Author Topic: FeelTech FY6600 60MHz 2-Ch VCO Function Arbitrary Waveform Signal Generator  (Read 216930 times)

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Offline Johnny B Good

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Re: FeelTech FY6600 60MHz 2-Ch VCO Function Arbitrary Waveform Signal Generator
« Reply #1925 on: August 04, 2019, 10:54:31 pm »
JBG,

Thanks for your advice, I will be adding a cooling fan. Once I finish the PS upgrade I will be upgrading to a D75J and THS3091.

Thanks,

Mike

 You might want to rethink the D75J option when you consider the fact that where the original crappy smd XO lives may well be running at 45 to 50 deg C as a consequence of all the heat being put into the board by the three LDO regulators located just one centimetre away. Those LDO regulators won't cool themselves you know, something has to handle the heat and that something is the PCB, including that smd XO. I'd measured 50 deg C on the XO with my IR thermometer with a 70 deg reading coming from the LDOs nearby.

 Mind you, this was whilst I still had the wick turned up by 10% on the 5 volt rail and fortunately before I extracted the 50MHz TCXO oscillator can from the "50MHz TCXO Power Board" I'd ordered as a cheap way to get hold of an oscillator to directly swap out with the smd XO (albeit by having to resort to the 'mount on stilts' bodge).

 In fact, I was still waiting for the oscillator board to be delivered when I made this discovery so was able to formulate a better use for the whole oscillator module to act as a deflector plate above the small 50mm square cooling fan I'd decided to fit into the base between the PS board and the back panel, adjacent to the main board where it could be held to within 2 or 3 degrees of room temperature rather suffer the 30 deg C temperature cycling of the original XO's location.

 As I mentioned, these temperature readings had been obtained during my "5.49 volt period", so would likely have been a few degrees hotter than the standard (4.96 volts) setting and by few, I mean less than 5 degrees.

 A couple of things that had put me off going the D75J route, aside from the delivered cost, was the absence of a calibration trimmer and the rather lacklustre +/-1ppm accuracy and stability. My motto being, "If a job's worth doing, it's worth doing well or not at all.", I felt the 20 fold improvement in frequency accuracy and stability being offered wasn't sufficient to justify the time and effort when, for pretty well the same money and just a modicum of extra effort, I could do ten times better on the stability front and somewhat better again on the calibration accuracy front, courtesy of the trimmer option gained by the purchase of that "oscillator power board".

 The JYEC DIP oscillator on that oscillator power board boasts a stability of +/- 0.1ppm over a a 0 to 25 deg C range and +/-0.2ppm over the -10 to +50 or 60 deg C range and, of necessity for this sort of accuracy and stability, boasts a trimmer to allow calibration against a reference frequency source such as a GPSDO.

 I've attached a photo of the oscillator board - it's now going spare, perhaps I can flog it as a CD player upgrade to some audiophool ;)

 The only thing going for the D75J option was that it was a simple drop in replacement (assuming smd reworking holds no terrors). The 50MHz +/-0.1ppm oscillator board, otoh, did offer the opportunity to avoid 30degC temperature cycling, allow calibration against an NPL standard, and a 200 fold improvement in stability and accuracy over the original XO versus the marginal 20 fold improvement offered by the D75J. The choice really was a no brainer, imho. ::)

 I was eventually able to calibrate that TCXO to within 30ppb before I gave up trying to improve my best efforts once I realised that it was destined to vary by around the same amount during each day's use. The only thing better than a TCXO being an OCXO but, at the time when I first read Arthur Dent's posts on his own OCXO upgrade project, my initial thought had been that he had gone just a little OTT in this upgrade exercise, especially considering the need to find an extra 3 or 4 hundred milliamps at 12 volts to power the OCXO's oven, necessitating either a PSU upgrade or else the addition of another 12v  half amp or better psu board inside the box[1].

 Strange to say, that's now where I'm at with my own pet FY6600 project having decided that such an OCXO upgrade wasn't so OTT after all!  :) It's amazing the things you can observe with a function generator that boasts a frequency accuracy better than 100ppt with a day to day stability of 20 to 30ppt. :)

 That's now more than sufficient to show the limitations of a basic PLL GPSDO based on a "cheap 'n' cheerful" navigation only GPS receiver module whose positional accuracy (and therefore timing data) is at the mercy of the vagaries of the ionosphere. I'm talking about the minute to minute nanosecond phase shifts rather than the long term precision which is not in any doubt.

 Anyway, enough about the issue of exposing a D75J to such temperature extremes as are to be found inside these Feeltech function generators. When I was suggesting there was no need to bump the 10μF 450v smoothing cap up to a 68μF 400v one, nor indeed any need even when powered off a 117v 60Hz mains supply, suggesting there was little point in such an "Upgrade" if you were powering it from 220 or 240 volt 50Hz mains supplies, I'd overlooked the Stars and Stripes flag signifying your location as being somewhere in the US. I had fleetingly thought of suggesting that a more modest increase of capacity to 12 or 15 or even 22μF (even 33μF if that's what you happened to have in your parts bin) could be applied for perhaps some marginal benefit to those on 117v mains power where the main benefit would be more a matter of riding through brief drop outs rather than improved smoothing.

