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JohnSwenson

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  1. JohnSwenson

    Mutec REF 10 Masterclock

    I'm NOT from Mutec, but I have a little bit of knowledge about crystal oscillators so I hopefully can offer some insight as to what aging is. First off we need to understand that there is not just one aspect about crystal oscillators that have numbers, people here tend to like to latch onto numbers as figures of merit, but this can be fraught with danger since there are at least there different aspect of crystal oscillators that have numbers, before you start comparing numbers you ABSOLUTELY HAVE to understand which aspects those numbers refer to otherwise you are comparing surface tension to the color of the peel of an orange. There are two primary aspects of a crystal oscillator: 1) phase noise (I have written exhaustively about this early in this thread so I will not duplicate it all here) This is not a single number, it is a graph. This graph is the phase noise as an off set from the "carrier", which is the frequency of the signal coming from the oscillator. In a nutshell no oscillator produces a perfectly "pure" frequency. They all vary a little bit over time. Phase noise looks at the rapidly varying frequency changes. It is plotted in regards to frequency. If the output frequency varies a little higher, then a little lower, then a little higher and does this at a regular rate, this will show up as a spike in the graph (refered to as a "spur"). Real oscillators rarely do this, they kind of randomly fluctuate in frequency, such that this plot looks like a jagged continuous line. USUALLY much higher in value at the lower frequencies than the higher frequencies. From listener reports it seems that the lower offsets, (around 10Hz), seem to be the most import for audio. Unfortunately these are usually the most difficult to improve. 2) Actual frequency of the output. Due to above there is no such thing as AN actual frequency, it is wandering around. So the term "frequency of the output" is some form of averaging over time. That process can vary all over the place and is very rarely specified. Which of course makes comparing numbers rather difficult unless the same test equipment is used in exactly the same way. For example I have a frequency counter which has at least 30 different ways of measuring frequency, which will all give slightly different numbers. #2 has several different subcategories: #2.1) Accuracy. This is just the frequency out of the box. A high accuracy oscillator might be within 10 Hz of the number specified on the can and a lower accuracy one might be within 200Hz of the number on the can. Usually specified in Parts Per Million (PPM), thus a 1 PPM 10MHz oscillator can be up to 10Hz off the specified 10MHz. Some are so good they are specified in parts per billion (PPB). Unless it is pretty grossly off, this is pretty much unimportant for audio. #2.2) Temperature coefficient. All oscillators will change their frequency with a change in temperature, the Temperature coefficient (Tempco) specifies how much. It is usually measured in PPM per degree C. Unfortunately it is not a single number. Take an oscillator at 25C, raise the temp 1C and you will have a certain change in frequency, Start with the oscillator at 50C and change it one degree and you will get a VERY different change in frequency. All crystal oscillators have some temperature where a small change in temperature makes almost no difference in frequency, if you are significantly away from this temperature the change can be VERY large for even a fairly small change in frequency. Because this is measured in PPM/C a lot of people confuse it and accuracy since they both have PPM in the units but they are VERY different things, You can have high accuracy and lousy Tempco, or lousy accuracy and low Tempco. This has SOME affect on audio, but not a lot. The primary effect is at warm up, when a device is is turned on and the temperature inside the box is increasing. During this time the changing frequency can make a small audio difference. After reaching thermal equilibrium the Tempco has almost no effect on audio. #2.3) Aging. This is the long term change in frequency over long time periods (measured in years). Most crystal oscillators have a fairly large change in frequency from year to year. During the first few years this is fairly large, then slowly goes down to almost no change after about say 15 years or so. Aging has essentially zero impact on audio. #1 is the only one that has any significant impact on audio. Of the #2 categories Tempco is the only one which will have some impact on audo, but only during warmup. After the temperature settles down, almost no impact. So in summary, spend money on low close in phase noise, money spent on high accuracy, low Tempco or low aging, is usually just throwing away your money. The OCXO is an exception to this, see below. In particular a TCXO (temperature compensated crystal oscillator) is almost never a good thing for audio. A TCXO, has a normal crystal oscillator and a temperature sensor of some sort. The voltage from the temperature sensor is fed into a port on the crystal oscillator which causes its frequency to change with a varying voltage. This setup so it does some degree of cancellation of the crystal Tempco. So now we have a temperature sensor with almost always some degree of noise on the voltage output, feeding an input port which changes the frequency, thus rapidly varying the frequency, what is this called? Phase noise. Thus TCXOs ALWAYS have higher phase noise than a regular crystal oscillator using the same crystal and circuit