Products > Test Equipment
FeelTech FY6600 60MHz 2-Ch VCO Function Arbitrary Waveform Signal Generator
GregDunn:
It sure does what I need with plenty of room to spare; mostly audio functionality testing, swept frequency, IM, etc. etc. and it can be quickly set up from the front panel to do rather complex stuff. If I need low distortion, I use my Heath IG-5218, and if I just need a signal at an approximate frequency to spot-check something, it's the Wavetek 182 (the two of which together cost even less than the FY6800). No, it's not a pro generator, or a real RF tester, but that's not what I expected when I bought it.
Johnny B Good:
--- Quote from: beanflying on January 13, 2019, 05:47:14 am ---Interesting reading back on this flawed but really good value for money Box as it gets to EOL. There are some very cheap 50MHz units on evilbay at present if anyone is in the market with not to many $$ to spend as of today.
Mine after 15 months or so is about to get mothballed (Replacement is a Siglent 2000X) rather than sold for the few $ I might get for it so I chased up the last versions of the Windoze software and any updated Labview drivers and such to pack away with it.
Overall unlike some here my experience has overall been a positive one after sorting out the floating power supply and with a little trial and the correct tongue angle improving some levels on the board. Frequency has always been out by a bit but generally this is a non issue and if it was I checked and tweaked a few counts if needed.
Sub 10Meg for the complete software package that allows Arb Signal creation and driving the front panel via USB kicks the butt of the Siglent by comparison and as per the couple of comparison waveforms @30MHz Sine and 10MHz Square it holds up fairly well against a Generator at current pricing 10 times more $$. Coin toss for the Sine and suffering a little on the square.
Remembered fondly as it goes to the 'cupboard' to maybe never return :)
--- End quote ---
Hi Beanflying,
I was beginning to think the next post would be another follow up from me. It seems a shame to retire your Feeltech AWG to the toy cupboard after all the fun times you've had turning it from a sow's ear into a silken purse. I guess you didn't put in quite as much effort as I did to be able to throw it aside like that (I can't remember just how much work you did put into it this past year, I just know you were a regular contributor to this ongoing thread). Mind you, new toys and all that, perhaps I'd do exactly the same if (when) I bought a more upmarket replacement. :-)
Anyway, it's been a remarkable 'Bean counteritus mitigation upgrade project' that makes all previous such projects I've had over the past 40 odd years pale into insignificance. I never realised there could be so many ways to waste a perfectly good AWG main circuit board by rampant beancounteritus. It's almost as if Feeltech could read the minds of their target market and went all out to give it the upgrade project of the century. :)
After spending a few weeks obsessing over the calibration accuracy of the 0.1ppm 50MHz TCXO module upgrade and lamenting the lack of any WWV transmissions (notably the 10MHz broadcast), I finally decided to tackle the PSU issue once and for all.
I've spent the past two or three weeks searching for low leakage smpsus I could use with or without add on DC-DC converters to create an ultra low leakage three rail PSU. I even considered medical grade 12W (5 or 15 volt) wall warts from which to extract the smpsu board but gave up when I realised the price premium on something that only cost a penny or two more for its shielded transformer would make a mockery of my penny pinching signal generator purchase.
The penultimate nail in the coffin of that "Holy Grail" search came when I discovered a complete lack of suitable DC-DC converter modules I could drive from a conventional mains transformer and rectifier smoothing pack to obviate the accursed Y cap. The final nail was when I discovered just how inefficient those specialised mains isolating transformers were as a consequence of their split bobbin construction.
This was when I decided to 'Think Outside The Box' and came up with the clever idea of linking the common zero volt rails of a pair of smpsus wired to the mains in 'anti-phase' so their leakage currents would cancel (I was thinking of using the original for the +/-12v and an additional one for the 5v rails). I was so convinced that this 'neat solution' would work, I jumped out of my bed in the middle of the night to put my clever hypothesis to the test. Sadly, it didn't work because it was based on faulty reasoning so was doomed from the beginning.
Never mind, I had another neat idea concerning a method to 'null out' (or buck) the unwanted half live mains leakage voltage. This idea was based on using a 1VA pcb mount 240 to 120 volt isolating transformer to provide an oppositely phased source of half live mains I could use to cancel out the unwanted touch voltage. Unfortunately, this was also doomed to failure (and for essentially the same reason that my "two smpsus in anti-parallel connection to the mains supply" hypothesis had been doomed).
