Joe's I-V circuit was not the standard opamp virtual ground arrangement but used a very low value resistor followed by a zero feedback gain circuit, from memory. As such, also, from memory, values much larger than 0.1uF could be used.
There were also others utilizing this idea and porting it to standard virtual gnd I-V but I'm not sure how successful this was.
Regardless, I did point out to Joe over phone conversations that a fairly low corner freq, single order filter will have phase distortion in passband and he would be better off using a 2nd or 3rd order linear phase filter such as Bessell at a higher corner freq which would have better RF attenuation at frequencies not too far out of the pass band (say 100kHz).
I think he subsequently moved to this arrangement but I'm not sure. I'll ask that question next week. Importantly, we'll have a listen to how it all sounds.
I presume you are referring to the circuit, P17 of AD797 data sheet.
Personally, I have always implemented zero feedback, discrete I-V stages. The RF content does not appear to worry or compromise them at all.
These have always been superior to opamp based ones sounding more natural, *if you can design them to have low enough distortion.
In the case of Sabre, this is very difficult because of the high current swings AND low OP Z of DAC.
T
That basic type of idea.
Myself, I used an output stage that would work pretty well, if not top audiophile preferred. Didn't want to dwell on output stages when there were and still are bigger problems affecting sound quality. However, I notice that Benchmark DAC-3 and Chord Dave both use opamps. That being the case, I don't feel too bad about using them too.
Do you have some way of reconciling all the use of opamps rather than discrete, even for a $12,000+ dac?
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FWIW replacing the 0.1uf with 0.022uf (all i have on hand) did not sound as good, again both were compared in mono (conveniently level matched)
Playing around with some digital EQ on the other channel to see if it could create a similar effect to 0.1uf wasnt succesful.
The cap appears to improve detail and imaging or create an extremely convincing illusion of it.
You can hear the HF roll off but it so high that you dont lose a sense of clarity, from a DAC designer's perspective it must be a form of blasphemy to have sabre DAC with HF roll off.
Sorry I cant provide anything of value of real value like measurements to rule out any issues.
Although the D50 has gotten so much praise for its measurements over on audiosciencereview.con that seems unlikely.
Playing around with some digital EQ on the other channel to see if it could create a similar effect to 0.1uf wasnt succesful.
The cap appears to improve detail and imaging or create an extremely convincing illusion of it.
You can hear the HF roll off but it so high that you dont lose a sense of clarity, from a DAC designer's perspective it must be a form of blasphemy to have sabre DAC with HF roll off.
Sorry I cant provide anything of value of real value like measurements to rule out any issues.
Although the D50 has gotten so much praise for its measurements over on audiosciencereview.con that seems unlikely.
Not sure because the time between the old breaking and getting the new one to work was pretty long, but I would like to assume it did a little.
The DAC wasnt bought with intention of modding, I was forced into after XMOS broke, but it was really a blessing in disguise, with this huge database of 9038Q2M specific info it was easy to learn and took away intimidation factor of DAC modding, the SQ gains are extremely rewarding and its good for cost saving.
Yes, read my last two sentences again.
a/ 'If you can design them with low enough distortion'.
I doubt these guys could design a really low distortion open loop I-V AND I doubt they even have a desire to do so.
Most designers that are heavily measurement biased feel that ZFB designs are more of a religion than anything else.
b/ 'In the case of Sabre....'
As stated, these modern DAC's have very low OP Z to achieve high DR. As such very very difficult to design really low distortion ZFB I-V
T
It depends.
Over the years I have done a lot of design with ZFB circuits and have become very very good at them. Particularly getting them to actually measure very low distortion. It's just one of those things that interests me.
As an example, I have a mic pre design that does < 0.001% distortion, but at 60dB of gain and almost unchanged up to 200kHz! Now - you can see where this sort of circuit has the potential to sound very good.
So - impractical, for Sabre I-V, yes it would require a LOT of bias current, heat sinking etc.
And you have to work with what you know and keep moving forward.
T
I was thinking of something like this, OK it's expensive.
Mini Precision GPS Reference Clock [mini-GPS-CLOCK] - 99.99GBP : Leo Bodnar, Simulator Electronics
Markw4,
You've posted a series of attachments labeled 'DAC Post List #.txt' that are littered throughout the thread. Could you gather all these post that reference them into a single post. Search doesn't seems to be too effective on attachments. I need these posts for my reference guide. Thx.
You've posted a series of attachments labeled 'DAC Post List #.txt' that are littered throughout the thread. Could you gather all these post that reference them into a single post. Search doesn't seems to be too effective on attachments. I need these posts for my reference guide. Thx.
redjr,
Maybe I misunderstand what you want, but the dac post lists are all the same except for their lengths. The newer versions just keep growing longer as I add more posts at the end.
