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About JohnSwenson

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  1. The EtherREGEN does in fact use a whole bunch(12) of very highly shielded very low emi switching DC-DC converters, each of which drives a carefully designed passive filter then into a linear regulator. This was the only way to run the power networks. Most of the current drawn is in the 1.0-1.2V range which would burn up linear regulators trying to drop the full range. Thus the power dissipation of the EtherREGEN stays almost constant as you change the input voltage. John S.
  2. I'm not quite sure exactly what you want me to comment on. If you are saying run the audio data into an ER A side port, then the B side port into a wifi AP, then a wifi client into the endpoint, then the ER is not going to be very effective. It might make a small improvement, but not much. If you are talking about audio data to wifi AP, then wifi client to an A side port of an ER, then B port to endpoint, then the ER will make a big improvement over the system without it. Having the wifi client upstrem of the ER may be a little worse than direct wire or optical connection, as usual that is a rather system dependent issue. John S.
  3. The 575 does have its own dual regulated supply, and the only thing it drives is the clock synthesizer (which has its own regulators) which only outputs LVDS signals. All clock distribution is carefully impedance matched differential pairs (I had a special board stackup used that allowed continued impedance matching as pairs changed layers). The reclocking flops are fully differential including clock. The chips which have a single ended clock input have a very low additive phase noise LVDS to CMOS converter right next to the clock pin. The result of all this is a system that is much less sensitive to ground noise than is usually seen. That was really the whole reason for the EtherREGEN, produce much less ground plane noise in the first place, and have circuitry much less sensitive to what ground plane noise that is there. Unfortunately I can't do anything about what is inside the chips themselves. I spent 30 years designing power networks inside large high speed chips, I have a VERY good feeling for what that can do to jitter for the circuitry inside a chip. Unfortunately we can't afford to do a full custom chip for every function we need, so all I can do is choose ones where it looks like someone did a fairly decent job on the internal PG networks. John S.
  4. What signal are you refering to that has 2GHz harmonics? If it is the clock signal itself, then yes, the harmonics go up quite high, that is on purpose, it is after all a square wave, the only way to get a good square wave is lots of high frequency harmonics. The higher the harmonics the faster the rise time and the lower the jitter. If you are referring to high frequencies on other signals, there are circuit implementation details to prevent that from happening. I spent a lot of effort in the EtherREGEN to keep those as low as possible. It is an interesting engineering trade off. The faster the clock edges the lower the jitter, but the higher the ground-plane noise you get from the circuitry operating with those fast edges. I have endeavored to find a good trade off between this that gives the lowest overall jitter in the output stream. John S.
  5. I spent a LOT of time and money on that project. I have several prototypes that actually work. It turned out the hardest part was laying out the back panel, there were 16 jacks on the fairly small back panel!! There were two XLR and two RCA, each pin fed by its own DAC channel, so it was actually a 6 channel DAC. Yep, you could have done a 5.1 system with it. This took some custom drivers to make it work. I even had a connector on the front of the board so you could take off the front panel and screw in a 7" LCD touch screen. I never built that but I did have the connector for it. We had someone ready to build and sell it for a reasonable price, but then the whole project was derailed by legal issues that I cannot discuss. I was so bummed by the whole thing I just dropped out of the forums.Every now and then I pick up the test boards and look at them and hold them in my hands and wonder how it would have gone otherwise. I probably would have spent the rest of my life supporting it! The microRendu was a completely separate design. John S.
  6. That is something I wind up saying a LOT! My favorite example is: Racing cars tend to have expensive tires, but putting expensive tires on a Yugo does not make it a Formula-1 car! John S.