In both cases, bucking (or nulling out) the unwanted leakage voltage relies upon tying the anti-phase generator to the neutral line wrt to the supply rather than to an arbitrary mains input wire on the smpsu(s) concerned as I'd originally considered. The key to such a scheme is that you need to identify the neutral by which to reference your anti-phase source in order to successfully cancel out the leakage voltage. Although it's not too difficult to automatically detect which way round the supply is connected and automatically correct the polarity so as to ensure such nulling out exercises will succeed, such complexity is needless.
The whole nulling out process becomes somewhat redundant since you can simply bridge the 0v rail to the neutral via a 100K high voltage safety resistor which will bog down the half live mains voltage on a 240v supply right down to a mere 7.5v - low enough not to harm any ESD sensitive devices under test. With that in mind, it then begs the question as to why invoke all the extra complications just to link the 0v rail via a safety resistor to a ground referenced connection (the neutral) to shunt the leakage voltage to a safe level when one might just as well use the safety earth to achieve the same effect without such complexity and less risk of a non-fatal but unpleasant electric shock when Sod's law inevitably messes up the auto polarity detection. Better yet, a real earth lets you use a 10K resistor, still large enough to avoid hum loops but even lower so as to reduce the leakage voltage to just half a volt on a 240v supply.
It was this which led me into finally using my variant of the "Upgrade from class II to a class I earthed" configuration by adding a 3 wire IEC connector (C6 or C12/13) solution which most everyone else had chosen as one of their very first modifications to the FY6600, typically electing to use a 10 to 100nF capacitor in place of my 10K leakage voltage suppression resistor or else directly bond the safety earth connection to the common ground rail, sometimes using a "Grounded/Floating" option switch to obtain the best of both worlds (risky if the switch isn't bridged by a leakage mitigation resistor in the range of 10K to 100K and also prone to operator forgetfulness).
I chose the slightly more tricky C6 socket option to avoid the "Tail wagging the dog" syndrome of hanging a 700g box on the end of a 10A 3 core mains lead, spending most of yesterday's free time fabricating the aluminium reinforcement and support plate required to accept the slot in C6 connector I'd recovered from a scrapped laptop charging brick. Unlike others' socket upgrades, this plate is simply bolted onto the flimsy rear panel which measure is more than adequate to prevent it bending and popping out of the case half retaining slots.
It's taken me this long to get around to doing this job because I wanted to avoid this messy business of a brute force and ignorance pragmatic fix since I'd once held out hope of a more refined and elegant solution to eliminating the half live mains leakage hazard. It's only now, after days of fruitless searching for affordable low leakage smpsus and trying to think up cunning ways around the problem that I've come to realise that the pragmatic brute force and ignorance approach turns out, in this case, to be the one and only sensible option after all. Who (honestly) knew? :-)
Following on from that, this modification seems to have cured a rather annoying feature whereby it would stop generating signals on both channels whenever connecting anything earthed produced an ESD event depending on the charge state of the Y cap at the time of connecting. TBH, I'm not sure whether this new symptom is a consequence of the TCXO modification or an existing feature that I only happened to notice after doing the TCXO mod.
Anyhow, as I'd been hoping, the PSU leakage fix does seem to have cured this annoying habit of disabling both channel outputs whenever connecting up to an earthed device under test (and even when disconnecting) requiring a power down restart to restore the signal. I've just assumed that this is an unmentioned foible of the FY6600 series in general as a consequence of the psu leakage current issue, perhaps largely limited to those of us running it from a UK 240 or a European 220v mains outlet. I wonder whether anyone else has noticed this particular quirk?
Incidentally, whilst on the question of funny quirks, has anyone else experienced the random loss of digit selection when using the left and right arrow digit selection buttons? This one is less annoying only because a simple disable/enable sequence on the channel select buttons restores the digit selection operation rather than require a power down/up reset. It's just a possibility that it might also be related to the psu leakage issue but I won't know whether this is the case until I've done some more testing.
