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Building the ultimate NOS DAC using TDA1541A
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Old 5th June 2006, 07:21 PM   #281
tubee is offline tubee  Netherlands
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Default spdif output and input

Ecdesigns, i found some ideas for spdif:

Output from SAA 7220:
http://www.diyaudio.com/forums/attac...amp=1131660111

Spdif Input in dac: (CS8414)
http://www.diyaudio.com/forums/attac...amp=1135100334

Thread:
http://www.diyaudio.com/forums/showt...=&pagenumber=1

Is it an idea to load the same value resistors and use a diy ringcore pulse transformer too in the CDP, this for right impedance match on SAA7220? Thanks!
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Old 6th June 2006, 02:13 PM   #282
ecdesigns is offline ecdesigns  Netherlands
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Default DEM clock synchronizing / SPDIF

Hi, Tubee

Thanks for your reply [post#279]

> The analog mainboard makes all connections between the modules, contains LCL filters and the DEM (Dynamic Element Matching) synchronizing clock circuit, BCK buffers and a separate 5V power supply. The DEM clock has been modified again, so wait until I post final schematics.

The modules that are placed on the analog main board are separate, the DEM clock synchronizing circuit is part-of the analog mainboard. But I can design a small circuit board, only holding the DEM clock synchronization circuit.

> The DIR1703 would be a good choice for the octal D-I dac, the DIR1703 with the SpAct (Sampling period Adaptive controlled tracking) seems to have a clock jitter of only 75pS, compared to 200pS for both CS8412 and CS8414. Since it has no RS422 input, a differential receiver chip needs to be added. I am planning to make modules for all 3 types. Currently I am using the CS8412.

> I plan to use the PCM2706 from TI for USB to I2S conversion, It's another separate module that plugs-in the digital mainboard, or can be used separately (like all modules of the octal D-I DAC).


[post#281]

About the SPDIF question, why not connect the DS8922 RS422 driver input directly to pin 14 (DOBM) of the SAA7220 (without the schmitt trigger circuit). Then you have a differential RS422 output driver with only one chip, and don't have to worry about pin 14 loading. On the receiving side you can experiment with the circuit I posted earlier.
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Old 6th June 2006, 09:28 PM   #283
tubee is offline tubee  Netherlands
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Default spdif

Ok thanks Ecdesigns for answering.
I will wait for the dem reclock schematic then, but will put the Kwak 7 in first.

For the Spdif will search a DS9822, its a pitty i bought a 74HCT14 this afternoon for 3 euro's! And not even a Philips!

I have a cs8414 waiting to be used in a dac, but in meantime better ones are seeing daylight.

Keep going with the very good work on the modular designed D-I dac. Still i am very curious on its sound.
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Old 7th June 2006, 03:02 AM   #284
MGH is offline MGH  United States
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Question balanced versus single ended

Just a curious question. I know this DAC is a balanced design at the digital and analogue stages, but most of us don't own balanced preamp or amp. So if we use the RCA single ended output of the DAC, does this defeat the purpose of balanced design? Or do we still get some benefit of the balanced design (eg, noise cancelllation) even though we are using the single ended output?
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Old 7th June 2006, 06:36 PM   #285
ecdesigns is offline ecdesigns  Netherlands
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Default Finally ready, the analog mainboard

Hi,all


Look what I found,

Mainbordus analogus maximus, a rare species of the octal D-I DAC family .

Sorry about that ,

but I'm in a good mood since the octal D-I DAC core is ready and is finally working now. The added photograph shows the Analog mainboard with all modules added. I will post some more photographs of the analog mainboard without modules, and the solder side.

Did it work the first time? no actually it didn't . After checking all power supply voltages and I2S signals, I placed the remaining modules on the analog mainboard and switched-on. Nothing, checked voltages again, they were ok, checked the I2S signals, all there. Then I removed the differential OP-amp modules and connected a resistor on the DAC outputs, still nothing. Then I had another quick look at what was left of the prototype board, it couldn't be, or could it? yes I swapped DATA and BCK signals on the analog mainboard . After some thoughts about how to fix this in an elegant way , I decided to swap the signals on both Quad-DAC modules. Put everything together, and switched-on, it finally worked like a charm.

