Thank you spikestabber.
Now, which one is R and which one is L?
There are inconsistent reports floating around: the manual (pp 11-12) shows P1/J6 are right channel, and P2/J8 are left channel.
But the drawings on glt's blog and dimdim's blog show the exact opposite.
Anyone know the truth?
Edit: Reading fail on my part: glt's blog says, "Note: in the diagram above the labels for “RIGHT CH” and “LEFT CH” are swapped. This was noted in the forums (1147) and I also checked it with a R/L test track."
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you schold not
that statistically hides errors at the LSB bit, i.e. something in the -140dB range, with 24 bit data.As I bypassed the filters and supplied the correct 24/384 signal no arithmetic in the DAM is involved.
Yes, at least for the 10-14 most significant bits. The voltage errors are in the region of 100, or some 100, ppm. The standard deviation of 100 measurements is mostely about 2 ppm (which of cause would not reflect linearity errors of the multimeter). The 24 h stability of the multimeter is specified as 20ppm. The absolute accurany does not matter that much as we are only interested in voltage ratios.
A problem is more that you should measure different things at (nearly) the same time to eliminate variations that are not resistor related. That the load of VRef varies with the number of bits set, which is not reflected in the one-bit measurements....
But I think soft correction has a certain potential and, if supported, would offer a new area to experiment in.
I think a lot of people here have used this schematic to add a coax s/pdif input to the DAM, including myself. What would you like to know?
Indeed, I use the same just without the 330R resistor since I'm driving parallel boards. Works absolutely fine.
If you can eliminate a transformer and capacitors and leave only two high quality resistors in place, one in series and one in parallel, you would expect a better SQ, assuming dam1021 will work with it.
A reverse question, why would you want to use a transformer? To drive longer cables with unknown capacitance, to isolate dc or reduce noise or any othe reason?
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If it could be simplified and used without transformer and capacitors.
This can be done with other dacs but I am not sure about soren's comment about 1.2V biasing. What is it for and will dam work without biasing?
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That makes no sense. If you do that, you should actually expect degraded performance. That is assuming your source has a transformer on the SPDIF output, otherwise it will probably not work at all.
I don't know why one would WANT or not want to use a transformer. The reality is that you NEED to use a transformer, mostly for galvanic isolation.
Well, we can agree or disagree re this topic, this is ok. But how would you know if you did not try it yet. I want to try and also trust some people that have done this and have reported (significant) SQ improvement. If you are interested I can give you links to explore yourself.
I probably should add, that at the moment I am talking about dam1021 integration into a cd transport (cd player without its own dac) which has an output transformer, a couple of caps and resistors in the SPDIF output circuit. I am going to simplify it. The only unclear thing is the stated requirement for connection to dam1021 to have 1.2V bias in this circuit. Is this really required? Anyway, I am going to test it next week. I will hook up a wire directly from the SPDIF signal output pin of the SPDIF chip to RCA terminal through L-pad resistor network (one in series and one parallel).
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Again, I do not know what source you are connecting to your dac and it might be that in your set up you need galvanic isolation. In my case, when connecting SPDIF signal generating chip (inside my cd transport) to dac input circuitry, I do not think I need galvanic isolation. What are you isolating from what? Think about meriads of chips inside your cd player or other source that communicate with each other without galvanic isolation and they are perfectly ok communicating.
So, what for exactly you need your transformers?
When you connect different boxes without galvanic isolation, you get a groundloop if both boxes have a connection to earth-potential. You might need it or not, but this is what you need a transformer for.
Yes it is possible.
One reflektor @ 3.3V for USB.
Two other reflektors running @ ~7V stacked to get (-/+) output.
An externally hosted image should be here but it was not working when we last tested it.
thanks finally. is there a cheaper way though? this solution is kinda expensive. ive seen people connecting the output of a triodal trans directly to the board. with no regulaor circuit. i would like a solution that provides decent quality DC with low noise but cheaper than building 3 reflektor Ds specially since i will need another one for the USB I2S mudule. so we aretalking 4 pcbs
If you are building it directly into a CD player and taking SPDIF signal directly from some chip, most likely that is a TTL output and you could just hook it up to the DAM1021 TTL input. Just make sure it is at 3.3V level. There is no need to mess around with differential signaling.
For the DAM1021 differential SPDIF input, 1.2V DC bias is needed to bring the voltage levels into the FPGA allowed input voltage range. Even ignoring the potential ground loop issue that was mentioned, the SPDIF input will have a 1.2V DC offset. The output circuitry of the SPDIF source is not likely to be built for that. If one side of the SPDIF signal would happen to be grounded at the source end, you will basically have a short circuit. This is not a question of tweaking for subtle improvements, it's about potentially destroying your equipment.
As for SQ improvements with or without SPDIF transformer - what kind of DACs are you referring to? A transformer can affect non-reclocking DACs by introducing additional jitter. For DAM1021 that should not be an issue. On the other hand, a transformer also attenuates some noise, which will affect all DACs, reclocking or not. So in case of DAM1021 having a transformer could actually improve the sound quality.
Hi, I just wired up my DAM1021 and connected it to my Twistedpearaudio mux4:1 with a transformer on the output. However, I cannot get signal lock. I also tried a USB to SPDIF and my cd player. Tried to connect to pin 5 (signal) and 6 (ground) on the J2 header. Any ideas on why I can't get a lock?