I think the only outstanding issue now is that of the attenuator used to handle the 1 to 500mV output range using the wrong resistor values, causing a terrible mismatch to 50 ohm loads. Feeltech have fudged this in the firmware by compensating for this error when driving Hi-Z loads. I did look into fixing this one with a change of the resistor values after working out what would be needed to create a 50 ohm pad with an attenuation that matches the Hi-Z loading condition they've actually compensated for (ie one that results in the 6dB drop when loaded with a 50 ohm load). Since this involves reworking smd components, I only want to do this job the once and get it right first time round so I've put it on the back burner for now until someone else can offer a sanity check on my recalculated resistor values. Has anyone else tackled this particular quirk?
The resistor values they've used are a 510 ohm series element with a couple of 100 ohm shunt elements which turns out to be a 22.26dB attenuator for an 84.456 ohm impedance line. I suspect they were aiming for a 50 ohm 20dB attenuator using 56 ohm shunt resistors with the 510 ohm series element and somehow landed up placing 100 ohm resistors instead of the specified 56 ohm ones through some sort of cockup in the manufacturing process and, rather than rework the boards with the correct resistors, they've chosen to compensate for the Hi-Z condition in the firmware and hope nobody important notices this blatant manufacturing error.
Luckily, there is a hardware fix for this cockup (just as well seeing as we're not likely to see a firmware plus hardware fix out of Feeltech support) which involves calculating a new 50 ohm attenuator network that produces an attenuation figure 6.02dB lower than the Hi-Z attenuation factor of the current attenuator network for which they applied their firmware compensation fix. I think, going from my rough notes on the back of an envelope (literally!), this calls for a 25.71dB 50 ohm attenuator network to correct the problem with the current firmware left unchanged.
Plugging the appropriate values into an on line matching Pi attenuator calculator, the ideal resistor values are 55.465 for the shunt elements with a 481.141 series element. trying alternate 'preferred values' in the hope of minimising the reworking, leaving the existing 510 series element as is and replacing the 100 ohm shunts with 56 ohm resistors will produce a reasonably close match giving a slightly higher attenuation value of 26.09dB with a 50.706 ohm matching impedance. Although this will produce a slight departure from monotonicity (not obviously apparent under Hi-Z conditions as things currently stand) as the level is stepped through the 500mV threshold, the very obvious discontinuity under 50 ohm loaded condition should all but vanish. I haven't delved any deeper into a more precise analysis to check just how big a glitch in voltage amplitude this might represent using those preferred 'quick fix' values. I'll leave that as an exercise for the interested reader to tackle. :-)
Regards, Johnny B Good
beanflying:
Putting in the cupboard and moving on is really an extension of gaining some more accurate equipment that you 'know' will output or input closer to the truth and provide a better series of ranges.
I made do for a very long while without one at all. Having one made life easier and saved me time using bread boarded or lashed up worse performing oscillators. So for someone without they are still a good thing with a simple mod to the power supply to improve the floating outputs. Much beyond that time and money spent to still get a box with still questionable accuracy and output limits doesn't make logical sense to me.
On a budget or after a first Sig Gen you can do way worse for more money. :)
Johnny B Good:
--- Quote from: beanflying on January 14, 2019, 01:25:15 am ---Putting in the cupboard and moving on is really an extension of gaining some more accurate equipment that you 'know' will output or input closer to the truth and provide a better series of ranges.
I made do for a very long while without one at all. Having one made life easier and saved me time using bread boarded or lashed up worse performing oscillators. So for someone without they are still a good thing with a simple mod to the power supply to improve the floating outputs. Much beyond that time and money spent to still get a box with still questionable accuracy and output limits doesn't make logical sense to me.
On a budget or after a first Sig Gen you can do way worse for more money. :)
--- End quote ---
Hi Beanflying,
I do take your point but, right now, I'm not at that stage where I'd care to invest double what I paid for my Siglent SDS1202X-E dso just to get a slightly more refined version of my modded FY6600-60M signal generator (actually, as far as the front panel buttons go, hugely refined! - it's only the 600 quid saving which makes this lack of refinement acceptable... for now).