minus the compensation. Yes it might have a smaller impact during warm up, but sound worse otherwise. Not usually a good use of money. The type of crystal used in common crystal oscillators is what is called an AT cut. Its primary claim to fame is that the temperature where the zero Tempco appears ( sometime called the Tempco threshold or "knee" of the Temcp curve) happens near normal room temperature. This gives pretty good temperature behavior without doing anything else. But they do not have the best performance in other parameters. In particular for audio the phase noise of a different cut, called the SC cut, is much lower. BUT the knee in the Tempco curve is way up in the 90C range, at room temperature the Tempco is so bad that even a small temperature change drastically changes the frequency, so even for audio it is useless. This is where the OCXO comes in, the primary purpose is to raise the temperature of the SC cut crystal so it is sitting right at the knee of the Tempco. This gives an oscillator with a very low Tempco, very low aging and very low phase noise. Not all OCXOs are created equal, in particular the less expensive OCXOs (say less than $100) do not use a crystal and circuit with particularly low phase noise, but they DO have very low Tempco and low aging, but the phase noise is no better than a $10 regular crystal oscillator. Again this is just a waste of money, you are spending money on something that doesn't make sound better. (note this is "new" price, not what you can get on ebay for a used one). BUT if you spend the money on a very special SC cut crystal and very special circuitry you can get the lowest phase noise of any oscillator known. It is not cheap, but this type of OCXO IS the way to get the lowest phase noise. OCXOs at this level also give you very low aging and very low Tempco, but these are not primarily the main reason for getting one of these OCXOs. Unfortunately for audio, most applications (other than audio) want very good specs for ALL the parameters, it should be possible for the manufacturers to optimize for phase noise only, thus giving us lower cost oscillators since they are not trying get say extremely low aging. One other VERY important aspect about phase noise: comparing charts can ONLY be done if the frequencies are the same. The phase noise for an oscillator increacess by 6dBc/root Hz per octave of the oscillator frequency. Thus of you have plot for a 10 MHz oscillator and one for the same model oscillator at 20 MHz, the numbers will be 6 dBc/ root Hz higher. If you take that 20 MHz output and run it through a good flip flop, dividing the frequency by two, you will get the same phase noise plot as the 10MHz version. So be VERY careful when comparing phase noise from different oscillators , they either need to be at the same frequency or you apply the 6 dBc/ root Hz rule. (explaining that rule is a little complicated so just take my word for it) Sooo as far as aging is concerned, spec sheet aging has nothing to do with audio. John S.
  2. Here it is, I have already been over this before, but it seems nobody remembers the details, so here it is once more, I'm NOT going to write this down multiple times. I'm in the process of starting the clocking tests and spending time on this is taking away from time I could be working on getting the clock test working so this is going to be it. Here is the story of my leakage tests and what I found. It all started about a year ago when someone else was testing one of our USB products and noticed some very low level increase in line frequency components (I'm in the US so that is 60Hz, 120, 180, 240 etc) at the output of a DAC whose USB input was fed from our product. I had recently moved so I didn't have my lab fully setup so it was difficult to try and reproduce what was happening. I attempted to get the test equipment setup as quickly as I could (not easy, the old HP stuff is VERY heavy) and finally had enough setup to get some testing done. I did manage to see the same thing but didn't know where it was coming from. I don't remember everything I did at that point, but I was trying out different hypothesis to try and figure out what was going on. After several weeks of this about the only thing left was leakage current flowing through the USB cable, through the DAC, through the audio interconnect to the preamp, through the safety ground connection of the preamp, the safety ground in the wall to the neutral/safety ground connection in the breaker panel and back to the power supply of the computer providing the USB source. So at this point I needed a way to measure the leakage current. The obvious way to do this is a resistor from the ground of the USB cable to a wire connected to the safety ground of a wall outlet on the same circuit as the PS of the computer. (I plugged the computer into a power strip and a plug with just ground wire into the same strip, about as short a path as I could get) I connected a piece of coax across both leads of the resistor and plugged the other end into the input of my spectrim analyzer and saw a nice line frequency spectrum, strong 60Hz and diminishing amplitude harmonics. I wanted to use the largest value resistor I could, the higher the value of the resistor the higher the voltage level I would have to look at. The resistor forms a resistive voltage divider with the source impedance of the leakage current, if the resistor is small relative to the source impedance doubling the resistor will cause a doubling of the voltage across the resistor. When increasing the resistor value there is some point when this relationship breaks down, as the resistor gets close to the source impedance it actually decreases