I have gathered together the schematics for the non oversampling TDA1545 DAC. Mind that I am only responsible for the shunt regulators, the microcontroller, and the input selector. The digital input circuitry was developed after reading some post from Jocko Homo on the diyhifi.org forum. The TDA1545 circuit is mostly from the Philips data sheet. The I/V stage is from rbroer on DIYAudio.

At some point in time I have made the following block diagram, and from memory it seems correct.


From the top here is the input selector board, the micro controller for the relays are on a second board, as per the block diagram.


After the relays, comes the SPDIF buffer/amplifier circuit based on Jocko Homo's. The CS8412 converts the SPDIF signal into the correct I2S format, I2S data goes both to the DAC board, and the micro controller board. The micro controller signal is buffered by one of the 7404 inverters, in the hopes that any noise from the micro controller, will be isolated.

The shunt regulators, are duplicates of the similar valued ones in the shunt regulator schematic, you do not need to build these twice!

Here is the DAC circuit.


Everything is in the puzzling Philips data sheet. The relay shuts off the data, while the micro controller scan through the inputs.

Here comes the shunt regulators

The one at the bottom is the one for the DAC, and the one that is not duplicated on the input selector board.

Here comes the I/V from rbroer, which is fed from the unregulated DC supply.


And the micro controller schematic.


I have redesigned the PCB layout's without saving the ones I used in the working DAC. Therefore they have not been tested, and I would rather not publish them, and have them blow up in some poor persons face.

I just thought I would publish design of the now deceased DAC, this is simple and easy to build, as it was my second working DIY project. Consider a better supply for the TDA1543 chip.

Shematic (PDF), PCB Layout (PDF), and Cadsoft Eagle 5.0 files

Tonight I finished an active I/V stage for the TDA1545 DAC. Up until now I have used a resistor I/V for both my TDA1543 and TDA1545 DAC, this has some undesirable effects as the current output of the DAC should be looking into a very low value resistor, and a fairly high valued one is needed to get a deecent voltage output (http://members.chello.nl/~m.heijligers/DAChtml/Analogue/IV.html). Besides presenting a better impedance to the current output of the TDA1545, the active I/V stage also brings the output to about 2Vpp, in it's current configuration. The I/V stage was designed by "rbroer" of diyAudio, the original thread is here: Single rail, active I/V for TDA1543, TDA1545A.

The sound with the active I/V is definitely better. My test setup is a long way away from my stereo, therefore the DAC has to drive a 20 meter long cable, which has always led to a "muffled" sound. Since the active I/V has better current and voltage driving capabilities, this is now gone. This is a wonderful experiences, no magic, simple logic, that manifests itself, in the way I would have expected. Everything is firm and in control. As far as I can see this can only improve things, even when the DAC is back in place, with a half meter of cabling.

I will post a the relevant layout files, when I have finished testing and tweaking.

As noted earlier, I had some trouble with C7 blowing the chips. I am no closer to being sure what the problem was, but I am beginning to suspect a bad batch of chips, anyhow the original value is according to Phlips datasheet, way to high. I have now settled for a 2.2uF WIMA cap, and everything is playing nicely.

I had some help with my troubles at diyhifi.org, the thread is here:

TDA1545 Vref cap and the death of several DAC chips

Finally after a thousand cups of coffee (for me that is) it is actually playing music again. This time through the last TDA1545 DAC chip that I haven't destroyed. This is a clone of the "Monica" DAC. I can not comment that much on the sound, since it has been a while since the TDA1543 DAC, was playing, but it sounds nice, and definitely different. If you have some spare chips and time, try it for yourself.

In the final version, R1 is 33k, and C7 has been omitted. C7 seemed to be the part causing the 2 DAC chips to die, I'm not sure why, and I'm not sure the final solution is to leave it out, but since I'm at my last chip, It'll stay that way for a while. Also check the output from the current source between R4 and D1, if above 6V, short out D1, D4, and D7.

TDA1545 NONOS DAC Cadsoft eagle project files

TDA1545 Datasheet

Damn that horse! I have spend much of the day building a TDA1545 version of my DAC, but with no success. The CS8412 SPDIF -> I2S/EIAJ converter locks to the signal, but only noise comes out from the DAC. Maybe I will have to resurrect the TDA1543 board, to make sure everything in front of the DAC, still works.

Nice little horsee ;). Well this nice little horsee, and my daughter teamed up to kill my TDA1543 DAC, that I had been stupid enough to leave on the floor for a while during some tests. The heat sink on the 317 regulator was shorted to ground, while the horse had one of its feet planted firmly inside the case. This led to some very disturbing movements of the speaker cones, but everything except the DAC, seem to have survived. I could probably resurrect it with a new regulator, the TDA1543 chip has proven very sturdy, but I think it has had its time. I'm going to build a new one using the TDA1545, because it simple, and later I will upgrade to the Wolfson WM8740.
   

Yes it has always looked like this, no wonder my daugther didn't think it was of value.

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