Dan,
You seem to have a problem with sales guys, even the ones with knowledge and integrity. Max never states anything without backing it up with engineering.
Those are confrontational comments, not technical ones.
So here is an engineer, who speaks your language and tells you, you are wrong. Sure, jitter is bad, we never said anything different. Just like you, I was convinced that internal clocking was the best thing to do. But here is what I found:
OK, lets hear why internal clock is not the best thing to use:
I have designed several PLL’s most of them hybrid and as you very well know there is not a perfect world. The VCO solution is more jittery but has a wider capture range, the VCXO solution is almost perfect but has a very narrow capture range.
Good you admit that the VCXO is almost perfect. The fixed Crystal is better than VCXO. The difference is that fixed crystal is optimized fro fixed frequency, the VCXO must operate over a tiny range such as +/-100 parts per million. So again, the fixed crystal is better, and that is what one uses (or should) for internal clock.
You see, I worked in recording studios for two decades and found myself 9 out of 10 switching to wide capture range mode, because the situation forced me. So that is why you never find a VCXO on an Apogee device, it is simply a pretty useless PLL, not to mention the lack of being able to varispeed.
My gear uses VCXO for external lock, and we do not have customers loosing lock, not 9 out of 10, not 1 out of 1000.
BUT we need PLL’s and PLL’s have diametrically opposing requirements.
You are getting off the track. The subjects at hand are:
1. INTERNAL CLOCK vs PLL
2. THE BEST TECHNOLOGY FOR EXTERNAL CLOCK SOURCE
So you are redefining the “starting point” as a need for PLL. I say we need a fixed crystal with no PLL for best jitter. You are getting off the subject.
They need to be fast to follow sudden changes in the clock source, they need to be slow to have very low jitter…. Until I found a DDS which I really liked, one that I could use in a non-standard solution and I was able to improve on, in its specs. Let me give you some hints, its filtering, layout…all that analog crap again…
Nuts. Let me give you some hint: Before you talk about filtering, remember that a fixed crystal is a far superior filter to anything you are talking about. It is about DEVICE PHYSICS, where the alignment of the quartz molecules is such that the device yields the narrowest bandwidth possible, thus the bandwidth of operation is tiny, the Q factor is HUGE. Putting a device like that in a loop is THE BEST way to overcome power supply variations, and what you call “analog crap’. By the way, I love analog and it is not crap to me.
A VCXO for external locking is almost perfect (YOU said it yourself). A fixed crystal (for internal applications) is so much better.
“…of course our implementation. And that is as far as I am willing to go in telling how it works. We even decided not to get a patent on it, because that would be a giveaway as well. So yes we are very proud of our work and can imagine you don’t like to see someone succeed in something you thought was impossible.”
You totally side stepped the issues of:
1. INTERNAL CLOCK vs PLL
2. THE BEST TECHNOLOGY FOR EXTERNAL CLOCK SOURCE
During the development of or C777 PLL we also did some listening tests and found to our surprise that a lot of other converters sounded better (meaning more accurate, closer to the source) when clocking to the C777, against all theory! This was one of those moments where the engineer in me was dumbfounded, it did not make sense at all.
Ah, so we are back to marketing. I agree that the engineer in you is dumbfounded and what you say still does not make sense, nor is it to the point.
“Yet the tests were conclusive and repeatable. So we researched that and developed a clock that not only performs great as a PLL but as a master clock as well.”
More marketing.
“Again, I would hurt my own research if I tell you why that is, we did find something and as usual it is not that complex. But why should I give it away? It is my product and it allows me to make a decent living, sorry. To give you an idea, we have the same C777 in the AD16X. There is no difference in performance whether you have the unit on internal or external clock, if you have been to the Rhode & Schwartz booth on the AES show in San Francisco you could have seen the performance yourself, since we loaned the unit to demo their new test-equipment: -111 dB THD+N at -1 dBfs. Now that is what I call “unsurpassed excellence” (to quote your website), for a 16 channel AD converter retailing for $3500.- It is up to you to beat that…At the same booth you were also able to see all kinds of other measurements, including an FFT and those who have been there, can acknowledge the “crystal” performance we get out of our C777.”
Maybe I should start talking about the music I play with my Klezmer band. A bunch of words petting yourself on the back, but NOTHING about the subject at hand!!! It certainly seems like you are running away from the technical. I know why you are.
Bottom line is Dan, technology and measurements are only one part of developing equipment. Of course we all want absolute values, facts. But experience has taught me that objectivity always comes after the subjective: why does something sound good?
Instead of: this will make it sound good. The list of examples when this happened is infinite. So I suggest, and I am told you have good ears, to listen to a Big Ben clocking a converter and then come again…you will be surprised.