 I'm not suggesting that you need to remove that 33μF cap: that's obviously fine in view of the fact that quite a few modders must have already proved that the 68μF has only harmed their bank balance with no ill effect to the PSU board itself. Of course, if you want to save that 33μF cap for 'better things', you might want to swap the original back in or select a 12 or 15μF cap instead. Choices, choices, choices! >:D

[NOTES]

[1]  I had to add a 12v 500mA smpsu board I'd removed from a small Linksys psu I'd had going surplus to requirements to power the OCXO board since I'm still running with the original (though modified) smpsu board. That actually gives me an advantage over Arthur Dent's version where, afaicr, he relied upon an upgraded PSU to power the OCXO. The advantage being I can now shut the whole signal generator down on the rear panel switch without interrupting power to the OCXO since I wired its dedicated psu directly to the mains socket so that for as long as it's plugged into a live mains outlet, it can maintain the crystal oven temperature indefinitely.

 The OCXO draws 5 watts from the mains when first powered up from cold but once up to temperature (after a 2 or 3 minute warmup time), this drops to a mere 1.3 watts (about half a watt lost in the psu with the OCXO taking some 700 to 800mW from the 12v supply). Putting the signal generator into standby using the front panel  on/off button, only saves a watt at most with a typical standby consumption of around 5 watts so this is a very worthwhile economy and life extending feature in an item of test gear you'd otherwise tend to keep powered up 24/7 in the interests of maintaining frequency stability.

 There is a tiny penalty in shutting it down overnight in that there seems to be a 30 to 60ppt 'warm up drift' (it's hard to quantify exactly with my current GPSDO lashup). For most practical purposes this is insignificant and later on, after I've installed an external reference input socket to feed it from a GPSDO, that isn't going to matter any more for any tests involving the need for such accuracy.

JBG
« Last Edit: August 06, 2019, 12:57:31 pm by Johnny B Good »
 

Offline DaveR

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Re: FeelTech FY6600 60MHz 2-Ch VCO Function Arbitrary Waveform Signal Generator
« Reply #1926 on: August 07, 2019, 04:02:42 pm »
The analogue psu can be an effective solution but the downside is that you'll introduce greater thermal stress than the original (typically 70 to 80% efficient) smpsu board on the unit if you neglect to add a cooling fan to prevent an already hot running generator from overheating.

 If you're going to build a custom analogue psu, you need to be very mindful of this thermal issue.

Use an R-core transformer instead of a standard EI one.  They run very cool and heat from them isn't an issue.  No fans necessary.

Regards,
Dave
 
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Offline aliaj00

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Re: FeelTech FY6600 60MHz 2-Ch VCO Function Arbitrary Waveform Signal Generator
« Reply #1927 on: August 07, 2019, 07:08:36 pm »
Guys i just bought the FY6800.

As i am new i could find is the specs the max current this one can provide and the single channel.
 

Online ArthurDent

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Re: FeelTech FY6600 60MHz 2-Ch VCO Function Arbitrary Waveform Signal Generator
« Reply #1928 on: August 07, 2019, 11:44:12 pm »
It’s been a while since I posted an update because basically I haven’t made any changes to my FY6600 for about one year. Here is a recap of what I did.

As you can see from the photos I’m still using the same FY6600 I bought originally with V3.1 firmware. I’m also using the same output amps that came with the unit. The high quality SMPS I settled on as a replacement for the crappy one is about 25W, is quiet, runs cool so no fan is required, and is quite small.

The timebase modification I made using the 5X PLL chip and the 10Mhz OCXO is working well and if I don’t mind waiting about ½ hour for it to warm up and stabilize, I don’t have to use the external GPSDO 10Mhz at all. This 15 year old OCXO is very stable and is good to about the first 10 digits. Keep in mind that this OCXO is far more accurate than the original and warms up fast so I could use it within minutes of powering it up but I prefer to wait until the drift rate is almost nil. When I do check it I use my scope with the time/division set to 2ns/div. The DDS circuit they use is damn good to another few digits as well if fed from the GPSDO or Rb standards.
 
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Offline Johnny B Good

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Re: FeelTech FY6600 60MHz 2-Ch VCO Function Arbitrary Waveform Signal Generator
« Reply #1929 on: August 08, 2019, 03:29:03 am »
 Thanks for posting those pictures, Arthur.

 When I first read your exploits with the OCXO, my first thought had been that such a modification was a little OTT but that was before I'd bagged myself a bunch of CQE OCXOs for experimenting with building GPSDOs after realising that a decent OCXO was the starting point rather than just an inconvenient add on to deal with the jitter from a u-blox M8N GPS receiver module's programmed 10MHz output. :-[

 I've long since come to properly appreciate the value of such an upgrade so my thanks to you for the inspirational use of a 3N502 clock multiplier chip. The initial choice I made in using a TCXO instead of the full fat solution of a TCXO, was driven by the fact that I wouldn't have to replace the existing PSU with a more powerful one for the sake of keeping an OCXO's oven up to temperature. In the end, I still avoided replacing the original psu by the expedient of adding a separate 12v 500mA smpsu board to power one those 12v CQE OCXOs I'd decided to put to good use as the generator's frequency reference.

