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Old 15th October 2019, 05:49 PM   #5101
laserscrape is offline laserscrape
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I didnt use an RC snubber, the distortion was familiar from using the transformer with the sabre DAC so dont think there is much that could change.

My vague understanding of delta sigma DACs is that they first interpolate the PCM data to higher sample rate and then a DS modulator reduces bit depth and increase sample rate further. With a 1 bit DS modulator the output wouldnt be essentially DSD?
The AKM block diagram shows these stages, similarly HQPlayer has options for oversampling filter and modulator with a DSD output.

Now AFAIK these newer DACs are multibit DS DACs, it isnt easy finding info on differences between multibit and single bit DS DACs, there is a lot of overlap and confusion. ''multibit'' almost always leads to information on >16bit DACs compared to DS DACs, these >16bit DACs are almost described as ''R2R'' too when non R2R DACs like TDA1387 exist.
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Old 16th October 2019, 01:35 AM   #5102
Terry Demol is offline Terry Demol  Australia
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Quote:
Originally Posted by laserscrape View Post
Eventually learning how to do some basic programming of a DAC would be great, better to leave till the DAC gets a stronger DIY following and there is more of an audience who can benefit.

I never understood the use of the SRC,
The idea was a one stop shop to solve jitter and clocking issues. It certainly
worked very well, just look at the number of DAC's out there running a single
100MHz clock.

The original ASRC concept was discussed here briefly by Dustin and the
measurements were very good. Then they decided to amalgamate the ASRC
into the DAC.

Gordon Rankin (Wavelength) was the first to run Sabre sans ASRC in sync mode and note the improvement. The rest is history. It took a little time for
people around here to catch on.

Quote:

if the DAC essentially converts to DSD already. the idea with pre-conversion to DSD was using powerful PC processor to run more complex filter and modulator algorithms.
The DAC is limited in its processing power and cant see how SRC would be any different, is that off the mark?
The PCM side of the DAC is much more complex than native DSD. There are
all sorts of things going on.

Quote:

IME I think a transformer would bottleneck the Ak4499.
I found 1:4 transformer distortion unacceptable with 9038Pro DAC with little improvement over just a resistor, the 9038Pro did not like anything but op amps for I/V.
Yep, as I speculated in my first reply. It's a balancing act that may or may
not work. The trnasformer quality is paramount.

What sort of transformer did you use?

Quote:

If using only a resistor for I/V for AK4499 does not give acceptable performance then I think with a trafo either the ratio will be too low to be effective or the distortion will be too high.
The TDA1387 worked decently with resistor I/V and that trafo happened to be a better match for it. However with TDA1387 paralleling chips and lowering the I/V resistor reduced the positive effects from the trafo step up, at 20 or so chips the DAC sounded better with just a resistor than with the trafo, at that point trafo distortion was greater and more offensive. The TDA1387 sounded its best like that, even OPA1612 I/V couldnt compare.
More than likely the 4499 will be the same as 9038Pro, but they arent identical so who knows.
TDA1387 has true current out. I don't know what the voltage compliance is
but the best option for it would be a grounded base, open loop I-V.

T
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Old 16th October 2019, 02:17 AM   #5103
abraxalito is online now abraxalito  United Kingdom
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Quote:
Originally Posted by Terry Demol View Post
TDA1387 has true current out. I don't know what the voltage compliance is
but the best option for it would be a grounded base, open loop I-V.
Tried that in various guises - transformer sounds better. In particular the difference is that along with the transformer comes a much greater apparent quantity of low frequency ambience. That is on recordings that have it. It could be as a result of the inherent noise reduction of paralleling devices, I've not tried a trafo with a single TDA1387, I generally use upwards of a few dozen.
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Old 16th October 2019, 10:53 AM   #5104
laserscrape is offline laserscrape
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Originally Posted by Terry Demol View Post
What sort of transformer did you use?
Output transformers for DACs
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Old 16th October 2019, 01:45 PM   #5105
Terry Demol is offline Terry Demol  Australia
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Quote:
Originally Posted by laserscrape View Post
I have gone through a few of the measurements and they are a mixed bag.

