sheet to the maximum value of 22uf. However, that will increase start up time of the regulator to a few or several minutes. Fixing that requires using the fast start up capability of LT3042 also described in the data sheet using the power good (PG) terminal.
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File Type: jpg LT3045_with LTC6655reference.jpg (63.1 KB, 333 views)

Last edited by Markw4; 30th September 2018 at 01:11 PM.
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Old 3rd November 2018, 04:01 AM   #143
mateusfig is offline mateusfig  Brazil
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Quote:
Originally Posted by Mikett View Post
During the modification of my 9038Q2M dac as on this thread ES9038Q2M Board - diyAudio

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.
Hi, could help me how to connect my 2 transformers to this DAC? Your first image helped a little, but I'm in doubt about what + and - in the DAC connectors. I say it for the 6v (2 connectors with 2 pins each ) and 15v (1 connector (right) with 3 pins) input.

I could not locate this info nowhere.
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Old 5th November 2018, 06:53 PM   #144
Mikett is offline Mikett  Canada
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Quote:
Originally Posted by carlmart View Post
Mikett,

Just curious: have you compared or tried the LT3042 regulator versus the Super Regulator?

Which LT3042 board or kit are you using?

Markw4,

Isn't there a way to cure that LT3042 LF noise? A different or larger cap perhaps?
I have been busy and did not notice this.
A super Reg will not be easy to implement for the AVCC because you will need to find an op amp that can work withing the output voltage and that is 3.3V.
You might be able to, but it is going to be difficult.

I have not had the time to put together the LTC6655 LME49600/LME49710 variant as yet but I soon will. Whether that sounds better or not, I don;t know. However each mod I do, I try and keep the system in a state that I can easily backtrack.

For me there's no rush on this as in the current state it sounds nice to me and there is no urge to push ahead but I will anyways just to see.
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Old 5th November 2018, 06:58 PM   #145
Mikett is offline Mikett  Canada
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You should be able to backtrack a bit and find the inputs to the op amps for the dual op amps. Take the op amps out and tap the signal from the socket if desired. You can take a normal op amp socket, push a couple pins out and solder the pins to the two leads on the transformer. Then stick the pins into the op amp socket. Do you have a schematic for the board from your vendor? This should allow a reversible mod and see if you like the result.
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Old 6th November 2018, 11:51 PM   #146
Terry Demol is offline Terry Demol  Australia
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Quote:
Originally Posted by Markw4 View Post
There are a couple of things. Best way is probably given in one of the LT3042 or LT3045 data sheets. See diagram below. Main problem I have found with using LT6655 is that it requires a physically big 10uf film cap for best performance, but I think Mikett found a prebuild LT6655 module that looks like it would work. Mike?

The usual way people try is less effective, and can be hard to retrofit. It involves increasing Cset in the LT3042 data sheet to the maximum value of 22uf. However, that will increase start up time of the regulator to a few or several minutes. Fixing that requires using the fast start up capability of LT3042 also described in the data sheet using the power good (PG) terminal.
The use of LTC6655 with LT3045 is, to some degre, a conundrum. There are
no measurements of the total (wideband in nV/rt Hz) noise performance on
either devices data sheet.

What we can probably assume, is that the VLF noise limitations of LT3045
are largely a result of ref current noise // set resistor noise as opposed to
the internal opamp itself.

As such a simpler way to get better 1/f noise is just use a much bigger, say x
10 = 220uF set pin capacitor and a pull up circuit on start up.

There are a few fairly simple ways to do this.

Are there any other reasons than slow start up why the set cap is limited to
22uF?

T
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Old 7th November 2018, 12:34 AM   #147
Markw4 is offline Markw4  United States
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Quote:
Originally Posted by Terry Demol View Post

Are there any other reasons than slow start up why the set cap is limited to
22uF?
Just what it says in the data sheet. More than 22uf reduces regulation loop bandwidth, maybe a concern if one wants fast response time. Probably better to do as they recommend as use LT6655 as the reference.

In addition, the performance graphs of LT304x don't show what happens with noise below 10Hz. However, we happen to care about that because LF AVCC noise will intermodulate with the dac analog outputs to increase distortion.

Might be a good idea to use one LT6655 as a reference for multiple LT304x 3.3v regulators: one for the clock, one for AVCC (if using a PRO chip), maybe one for VCCA. Probably would work very well, have to try it and see though.

Also, probably a good idea if trying such a thing to bear in mind that LT304x regulators are precision high gain, high frequency devices which can cause problems if layouts and wiring are not well implemented. Some interesting commentary here: Anyone tried Chinese LT3042 board?
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Old 7th November 2018, 01:11 AM   #148
Terry Demol is offline Terry Demol  Australia
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Quote:
Originally Posted by Markw4 View Post
Just what it says in the data sheet. More than 22uf reduces regulation loop bandwidth, maybe a concern if one wants fast response time. Probably better to do as they recommend as use LT6655 as the reference.
This doesn't make sense on many levels.

Provided the cap on set pin has suitably low ESR, it won't affect the HF loop
BW. The obvious solution is to parallel another smaller cap, if that is a concern.

Quote:

In addition, the performance graphs of LT304x don't show what happens with noise below 10Hz.
That is exactly what I am saying. If there is a benefit in the sub 10Hz
region in using LTC6655, then the LT3045 MUST not be the bottle neck or
it would dominate.

The circuit you have posted above from data sheet merely over rides the self noise of the 3045's CCS and the set resistor. It's internal opamp noise can
not be reduced by this arrangement.

Quote:

However, we happen to care about that because LF AVCC noise will intermodulate with the dac analog outputs to increase distortion.

Might be a good idea to use one LT6655 as a reference for multiple LT304x 3.3v regulators: one for the clock, one for AVCC (if using a PRO chip), maybe one for VCCA. Probably would work very well, have to try it and see though.
Not a bad idea, however I would be using more aggressive filtering on it's
OP by at least a factor of 2.

Quote:

Also, probably a good idea if trying such a thing to bear in mind that LT304x regulators are precision high gain, high frequency devices which can cause problems if layouts and wiring are not well implemented. Some interesting commentary here: Anyone tried Chinese LT3042 board?
[/QUOTE]

What he is saying is very true, so in many cases of non local use, good idea
to have OP damped. Data sheets should give more info on this.
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Old 7th November 2018, 03:25 AM   #149
Markw4 is offline Markw4  United States
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Quote:
Originally Posted by Terry Demol View Post
The circuit you have posted above from data sheet merely over rides the self noise of the 3045's CCS and the set resistor. It's internal opamp noise can
not be reduced by this arrangement.
Agreed. Might be good enough though, or at least better than what people are getting now when TL304x are used for dac voltage regulation.
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Old 7th November 2018, 11:56 PM   #150
Itsmee is offline Itsmee  England
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Quote:
Originally Posted by carlmart View Post
...Just curious: have you compared or tried the LT3042 regulator versus the Super Regulator?
Quote:
Originally Posted by Mikett View Post
...A super Reg will not be easy to implement for the AVCC because you will need to find an op amp that can work withing the output voltage and that is 3.3V...
If you ran a +V super reg* off the the +-15V supplies; link out D2, connect Pos Vout to Pos Vout sense, connect Pos return sense to 0V; replace the Vref with a NiCd**, set the gain to 2.75 (x1.2V=3.3V).

The output can only source current, it cant sink - unless you add a shunt (think single ended output stage), is this what you need?

*The Superregs | Linear Audio NL
**https://tf.nist.gov/general/pdf/1133.pdf
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