 I'm planning on adding an external 10MHz reference input socket and use the injection locking technique to avoid the risk of glitching the front panel micro controller from switching between the local and external references - it had become a little twitchy in that regard after I'd installed the 50MHz TCXO board. It seems to have lost that twitchiness since upgrading to the OCXO but I'm still mindful of the potential problem such mechanical switching of oscillator sources might cause. Also, of course, it's a neat way to avoid the need for an actual switch to be fitted on the back panel. :)

 As for both yours and DaveR's view that there's no need to fit a cooling fan if either a more efficient smpsu is fitted or else an R type transformer is used for an analogue PSU replacement, I feel I must point out that you're overlooking the fact that both the FY6600 and Fy6800 models were already running uncomfortably hot before any additional heat sources were introduced into the box.

 The 25W rated smpsu might be cooler running from its point of view but the fact remains that its efficiency at a relatively low loading may be no better than the crappy original and quite likely adding a little more heat into the box. R type transformers in an analogue PSU aren't the problem, it's the waste heat from the analogue regulators that poses the real threat. R transformers are a good way to go but I'm not so sure about the analogue aspect unless it's being used to eliminate the high frequency ripple of a switching psu with consideration to the penalty of additional waste heat this introduces.

 At the time when such psu mods were a popular pastime, it seemed to be largely driven by the need to eliminate the half live mains 'leakage' esd risk inherent to all small class II smpsus through the mandated Y cap EMC bodge to reduce common mode conducted interference.

 Unfortunately, without ready access to the safety earth, even a conventional mains transformer analogue supply will still represent some esd risk to a poor defenceless DUT. That being the case, the pragmatic solution to that particular problem is simply to replace the non polarised two pin mains lead connector with a three pin type to give access to the safety earth by which to short out the unwanted leakage with a 1 to 10k 'drain resistor'. You could hard wire the BNC grounds if you like but this introduces a whole new can of worms to the FY6600 in the form of an unwanted mains wiring routed grounding loop (along with undesired galvanic and thermocouple induced dc offsets when working with millivolt level signal voltages).

 The main problem with the original PSU board after replacing the rectifier diodes with ones more suited to the task and doubling the 12v rail cap values to 16v 470μF types (the voltage rating isn't an issue here) and adding a single turn winding to buck the 5v secondary to get a better balance of power distribution to the 12v rails without making the three stooges (LDO regulators) get unnecessarily all hot and bothered, is the high level of HF ripple being both conducted and radiated to pollute the signal processing circuitry with noise. There's no doubt a much quieter PSU would improve the quality of the signals being generated whether it be an analogue or a switching psu.

 Most all modern T&M gear these days relies on SMPSU technology so it's obviously possible to design and manufacture low noise smpsus - I've just been too frightened to ask the price of such specialised ultra low noise switching psus and dc-dc converter regulator modules so I've put the question of improving the PSU on the back burner for now.

 I suspect it may be a lot easier to tame the problem of switching noise in DC-DC regulator converter modules than it is to deal with the high voltage switching noise in a conventional smpsu so a better approach might be to use an R transformer with conventional rectifier and smoothing to power switching DC-DC converter modules in the place of your typical 7805, 7812 and 7912 regulators.

 As it happens, I've just ordered a couple of small DC-DC converters from BangGood (along with a KSGER V2.1S T12 Digital Temperature Controller Soldering Station and other bits 'n' pieces) to try out with my current GPSDO project as an alternative to using a 7805 bolted onto the aluminium case to handle the 9 or 12 volt wallwart voltage conversion to the single internal 5 volt rail supply (I'm using the original 5v 13MHz CQE OCXO I'd fortuitously spotted and purchased for just 4 quid at the Blackpool amateur radio rally last April) so I'll be able to check the <30mV ripple claim made for the fixed 5v output module (the other module does 3.3, 5, 6, 9 and 12 volt but is silent on the subject of output ripple).

 A small efficient mains transformer using low noise switching converters may provide a more efficient solution to the problem of power supply ripple noise with the present PSU board. I don't really want to speed the fan up to compensate for an extra 5 to 10 watts heating load from an analogue PSU solution if I can help it.

JBG
 

Offline svetlov

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Re: FeelTech FY6600 60MHz 2-Ch VCO Function Arbitrary Waveform Signal Generator
« Reply #1930 on: August 08, 2019, 12:09:32 pm »
Hello ! Comrades  :) - but there is a photo of the insides of the generator model 6900
it’s mostly interesting to see the main board of the generator - and in particular its output part
Thanks friends
 

Offline DaveR

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Re: FeelTech FY6600 60MHz 2-Ch VCO Function Arbitrary Waveform Signal Generator
« Reply #1931 on: August 08, 2019, 02:17:33 pm »
As for both yours and DaveR's view that there's no need to fit a cooling fan if either a more efficient smpsu is fitted or else an R type transformer is used for an analogue PSU replacement, I feel I must point out that you're overlooking the fact that both the FY6600 and Fy6800 models were already running uncomfortably hot before any additional heat sources were introduced into the box.

 The 25W rated smpsu might be cooler running from its point of view but the fact remains that its efficiency at a relatively low loading may be no better than the crappy original and quite likely adding a little more heat into the box. R type transformers in an analogue PSU aren't the problem, it's the waste heat from the analogue regulators that poses the real threat. R transformers are a good way to go but I'm not so sure about the analogue aspect unless it's being used to eliminate the high frequency ripple of a switching psu with consideration to the penalty of additional waste heat this introduces.