The ES9038Q2M results are not the best. Even at 1kHz there is a lot of
distortion and the noise floor is very high. There are also many harmonic spikes past the 5th, maybe this is a consequence of running Sabre in voltage
mode, not sure.

If your DAC had similar results then I can understand your POV.
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Old 19th October 2019, 10:24 AM   #5106
laserscrape is offline laserscrape
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Quote:
Originally Posted by Terry Demol View Post
I have gone through a few of the measurements and they are a mixed bag.

The ES9038Q2M results are not the best. Even at 1kHz there is a lot of
distortion and the noise floor is very high. There are also many harmonic spikes past the 5th, maybe this is a consequence of running Sabre in voltage
mode, not sure.

If your DAC had similar results then I can understand your POV.
These trafos were really good value and also had some reassurance they were suited to this particular application which is the worry with Lundahls or similar trafos, it was the only realistic entry point into transformers for me but perhaps it also tainted my view of them.

I used 9038Pro with HPs so there was a lot of current to play with on the DAC output. Generally going as low possible with resistor value on secondary was best but there was lower limit where sound started to deteriorate, another balancing act to consider for the trafo possibly?
Having to accept unwanted volume at the potential cost of improved DAC performance was the most frustrating aspect of those trafos paired with the 9038Pro.
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Old 20th October 2019, 08:59 PM   #5107
damiangt3 is offline damiangt3  United Kingdom
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Well I've been busy with work but managed to spare an evening to do some mods to my board. I'd built an opamp regulated supply on a piece of breadboard but took the opportunity to make use of the opamp and pads on the mainboard so I desoldered all the unnecessary components, cut a few lines and now I have quite a neat opamp regulated supply, just a couple of wires running underneath to the 47uf caps on the AVCC feed. All the other necessary power sources have been replaced, just leaving the onboard 7805/1117 to power the Atmel and inputs.

I still need to solder two LT1763 with the necessary caps to the underneath so I can separate the some of the shared power sources.

I have my pair of +/- 15v Salas BIB powering my Twisted Pair Ivy and the opamp regulator and the 7805.

A separate 7v BiB powers the 3045s regulator providing my 3.3s, I'm in two minds whether to replace the 7805 with the BIB reduced to 5v and use this to feed the board but also the 5v supply to the 3.3v 3045s.

It's almost time to reintroduce the AK4137 SRC although I do need to understand what power supply/circuit improvements can be made to this.

Another question to ask, I need to install a USB XMOS/Amanero board, what do I need to look for? How important are the onboard crystals?
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Old 21st October 2019, 01:25 AM   #5108
Markw4 is offline Markw4  United States
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Originally Posted by damiangt3 View Post

Another question to ask, I need to install a USB XMOS/Amanero board, what do I need to look for? How important are the onboard crystals?
Good to hear of your progress so far

Regarding XMOS/Amanero, I am currently recommending JLsounds I2SoverUSB. Jitter is very low which can matter if you decide to try synchronous mode with the dac and or if you want to get DPLL bandwidth setting as low a possible (for best sound quality).

Amanero also makes a good USB board, but the clock frequencies are half what is available from JLsounds. That would be okay except if you wanted to try ES9038Q2M in synchronous mode. In that case you would want the higher clock frequencies to be available.

Both the above mentioned USB boards include ASIO drivers, something necessary for using native DSD in Windows. Strongly recommended the above boards on that basis.

Regarding AK4137, that gets a bit complicated and I don't have a simple answer at the moment although I would like there to be one. Suggest we discuss those issues separately. That discussion would probably also apply, at least in part, to using ES9038Q2M in synchronous mode.
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Old 21st October 2019, 12:03 PM   #5109
damiangt3 is offline damiangt3  United Kingdom
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Quote:
Originally Posted by Markw4 View Post
Good to hear of your progress so far

Regarding XMOS/Amanero, I am currently recommending JLsounds I2SoverUSB. Jitter is very low which can matter if you decide to try synchronous mode with the dac and or if you want to get DPLL bandwidth setting as low a possible (for best sound quality).

