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| FeelTech FY6600 60MHz 2-Ch VCO Function Arbitrary Waveform Signal Generator |
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| Bad_Driver:
Thanks for sharing this result of your PSU-Modification. --- Quote from: maxwell3e10 on June 13, 2020, 05:09:11 am ---Once I started playing with my FY6600 to replace the NEC relay, I thought would be nice to replace the switching power supply as well. There has been a lot of discussion of various power supply options here, but I noticed this triple +5V, +/- 12-15V low-leakage linear power supply is available inexpensively: https://www.ebay.com/itm/SL-Power-Electronics-Linear-Power-Supply-MTLL-5W-A-5V-5A-12-12V-NEW/172432850496 (Attachment Link) It's a bit underpowered, rated only for 0.1A for +/- 12V, but fits nicely in the box. I measured the current limit is actually about 130 mA, which is sufficient for most cases. Reducing the current sense resistors from 3 Ohm to 1.5-1.8 Ohm increases the current to 250 mA without introducing any ripple. Here is the spectrum of the 10 MHz sine output (taken with Owon XDS3063A scope), showing that linear supply gets rid of some spikes in the spectrum. The box runs a little hot, so probably putting a small fan in there would be a good idea. (Attachment Link) --- End quote --- After reading for weeks now all the postings of FY66/68/69 I think it is one of the few (or the only one?) with a before/after comparison. There are many ideas and projects on PSU-improvement here but I believe that this makes only sense when you can measure the results! I'm improving these days my PSU to get the additional power for an OCXO-Mod (with my FY6900) and think about a before/after-measurement setting. |
| Labrat101:
Hi We all spent many hours of research. Like I chose the 20MHZ OCXO opposed to the 10Mhz . 2 reason 1st they are cheaper for high PPb and I reconnected if you multiple anything you also multiply any errors as well . And I found that dividing my 20Mhz 0.02 PPB OCXO by 2 from the PLL pin 4 buffered out . I get 10Mhz reference signal for calibration which is 0.01 PPB which has to be good enough for any Nerd standard. and times 2.5 of the 20Mhz give me only a 2ns jitter apposed to 4ns of the original . Which at 25mhz square wave is pretty good plus I can push it to 28MHz before it fails to be a square wave. Sine is ok all the way to 60Mhz. :-+ Also put a few tautanium 10uf caps on all the power lines & ferrite rings over the ocxo supply. The Relay have a contact noise place a 100pf ceramic or smaller on the relay inputs from the op amp line. the cap can be between 10 - 100pf depending on the relay . only the color is the same the contact resistance varies from relay to relay. This will give a cleaner Square wave & also the sine . The Power supply as with most was a small challenge I used the transformer from an old dual tape deck from a PA system that was binned . so it had the metal screening plus a copper screen raped round the winding. If you are going to buy I would go for a torridial transform that have a really good performance. There is good stuff that can be pulled from old audio devices . :-+ The Link to that power supply looks good as well but it is only 5W . IF you are going to add more mods My FY6800 actually uses near 8W .After all mods .. .. I don't have a before Pictures as my SMP failed within 2 hours of use. The power supply totally crispy .. :scared: These are after all mods @ 40Mhz sine . Mains ripple is about 40 uv . but that maybe lead or connection noise. Have Fun :popcorn: RNS |
| Bad_Driver:
Hi Maxwell I tried to repeat your measurement with my Oscilloscope (Siglent SDS 2000X+ 500 MHz) with my FY6900 before my scheduled PSU-improvement. As far as possible I used your settings (50 Ohms termination) You find all settings in the screenshot (Windowing is Blackmann). The O is "only" 10 bits. What FFT-Windowing have you used? It looks different from youre findings. The FY6900 (with 5.6 k drain resistor between outlet earth and grounding as only modification) has a different PSU than FY6600, may be this can be the reason as well. I learned a lot during the last weeks about O-FFT with the help of https://www.edn.com/ffts-and-oscilloscopes-a-practical-guide/ and that the combination of the weak BNC-connectors of the FY and cheap Coax-Cables result in nonsens :bullshit: I repeated the measurement of Ebel0410 (post #281 in this topic) which he has done with a R+S SA with my O's FFT and the results matched surprisingly good. If someone is interested I can provide my measurements. |
