Impressive start, you've jumped straight into the deep end.
1Volt drop with load sound about right, I see you have a bleeder power resistor in the picture. Try and use a low value somewhere between 10R-30ROhm. If you put the first choke in "common" mode, you'll drop some more voltage too.
One trick I like a lot, is to unwind the secondary on your tranformer to the right voltage.
Thanks stijn001. I tried all of your advises, and no changes. I couldn't unwind secondary because my trafo is fully encapsulated.
But, as I'm still learning
I found where I was wrong. I have put wrong load on psu. As I don't have proper dac boards yet I had to improvise and do proper counting. So I did small probe bulb 12Vdc 15W which is equal to 1,25A load. Just like whole dac set. And guess what! I have got 11.58Vdc stable!Hehe, yes I jumped on deep water all right! But there is no much time to listen to beautiful music! And as we do, we do best we can :-D that brings a lot of fun! I've got hooked by all of you guys! At the end of this project I'll get transformation from a bartender to an electronic technician haha!
OK, let me jump in here. Nice detective work from Hermann by the way, this makes our common hobby so interesting. Always some new perspectives
What we see here is that the dac chip is outputting its analog level (a current) within a few clock cycles. Indeed this has nothing to do with jitter, delay lines or what so ever. We should remind ourselves that the 1794 is a complex 1 bit converter with some 6 bit tricks in it. The datasheet is so vague (I guess on purpose) that we do not know what really goes on, except that it is a mash converter. What I expect is that what you see here is the effect from the dithering which happens inside the chip. We also should not forget that these clock cycles are far away from the 44.1 kHz sample frequency and that this experiment is done with square waves of 22.1 kHz. You will not find these in CD recordings of course.
Now it might very well be, that the resulting step case of 3 clock cycles helps a bit smoothing the digital output. In fact what you see is a kind of Low Pass Filter on a one bit signal.
If you would run a normal sine wave through this test it will be much harder to see the effect of course.
Nevertheless, I think Hermann contributed very nicely to understanding why more decks sound better than one single deck. The HF filtering and the averaging out out of the mash converter effect does the trick it seems
On the point if controlling this would help. As said above, you will create a kind of FIR filter with no feedback, so a straight Low Pass Filter. And that is exactly what we saw in Hermann's scope pictures. Not sure if this is really needed. you can also put a capacitor on the Output as is already an option on the DDDAC Blue board...
Thanks for your reply, so my theory is somehow confirmed now - and I'm glad to know that nothing is broken in my setup but this is simply the normal behaviour of the circuit!
Btw., it can indeed be seen for a sine wave, although much harder.
Best Regards,
Hermann
Like Simon, I am just about to build a DAC board with both 3.3v and 8v Tentlab shut regulators, and I am also a little unclear about what components other folks have removed from the original DAC board design and what is really needed.
Tentlab's application notes suggest that a 10uF capacitor is placed close to the shunt regulator's input, and that nothing is required on the shunt regulator’s output as long as the output is close to where the supply is needed.
So, presumably, when shut regulators are used, chokes L1 to L4 (10uH) are not required. Is this correct and have folks removed these?
Do we need to keep C1 to C4 and C7 to C10 (47uF)? If so, what purpose do they serve?
I guess we need to keep C5, C13, and C11, C15 (47uF) to act as the input side capacitor mentions in the shut application notes. Is this correct?
It looks like we don’t need C18, C27, C32 and C20, C29, C34 (47uF) on the output side of the shunt regulators. Is this correct?
What about C6 and C12 (1uF)? Do we need these? And if we can position the shut regulators very close to the PCM1794s, do we really need C17, C28, C31 and C19, C30, C33 (100nF)?
Thanks for you help.
I would suggest reading up on decoupling digital devices and circuitry.... First.
The 100nF devices will be local decoupling next to the device pins, removal is NOT reccomended
I would also look at stuff like this:
http://www.ti.com/lit/ml/slyp167/slyp167.pdf
And Ti's Analog Application Journals are a good source of reference material...
As well as other manufacturers information sources.
The 100nF devices will be local decoupling next to the device pins, removal is NOT reccomended
I would also look at stuff like this:
http://www.ti.com/lit/ml/slyp167/slyp167.pdf
And Ti's Analog Application Journals are a good source of reference material...
As well as other manufacturers information sources.
update
Hello,
When you start reading this thread as a newcomer chances are very big that you will get confused by the big load of information available.
What you can do is just try to copy and paste the info that seems valuable to you.
Many things have been said and they are repeated by others so you will probably be ending up with 20 % of the complete content.
There are some threads that deal with where to spend your money if you have a limited budget.
Would it be better to have a four board dac with an average power supply or one board with a much better power supply. The lundahls chokes are not that expensive?
Should we wait for the new dac board to arrive with the essential modifications described in this big thread already installed?
I think i will.
Sincere greetings, Edward
All the power supply parts ll2733 and ll1694 and transformers and Elna caps are already in the house.
Hello,
When you start reading this thread as a newcomer chances are very big that you will get confused by the big load of information available.
What you can do is just try to copy and paste the info that seems valuable to you.
Many things have been said and they are repeated by others so you will probably be ending up with 20 % of the complete content.
There are some threads that deal with where to spend your money if you have a limited budget.
