The transistors in the current mirror, and differential amplifier will benefit from having thermal contact, to keep the temperature difference as small as possible, thereby minimising the DC output offset. I have taken the best picture I could, of this coupling for one channel, in my amplifier.
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.
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:
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.
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.
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