I would appreciate your help in troubleshooting my dac. - Page 2 - diyAudio
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Old 9th November 2004, 01:30 PM   #11
protos is offline protos  Greece
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Thanks guys.
In the end the original suspect was guilty.
When I replaced the last output chip everything was ok.Because of the strange architecture when I took out of circuit the last(2nd) chip and put in a new chip in the 1st stage I could see distortion so I naturally thought that the problem was not in the second stage but before that.However the fact that the 2nd chip was either dead or out of circuit probably affected the feedback to the first chip and produced this distortion.I still can't really understand the 2nd stage in this circuit and I haven;t seen it before . Can anyone explain?
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Old 23rd November 2004, 10:58 PM   #12
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Default Figuring out how circuits work.

Hi Protos.

Yes the fault is usually found to be what the original guess was.
Fault finding is a nasty business especially at the junction of digital and analog.

National Semiconductor's staff scientist (Bob Pease) has a VERY good book on analog stuff and I'd thoroughly recommend it! A very bright (if not slightly eccentric - sorry Bob!) guy!

I find that if I cannot figure out what a circuit does I break it up into blocks, and simplify the hell out of them.
Consider what happens at dc, then what happens at HF. What are the voltages doing? What do you think the currents are doing? Consider the loading of following and preceding sections...

For particularly complicated circuits I redraw them on paper (you will find that most people cannot draw circuit diagrams that make sense!). If this fails download a simulation program (even eval versions) and simulate it.

Just remember that just because the simulation says it does something doesnt mean that that is what happens in reality!

Remember that even if you spend an hour or 10 on it you will at the end; understand the circuit better; know why the topology was used; know its problems (or at least suspect them) and add to your knowledge/experience base!

Resist the temptation to ask for the answer! Find it yourself!

apollyon25
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Old 29th December 2004, 11:25 AM   #13
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Hi Protos,

just stumbled on this thread.
Good to hear its working again!
I simulated the schematic I drew and it seems to work.......
All it does to the input signal is to make it single ended and form some kind of low pass filter with a quite high -3dB point.

Meanwhile Im not using it anymore. Instead I sent the output of the DAC through a passive filter into a X-BOSOZ for balanced operation. Does make a nicer sound than the OPA627

William
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Old 29th December 2004, 01:34 PM   #14
protos is offline protos  Greece
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Unfortunately or fortunately as the case may be during my troubles with the PT dac I decided to order the dddac as a standby and because it was such a good deal.I did not really expect it to be as good as it turned out .In fact it beats my PT combo easily which is astounding when you think of the price difference and the fact that the the PT is a bit of a giant killer itself.
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Old 29th December 2004, 01:38 PM   #15
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Hi,

do you have some more details on this?

William
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Old 29th December 2004, 01:44 PM   #16
protos is offline protos  Greece
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Doede Dourma is a member here and has a very nice site with projects , tips and the dddac kit.Unfortunately I have moved and temporarily not able to access my files so you will have to do a search on the above name or the dddac kit.Recommended for sure.
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Old 29th December 2004, 02:20 PM   #17
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Hi Protos,

I found the site and it shure looks like something to try

Could you describe the differences in sound?

It would be nice to use two and get a symmetrical output. Maybe this is possible by inverting the signal in the digital domain?

William
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Old 29th December 2004, 02:37 PM   #18
protos is offline protos  Greece
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The differences IMHO always were quite obvious and not really a matter of taste or a 'better compromise'.The most obvious were the increased dynamics and better imaging and soundstaging plus more 'live' sound and a feel that you were allowed to see more of the info on the recording.There was no hard digital sound at all and the extension both ways seemed better and more natural.Precise adjustment of the voltages is absolutely necessary though for best sound.
I would not worry too much about balanced output but I can see why you want it.I can't get my head around it right now but Doede is very helpful and could give you the lowdown on it.
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