I have to admit being rather puzzled by your statements about "running uncomfortably hot" initially, Johnny, as neither my 6600 nor my 6800 has ever run anywhere near a temperature I'd describe as hot.  "Moderately warm" is how I'd describe it, but perhaps it's a subjective assessment?  The biggest source of heat, by far, after I did the PS mods in the 6600 was from the 7805 regulator, which got to around 75C and created a local hot spot on the top of the case, but I cured this by swapping it for an OKI 78SR regulator, which runs as cool as the rest of the PS.  Any heat inside the case now comes from the Cyclone chip and the 3095 op amps, but even then I need to run them very hard for a couple of hours (something I've only done once, as a test) to get them to an elevated temperature.  (In real world usage I rarely use more than about 1Vp-p output, so everything stays very much cooler.)  In the same test the D75J TCXO had no problem in coping, with only a 0.1Hz drift at 10MHz after the first 10 minutes of warm up, and no drift after the next 15 minutes - pretty much in line with what you'd expect from an OCXO, depending on the level of sub-Hz accuracy you want.

I still haven't bothered to modify the 6800's PS or op amps even though I've had all the parts to do it since I bought the generator about a year ago - the D75J is the only change I've made, as the awful drift caused by the original XO just had to go.  The distortion produced by the original op amps is minimal at the levels I use, so I can live with them, and they run cooler than the the 3095 upgrades so heat produced in the case is even less than that in the 6600.  Looking back, the 6600 mods were done more for the challenge than out of necessity, but the 6800 works well enough as it now stands, so I'll probably wait until they do become a necessity before I do anything else to it.

Finally, it's nice to see you back Arthur, and thanks for the update on your mods!

Regards,
Dave

 

Offline DaveR

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Re: FeelTech FY6600 60MHz 2-Ch VCO Function Arbitrary Waveform Signal Generator
« Reply #1932 on: August 08, 2019, 02:23:32 pm »
Hello ! Comrades  :) - but there is a photo of the insides of the generator model 6900
it’s mostly interesting to see the main board of the generator - and in particular its output part
Thanks friends

Is there a link to the photo, Svetlov?
 

Offline maxwell3e10

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Re: FeelTech FY6600 60MHz 2-Ch VCO Function Arbitrary Waveform Signal Generator
« Reply #1933 on: August 18, 2019, 08:37:39 pm »
I just got one of these generators. One of the limitations I found (it may have already been discussed here before), is that the number of time points is 8192 even for a sine wave. As a result the "14 bit" resolution is not really realized. There are very visible steps in the sine waveform every 1/8192 of the period and the voltage steps correspond to about 11 bits of vertical resolution. To do it properly the number of time steps should be 2*Pi*(#vertical steps).

I am not sure anything can be done about it, just something to be aware of. Other function generators typically use more time steps.
 

Offline rhb

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Re: FeelTech FY6600 60MHz 2-Ch VCO Function Arbitrary Waveform Signal Generator
« Reply #1934 on: August 18, 2019, 10:42:25 pm »
FYI  I just sent service@feelelec.com an email asking that they replace the front panels for the 4 people I was able to identify who are forum members with borked V 3.0 units.  I was able to furnish shipping information for 3 of them.  I never heard from @canyon.

As before I held out my carrot of a detailed comparison against a Keysight 33622A using my HP 8560A spectrum analyzer.  I attached some screen shots at under 5 V output levels which are close enough that I don't think you can tell them apart.

So we shall see if there has been a change in attitude or if it is just more BS.

Reg
 
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Offline evgen.05

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Re: FeelTech FY6600 60MHz 2-Ch VCO Function Arbitrary Waveform Signal Generator
« Reply #1935 on: August 19, 2019, 06:20:37 am »
Video. PCB - is blue now.

 

Offline CDaniel

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Re: FeelTech FY6600 60MHz 2-Ch VCO Function Arbitrary Waveform Signal Generator
« Reply #1936 on: August 19, 2019, 07:22:11 am »
The jitter problem wasn't checked ... in the video  5MHz for the square wave is a frequency where the jitter is not present .
Same crappy power supply .
Same interface .
24Vpp = exactly 2x12V power supply rails  ;D ,
 

Online radiolistener

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Re: FeelTech FY6600 60MHz 2-Ch VCO Function Arbitrary Waveform Signal Generator
« Reply #1937 on: August 19, 2019, 12:50:58 pm »
The JYEC DIP oscillator on that oscillator power board boasts a stability of +/- 0.1ppm over a a 0 to 25 deg C range and +/-0.2ppm over the -10 to +50 or 60 deg C range and, of necessity for this sort of accuracy and stability, boasts a trimmer to allow calibration against a reference frequency source such as a GPSDO.