the current flow through the loop, preventing the voltage across the resistor from doubling with a doubling of the resistor value. As the resistor increases further the voltage across the resistor starts going down and with increasing resistance will go to almost zero. Well this nice simple progression did not happen. As the resistor value went up the voltage leveled off but didn't go down again, it continued to go up but not as fast as before. WHAT? This shouldn't be happening. The only reason for this is that there were two current sources in parallel, one which had much higher source impedance than the other. (at this point I'm not sure if it is JUST two or if there are more than two involved). If this was true if I kept on increasing the resistance at SOME point it would start leveling off and go down. I then started thinking about my measuring setup, I had the top of the resistor connected to the 1 mega-ohm input of the spectrum analyzer, I was thinking that could start causing a problem, the resistance was starting to get pretty high. So I went with a 10X probe (10 mega-ohms) . So then another round of increasing the resistor and STILL it didn't level off, the ten mega-ohm was looking to be too small. At this point I realized I needed a really high impedance differential probe, at this level the ground connection to the spectrum analyzer could cause all kinds or weird effects, it really needed to be high impedance differential. Such things are NOT cheap. I finally decided to build my own using an Analog Devices instrumentation amp chip, they have one that is theoretically rated for 20 giga-ohms. Of course in reality it would never get that high, so I'm guessing the real implementation is in the 2-3 giga-ohms range. It turns out that all the ADI instrumentation amps have the same pinout and they sell a development board for it an a kit with 6 of their most common chip models. So I ordered a bunch of resistors and caps for this and built one using the high impedance chip. I powered the amp with a pair of LiFePO4 battery packs. This is what I have used for all subsequent tests. At this point I needed to change the test setup a bit, the voltage across the resistor was getting too high for the instrumentation amp chip, so I decided to go with a small resistor (I chose 10 ohms rather randomly) which was across the inputs of the instrumentation amp chip, with the resistor I was changing between that and the ground of the PS. At this point I came to the conclusion that this was all about the PS powering the computer and really had nothing to do with USB per se, so I just started measuring the PS, it cleared a lot of things off the bench. So increasing the resistor did eventually cause the voltage across the 10 ohm resistor to go down, I had finally found the source impedance of this current component of the leakage from the PS. It was around 400 mega-ohms. With this high an impedance it is very difficult to "block" it by putting a resistance in series. Given the frequencies we are interested in you can't just put a giga-ohm resistor in series with the ground of a cable or put an inductor in series. Fortunately there is another approach which is to shunt the leakage current to the safety ground before it gets to computers, DAC, preamps etc. This works quite well. So this means that the leakage coming from an SMPS seems to have at least two current sources one which is around 400 mega-ohms and one much lower. I tried increasing the resistor across the instrumentation amp to try and see if I could figure out the impedance of the low source impedance component and I didn't get too much higher than 10 ohms before it started going non-linear. Hmm, this seemed awfully low, so I tried several more tests which seemed to point at something much higher. This is why I think there might be more than two components to the leakage. At this point I decided is wasn't worth my time trying to dig into exactly what is happening inside an SMPS, especially since each one seems to be a bit different. At this point I had enough understanding to have a good idea how to deal with this in audio systems, which was the whole reason for doing this, trying to find out what is going on, not just for pure science, but for how to cut down on its effects on actual audio systems. Oh yeah, I did over 500 tests on many different SMPS and LPS and found that LPS models do not have this very high impedance components, this seems to be the realm of the SMPS. So conclusions of all this: the leakage from an SMPS seems to be comprised of at least two components, a high source impedance one and a lower source impedance one. The high source impedance component can be shunted to safety ground right at the PS, preventing it from entering the audio system. Even with the shunt there still is a low source impedance leakage which needs to be dealt with. What you need to do varies with with where in the chain the output of the PS is connected. A standard Ethernet transformer will easily block the low source impedance component, but does not block the high source impedance component. This can be a problem with a wired network connection since the high source impedance component will go right through the transformers in switches and routers etc. So I did some more testing and found that SOME switches when powered by a PS with the negative output connected to safety ground would actually shunt the high impedance source component. I tested a number of switches and only a few did this. At this point I have NOT exhaustively tested all of them to find out what makes the difference, why some switches shunt and others don't. Preliminary findings seem to point at differences in the connections of the center taps of the Ethernet transformers. So there you have it, a much abbreviated account of the testing I did and the conclusions drawn from that testing. The process took over six months and took up a HUGE amount of my time. I have over 500 plots from the spectrum analyzer from all the different phases of this trek. So do I REALLY need to say "high impedance source component of the total leakage current" EVERY single time I'm talking about this or can I use the shorthand "high impedance leakage"? It seems like things are going to get very verbose if everybody is insisting I use the long hand every single time I talk about it. John S.
