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Old 22nd June 2006, 05:48 PM   #411
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Quote:
Originally posted by Bernhard

Ok, samples are original, but only on the digital side.
The DACs get them with different delays.
The delays are < one sample so the samples overlap and that is where the DACs are parallel.
On the analog side x DAC-currents from a previous sample are added to y DAC-currents from the next sample, and the I/V does see it as a new & wrong sample.

Quote:
Originally posted by philpoole
I agree with Bernhard, a DACs output is held until the next sample value is reproduced. So all the DAC outputs, at any given time, will be providing a current - so they are all summed as they are connected in parallel.
Tiime was when I would have felt obliged to the show you two the error of your ways as others have done for me for no other reason than they were able to but these days I can't be bothered.
Having done this stuff professionally, I'd like to think I have some idea of what I am doing but if you two think you are right and I am wrong, good luck to you.

Quote:

rfbrw, I think you are unreasonable to comment like you did. I am incredibly distracted, and I rarely make much kit at the moment. Everybody's commitments and distractions elsewhere in life impact this. I envy you as you obviously have more time than I (and perhaps Bernhard) to craft things. However, there is nothing wrong at all with theoretical discussion, and sensible measurement. They have their places.
Perhaps next time, before parachuting in, you would seek to make yourself aware of the history involved.
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Old 22nd June 2006, 05:50 PM   #412
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Dear Ecdesigns:

I feel honoured you even take the time to answer my "supporting" post.

Quote:
No, I'm not angry
I know. You are very patient!
Sometimes I wish I could be here, to avoid thread's contamination.
Solid technichal advices are good for the thread's progresion but "bad vibrations" replies are better avoided, gentlemen.

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I already invited one DIYaudio member for a listening session.
Excellent! I wish his credibility won't be questioned.

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I have been working for over 15 years now without a holliday.



Good luck
M
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Old 22nd June 2006, 07:23 PM   #413
tubee is offline tubee  Netherlands
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Default off topic again

Ecdesigns: here are my surround speakers with round radiating tweeters:
Round radiating tweeter, aka "Enterprise 1" tweeter!
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Old 22nd June 2006, 08:06 PM   #414
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Default DAC combined outputs

Hi all,

I tried to draw a graphical representation of what happens with the 8 combined DAC outputs. If I am correct, overlap in the combined sample is about 73.4375%. Note that the combined sample has a delay of approx. 43.75% when compared to the main sample. One complete sample time = 100%. Full scale current is 23.5mA, full scale voltage is 13.86V when using 590 Ohm in the I/V stages.

Each DAC is represented in a different color for clarity. Combined graphic representation is in diagram below. Current sample = n, previous sample = n-1, next sample = n+1. Scale below is 8 BCK/division.

Hope this will clear things up a bit
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Old 22nd June 2006, 08:23 PM   #415
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Default Adjusting MSB

Hi Bernhard,

thanks for the information [post#377]

I have spend the last days solving oscillation and hum problems with the modified tube output stage. I ended up re-arranging ground / screening scheme, modified tube power supplies and used screened cable exclusively. Finally the tube output stage is whisper silent, only weak noise is audible at maximum volume setting, hum is inaudible.

Then I played the -60dB dithered sinewave again and turned the volume all the way up. It sounded clear, hardly any background noise.

The PCM56 is a DAC using a resistive ladder network, MSB switch causes most interference as all switches change position simultaneously. Adjusting MSB could reduce the audible effects of this MSB switchover.

