I finally ordered all the parts and PCB, and built a power supply. I want to ask if the output of this circuit can drive a headphone amp directly, or some intermediate amplification is needed (and what sort would be recommended?).
For the amp I've built a tube design from Headwize (figure 10 at http://headwize2.powerpill.org/projects/showproj.php?file=cmoy5_prj.htm).
If the output is not enough, what would be a good solution? Thanks.
For the amp I've built a tube design from Headwize (figure 10 at http://headwize2.powerpill.org/projects/showproj.php?file=cmoy5_prj.htm).
If the output is not enough, what would be a good solution? Thanks.
There are three ground connections: the Molex one at the top, a via on the left, and one at the lower right. In a previous post you said that the one on the left is connected to the chassis; what about the one at the lower right?
Also, what do you think about separating the ground planes all the way back to the power supply through a ferrite bead? I already ordered the PCB, but it would be an easy change to make.
Also, what do you think about separating the ground planes all the way back to the power supply through a ferrite bead? I already ordered the PCB, but it would be an easy change to make.
I read JWB:s post about shorting the decoupling traces, I did rework the mounting of the decoupling caps, and i have changed and added a CLCLC filter for the VA and some smaler inductances (recomended by Guido T) and this will be the board I will send to Olimex, It would be great if anyone of you could take i quick glance at it I will do so to in a couple of days..with a fresh pair of eyes..
/micke
edit: and yeah the unroated trace under the CS8420 is for the reset pulse.
/micke
edit: and yeah the unroated trace under the CS8420 is for the reset pulse.
Attachments
Thanks. I have a couple more questions:
Was the issue with the SCxx-04 you noted in a separate thread corrected on this layout?
On the schematic, the three pins which make up the serial audio input appear to be unused. Could this design be modified to add the separate I2S input, WITHOUT using the software mode, or changing the rest of the circuit?
and finally,
Is the bare board available for purchase from someone, or is it up to each individual to have it fabricated?
Was the issue with the SCxx-04 you noted in a separate thread corrected on this layout?
On the schematic, the three pins which make up the serial audio input appear to be unused. Could this design be modified to add the separate I2S input, WITHOUT using the software mode, or changing the rest of the circuit?
and finally,
Is the bare board available for purchase from someone, or is it up to each individual to have it fabricated?
The problem with the input transformer is corrected on this layout.
To use the serial data input, you would need to modify the hardware operating mode of the CS8420. The modification would be one or two pull-up/down resistors. Check the CS8420 Hardware Modes in the datasheet. You would not be able to switch back and forth between serial input and SPDIF input without asserting RESET (or power-on reset).
I do not have any boards of the Rev. B, but perhaps someone else does. I have two boards of the Rev. A but they have a number of bugs.
To use the serial data input, you would need to modify the hardware operating mode of the CS8420. The modification would be one or two pull-up/down resistors. Check the CS8420 Hardware Modes in the datasheet. You would not be able to switch back and forth between serial input and SPDIF input without asserting RESET (or power-on reset).
I do not have any boards of the Rev. B, but perhaps someone else does. I have two boards of the Rev. A but they have a number of bugs.
Understood. I have seen that, but I was wondering if there was something else because you mentioned operating in software mode and problems with the hardware mode. I was wondering if the I2S input was left off for that reason.
Sure. I need a few days to figure out if this can actually be used with I2S and S/PDIF out the way I think. Connecting the output is easy, inputs may be a little more tricky. Even if not, I may still be interested because it seems like such a simple and elegant solution compared to wrestling with two Cirrus CDB's and associated power supplies, and, and... not to mention that I have been looking for a good excuse to build some of the circuits posted on this board for a while.
Thanks jwb,
Output level
I have been trying to undestand the output ckt, finally took the time to scan the earlier 24/96 DAC thread, and came across this:
jbw, can you or anyone else who has built this board comment on that? What is the full scale output, (p-p), and what is meant by "ruin the character of the DAC"?
I have been trying to undestand the output ckt, finally took the time to scan the earlier 24/96 DAC thread, and came across this:
jbw, can you or anyone else who has built this board comment on that? What is the full scale output, (p-p), and what is meant by "ruin the character of the DAC"?
clock
JBW:
I'm going to try your dac. But:
-Do I need to use a clock with the same frecuency than the one in your "bill of materials"?
Because I'd like to buy one from Guido but I'm afraid he hasn't got them in that frecuency.
-What happend if I connect the clock pins of your DAC to the my XO clock circuit that I have already installed in my Marantz?
Pedro.
JBW:
I'm going to try your dac. But:
-Do I need to use a clock with the same frecuency than the one in your "bill of materials"?
Because I'd like to buy one from Guido but I'm afraid he hasn't got them in that frecuency.
-What happend if I connect the clock pins of your DAC to the my XO clock circuit that I have already installed in my Marantz?
Pedro.