 I've attached a photo of the oscillator board - it's now going spare, perhaps I can flog it as a CD player upgrade to some audiophool ;)

these Chinese TCXO has terrible jitter due to phase noise, because they are actually build on synthesizer. So this is not suitable for audiophiles at all :)

I tested one from aliexpress: https://www.aliexpress.com/item/32794136550.html

And I can clearly see synthesizer steps of frequency even with RTLSDR. That's a total shit with spurs each 2 MHz  :horse:
« Last Edit: August 19, 2019, 01:35:29 pm by radiolistener »
 

Offline jleg

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Re: FeelTech FY6600 60MHz 2-Ch VCO Function Arbitrary Waveform Signal Generator
« Reply #1938 on: August 21, 2019, 10:18:17 am »
FYI  I just sent service@feelelec.com an email asking that they replace the front panels for the 4 people I was able to identify who are forum members with borked V 3.0 units.  I was able to furnish shipping information for 3 of them.  I never heard from @canyon.

ah, so you did it again!  ;) - I was a bit baffled, when a few days ago somebody from "FeelElec" sent an email with "We know your FY6600 have some problems" - 18 month after i contacted them with the complaint! They also used an email address i never used with them, which was also a bit strange for me.
They wanted to have some photos (which i did already send 18 months ago), and now they want to send me "a chip which solves the problem". I will believe this when it arrived...  ::)
 

Offline rhb

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Re: FeelTech FY6600 60MHz 2-Ch VCO Function Arbitrary Waveform Signal Generator
« Reply #1939 on: August 21, 2019, 12:46:09 pm »
It's a bit strange that I happened to read the thread and see the post from the new person at FeelElec.  I've generally not followed it much except to occasionally read Johnny B Goode's  posts.  When I saw it, I resent my old email to the new address.

I'll believe it when everyone tells me they  got the part and the unit is working, but maybe it will happen.  I hope they send an entire panel and not just the chip.  However, the new presence might simply be an EE at the company able to get some chips, but not able to get front panels approved by management.

I've been rather baffled by their behavior as there is clearly a good market for them if they simply improve customer relations.  And plenty of very fine engineering talent on offer for free.

Look at where Rigol is today relative to 10 years ago.  Their top line gear is definitely not hobby priced.
 

Offline CDaniel

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Re: FeelTech FY6600 60MHz 2-Ch VCO Function Arbitrary Waveform Signal Generator
« Reply #1940 on: August 21, 2019, 01:04:07 pm »
I received the microcontroller with firmware V3.1 from Feeltech , as they said that will send for free if you ask . Thx .
I will change the IC these days .


« Last Edit: August 21, 2019, 02:08:41 pm by CDaniel »
 

Online radiolistener

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Re: FeelTech FY6600 60MHz 2-Ch VCO Function Arbitrary Waveform Signal Generator
« Reply #1941 on: August 21, 2019, 02:00:45 pm »
that's the price for Chinese no name things... If you want guarantee and service, then buy known brands :)
 

Offline rhb

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Re: FeelTech FY6600 60MHz 2-Ch VCO Function Arbitrary Waveform Signal Generator
« Reply #1942 on: August 21, 2019, 02:16:03 pm »
I received the microcontroller with firmware V3.31 from Feeltech , as they said that will send for free if you ask . Thx .
I will change the IC these days .



I was sent a complete front panel, but with V3.1 FW which was already out of date by the time I got it and which has a known issue.  The 6600 sits on the spares shelf with my Rigol DS1102E and similar gear.

I guess it's time for me to look at FY6900 reviews and see how thoroughly it's been tested.  I *think* I can measure every relevant parameter now.  And if not, I'll get what I need.  I'm suffering from a *very* bad case of TEA syndrome.
 

Offline CDaniel

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Re: FeelTech FY6600 60MHz 2-Ch VCO Function Arbitrary Waveform Signal Generator
« Reply #1943 on: August 21, 2019, 02:28:35 pm »
To be clear , my unit is working fine with V3.0 , I didn't ask this for a repair .
I don't think FY6900 is better if you already got FY6600 . Just minor improvements for front panel butons .
What is the isue with V3.1 ?
 

Offline rhb

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Re: FeelTech FY6600 60MHz 2-Ch VCO Function Arbitrary Waveform Signal Generator
« Reply #1944 on: August 21, 2019, 03:36:24 pm »
The V 3.0 FW will corrupt itself completely borking the unit.   It can happen at any time.

https://www.eevblog.com/forum/repair/reflashing-or-resetting-a-feeltech-fy6600-signal-generator/msg1350260/#msg1350260

It happened to mine just after I finished adding a 3 wire connector and grounding the BNCs.  I ran it for several hours, turned it off and went to bed.  The next morning it looked like the photos in the link above.

It happened to another person right after they had replaced the PSU, XO, and output amps.

IIRC, the V 3.1 will corrupt the sine wave, but that is recoverable.  You'd have to go back through to pages 15-20 in the thread for details.

I just watched the FY6900 video linked above.   It's pretty basic.  If FeelElec comes through with taking care of users with corrupted FW I'll have some very interesting posts as I have an 8560A, 8566B, 8648C, 5386A, GPSDO, 438A, 33622A and an Owon XDS2102A 12 bit DSO which will collect a 20 Mpt trace at 1 GSa/s.  The Owon will let me make some *very* sophisticated analyses using Octave.  I spent 30 years doing DSP in the oil industry.
 

