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.
There was an error in the last PCB posted, here comes the correct version.
I have just assembled and tested the prototype shunt regulator for the DAC. Inpsite of long wires and veroboard it performs a little better than the LM317+CSS+diode shunt I've been using so far. When they arrive I will try replacing the transistors with some low noise BC560 types, to see if they perform better.
The peaks at 50Hz, 100Hz and so forth comes from the SPDIF -> I2S converter board, where the PSU has not yet been optimized.
Here's a list of things to be done before the final product is posted:
New PCB layout At least testing a better power supply, I'm thinking TL431 shunts
- Try some BC560's in the shunt regulator.
- Testing some bypass tricks, around 22pf from supply to ground, and the same value from Iref to ground
Low noise BC550/BC560 transistors instead of BC547/BC557
Testing a better power supply for the CS8412, again I'm thinking TL431 shunts The SPDIF input circuit is bypassed, figure out why it does not work
- Possibly a new PCB layout
uC input selector:
- Install some bilateral switches to avoid switching the actual signal to the DAC before we know there is a signal
- Ponder on SPDIF signal detection, do I a need to program a PLL?
I know that nothing has been posted about the uC input selector yet. Basically I'm not the least satisfied with the way I have solved the problem up until now.
A PIC16F628 switches the input relays, until a signal shows up on the DATA line of the CS8412. meaning that the actual sound is output from the DAC as well. I have decided to try measuring at the SPDIF inputs by using bilateral switches instead. I may have to lock on to the SPDIF signal to detect audio data. the solution that I'm hoping will do, is to establish the length of the pulses on the SPDIF line, if there is data, some pulses should be half the length. I'm yet uncertain as to whether the preambles will screw this up. If so I will have to detect these.
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.
The TDA1545 DAC is nearing completion. I'm trying, for once, to make a nice product, somewhat operational by a simple human being. The DAC has gotten a new 5 channel input selector. This is basicly 5 SMD relays (mounted on the solderside), the CS8412 receiver, and a basic cap filtered PSU. The TDA1545 DAC board fits on top, this way, when finished, everything is firmly attached to the receiver board. I will post the PCB layout, and schematics, when the last bugs have been squashed, and the values of some components have been optimized.
Let me just say, that this is a big step for me, as it is the first of my HIFI projects in 5 years, that is actually in feature freeze, and will reach a final and generally usable state.
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.
Generated on 2018-05-03 01:14:21.924401