Ah, the famous lecture about sounding good. I thought we are taking about JITTER. You literature claims that you C777 is “THE CURE FOR THE JITTERS”!
Now finally, about Soft Saturate and UV22, when you see our current line Soft Saturate does not exist anymore, it has been replaced by the much more subtle and better sounding Soft Limit circuitry, but that is besides the point I want to make. These are still part of our current converters, of course, why wouldn’t it be? We also continued to design our products around a converter chip! Are you going to claim that as one of your achievements as well?
Regards,
Lucas van der Mee
Sr. Design Engineer
Apogee Electronics
I did not invent the resistor, nor did I invent the IC. I did co-invent the UV22. Trying to attack me and lower me is a reflection on you.
Lucas,
I did not go after Apogee. I was talking about clocking. Max came in and now you. This is a technical forum.
Lets get back to technical. If you can not do it, I can:
THE FIRST ISSUE IS ABOUT USING INTERNAL CLOCKS VS EXTERNAL.
YOU ADMITTED THAT JITTER IS BAD. Then, you ramble on saying nothing short of a few words about filters or implementation of a non fixed source, then name throwing (Rohde and Schwartz), then how things sound.
Meanwhile, you guys are telling people that using your clock will be a “CURE FOR ALL JITTERS”. Technically speaking, even if your external clock had no jitter, THERE IS NO WAY THAT IT COULD REMOVE, CANCEL, REDUCE the noise picked up at the other end of the interconnecting cable, the receiver, the internal PLL. Your clock box DOES NOT KNOW WHAT IS AHEAD, and therefore CAN NOT COMPENSATE FOR IT!
THE SECOND ISSUE IS COMPARING YOUR CLOCK JITTER TO A GOOD CRYSTAL CIRCUIT.
Your DDS is, at best, based on a crystal that operates on an overtone, thus the “engine” of your design is already inferior. Go to analog Devices site and read about the impact of the reference clock on the DDS. It can not be corrected for, by DSP or any filter. That clock is the ONLY referance. If it moves, there is nothing else to know that there is a need for correction! The ONLY reference is your reference clock, and when it jitters, everything follows!!! Also, think about all that “analog crap” as you call it, where every device in series at the DDS demands the cleanest supply. Think about the fact that the more devices in series, the more jitter accumulates. That a Crystal oscillator can operate with one or two transistors in series and everything is designed to be FIXED, while your DDS has all the extra circuitry to deal with (for additional features) thus more buildup of intrinsic device jitter. Realize that the best way to filter the jitter noise is with the best filter – a crystal. Realize that a supper high Q narrow bandwidth device – a crystal, when operated with the proper feedback gain, can be optimized to yield a pure sine wave at one frequency, in contrast to the square wave of the digital devices.
Did you know any of it, or are you out of your league? So far, you did not come up with a single technical point to refute what I said. I am surprise you showed up here saying what you said, letting yourself be so exposed, almost all sales and no engineering. I told Max to send the engineer.
It would not be uncommon for a manufacturer to sell something with poor specs saying “it sounds good”. But it is an altogether different to call it “A cure for the jitters”. I would not argue with someone that decided they like the sound of more jitter, more distortions or anything that is a matter of taste. I do not hear you admitting that the internal clock is less jitter. That using any external clock to drive an internal PLL yields more jitter than internal fixed crystal. I do not hear you admit that a fixed crystal is less jitter than your DDS. You stated that a VCXO (pull able crystal) is almost perfect. Are you saying your DDS is better than almost perfect?
THE BOTTOM LINE:
QUESTION: WHICH SOLUTION PROVIDES LESS JITTER AT THE AD LOCATION?
1. A REASONABLE FIXED CRYSTAL
2. BIG BEN DRIVING A CLOCK INTO A CHASSIS EQUIPED WITH A PLL VIA A 10 FOOT CABLE?
QUESTION: CAN YOU EVER CANCEL OR REDUCE A RANDOM NOISE AT ONE END OF A CABLE WITHOUT KNOWING WHAT IT IS AT THE OTHER END?
(can you cancel, remove or reduce the receiver and PLL noise, some of it unknown, some totally random, by driving it with a clean low jitter clock? Driving it with any clock?)
That is in fact what you are selling!
I remind you that before you or your sales guy entered into this forum, no one was saying names, or directly criticizing any company. If you read the posts, for every question we have tried very hard to remain technical and elicit technical responses. We are not about subjective listening here but you can certainly find chat rooms that are. Perhaps you believe what you say as does your sales director. The facts remain that putting aside your personalized comments you have not edified or elevated the technical level. I speak not only for myself, but for others who are reading these posts, we want very much to have intelligent conceptual inputs in the spirit of positive interaction. I gain no joy at having to put you down.
You are missing much by not understanding analog design as are so many other young designers.
Dan Lavry