I finaly received the sowters trafos 1495 and connect them to my setup , after some testing it seems that i/v resistors are mandatory at the dac output to ground , I have 80 ohms , and no resistor at the secondaries , it does not work
0 mv DC , thanks to the biais trimmer , and the lowest distortion figure thanks to the 10 ohm trimmer
things could get a bit better I think , matter of time
I decided to go parallel , and I got this first result in the audio domain :
secondaries in series give twice the voltage but an slightly higher distorsion figure
now I have to find the good HF filtering method , any passive advice welcome
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0 mv DC , thanks to the biais trimmer , and the lowest distortion figure thanks to the 10 ohm trimmer
things could get a bit better I think , matter of time
I decided to go parallel , and I got this first result in the audio domain :
secondaries in series give twice the voltage but an slightly higher distorsion figure
now I have to find the good HF filtering method , any passive advice welcome
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Well , at the moment the setup does not work properly , it only work on mono mode 24 bit , this way it sound great , but only that way , if I set 16 bit and stereo I have the music in the background but the overall is highly distorted
I have verified the all thing many time and the pcb and components are exactly as per John's schematics at post 6116 , left justified not I2S
and measurements shows good numbers as is
fact is I am not able to tell if the schematics are good or not in the first place , so it's a bit difficult for me to find where the error is
not to mention that nobody has ever report listening session on this setup as is
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I have verified the all thing many time and the pcb and components are exactly as per John's schematics at post 6116 , left justified not I2S
and measurements shows good numbers as is
fact is I am not able to tell if the schematics are good or not in the first place , so it's a bit difficult for me to find where the error is
not to mention that nobody has ever report listening session on this setup as is
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Ok, so it means the 17bit configuration is still not proven working...? How are you feeding the 17bit data stream into the logic circuit? Do you use 18bit and discard one bit?
BTW I am using the TDA1541A with PMD100 in 8x oversampling mode (simultaneous input), it sounds great, but with very low levels I get distortion, similar to what's described with regard to DEM not working properly. I have the usual 470pF cap connected to the DEM pins, the bit decouplers are 220nF each. When I convert a file from 44.1kHz to 22kHz the distortion becomes less disturbing (but still audible), hence I wonder if the DEM cap needs to be half the value (i.e. 220pF) for fs=384kHz?
BTW I am using the TDA1541A with PMD100 in 8x oversampling mode (simultaneous input), it sounds great, but with very low levels I get distortion, similar to what's described with regard to DEM not working properly. I have the usual 470pF cap connected to the DEM pins, the bit decouplers are 220nF each. When I convert a file from 44.1kHz to 22kHz the distortion becomes less disturbing (but still audible), hence I wonder if the DEM cap needs to be half the value (i.e. 220pF) for fs=384kHz?
The THD should be in the ballpark , this is why I set it first , if it's not there's no way to get any further
the all thing is battery ( lipo ) powered , may be the best way for very low level of noise , and the cap I choose are the best for the job
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I see. And do you feed the DIR9001 with 24bit data? Or is it 16bit and the other 8 bits are padded with zeros?
Look (taken from here):
John calls his solution "17bit signed magnitude" DAC, but the DIR9001 outputs "two's complement":
The TDA1541A expects "offset binary" if used in simultaneous mode:
Correct me if I am wrong, but it seems there could be some confusion that leads to the problems you (and others) describe. Did John mention the modul or chip he used as a source for his 17bit DAC?
John calls his solution "17bit signed magnitude" DAC, but the DIR9001 outputs "two's complement":
The TDA1541A expects "offset binary" if used in simultaneous mode:
Correct me if I am wrong, but it seems there could be some confusion that leads to the problems you (and others) describe. Did John mention the modul or chip he used as a source for his 17bit DAC?
I am not able to tell you if you are right or not , I suppose you are
I found reading back in this threads that Johns has made a mistake in his first release of the simultaneous converter they talk about at post 6227 , so it is possible that he has made the same error making the glue logic converter for the 17 bit Signed Magnitude version , but still I am not able to see it
at the time there were guys who said it wont work but nobody tell why , nor point where in the schematics was the problem
so now I know it does not work but I don't know why , and even if it is an issue of binary offset I am not able to fix it
hope someone who knows about that matter will help
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I found reading back in this threads that Johns has made a mistake in his first release of the simultaneous converter they talk about at post 6227 , so it is possible that he has made the same error making the glue logic converter for the 17 bit Signed Magnitude version , but still I am not able to see it
at the time there were guys who said it wont work but nobody tell why , nor point where in the schematics was the problem
so now I know it does not work but I don't know why , and even if it is an issue of binary offset I am not able to fix it
hope someone who knows about that matter will help
.
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iirc John did make various versions of logic for i2s and left justified, but I don't know if he fed his simulations with 2s compliment or COB. What I know from my own TDA1541A project is that I need to program my PMD100 to output COB, otherwise the TDA1541A wont work. I am no fan of NOS, but I would love to use the PMD100 to feed the 17bit signed magnitude DAC. I think that should allow to further simplify the logic - but that's another topic...