Offline kahe40

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Re: FeelTech Service
« Reply #1945 on: August 21, 2019, 06:31:25 pm »
FeelTech has created a service-thread not long ago,
maybe it is not known to all members here in this thread.


https://www.eevblog.com/forum/testgear/re-feelelec-fy6600-series-signal-generator-after-sales-services/


 :-+


 

Offline Johnny B Good

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Re: FeelTech FY6600 60MHz 2-Ch VCO Function Arbitrary Waveform Signal Generator
« Reply #1946 on: August 21, 2019, 06:59:47 pm »
The jitter problem wasn't checked ... in the video  5MHz for the square wave is a frequency where the jitter is not present .
Same crappy power supply .
Same interface .
24Vpp = exactly 2x12V power supply rails  ;D ,

 Actually, since you need a jitter free reference, using 5MHz for the triggered channel whilst applying a small mHz frequency offset on the other channel, was exactly the right way to perform this test.  :)

 However, it's quite obvious that he hasn't been reading this forum thread otherwise he wouldn't be (rightly, however) obsessing over the glass fuse and the abuse of a ribbon cable wire stolen from the connection between the PS and main boards (you could actually see where the grounding wire had been chopped from the main board end of this ribbon cable connector) to link the ground to the safety earth connection on the C14 socket to the detriment of the common rail connection's increased inductance and the needless introduction of a low impedance grounding loop via the mains earth wiring.

 In view of the 24Vpp claim in the 0 to 5MHz frequency range, it's very surprising to see the continued use of a nominally +/-12v supply. At an absolute minimum, considering the 1.2v maximum 'headroom' figure for a THS3491 (I'd expect similar headroom figures for the THS3002i and THS3095 opamps), you'll need a minimum of +/-13.2v to achieve a 24Vpp capability, with preferably +/-13.5 to 14 volt rails to provide a small tolerance margin. I had expected to see the use of a PSU board with a nominal +/-15v output to satisfy the 24Vpp specification.

 Surprisingly, Feeltech have simply repeated the same grounding sins perpetrated in the FY6800 rather than properly address the issue of mains leakage and grounding loops with a 1 to 10KR "drain resistor" connection to the safety earth in the C14 connector. This does beg the question as to whether they've also wasted the opportunity to replace the 86R attenuator pad with a proper 50R pad. In view of this earthing bodge, I suspect this ridiculous "Skoolboy Howler" still remains unaddressed.

 Apropos of which, I still haven't gotten round to having another go at addressing this issue with my now venerable FY6600-60M generator. I'm still "In Recovery" from my last brain bursting attempt to come up with a new BOM for a 50R attenuator pad which currently sports an impedance of ~45 ohms since my last attempt to correct this particular annoyance - a little closer but still no cigar. >:(

 I see BangGood are now selling the 60MHz version for just £81.08 which is little more than I paid for my FY6600-60M just over nine months ago. Whilst it offers very little more than its predecessor models, it's a bargain for any cash strapped hobbyists looking to buy a cost effective signal generator with the bonus that virtually all of the modifications and upgrades that apply to the FY6600 and the FY6800 models still apply.

 Even the half mains live leakage suppression with a 10KR 'earth drain resistor' mod that so neatly solved this issue in the FY6600 without introducing the spectre of tens of millivolts of DC offsets and other assorted earth loop induced interference whereby, as with the FY6800, all the brute force and ignorance approach of swapping the C8 connector for a C6 or C14 mains socket has already been applied, leaving just the addition of a 10KR and some remedial work on the PS to Main board ribbon cable connector to be implemented, would be worth doing.

 One other thing I did noticed in that video was that the rear panel cooling fan location had not been populated with an actual fan. Presumably this will be an optional after-market add on. I suppose there's some consolation in that at least such an end user improvement won't be requiring the use of a hole saw and drill to modify the case in order to upgrade the cooling provision from almost none to barely adequate.  :)

 Feeltech do seem to have kept the home hobbyist who revels in such home improvement projects in mind with this "toy signal generator", leaving as they do, so many loose ends for the enthusiast to tidy up post purchase. Considering its price point, is that really such a bad thing?  >:D

JBG

« Last Edit: August 24, 2019, 04:28:39 am by Johnny B Good »
 

Offline Johnny B Good

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Re: FeelTech FY6600 60MHz 2-Ch VCO Function Arbitrary Waveform Signal Generator
« Reply #1947 on: August 21, 2019, 10:18:54 pm »
As for both yours and DaveR's view that there's no need to fit a cooling fan if either a more efficient smpsu is fitted or else an R type transformer is used for an analogue PSU replacement, I feel I must point out that you're overlooking the fact that both the FY6600 and Fy6800 models were already running uncomfortably hot before any additional heat sources were introduced into the box.

 The 25W rated smpsu might be cooler running from its point of view but the fact remains that its efficiency at a relatively low loading may be no better than the crappy original and quite likely adding a little more heat into the box. R type transformers in an analogue PSU aren't the problem, it's the waste heat from the analogue regulators that poses the real threat. R transformers are a good way to go but I'm not so sure about the analogue aspect unless it's being used to eliminate the high frequency ripple of a switching psu with consideration to the penalty of additional waste heat this introduces.