  7. The specific reason: the clock input goes into a very low additive phase noise clock synthesizer and all its inputs are designed for square waves. More general reason: all the digital circuits that use clocks actually use squarewaves so feeding a sinewave into the system either doesn't work at all or gives much higher jitter. Technical explanation of the above: All clock receivers have some form of threshold circuit, it changes state when the clock voltage goes through that threshold voltage. NO signals are ever perfect, there is ALWAYS some form of amplitude noise on the signal, AND the receiver itself always has some form of fluctuations on the threshold voltage. So think of the clock signal rising towards the threshold, as it gets nearer to the threshold the amplitude of the noise comes into play, the threshold might get passed when the noise is at its peak or at its lowest point, or some place in between. This noise on the signal causes an uncertainty as to when it will actually get to the threshold, otherwise known as jitter. The faster the voltage rise of the signal the lower the time uncertainty for a given noise amplitude. Thus a square wave with very fast rise and fall times will have much lower jitter than a sinewave which has a much slower changing voltage. This is the reason a circuit designed for square wave input MAY still work with a sinewave, but the jitter in the circuit clocked by the signal will be higher. There ARE some ways to convert sinewaves into square waves, but the simple ways actually increase the noise on the signal making the jitter even worse. There are some ways to do it well but they are complex and expensive and take a lot of power. Putting one of those on the clock input of the EtherREGEN would have at least doubled the cost of the device, not worth it in my opinion. BTW these master clocks provide both sinewave and squarewave outputs for different applications. Radio systems that need a very stable frequency reference for running into mixers etc want a sinewave. Digital systems want a square wave. Either system CAN use the other type, but won't work nearly as well. So it is best to get the type of master clock that works well with what you want to use it for. I hope that makes some sense. John S.
  8. Yes, a mismatch has a larger affect on a square wave than it does on a sine wave, BUT the sinewave is already significantly worse than the squarewave. i still think a single mismatch on the squarewave will probably be better than the mismatch on the sinewave. But that is just a guess, I haven't actually done that test and actually measured the output of the clock circuit. John S.
  9. I can tell you what happens technically with the waveforms on the wire, but how that shows up as sound difference is a completely different issue. Every time you have an impedance mismatch there will be a reflection, the bigger the mismatch the bigger the reflection. The worst thing is a mismatch at both ends, this causes multiple reflections, each edge bounces back and forth, this is can definitely cause problems with reception of signal. If say the source is matched (50 ohm electronics, 50 ohm connector, 50 ohm cable) but the receive side is mismatched, each edge will reflect at the mismatch back towards the source. But since the source is properly matched that reflection gets absorbed by the proper impedance match. So if a clock box has proprer electronics and connectors and cable, a mismatch at the receive end probably will not make too much of a difference. The edge bouncing off the receive end and winding up at the source can cause some distortions at the source itself, but how much and what they look like vary wildly from design to design. John S.
  10. That port on the right is a single port that can be EITHER optical or copper, but not both at the same time. The second is the correct way, the right port with optical then any of the other ports for the other connection. John S.
  11. That was the right choice. What the GPSDO brings is much better stability over very long time frames, something that is not needed for audio and adds a LOT of complexity and potentially more noise. I have a good GPSDO (well actually two!) but that is for use as a time base for my very sensitive time measuring equipment, not as a clock for digital audio. Yep getting a good signal to the GPSDO is a major pain. I just bought a new one because it has a MUCH better GPS receiver than the old one, which meant I didn't need an outdoor antenna, one in the window works fine. John S.
  12. Just swapping the connectors to 75 ohm is not sufficient, the output circuit has to be adjusted to also be 75 ohm. It may just be just changing a resistor, it depends on what the output circuit is. John S.
  13. The safety grounds on all the circuits in your house are SUPPOSED to be connected together, so it doesn't matter if the two power supplies are connected to the same circuit. In many cases connecting to the same circuit will sound Better than separate circuits. But there is no hard and fast rule about that. This sort of thing is very system specific. My usual suggestion is plug the power supplies into whatever is convenient. Most of the time that will get you quite close to "the absolute best no matter what" so just make it easy and don't worry, unless you have a LOT of money and time and don't know what to do with them.
  14. There is an interesting trade off here, hotter parts can can generate less noise, but hotter parts can have a higher probability of failing over time. The semiconductor parts used today generate noise when they switch, the faster they switch the more noise they generate. They run slower the hotter they are. BUT the slower they switch the more jitter they have so there is an "optimal" point where the noise and jitter are at their lowest. I can't tell you what this point is, due to manufacturing tolerances, it varies a lot from chip to chip. There is a BIG impact on longevity produced from turning things on and off, every time you turn a device on and off things expand and contract. Over time this can cause solder joints to fail. The hotter things are the more they expand and contract each time they are turned on and off. So if you turn the device on and off every time you listen, you should probably opt for a cooler temperature if you want the device to last a long time. If you leave it on all the time you can run it hotter and still have good longevity. At the temperatures we are talking about the parts themselves will last a very long time, it's the solder joints that usually cause failure. John S.
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