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Old 25th April 2004, 02:17 PM   #11
garbage is offline garbage  Singapore
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hi Bernhard and till

thanks for the input.

i have added 680R for pin 6 and 8 to Ground. now i don't need to turn the volume of my passive-pre too much, but max is still required to real loud listening levels.

seems like the buzzing noise would be the resistor values at Vref and between pins 6/8 to ground. after adding the 680R for those pins, the buzzing is not as noticeable except at loud volumes.

i'll build a nonoz dac portion of the circuit to compare with my current one. will do that at a later date. will keep you guys posted as well.

cheers.
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Old 25th April 2004, 05:27 PM   #12
Giorgio is offline Giorgio  Italy
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Hi Garbage,
the buzzing sound is puzzling me a little.... I have never had any serious problem of that kind.

I would not suggest using the Convertus for driving low impedance passive pre-amps, but it should work provided the input is 47K or more.

If you are sure everything is now ok with respect to the original convertus design, you should even unfortunately take into account the possibility that one or more of your 1543 have got burned up by during previous tests with connection problems. The fact that they were in parallel does not grants that they have all broken down in the same way, by the way: once I had to substitute one single DAC chip in the Convertus, and never understood why....

Hi Andrea,
thank you for your welcome.

Sorry for not answering to your previous message on another thread, I just run over it months later than the thread was abandoned. I am from Milan too, I think we could find a way to meet... you have my e.mail.

Kind regards to everyone
Giorgio
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Old 25th April 2004, 05:35 PM   #13
Giorgio is offline Giorgio  Italy
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One more note: the Convertus prototype is completely wired, so the different length of connection is not a cause for sensible misalignment of DACs or echoes.

In any case, the shortest path the better. In the prototype, all DAC chips and related components are packed in a line in less then 6cm... and wiring that has been a nice sort of nightmare that I would not like too much to repeat...

Giorgio
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Old 26th April 2004, 02:41 AM   #14
garbage is offline garbage  Singapore
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hi giorgio

thanks for your comments. (always good to hear from the maker of tnt-convertus dac)

i have added the 680R to ground on pins 6/8. volume is more managable now. the buzzing also is less severe.

currently i have only the 680R, the 3.3R and the output caps. on pins 6/8.

i wonder if adding the 680pF caps will help reduce the buzzing... will try that later this week.

after i scrapped my 4 paralleled dac board, i also do not wish to attempt it the 3rd time. it is really tedious to wire up.

i am still keeping the PSUs and the receiver sections. so this point onwards, i am going to try out different configurations of the dac design.

cheers.
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Old 26th April 2004, 10:09 AM   #15
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What value do you have at pin 7?
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Old 26th April 2004, 10:18 AM   #16
garbage is offline garbage  Singapore
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hi till

pin 7 is 330R to ground.
with pins 6/8 using a 680R to ground.

i realised that this config is for 4 dacs. i'll stack up the dacs for a quick try when i get home tonight.

will report my listenings later.

pins 6/8 also has a 3K3 in series after the 680R, but before the caps.
any idea what purpose the 3K3 serves?

cheers
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Old 26th April 2004, 10:31 AM   #17
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The value Till asked is quite important, as it sets the bias current (and it definitely sets the DC level on pins 6-8 together with the resistors attached to that pins.. what is that DC level on your DACs?).
It seems to me that your bias setting might be making the output of the TDAs hit their limit.

Remember that this DAC is a current out type, so output current has to be set properly to have it work right.

Cheers

Andrea
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Old 26th April 2004, 10:42 AM   #18
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The "right " value for The R at pin 7 and the values at pin 6 & 8 are related from my experience.

I would use 1100R or so at 6&8 and put a trimmer at pin7. Now adjust for best setting. If you want take the trimmer out, measure it, and put in a fixed resistor now. I did and got for the 1100R a value must be below 400R at Vref, else THD increases. But i was told at this board this value must be wrong and my TDA may be damaged. I got this with 3 different TDA1543 i tested.

For the 3k3 no idea, filter together with cap? output protection aginst to small load?
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Old 26th April 2004, 12:09 PM   #19
Coulomb is offline Coulomb  England
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Quote:
Originally posted by audionut
you could go to Doede Duama's web site and order a printed circuit board for 20.00 U.S. Doede makes available all of the required parts....I powered mine from a 12 volt gel cell (for the DAC Tower that Draws almost half an amp) and 3 sets of Ni Cad batteries (for the reciever analog and digital supply and the clock) for a total of 4 supplies.

Sounds unbelievably good...and follows the TNT webb site ideas pretty closely.

just look up dddac 1543

Link Please.

Anthony
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Old 26th April 2004, 01:54 PM   #20
garbage is offline garbage  Singapore
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i read some where in diyaudio that Doede's values for one dac to start experimenting with is 1.35k Vref and 2.2k Rload at 8.5V.

so for 4 dacs it should be 330R(1.35k/4) Vref and 680R(2.2k/4) Rload.

anthony, the link for the site is
dddac

btw, after i stacked 4 dacs with 330R Vref and 680R Rload, it sounds much better and the buzzing is very slight. cannot really hear the buzz unless u stick your ear next to the tweeter.
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