I think the answer to the question about crystals and clocks may be in an app note on the Cirrus Logic web page, about the CDB8420 evaluation board.
http://www.cirrus.com/en/pubs/rdDatasheet/cs8420eb-3.pdf
or search for CS8420, and click on the link to the CDB8420 from that page.
That board ships with three different crystals, and you use the one which corresponds to the output sampling frequency you want. The CS8420 is a sample rate converter with high clock jitter rejection, which is what makes this board especially interesting to me. I did not realize you could make such a simple circuit with just the 8420 and a DAC chip.
The 24-MHz crystal corresponds to a 96kHz sampling frequency.
I assume you would only use a different crystal if you wanted to improve on the stability which is already in the range of 20 ppm, or do you think the Epson part does not really have that spec?
http://www.cirrus.com/en/pubs/rdDatasheet/cs8420eb-3.pdf
or search for CS8420, and click on the link to the CDB8420 from that page.
That board ships with three different crystals, and you use the one which corresponds to the output sampling frequency you want. The CS8420 is a sample rate converter with high clock jitter rejection, which is what makes this board especially interesting to me. I did not realize you could make such a simple circuit with just the 8420 and a DAC chip.
The 24-MHz crystal corresponds to a 96kHz sampling frequency.
I assume you would only use a different crystal if you wanted to improve on the stability which is already in the range of 20 ppm, or do you think the Epson part does not really have that spec?
The Epson part is *not* a good clock. It is a standard integrated clock. The 20ppm figure is the long-term frequency stability, which is not relevant to audio purposes. One of the major upgrades to this design would be a superior clock. That is why I added the MMCX connector in the latest drawings. You can use it to attach an external clock module.
I think you should wait to build this board until you understand the relationship between the master clock frequency and the output sample rate, which can be learned from the CS8420 datasheet.
The full-scale differential output of the DAC is more than enough to drive amplifiers without a voltage gain stage. However I'm not sure exactly what it is, because I didn't write it down after measuring. What I mean about "ruining the character of the DAC" is that this design has <b>no</b> voltage gain stage on the output. It has a passive low-pass fiter and a simple buffer to drive the line. I believe that adding a voltage gain stage would degrade the sound significantly, and detract from the minimalist philosophy.
I think you should wait to build this board until you understand the relationship between the master clock frequency and the output sample rate, which can be learned from the CS8420 datasheet.
The full-scale differential output of the DAC is more than enough to drive amplifiers without a voltage gain stage. However I'm not sure exactly what it is, because I didn't write it down after measuring. What I mean about "ruining the character of the DAC" is that this design has <b>no</b> voltage gain stage on the output. It has a passive low-pass fiter and a simple buffer to drive the line. I believe that adding a voltage gain stage would degrade the sound significantly, and detract from the minimalist philosophy.
jwb, thanks for correcting me on the clock, and explaining the output.
Earlier in this thread Prune asked about the power supply and using a wall wart type. This may work well with some wall warts, but in the past I have noticed that they are often not so good when you look closely, and that "regulated" only means DC voltage but not ripple. The regulated ones sometimes add noise from a HV switcher where the sw. frequency is close to the serial clock, and not really suitable for (digital) audio.
Also, the supply in the circuit on headwize which someone mentioned earlier may be perfectly fine for a headphone amp, but even the author of that article writes,
Can someone comment on what type of supply would work best here, maybe Per-Anders (he has a ps design w. circuit board on his web site) if he is still monitoring this thread.
Earlier in this thread Prune asked about the power supply and using a wall wart type. This may work well with some wall warts, but in the past I have noticed that they are often not so good when you look closely, and that "regulated" only means DC voltage but not ripple. The regulated ones sometimes add noise from a HV switcher where the sw. frequency is close to the serial clock, and not really suitable for (digital) audio.
Also, the supply in the circuit on headwize which someone mentioned earlier may be perfectly fine for a headphone amp, but even the author of that article writes,
Can someone comment on what type of supply would work best here, maybe Per-Anders (he has a ps design w. circuit board on his web site) if he is still monitoring this thread.
Scientific Conversion SC982-04
Yah, Jon Paul does not publish data sheets for his transformers on the Scientific Conversion Web site. Assuming you are asking about the SC982-04, the transformer is a 1:2 ratio, primary:secondary, and the red dot is on the primary side. You can also measure the resistance to confirm, primary should be around 0.1-0.25, and secondary 0.8-1.2 ohm. (I do not mean to say his impedances are that sloppy, but the meter I keep in my desk, is. Errr... thinking about it, I suppose I could have just said, look at the gage of the wire coming out of the two sides...
Yah, Jon Paul does not publish data sheets for his transformers on the Scientific Conversion Web site. Assuming you are asking about the SC982-04, the transformer is a 1:2 ratio, primary:secondary, and the red dot is on the primary side. You can also measure the resistance to confirm, primary should be around 0.1-0.25, and secondary 0.8-1.2 ohm. (I do not mean to say his impedances are that sloppy, but the meter I keep in my desk, is. Errr... thinking about it, I suppose I could have just said, look at the gage of the wire coming out of the two sides...
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