I have to admit being rather puzzled by your statements about "running uncomfortably hot" initially, Johnny, as neither my 6600 nor my 6800 has ever run anywhere near a temperature I'd describe as hot.  "Moderately warm" is how I'd describe it, but perhaps it's a subjective assessment?  The biggest source of heat, by far, after I did the PS mods in the 6600 was from the 7805 regulator, which got to around 75C and created a local hot spot on the top of the case, but I cured this by swapping it for an OKI 78SR regulator, which runs as cool as the rest of the PS.  Any heat inside the case now comes from the Cyclone chip and the 3095 op amps, but even then I need to run them very hard for a couple of hours (something I've only done once, as a test) to get them to an elevated temperature.  (In real world usage I rarely use more than about 1Vp-p output, so everything stays very much cooler.)  In the same test the D75J TCXO had no problem in coping, with only a 0.1Hz drift at 10MHz after the first 10 minutes of warm up, and no drift after the next 15 minutes - pretty much in line with what you'd expect from an OCXO, depending on the level of sub-Hz accuracy you want.

I still haven't bothered to modify the 6800's PS or op amps even though I've had all the parts to do it since I bought the generator about a year ago - the D75J is the only change I've made, as the awful drift caused by the original XO just had to go.  The distortion produced by the original op amps is minimal at the levels I use, so I can live with them, and they run cooler than the the 3095 upgrades so heat produced in the case is even less than that in the 6600.  Looking back, the 6600 mods were done more for the challenge than out of necessity, but the 6800 works well enough as it now stands, so I'll probably wait until they do become a necessity before I do anything else to it.

Finally, it's nice to see you back Arthur, and thanks for the update on your mods!

Regards,
Dave

 Hi Dave,

 Apologies for the delayed response but that was the day me and the XYL started a ten day cruiseship holiday and it's taken me two and a half days to catch up with my TV recording schedule (downloading and converting the iPlayer downloads for future viewing rather than actually watching them!) and sorting out ebay problems with a couple of sellers (including hgfurniture2018's failure to successfully ship that bargain FY6600-60M I'd paid £40.41 for two months ago in spite of a second attempt (allegedly) to ship me another one).

 The problem with the FY6600 is that the ventilation slots do very little as far as passive cooling is concerned, even to the extent that tilting it up on its bail makes the situation a little worse. In essence, most of the heat escapes via conduction through the plastic case rather than a more desirable exchange of interior air with that of the cooler ambient air.

 This means that the interior air has to absorb the heat dissipated by the components to raise its temperature sufficiently to warm the plastic casing to set up a flow of heat to the outside surfaces in order for the ambient air to conduct the heat away. All these additional thermal gradients between the actual semiconductor junctions generating the heat and the outside thermal environment result in much higher component temperatures than would result from a modest flow of cooling air produced by even a small (50mm square 10mm deep) 12v cooling fan running off the 5v rail.

 A simple solution to improving the passive cooling would be to upend the generator to stand it upon its right hand side where the case orientation would provide a chimney effect to speed up the thermo-siphon induced flow of the interior air to improve this transfer of heat to the outside surface of the case (with perhaps some small boost of exchange of air between the interior and exterior of the case). However, the improvement would still be rather marginal for the inconvenience involved, making the addition of a cooling fan the clear winner.

 When I remembered that I actually possessed an IR thermometer and used it to check component temperatures, I found that the smd XO ic was running at 50deg C and the three nearby LDO voltage regulators running at 70deg C. The FPGA showed 50deg C as did the base of the heatsink. Since, out of necessity, I had to take these readings with the lid removed, I've no doubt these temperatures would have been a lot higher again in normal use (possibly another 10 to 20 degrees higher but I still don't possess a suitable thermal probe to measure with the lid in place).

 I've no doubt that my initial attempt to raise the 12v rails above the 11.7v mark by boosting the 4.97v to 5.49v was adding to the heat stress via the LDO regulators (probably by another 5 deg C) exacerbating this issue a little but even so, a slight 5 degree drop in temperature would still leave the innards on the wrong side of the 50 degree mark with regard to component service life (notably the electrolytic caps which are short enough lived to begin with).

 A cooling fan seemed to me an essential necessity, especially when considering that, in the interests of frequency stability, it would likely be spending more time powered up than powered down (good from the point of view of reducing thermal cycling stress induced fatigue but bad for the service life of the caps).

 When I do finally get hold of a suitable temperature probe, I won't be in the least surprised to see something like a 15 to 25 degree drop in internal air temperature between fan running and fan stopped test conditions.

 In the interim, I have the fact that before fitting the fan, I could detect three notable hot spots, two on the top of the case (PSU and heatsink locations) and one on the underside (heatsink location) the top two of which have now disappeared with the underside one now downgraded to a warmish spot to indicate the effectiveness of my fan cooling upgrade.

 I have been rather mindful of the need for quiet efficient effective cooling since before the turn of the century when building desktop PCs. It's all too easy to overlook the fact that temperature gradients can accumulate alarmingly high temperatures at the heat sources (typically semiconductor junctions with limits no higher than 125 deg C in most cases) if care isn't taken to minimise the intermediate thermal gradients.

 I marvel at how unventilated smpsu wallwarts manage to cope using conduction via internal air to pass heat to a plastic thermal conductor to the outside surface actually exposed to the cooling room air which is why I have so much confidence in their longevity when I salvage their innards for use inside of a ventilated case as an auxilliary psu such as the half amp 12v smpsu board I'm using to power the OCXO in my FY6600 generator (a grand total addition of another 1.3W to the heating load within the box).

