I want to relate a situation that happened to me more than 25 years ago.
I went to the local electronic parts store and there was a new RCA tube catalog with the latest tubes in it. I bought it, and fairly soon I was contacted to meet a Dutch vacuum tube amp engineer. We met, and I decided to give him the new RCA book, as he needed it more, and I could most likely be able to replace it.
Once I told him that I had only a BA in Physics, he said that we could not be colleagues, as he had a Masters in Engineering. Big deal! But for him, it was everything. We never met again, AND I could not replace the RCA manual, because it was a special order that had not been picked up. I am STILL looking to replace that RCA tube manual.
I went to the local electronic parts store and there was a new RCA tube catalog with the latest tubes in it. I bought it, and fairly soon I was contacted to meet a Dutch vacuum tube amp engineer. We met, and I decided to give him the new RCA book, as he needed it more, and I could most likely be able to replace it.
Once I told him that I had only a BA in Physics, he said that we could not be colleagues, as he had a Masters in Engineering. Big deal! But for him, it was everything. We never met again, AND I could not replace the RCA manual, because it was a special order that had not been picked up. I am STILL looking to replace that RCA tube manual.
Joshua_G said:
Joshua,
Please look it up again. While burning up was my wrong assumption, the core problem is AD797 unstable in capacitive loads. Do yourself a favor and spend an hour to build the thing on an 1 sq. inch of vero board. I tried (occasionally I enjoy experimenting all kind of crazy things) and it's hell on earth. You'll find it yourself, even by using a low end scope.
No further comments.
john curl said:
Hi John,
Seriously, I have a copy that you can have. It is copyright 1975, RC-30. It just sits on my bookshelves gathering dust. My focus is elsewhere and I doubt I'll make use of it so it's yours if you have an interest in it. Send me an e-mail and I'll direct it your way. If it's not the version or vintage you're interested in that's cool too.
Mike.
Joshua_G said:
Joshua,
To me, that DAC, manufacturer and application notes suck big times.
- A completely and tediously wrong comparison with other current DACs.
- Lack of any architectural description of what and why makes this DAC special. Other manufacturers are always disclosing such information.
- Lack of some crucial information/spec. The final datasheet is not out yet, perhaps that will be more enlightening.
- The AD797 "power supply" is flat wrong. If you don't believe me, try it yourself. Publishing such :bs: is not helping at all the manufacturer's credibility.
- For the performance, the pricing is ridiculous. PCM1794A from TI (having more or less the same - but real, guaranteed, final - performance) costs $13.35 and free samples are readily available. To my experience, setting the price much under or much over the direct competitors already smells like scoundrel. Granted, that thing seems to have 8 channels, but who needs such an 8 channel DAC in the high end world (that, based on the claimed performance, seems to be the target for this product)?
Of course, a final comparison will happen when this DAC is going to be in production. Until, it smells fishy to me, even if I don't qualify as an expert in the digital world. Anyway, for the moment, I wouldn't touch that thing with a stick.
Good for you.
In order to get those, you'll have to sign NDA.
In discord with your criticism, such "power supply" actually works successfully. Look here:
http://www.twistedpearaudio.com/docs/digital/buffalo_schematic.pdf
So, who is flat wrong?
Again, this "power supply" actually works. Originally it's being fed from an onboard LDO, which is being fed from an external LM317 regulated PSU. What I did was to add a JFET CCS between the LDO and the opamp's input, in order to feed the opamp with a quieter, or cleaner, reference voltage.
Don't you see the benefit of paralleling DACs?
This DAC is in production for about a year and there are hundreds of happy users of it in a DIY kit:
http://www.twistedpearaudio.com/digital/buffalo.aspx
It depends on the chip. Some will go crazy with certain values of capacitance on their outputs, especially at unity gain (where the feedback is the highest). Lower is OK, higher is OK, but I won't trust something that is metastable.
I've done a similar supply with BUF03, and it worked, but had much lower performance than I've gotten from sampling the supply output and feeding that back. If mediocre regulation is acceptable (and it often is) and one wishes to make such a supply from a buffered reference, the buffer can be stabilized by putting a series resistor at the output, then taking the feedback from that point.
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