Would it be better to have a four board dac with an average power supply or one board with a much better power supply. The lundahls chokes are not that expensive?
Should we wait for the new dac board to arrive with the essential modifications described in this big thread already installed?
I think i will.
Sincere greetings, Edward
All the power supply parts ll2733 and ll1694 and transformers and Elna caps are already in the house.
Hi, there has been a lot of trial and error in the past and in the end it turned out (for the people who tried) that the best result was to only omit the two caps at the analogue side (when using shunts), I'd have to look up the nrs., but you'll be able to tell from pictures from me, James & Supersurfers. Some have removed the chokes, but I haven't. But don't let this discourage you from trying different options and making your own choices, it all comes down to personal preferences in combination to the rest of your system.
You will learn a lot in the process, to know what each cap "does", to the sound.
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Rating can be same as I mentioned before for the diodes.
However I would advise Shottky diodes or bridge, they will sound better than a standard bridge.
regards,
A bit off topic but what the hell
All directly heated triode tubes.
EML AD1 two channel amp outputs (Sakuma style), WE VT-25 driver, EML 20A input tube, packed with interstages and chokes.
Nixi shows volume setting.
This is not the bottle neck in my audio system.................................
...please allow me a question: what is it then ? I can't believe that it might be your DDDAC ?
Thanks Supersurfer
I bought four Schottkey 2A 60v diodes for the rectifier
Chokes are on their way to me as well as caps do we should have a new psu soon. Thanks for your help
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Hi, there has been a lot of trial and error in the past and in the end it turned out (for the people who tried) that the best result was to only omit the two caps at the analogue side (when using shunts), I'd have to look up the nrs., but you'll be able to tell from pictures from me, James & Supersurfers. Some have removed the chokes, but I haven't. But don't let this discourage you from trying different options and making your own choices, it all comes down to personal preferences in combination to the rest of your system.
Thanks.
I had already been looking at what your folks have already tried, and it looks like you all do something slightly different - hence my question
I was hoping that a consensus had already been reached, but it appears not. I guess I'll have to try some different combinations out and see.--nick
Hi, I think they are just there for HF filtering, but I agree with you that removing them all to gether is not a good idea.
From looking at the various uploaded photos, some folks appear to have removed 100nF capacitor to make way for attaching the shunts right next to the DAC chip.
So, for example, to place the 8v shunt closest to the DAC chip, some folks have removed C23/C26 and reused this position to locate the shunt millimetres away; and to place the 3.3v shunt closest, other folks have removed C28/C30 and reused this position.
Or maybe I am missing something and these folks have mounted these capacitors underneath the board.
So, for example, to place the 8v shunt closest to the DAC chip, some folks have removed C23/C26 and reused this position to locate the shunt millimetres away; and to place the 3.3v shunt closest, other folks have removed C28/C30 and reused this position.
Or maybe I am missing something and these folks have mounted these capacitors underneath the board.
This is wrong they are the local decoupling caps, even a few millimetres is a long way, as I have said look up the basics of digital decoupling...
The low value decoupling caps need to be next to the pins as near as physically possible, any added inductance makes them useless... The shunts even a few mm's away cannot react fast enough... Doing this is SO WRONG and will add noise to the system as well as other problems.
The low value decoupling caps need to be next to the pins as near as physically possible, any added inductance makes them useless... The shunts even a few mm's away cannot react fast enough... Doing this is SO WRONG and will add noise to the system as well as other problems.
I see. Some examples I've seen had the HF filter cap moved onto the shunt PCB (there is a position for it on the Tentlabs) , in case of a shunt close to the PCM1794 the use of this filter cap might be less relevent, but I have personally not tried this. It's not the way I wanted to take the sound.
What is a HF filter cap... do you mean the 100nF capacitors, these if across the power supplies are decoupling caps, there is gigabytes of information regarding decoupling and its importance to digital designs and moving any low value cap renders it useless as the added inductance of the tracks (or plane) between it and the power pins mean it cannot function as it is required.....
To get the maximum resolution out of any ADC/DAC then you have to follow the rules, if you are attempting to get 24bit resolution you have to be even more careful of what you are doing..... Getting true 24 bit is not easy and probably not achieved with most DIY designs and a few professional designs as well everything becomes critical and as Eric Bogating says on his site... "No myths allowed".
To get the maximum resolution out of any ADC/DAC then you have to follow the rules, if you are attempting to get 24bit resolution you have to be even more careful of what you are doing..... Getting true 24 bit is not easy and probably not achieved with most DIY designs and a few professional designs as well everything becomes critical and as Eric Bogating says on his site... "No myths allowed".
The Tentlabs shunts already include a capacitor across the output as delivered - seems like the latests deliveries have moved to using surface mount capacitors at this position rather than the Wima through-hole ones used in the earlier versions.
I guess you are saying that both the DAC board 100nF decoupling capacitor *and* the capacitor on the shunt are required event if the shunt is mounted at the position of the DAC board 100nF cap.
I guess you are saying that both the DAC board 100nF decoupling capacitor *and* the capacitor on the shunt are required event if the shunt is mounted at the position of the DAC board 100nF cap.
Marce, you are obviously the expert. I'm still not sure what, and why, it was you were asking.