I will run some more tests to see if things can be optimized. PCB's will need some minor modifications, then this major part of the octal D-I DAC project is finally ready
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Old 7th June 2006, 06:47 PM   #286
ecdesigns is offline ecdesigns  Netherlands
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Default Analog mainboard without modules

Hi, MGH

Thanks for your replies [post#280,#284]

> Circuit boards: I am planning to use glass epoxy boards with thick gold-plated copper tracks and a blue laquer anti-solder mask.

> The octal D-I DAC is a fully balanced design, starting with the differential SPDIF input to prevent jitter. Then a differential DAC arrangement (4 non-inverted DAC outputs and 4 inverted DAC outputs) to cancel out some more interference AND cancel-out DC offset, so a grounded grid and DC coupled signal (OP-amp) can be used. The differential OP-amp and Tube amplifiers are necessary to combine the inverted and non-inverted signals into a non inverted signal with twice the amplitude.

The tube stage in addittion has a differential output setup (2 cathode followers) for a fully equal balanced "load" on the differential amplifier, this significantly increases stability and symmetry, reducing distortion and increases CMMR.

Don't worry about the single ended RCA connections, my set is also single ended. So I am not going to use a balanced output either.

I have added another photograph of the analog mainboard without modules placed.
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Old 7th June 2006, 07:05 PM   #287
ecdesigns is offline ecdesigns  Netherlands
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Default Analog mainboard solder side

Hi, tubee

Thanks for your reply [post#283]

> New DEM clock schematics will be posted soon, it's no pitty you bought the 74HCT14, if you put 2 schmitt trigger inverters between the SAA7220 and the DS8922 (so the signal is not inverted) you can increase slew rate.

> I am curious about the Kwak 7 oscillator. I had a look at the schematics, what frequency does it generate and how is it connected? I have seen some spectrum analysis of the Kwak 7 oscillator on the internet, that showed a strange continuously varying spectrum.

> I will do some testing with the DIR1703, specifications look good

I added another photograph of the analog mainboard (solder side)
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File Type: jpg amb1b.jpg (92.3 KB, 2405 views)
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Old 7th June 2006, 07:48 PM   #288
MGH is offline MGH  United States
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Thanks ecdesigns.

Good to hear everything is comming together nicely.

Regarding the PCB, have you conidered a black lacquered PCB instead of blue? I've seen black PCB board with gold plated copper tracks - I must say it really looks nice that way, and it's rare to have this combination. It really would stand out. Anyway, it's a minor point, but I'd thought I give my 2 cents on the look of the PCB.

BTW, the board with all the chips look very well thought out with efficient use of space - very professional.
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Old 7th June 2006, 09:28 PM   #289
a333bt is offline a333bt  Slovenia
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Hi ecdesigns,

very nice work. I am very enjoying to read this thread.

I would be satisfy also with this PCBs.

Will be in NOS DAC using also 74HC161?

I ordered by mistake 50 pieces of 74HC161 Philips, instead 50 resistors.

Would be here any improvements, if we put copper EMI (3M) shielding tape on ICs?

I can ask for lower prizes (group buy) for TDA1541A/R1, if will be interest to do this. I got mine for 15US$ per piece.

I guess that best for 470pF would be silver-mica capacitor.

regards
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Old 7th June 2006, 09:43 PM   #290
stefanobilliani is offline stefanobilliani  Italy
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hallo ecdesigns and all .

I also like very much this thread and will be interested in the realization or the DAC ... I am thinking of a "quad" version for now but ready to change my mind in future .
Would be nice to have a group buy for pcb also .

By the way I have not clear in mind how the analog signals are mixed at the output ... and ... are in the last pictures of the "analog board" op amps used for the outputs ready on the board ??

Thanks and compliments for a nice work
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