  3. I did a lot with 1543 DAC chips MANY years ago. What I found was that a single 1543 chip did not sound very good at all. The people that were getting decent sound from them were stacking 8 chips on top of each other, one gets soldered into the board, the others literally stacked on top of each other with the stack of pins soldered together, this actually sounded MUCH better, not too bad. The explanation at the time was that the paralleled DAC chip decreased the output noise. It turned out that had nothing to do with it, the actual mechanism turned out to be temperature. The 1543 uses a fair amount of power, when stacking them the stack got HOT. I did a whole bunch of experimentation on them, they hotter they got the better they sounded. Someone made a 8 chip board, but had each one spread out, sothey didn't get very hot, it sounded terrible, worse than a single one. One test I did was have one chip and glued a power resistor on top and ran some DC current through it. This heated the chip up, and low and behold, the hotter it got the better it sounded. At some point it stopped working altogether as the temperature increased, the best sound was just before it stopped working. The best I got out of this was significantly better than the 8 stacked chips. Even at the best it is no mach for a 1704, properly implemented 1704s blow it out of the water. But of course 1704s are very expensive these days (I remember when they were $15 and thought that was ridiculous!) and making a GOOD output stage is not that easy, but if you get it right the results can be amazing. John S.
  4. I would recommend against using such sort Ethernet cables, I have been doing a LOT of experimentation with Ethernet interfaces recently and found that many PHYs need a certain amount of capacitance on the pairs in order to work properly, a 6" cable just doesn't have enough. I had a situation where a 3ft cable worked fine, a 1ft was marginal (significant packet loss) and 6" did not work at all. I soldered some small value caps across the pairs and presto the 6" cable worked great. This tends to support the "not enough capacitance" theory. So going for very short Ethernet cables may not be a good thing. I personally would not go shorter than 2ft of cable between PHYs. Of course not ALL devices are going to have this problem, but I found it on a high percentage of the devices I was testing. John S.
  5. The actual measured accuracy is around 0.03mm with backlash compensation turned on, with it turned off it is much worse, but faster. The requirements are that both pins of an 0402 component touch solderpaste, 0.03mm is more than enough to achieve this. In reality not every component gets placed correctly, on this board three parts wound up with only one pin touching solder paste. This happens to other people as well, there is a lot of speculation and testing on this, it seems to be that the parts move on the nozzle as they undergo acceleration and deceleration. I slowed down the acceleration a lot from what it can do to improve this as much as I can. Speculation is that we need to use a more powerful vacuum pump, but then the whole vacuum system has to be tweaked including the solenoid valve and tubing sizes etc. Other options are looking at maybe working on the surface of the nozzle, but every attempt so far has serious downsides so I just left that alone. JSSG stands for John Swenson Shielding Guidelines. I did not come up with it. I'm terrible with names. It is sold by an individual: Juha Kuusama . The website is liteplacer.com. He designed the whole thing, wrote the instructions, puts all the kits together himself and does all customer support. Amazing for one guy, I don't think he ever sleeps. He did take a vacation once. I do watch it while it is doing its thing, it really isn't as noisy as it sounds in the video, that was the AGC in audio channel of the camera. The vacuum pump is the noisiest part of the machine, some people use a different pump that doesn't make as much noise. I do monitor it, with my hand near the big red button, the first couple times I tried it out it did some strange things. They all turned out to be operator error, things like a tape being vertical on the board but the tape descriptor saying it was horizontal, things like that. Once I get all the descriptors right it does what it is supposed to. This is an $1800 kit, not a $100000 pro machine, yep it does not run as fast. But it is for one off prototypes, not high volume production. I'm actually running it quite a bit slower than it CAN run in order to try and increase the accuracy. I'm fascinated watching it doing its thing, knowing that I'M not over a microscope for hours doing it myself! One guy built one in 4 days, but most people take several months to get one built, it took me almost 2 years, but there was a 1 year hiatus, which was a good thing, Juha improved the design a lot over that period of time. For me, definitely worth it. John S.