 It's all too easy to overlook the importance of effective cooling, especially when adding such items as replacement analogue PSUs with their own critical cooling requirements to an existing box full of electronic components regardless of all the empty unused space within just crying out to be filled with all that analogue psu goodness.

 Many have fallen foul of the 7805/7812/7912 regulator's thermal requirements but I see, now that I've googled "OKI 78SR", that you've discovered  a rather neat solution (90.5% efficiency!).  :)

 JOOI, have you measured the ripple noise output of this dc-dc converter substitute for the classic 7805 yet? I've got a similar dc-dc converter module on order from BangGood which claims less than 30mVpp ripple which I'm hoping to use in my very first basic GPSDO. It was part of an order totalling well below the 25 quid point at which you get free expedited delivery so is on a slow boat from China meaning it may be a few weeks before I get the chance to test its ripple noise performance. I've also got a step variable voltage dc-dc module in that order which made no mention of ripple noise performance which I'd also like to test.

 I rather suspect that despite some level of ripple noise in these dc-dc modules, they'd be a good compromise between the high ripple noise of an efficient mains voltage smpsu and the lower noise of an analogue R type mains transformer psu based on these converters in place of the classic 7805 type regulator.

 At the very least, such a solution should eliminate the direct radiation from the high voltage switching in a conventional cheap mains voltage smpsu from polluting the analogue circuitry of the signal generator either directly or via common mode conduction to the main board's low level voltage connections. The ripple noise of a dc-dc converter module should be easier to filter out than any common mode noise injected by a high voltage switching chip. However, whether any of this has any basis in fact remains to be seen but I do have high hopes that this turns out to be case.

 As for the need to modify any of these signal generators, it does, as you point out, rather depend on the use you plan to put them to. For audio use, they'll be fine as they are, especially if you invest in a decent external 50 ohm 20dB attenuator with perhaps a further selection of attenuation steps allowing you to avoid the internal 86 ohm attenuator pad for voltages below the 500mVpp mark, eliminating the risk of noise from the psu leaking past this built in attenuator onto the BNC outputs.

 Although audio signals are typically carried on notionally 600 ohm circuits (balanced or unbalanced) or simply passed from a low impedance source into a high impedance sink, it's still desirable to stick with a 50 ohm attenuator pad, if only for the sake of consistency. If impedance matching is important, a simple resistive matching pad can take care of that at the volt level since there's plenty of surplus voltage swing available to compensate the additional loss of such a matching pad.

 As I see it, all of these signal generators will benefit from the addition of a cooling fan and the suppression of the half live mains voltage leakage with a 1 to 10K "static drain" resistor connection to the protective earth on a three pole mains socket, neatly avoiding the ground loop issue. If nothing else is required, these two modifications are, imo, essential prerequisites for a long service life and protection from the ESD risk posed to any devices under test.

 A virgin FY6600 requires the most effort to complete these two mods, the FY6800 is already blessed with the required three pole mains socket for the leakage suppression mod leaving just the cutting out of a hole to accommodate a cooling fan whilst the FY6900 needs no such gross mechanical modifications, blessed as it is with both a C14 mains socket and an unpopulated fan aperture on its rear panel which I guess was just an incidental feature of the case Feeltech had bought in (I rather doubt they specifically asked for it).

JBG
« Last Edit: August 24, 2019, 04:36:15 am by Johnny B Good »
 

Offline maxwell3e10

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Re: FeelTech FY6600 60MHz 2-Ch VCO Function Arbitrary Waveform Signal Generator
« Reply #1948 on: August 22, 2019, 12:07:27 am »
Here is a picture of a zoom-in on a 1 kHz 20Vpp sine wave. The scope scale is 10 mV/100nsec per division. One can see steps of 7.5 mV every 120 nsec, as expected for a 8192 points sine wave. So the vertical resolution ends up being 2666 levels or about 11-12 bits.
816684-0
I am not sure if this is a limit of the FPGA or if one could make a longer waveform with firmware changes.
« Last Edit: August 22, 2019, 08:35:24 am by maxwell3e10 »
 

Online radiolistener

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Re: FeelTech FY6600 60MHz 2-Ch VCO Function Arbitrary Waveform Signal Generator
« Reply #1949 on: August 22, 2019, 06:47:53 am »
One can see steps of 7.5 mV every 120 nsec, as expected for a 8192 points sine wave. So the vertical resolution ends up being 2666 levels or about 11-12 bits.

Did you used 50 Ohm pass through dummy load on the oscilloscope input? Without it you will see random amplitudes. If it properly terminated, then full scale is 10 Vpp, not 20 Vpp, because FY6600 uses invalid "HiZ" units.

So, if this picture taken with properly terminated 50 Ohm, then:

10 Vpp / 7.5 mV = 1333

It means that there is just 11 bits DAC.

Such thing may occurs because some Chinese manufacturer used DAC902 instead of DAC904. It has the same pin-out, but it is more cheap and has 12 bits resolution instead of 14 bits.

It may be because manufacturer trying to get more money by selling cheap things, or it may be because DAC chip supplier provided fake chips (for example remarked DAC902 instead ofDAC904)...

You must be very careful and check all the details when you buy something on the Chinese market.
« Last Edit: August 22, 2019, 07:09:40 am by radiolistener »
 


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