If I was relying upon such T&M gear for my living, I'd certainly be prepared to make a greater financial investment but I'm now three years retired from the business of repairing desktop PCs, a trade which more or less died off some 4 or 5 years before I finally called it quits to collect my pension. Whilst I do have a reasonable lump sum languishing in low interest rate accounts to be burnt through, I can't really justify blowing some 10 to 15 grand of it on 'low end' decent gear, at least not right now.
As you say, it's best to just shelve the FY6600 as a "get you by spare" rather than just sell it off for a paltry sum, especially when you've invested some time and effort improving its performance into the low end quality gear territory with price tags an order or two of magnitude greater. The factory upgrade option to a 0.1ppm TCXO on the Keysight 120MHz AWG is 700 quid alone which rather puts my 15 quid investment to do the same upgrade somewhat into perspective. ;D
I've applied several mods in the past two months since I purchased the unit last November. The list (in order of priority with the benefit of hindsight rather than the actual order I did them in) is:-
Add a cooling fan, a highly desirable upgrade on the woefully inadequate passive ventilation, destined to cook it into an early grave.
Add a C6 mains socket (in preference to the larger C12/13 socket if wish to avoid the "Tail wagging the dog" effect) and use a 10K resistor (not a 10 to 100nF cap) to link the 0v line to the protective earth pin to kill the unwanted half live 'Touch Voltage' without creating an earth loop problem,
Modify the PSU to raise the 5v rail (4.95v measured) to 5.49v in order to raise the +/- 12 rails from the 11.4v mark into 13.7v territory upgrading the 12v rectifiers to heavy duty 20A rated dual shotcky rectifiers, leaving the 5v diode as is to maximise the voltage boost obtained by winding an extra two turns per "12volt" winding on the transformer (don't bother fitting 25v caps) and definitely don't try converting the 12v rectifier into a fullwave bridge by adding the 'missing' diode elements, DAMHIK, IJK. :-[
[Edit 20190722]
I found a much better alternative (which I described in a later posting) to adding two turns onto each end of the 12v windings - leave the 12v secondary untouched (I'd had to undo this modification) and wind a single turn to buck the 5v winding output voltage (easily accomplished without the need to remove the transformer).
I'd used thicker wire than was needed, making a rod for my own back when Sod's Law ensured I'd connected it the wrong way round - put half a dozen single turn windings wired in parallel (plenty of room on the bobbin) to get a well coupled low resistance/leakage single turn winding to connect in series with the 5v rectifier diode (lift the anode out, wire one end in the vacated hole and the other end soldered to the lifted out anode lead).
In spite of the voltage increase on the +/-12v rails (now at +/-13.7v mark), the power consumption actually dropped a fraction of a watt. Mind you, I'd replaced the 47K resistor in the voltage feedback network with a 200K to reduce the 5.49v on the 5v rail down to 5.09v which would have made some modest contribution to the achieved energy savings but I suspect most would have come from the efficiency improvement I'd achieved over the original adding of two turns at each end of the 12v winding modification.
[EndEdit]
Upgrade the single THS3002 dual opamp to a pair of THS3001 (at a minimum) or, better yet, THS3095 or ( a little OTT) THS3491 opamps to eliminate sine wave distortion at 20V p-p when close to the 20MHz limit and driving 50 ohm loads.
Upgrade the really shitty little commodity 20ppm rated 50MHz clock chip to a 0.1ppm TCXO module that can be located away from the vicinity of the three analogue voltage regulators that raise the board temperature up to 70 deg C, causing the original shitty oscillator chip to run at 50 deg C - the TCXO module can be located in the incoming airflow provided by the cooling fan.
[EDIT 2020-04-14]
Finally, correct the output attenuator network that's used to reduce DAC and amplifier noise in the voltage output range of 1 to 500mV by...
paralleling each of the four 100 ohm shunt resistors (marked RS 1,2,5,6) with 124 ohm resistors and placing an 8K2 resistor in parallel with each of the two 510 ohm series elements (RS 3,4).
You can use 120 ohms instead of the 124 ohm values since you'll likely have to trim the 8K2 resistors anyway to get an exact match to the unloaded attenuation corrected for by the firmware for the original 84.46 ohm impedance 22.26 dB attenuator that had been erroneously created (it looks like the 100 ohm shunt elements were placed in error for 56 ohm resistors which would have created a 26dB 50.706 ohm attenuator with that 510 ohm series element value). You can compensate such an error in the firmware but only for either the terminated condition or the unterminated Hi-Z condition, not both, so it looks like Feeltech opted to compensate for the Hi-Z condition with their firmware fix and hope no one notices the glaring error in the terminated case.