  6. The "overshoot" is backlash compensation, there is a little bit of slop in the mechanical system, in order to compensate for that all moves go in to rest from the same direction, it moves to a slight offset from the final position, then does a separate small move to the final position, this move is always in the same direction and speed. This dramatically improves accuracy. John S.
  7. Some general words on the LitePlacer. First off the designer (Juha) is VERY responsive to questions and the times I had some bad parts he shipped them overnight international FedEx without charging me anything! This is a daunting kit, there are a LOT of parts as you can see in the pictures, but Juha has written incredibly detailed instructions. He designed the whole thing in 3D CAD and includes exploded 3D renderings of every step it is not hard to follow, just a LOT of it! Part way through the construction he came out with a major upgrade, an automatic nozzle changing system, I was getting to the step where that needs to be installed, so I ordered the upgrade kit and tried to install it. The nozzles are held in some slots by magnets with holes in them, in some of my magnets the holes were too small. He checked his stock and found a few percent WERE undersized, he sent me some new ones, but I had to pack it all up for the move before I got it all assembled. Unfortunately it was Almost a year later before I could start working on it again. The holder went together great now, but the nozzles would not go all the way on the shaft! I fussed with it for weeks and could not get it to work. Juha sent me a new set of nozzles but they didn't work much better. He then decided to check his stock and found that 20% of his stock didn't fit either. SO now hew checks every single one before he sends them out, while he is trying work with his supplier to fix the problem. Even with the third set I still had problems, but I did get them to work by modifying some software parameters (push harder) This design has a camera that figures out exactly where the parts are in a tape by looking at the holes in the tape, and looking at fiducials on the boards (little circular pieces of copper), with this it can build precise coordinate systems between the tapes and the locations on the board. This allows it to have an inexpensive mechanical system that is not the best on the planet, the camera takes care of a lot of the slop in the mechanical system. The kit comes with the controller board but no power supply or case for the board, or any wiring. The instructions make a great deal about using shielded cable and grounding the shield to keep radiated noise from the motor controllers from messing up the camera, USB lines, computer etc. Being me I decided to use starquad cable and JSSG (which works great BTW). I used Canre starquad microphone cable since it is very flexible, but it took two cables per motor to do this. When I was installing the wiring I found he recommended cable chains did not works, that large amount of microphone cable would not fit! So I needed to buy some much bigger cable chains to hold all this wire. (one of the pictures is putting all the cables through the cable chain) The instructions say the controller board can get hot so it needs an enclosure with a fan, being the weird guy I am, I decided to use a thermal chimney instead. So instead of the board laying flat, I have it vertically oriented in a case which forms a thermal chimney that creates its own air currents effectively cooling the board without a fan. So I used a CNC router to mill out the "D" holes for the connectors and a laser cutter to cut out the acrylic cover and a 3D printer to make the "feet" that holds the assembly up off the table so air can get in underneath. This thermal chimney works extremely well, the board just barely gets warm at full motor current. I also used the laser cutter to make the "parts boards", I engraved the "ruller" on the board for each tape position. This means I only need to work out the position of the tape once,. With the board I can setup a set of tapes in advance over at the bench where it is easier to do than on the placer itself. I'm using repositionable adhesive spray to keep the tapes stuck to the board. The software figures out the parts locations by looking at the holes in the tape, this is easy for white tape and even easy for black tape, but some parts come in clear tape, this was NOT easy, there is almost no contrast between the tape and the hole. I eventually got it to work by using a black background under the holes and setting up the light for the camera so it reflects off the surface of the clear tape, this gave enough contrast so the software could reliably find the hole. This took a lot of work to get built and working properly, Juha gave fantastic customer support, I eventually got it working well, it was definitely worth it. John S.
  8. I was wondering if anybody would notice that! Yep, this board is a switch test board. It doesn't have any of the special magic sauce, just testing out the functionality. As shown it took about 20 minutes to place the parts, and about an hour to put all the pieces of tape on the parts boards and setup all the tapes in the software. So about an hour and twenty minutes from opening parts box from Digikey to placed board. Versus about 6 hours under a microscope with tweezers. Being able to do this totally changes what I am willing to do myself, the big boards just take so long to do and are very difficult to do, (you can't stop and take a break, you have to get it done while the solder paste is still good). Now I'm willing to take on quicker turn arounds and explore more things. It was a lot of work to get done, but it finally works great now. John S.
  9. JohnSwenson