| maxwell3e10:
For FFT measurements I use the scope to acquire the maximum number of points at maximum sample rate (40M points at 500 MS/sec with 12 bit for Owon XDS3062A) and then transfer to computer for analysis with Matlab. I used Kaiser window and scaled the FFT to give PSD relative to fundamental in 1 Hz width. You can see some other measurements here https://www.eevblog.com/forum/testgear/signal-quality-of-budget-waveform-generators/msg3047624/#msg3047624 In particular, the broad peak near 25 MHz is due to the scope. But the white noise background level is pretty good. My Fy6600 was initially completely not modified, so no grounding connection. One could see in the time domain some spikes from SMPS for low-level signals. With linear power supply there is still no ground connection and no spikes. |
| jchw4:
--- Quote from: pizzigri on June 20, 2020, 06:30:20 pm --- --- Quote from: jchw4 on April 22, 2020, 03:02:41 pm ---Another PS mod. Original one just died, so I had to invent something quick and dirty. I had old laptop power adapter and a few cheap dc-dc buck modules ($0.7 delivered), so you can see the result. One is connected according to http://www.ti.com/lit/slyt516 to get negative voltage. The output now is much more stable, so it's an upgrade for about $2 ;) If somebody is going to follow me, note that I disassembled the original adapter. Don't do it! I wanted to save cables, which turned out to be a bad idea. Disassembly is messy, everything is glued inside and it's very easy to damage something. Just cut the two cables. --- End quote --- Hi! I’m really sorry, however in the TI document linked, after the phrase “ where s is the complex Laplace variable and He(s) repre- sents the higher-frequency...” and a host of equations, I got quite lost. I’m a hobbyst and trying to learn, but not to the point of learning at 50+ this level of math.... could you please post a wiring diagram, as obtaining a neg rail from standard buck converters would be incredibly helpful not only in this application but generally as well? I would really appreciate it. --- End quote --- You don't need math. Just look at the front of the Ti paper. Take your module and align it with the fist picture. The module will have (V+,V-) In, (V+, V-) Out. You need to check with DMM that (V- In) (V- Out) are connected, so it's "GND" net on the first picture. Then you have (V+ Out) (V- Out) and they are both marked on the illustration. Now you need to align what you got from the previous step with the second picture. Basically you rotate the result 180 degrees and label nets according with the new image. This will give you negative pole. I.e common GND goes to module (V_out+), input(+) goes to module (V_in+) and you take -12V from module (GND). There are a few caveats. First, the DC-DC converter may not start in this configuration. But as I just had the modules I decided to give it a try. The paper mentions that in this arrangement the converter will have to supply twice the output current (P_out/V_in in case of laptop 19V to -12V should be less than 2, but I just rounded it to 2). But module is 3A rated and I guess that we are not going to pull more than 1A in the worst case so it should be OK. But you should check the voltages and currents after the assembly. And I guess that this module may not be actually 3A (I did not test it), but it should be cheap to replace when it dies. --- Quote ---By the way, I want to publicly thank both JBG and Masterx81 for their help and incredible patience in helping me in the PSU mods and TXCO replacement sourcing. I sincerely felt that the level of questions I asked both of you guys was really too low for the very high level of competence and skill this forum is known for, and that is why I sent you guys PM’s. To contribute in some way to the thread, here’s the thermal images of the main board and the psu board. On the PSU there is a frankly unsettling resistor (R3) that is running really hot, about 93 celsius. On the board, the three voltage regulators near the usb connector, are in dire need of a heatsink. The small and inexpensive ones built for the Raspberry are perfect for this. The rest of the board is running around 40or so celsius, and I think can go as is - see the other two images, one with the Cyclone, and the other of the components near the opamps under the big existing heatsink. Boy, I’m learning sooo much just by following this one thread.... --- End quote --- |
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