The TDA1541A uses three 2-bit active dividers (decoupling capacitors are connected to this circuit), operating on the dynamic element matching principle, in combination with a 10-bit passive current divider, based on emitter scaling. All 16 currents are derived from one single reference current source. According to descriptions of this chip, glitches at MSB change, like the PCM56 are reduced due to this different setup. Externally "adjusting" MSB could cause drift, as it's no longer in "sync" with the TDA1541A internal current reference source, It takes only 61 nA current change to flip 1 LSB (4mA full scale current), see the problem. Added switching noise of 16 MSB switches plus logic (L+R channels) could make things even worse.
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Old 22nd June 2006, 08:44 PM   #416
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Default Listening session

Hi tubee,

Thanks for your reply [post#413]

Those cones from PMMA look very professional. I use Delrin (Acetal copolymer) for the large, medium and small sonic resonators because of the sonic properties of this material. PMMA is also very good.

I tried to invite you for a listening session, but I couldn't find your email address.
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Old 22nd June 2006, 09:52 PM   #417
tubee is offline tubee  Netherlands
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Hi Ecdesigns

Thanks very much for invitation to listen to your creation: the D-I dac (and resonators)
There are now 2 things:

1 My wife is just operated on her knees, she can walk very bad now and i "nurse" her a little, difficult to get away here now.
2 the distance to your home-residence from mine is quite far, not easy to do in one evening or so.

Anyway, email is: tubee_7 at hotmail dot com

Btw i like to work with POM too, but i had some PMMA at hand.
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Old 22nd June 2006, 10:27 PM   #418
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Default Re: DAC combined outputs

Quote:
Originally posted by -ecdesigns-
Hi all,

I tried to draw a graphical representation of what happens with the 8 combined DAC outputs. If I am correct, overlap in the combined sample is about 73.4375%. Note that the combined sample has a delay of approx. 43.75% when compared to the main sample. One complete sample time = 100%. Full scale current is 23.5mA, full scale voltage is 13.86V when using 590 Ohm in the I/V stages.

Each DAC is represented in a different color for clarity. Combined graphic representation is in diagram below. Current sample = n, previous sample = n-1, next sample = n+1. Scale below is 8 BCK/division.

Hope this will clear things up a bit

Drawn that way, it looks like the samples overlap but add in the timing and WS and a different picture emerges. Look as WS the signal that triggers conversion. Each negative going edge of WS is separated by 8 BCK cycles when 8 TDA's are used. 8 BCK cycles amounts to 2.84us. The converted output appears at the first positive going edge of BCK after a negative edge of WS i.e half of a BCK cycle or 0.178us include setling time and the output is stable after 0.678us. The output stage does not see another sample for more than another 2us. This is the same as a single dac connected to a 8x oversampling filter where every sample appears at an interval of (22.7/8)us.
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Old 23rd June 2006, 12:59 PM   #419
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EC, don't want to waste your precious time

but you could clarify it by measurement , give each output an individual passive I/V resistor and show as many DAC outputs on your scope as it has got channels.
So we will see what is the matter with overlap and parallel.
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Old 23rd June 2006, 01:02 PM   #420
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Default 2 sample response

Hi rfbrw,

Thanks for your reply [post#418]

Yes you are right, there is a delay of DAC outputs 2...8, being 0.5 * BCK (177nS), typical settling time of the TDA1541A is 500nS. So a total delay of 677nS after WS negative going edge. But the same applies for DAC1 as well as it is also triggered after 0.5 * BCK. So relatively, there is only approx. 2.83uS between samples (BCK/8). Both DATA and WS are delayed by the synchronous serial shiftregister timing chain before applying them to each individual DAC2...8. At a given time all 8 DAC's have (part of) sample n at the output, as 8 individually controlled DAC's are used. This is the overlap of sample n. I used the difference between zero delay (DAC1) and max delay (DAC6) 56BCK and divided this by 2 (28BCK), being the centre point of the combined sample. Then I calculated the overlap with this point as reference.

I added a oscillogram of a squarewave transient, to illustrate this. Upper trace is the output of a a standard NOS-DAC, lower trace is the octal D-I DAC. So now we have only 2 different sample values, and can observe how the samples appear at the output. The 8 steps seen are created by sequential switch-off, of the DAC output currents. The average delay can also be seen.
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