    Fuses - and their effect on SQ

    In the last couple years I have looked into the guts of quite a few SMPS devices, they all had fuses, but they are soldered onto the board. If something happens that causes the fuse to blow, you do NOT want that incredibly cheap potentially dangerous circuit around any longer. I know the manufacturers do that because it's cheaper, but I actually think it is a very good safety feature as well. BTW even with all SMPS I have had around in the last couple years I have never had one blow a fuse, when severely overloaded they current limit (output voltage goes down) so the fuse doesn't blow. (the circuit works such as to protect the fuse) John S.
  10. "Where does this wire need to go? It can be either inside or outside the shield, but if it is inside it can couple to the signal wires inside, so it is usually best to have it outside the shield. Note it has to be insulated from the shield except for the ends where it connects to the shield. It should intersect as little of the external field as possible so it should NOT be tightly spiraled around the cable. Just running along side the shield is best, although a very loose spiral (say one turn per foot) is almost as good."

     

    Hi John,

     

    Since sharing your thoughts on "proper" cable shielding there has been a modification of your approach which you may already be aware of.

    If not, it's called the JSSG 360 whereby another metal braid is used on the outside with an intervening dielectric. Only the ends of the 2 braids are in contact thereby completing the electrical "loop".

    In this configuration, the outer metal braid acts as your wire loop. 

    Do you think this is a reasonable approach given that in you original description, the wire loop should be "loosely spiralled" around the metal braid shield.

    In the JSSG 360 however, the outer braid is firmly attached to the inner braid against the dielectric.

     

    I would appreciate your thoughts.

     

    Regards,

     

    Geoff

    1. Show previous comments  2 more
    2. JohnSwenson

      JohnSwenson

      It sound like the noise is being carried through the cable, JSSG does NOT help with this, it prevents a cable from picking up radiated noise (or being a source of radiated noise). When dealing with 2GHz you have to be VERY careful about what ferrite you use, most will have very little if any affect at 2GHz. I don't know if you can even get specs for most of the clamps out there since they are designed for consumer use they don't have detailed graphs which show the band they work in. You can get ferrite beads that might work, but you have to solder those into the circuit.

       

      John S.

    3. JohnSwenson

      JohnSwenson

      I found a high frequency clamp that just might work for you:

       

      875-HFA150066-0A2

       

      These are available at Mouser and I presume at other distributors.  This particular model is good for a cable up to 7mm in diameter, if yours is larger they do make ones with bigger holes.

       

      John S.

    4. HeeBroG

      HeeBroG

      Thanks so much for sharing John.