If you want to find all the posts with attachments in general then unfortunately, I don't have a way of doing that. The only feature of the forum software I know of that allows finding all the attachments in a thread doesn't show who posted them or in what posts.
We could start a new thread in the Administrative forum to request that Jason add a feature to add an 'contains attachment' check box to the thread search function. It has been said that the forum will be migrating to new software soon that is expected to be better, so maybe a way to search for posts with attachments will be forthcoming anyway, but we would have to ask Jason or just wait and see.
Maybe another possibility, I have copies of all the pictures and other items I attached, and much more, on my computer at home. So depending on what you are looking for I might be able to make particular things easier to find. I should add that there are some high-value posts (as posts go) with no attachments. However, maybe I could zip up all the pictures and put them in dropbox or something, if that is what you want to see. Might be a rather large download though, looks like its about 500MB.
Even though it may not have been exactly what you were asking about, you mentioned the problem of searching for attachments, something I have thought about from time to time. Maybe a good time to talk about it in a little more detail now.
Mark
Maybe I misunderstand what you want, but the dac post lists are all the same except for their lengths. The newer versions just keep growing longer as I add more posts at the end.
If you want to find all the posts with attachments in general then unfortunately, I don't have a way of doing that. The only feature of the forum software I know of that allows finding all the attachments in a thread doesn't show who posted them or in what posts.
We could start a new thread in the Administrative forum to request that Jason add a feature to add an 'contains attachment' check box to the thread search function. It has been said that the forum will be migrating to new software soon that is expected to be better, so maybe a way to search for posts with attachments will be forthcoming anyway, but we would have to ask Jason or just wait and see.
Maybe another possibility, I have copies of all the pictures and other items I attached, and much more, on my computer at home. So depending on what you are looking for I might be able to make particular things easier to find. I should add that there are some high-value posts (as posts go) with no attachments. However, maybe I could zip up all the pictures and put them in dropbox or something, if that is what you want to see. Might be a rather large download though, looks like its about 500MB.
Even though it may not have been exactly what you were asking about, you mentioned the problem of searching for attachments, something I have thought about from time to time. Maybe a good time to talk about it in a little more detail now.
Mark
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Right. What is important for dac use is the column of information about phase noise at different frequencies. If you look at the phase noise specifications for the best crystal clocks we can buy, they are even a bit better than the GPS unit. For example, the GPS phase noise is rated for when it is outputting 10Mhz. Its easier to get low phase noise at low frequencies, and much harder at high frequencies. For audio we don't usually use clocks down around 10Mhz where the GPS happens to be specified, and the GPS probably looks worse at higher frequencies. The Crystek clocks we use for 100MHz have a bit lower phase noise than the GPS does at 10MHz. So, bottom line is that good crystal clocks are best for dacs.
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My misunderstanding Mark. I did not know they were cumulative updates. That's even better! WRT attachments. Many, many posts include images. Finding them is another matter all together. Before I start this project, I find pictures are worth 10k words, and best for me to understand how the individual mod must be done. As I do for most of my projects, I put together 3-ring binders, or all relevant, useful information. BOMs, schematics, posts, pictures, etc. It's my way of helping to insure a successful build. My OCB showing through I'm afraid!
This particular project is more advanced than I typically tackle, but I still plan on doing it - at some level.I did learn last week that my retirement came a couple years earlier than planned. So, I'll have some time on my hands, until I start some PT consulting work later in the Spring. Lots of 'honey do' lists to work on too.
Edit: Zipping up all images would be most helpful to me and possibly others lurking around on this thread.
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Anyone who google a bit for "ES9038Q2M" has a datasheet but very short one just list of register, without application info. And I can't get output in spdif configuration. Actually, I didn't try I2S because my PCB is too compact for such kinda rework. Reading from reg#96 bit#2 and if no SPDIF on the input, I see that bit is always 1 but with SPDIF signal I see there sometimes 0 sometimes 1. It is very strange to me because according to datasheet reg#96/bit#2 set to 1 if SPDIF signal detected..
PS: AVCC = 3.3VDC there is no problem, however, I had a mistake with RT1 pin#22 which I forgot to tie to GND and the very first time my PCBA was turned On with pin#22 in a floating condition. I believe that's not a big deal because RT1 marked as 3 state pin in the pdf, probably it is some technological test switch but who knows.
PS: AVCC = 3.3VDC there is no problem, however, I had a mistake with RT1 pin#22 which I forgot to tie to GND and the very first time my PCBA was turned On with pin#22 in a floating condition. I believe that's not a big deal because RT1 marked as 3 state pin in the pdf, probably it is some technological test switch but who knows.
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I did a direct comparison between SD and SDA; the SDA is much better -> detail retrieval improves substantially, but what is really great about SDA's very low phase noise is the more natural presentation - very nice and so hard to achieve with digital audio reproduction.