Amanero also makes a good USB board, but the clock frequencies are half what is available from JLsounds. That would be okay except if you wanted to try ES9038Q2M in synchronous mode. In that case you would want the higher clock frequencies to be available.

Both the above mentioned USB boards include ASIO drivers, something necessary for using native DSD in Windows. Strongly recommended the above boards on that basis.

Regarding AK4137, that gets a bit complicated and I don't have a simple answer at the moment although I would like there to be one. Suggest we discuss those issues separately. That discussion would probably also apply, at least in part, to using ES9038Q2M in synchronous mode.
Thanks Mark, on your recommendation I've ordered the JLsounds board, hopefully shouldn't take too long to arrive being on 'this' side of the pond.

Before I undertake the LT1763 solder to the back plane, are the cap values that Analog suggest sufficient for this, is there anything else I need to consider? Should I use LT3045 or LT1763 for digital (or vice versa)?

For the AK4137 I'll give it a clean 5v, I've got a spare secondary with plenty of 5v PSUs to choose from and if necessary a NewClassD 5v reg so I should have that covered....until mods can be worked out.
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Old 21st October 2019, 02:58 PM   #5110
Markw4 is offline Markw4  United States
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Quote:
Originally Posted by damiangt3 View Post

Before I undertake the LT1763 solder to the back plane, are the cap values that Analog suggest sufficient for this, is there anything else I need to consider? Should I use LT3045 or LT1763 for digital (or vice versa)?

For the AK4137 I'll give it a clean 5v, I've got a spare secondary with plenty of 5v PSUs to choose from and if necessary a NewClassD 5v reg so I should have that covered....until mods can be worked out.
For LT1763, probably wise to follow the advice in the data sheet on choice of input, output, and noise suppression caps.

Whether LT1763 or LT304x would be better may depend more on layout rather than regulator data sheet specifications. It helps for regulators powering HF/RF circuits to be dedicated to particular loads, located very near the load, and be mounted on the same ground plane as the load (in order to minimize ground inductance and or noise effects).

What might be best for you may depend a lot on your experience/skill at fabrication using small parts.

Regarding AK4137 board power, I used a Chinese LT3042 (with pass transistor) board as a +5v digital supply pre-regulator. AK4137 was powered by that since there are secondary 3.3v regulators on the board, just as there are on the dac board.

One thing I did find when using one LT3042 board to power all digital board functions is that a ground loop was formed between the +5v ground returns from the dac board and the AK4137 combined with the I2S ground connections between the two boards. Some I2S ground return RF was apparently flowing between the two boards through the +5v power grounds rather than the I2S connection grounds, and that caused some audible degradation of sound quality.

What I did to verify and correct the problem was add some cable clamp ferrites on one of the power supply ground returns to the 5v supply. Adjust the number and size of the ferrites for best sound quality.

As an alternative to that I probably could have used two transformer windings and two LT304x regulators to independently power the dac board and the AK4137 board. Then I2S ground currents might stay where they are wanted and not go where they are not wanted.

For best primary to secondary transformer isolation of low voltage circuits, I found R-core transformers to work best.

Also, probably no reason to use New Class-D regulators for digital loads. I use LDOs for digital loads and other types of regulators for analog loads, say, such as for output stage opamps. Right now I like LT1083 or LT1086 type regulators for opamps, but they are positive regulators only. To use them for + and - rails requires there to be two separate 15v transformer windings rather than one 30v center-tapped winding. With separate windings then a dual regulator board can be used, maybe such as: LT1083 HIFI Linear Power Supply Dual Output High Adjustable Power Supply Board | eBay

However, since LT1083 regulators, and other good sounding analog stage regulators, tend not to be super high gain error-amp regulators they don't fully eliminate all power supply ripple in one stage. For that reason it can help to use two stage regulators and or one or two-stage RC filters before the regulators. LC filters don't usually sound as good. If using multiple regulator stages it can be helpful to use transformers with maybe 20v or 22v secondary windings. Then some voltage can be dropped across the primary regulator and a little more voltage dropped across the secondary regulator. It all depends on what lengths one is willing to go to in order to get the best sound quality.

Last edited by Markw4; 21st October 2019 at 03:11 PM.
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