       

      Cheers,

       

      Geoff

  11. No, adding regulators does not block leakage current. The leakage current usually travels through the negative connection ("ground"), two regulators connected to the same supply have have their negative inputs connected together and to the single supply output, thus leakage current is free to flow through all of them. A separate LT3045 on each branch WILL isolate noise created by the changing load current from one load showing up on the other, but it will not block leakage current. John S.
  12. Whenever you have a single supply powering two loads you can have a situation where changes in load current from one device cause a small change in voltage on the supply output, and those voltage changes are seen by both devices powered by the supply. So yes it is always possible powering each device with its own supply might sound better than both off the same supply, but the LPS-1.2 has an extremely low output impedance, so any voltage change due to load current changes are going to be VERY small. Thus the LPS-1.2 is probably one of the best supplies out there for powering multiple loads (as long as the combination doesn't go over 1.1A) There is a special issue with the ISO REGEN. It contains an isolation circuit whose purpose in life is to prevent leakage current from traveling through a USB cable. If you power the ISO REGEN and the upstream device from the same power supply you are bypassing this isolation. This may or may not be an issue depending on what is driving the ISO REGEN and how things in your system are connected. It is hard to make a determination without knowing the details of the system. Note: the isolation is not the ONLY reason for an ISO REGEN, even with the isolation bypassed it can still significantly improve your USB signal. John S.
  13. There is a known issue with the LPS-1.2 and the microRendu. If the DC cable between the microRendu and the LPS-1.2 is already connected on both sides and then you turn on the LPS-1.2 the microRendu will not power up. If powering a microRendu from an LPS-1.2 you need to power up the LPS-1.2 first (wait until the LED is green), THEN connect the DC cable to the microRendu. This just happenes with this particular combination, the UltraRendu doesn't have the problem and an LPS-1 doesn't have this problem with the microRendu. The issue is caused by the LT3045s used on the output of the LPS-1.2, they have a long turn on ramp time (about 1/3 of a second), the microRendu does not like this. The LPS-1 has a shorter ramp time (1/10 of a second) which doesn't seem to cause the problem. The UltraRendu has a different internal power network which doesn't mind the slow turn on ramp of the LPS-1.2. I have used the LPS-1.2 extensively powering multiple devices in parallel it works fine, as long as the above issue with the microRendu is taken into account. SO there is not an "inherent" issue with driving multiple loads. Of course the total load has to fit within the 1.1A capability of the LPS-1.2 (same as the LPS-1) and many devices take more current at startup so that can sometimes cause issues, but that is the same for the LPS-1. There ARE small differences from unit to unit, (for both LPS-1 and LPS-1.2) so some units might be able to handle 1.18A and other "only" 1.12A so it is possible to have a total startup load that falls in this range and your LPS-1 is a unit that can handle 1.18A and the LPS-1.2 can handle 1.12A, and thus your LPS-1 can handle that particular combination load and your LPS-1.2 cannot, but that is not general issue with "the LPS-1.2 cannot handle multiple loads", just the normal manufacturing spread of units. If you have a situation where an LPS-1 can handle a certain set of multiple loads and the LPS-1.2 cannot, it is most likely one of these two scenarios. John S.
  14. There is a known issue with the LPS-1.2 and the microRendu: the microRendu will not start if the DC cable from the LPS-1.2 is already connected when power is applied to the LPS-1.2. The only way to get the LPS-1.2 to power the microRendu is to power up the LPS-1.2, wait until the LED goes green, THEN plug the DC cable into the microRendu. The ultraRendu and the LPS-1.2 work fine in all ways you can connect and turn them on, it is just the microRendu and the LPS-1.2. So however you want to do it, the LPS-1.2 LED must be green BEFORE you connect the DC cable to the microRendu. The output of the LPS-1.2 takes quite awhile to ramp up (about a quarter of a second) once the LED goes green. The power circuit inside the microRendu does not like this slow ramp time. Plugging the DC cable in gives a MUCH faster ramp time (a couple milli-seconds) which the microRendu is perfectly happy with. The ultraRendu has a different power circuit which doesn't care about the slow ramp time. Just to be clear it doesn't which matter which end of the power cable is plugged an after the grreen light, you can have: 1) the DC cable not plugged in at all, then after the light is green plug the cable into both LPS-1 and minroRendu 2) The DC cable plugged into the LPS-1.2 but not the microRendu, after the green light plug the DC cable into the microRendu 3) The DC cable plugged into the microRendu but not the LPS-1.2, after the green light plug the DC cable into the LPS-1.2 John S.
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