I'd originally envisioned this modification as an smd reworking task but, after looking at pictures of the mainboard, realised it could be done using the smallest of wire ended resistors in parallel with the existing smd resistors which otherwise would have been replaced with lower value smd resistors (480 ohm series element resistor with a pair of 55.36 ohm shunt resistor elements per attenuator pad assuming 0.1% tolerance resistors in the original circuit). Since it's highly likely Feeltech only used 1% tolerance resistors at best, a better way to make sure of a good match to the original Hi-Z attenuation, they seemed to have precisely compensated for in the firmware, is to wire up a variable 10K resistor across the series element after soldering in the 124 or 120 ohm shunt resistors into the circuit and adjust for no discontinuity in level as you transit the relay switching point at the 499/500/501 mV mark other than the selected mV setting. This test should be done at a low frequency (say 1KHz) so that the stray L and C in the foot or so of wire between the board and the 10K pot have no detrimental effect - we're just finding the exact resistive value required in order to pick out a fixed value resistor by selection testing suitable candidates from our parts collection.
The same 'select on test' procedure could be used to gather the desired 124 ohm 'rogues' from the 120 ohm parts bin - desirable but not essential although avoiding samples that are on the minus side of the tolerance range are best weeded out just the same.
This might seem to some as rather a lot of trouble to go to (selecting on test and a variable resistor to tweak to a precise Hi-Z attenuation value) but if you're going to have a go at fixing this manufacturing defect at all, that extra faffing about is a trivial thing compared to the process of soldering in the additional wire ended resistors. After all, if a job's worth doing, then it's worth doing well or not at all. The motivation in this case being a more tightly specced output impedance than you typically see in gear costing one or two orders of magnitude more. :) Any EE (amateur or pro) with any pride at all wouldn't need reminding about the worth of doing a job well.
Forget all that tosh. The design and its firmware had been predicated on the multiply by 10 add 20dB rule. That cockamamie 85 ohm attenuator just happened to be the cheapest way to get 20 dB in the Hi-Z load case. It had replaced the proper 20dB 50 ohm attenuator pad originally specified and made up from the most expensive E192 (0.5% tolerance) preferred values range using 61.2 ohm shunt resistors with a 249 ohm series pass element. I guess the chief bean counter must have threatened the chief designer with the sack if he didn't find a seriously cheaper alternative (meaning anything that could substitute for a real 20dB attenuator in the Hi-Z loading case and forget all about maintaining any semblance of 'Technical Standards').
[END_EDIT 2020-04-14]
The final improvement I may end up attempting, would be to improve the action of the rather horrible front panel buttons, in particular the left and right arrow ones beneath the rotary encoder with the emphasis on the right-hand button which still causes the selected digit cursor to vanish from time to time, necessitating a cycling of the channel select button to get it back (at least it doesn't require a power cycling reset like the esd earthing contact transient used to do prior to my mains socket and 11k earthing resistor mod).
The problem seems to be the result of the excessive force required in just the right place on the arrow button to get it to register the key-press possibly causing a cracked solder joint (hopefully not a cracked trace) nearby to open up on the front panel PCB causing a glitch in the cursor positioning subroutine. Whilst the left hand button produces a satisfyingly tactile toggling effect, the RHS one lacks such tactility, suggesting a faulty switch behind the membrane (hopefully an actual solderable into/onto the board micro-miniature momentary contact pcb mounted switch rather than a rubber membrane switch with a carbonised tip to bridge contact traces on the underlying PCB after the fashion of a cheap TV remote controller).
The front panel is the one component I've not removed for closer inspection since, until recently, I've not had cause to apply an 'upgrade' to it. It's only now that I'm considering taking a closer look, not so much as an upgrade exercise (although a repair could be deemed as an upgrade from 'not working' to 'working') so much as a repair job, so I'm in blissful ignorance as to what lies beneath the actual switch locations underneath the membrane bumps. Has anyone taken a closer look at the front panel switches?
At some time in the not too distant future, I'll be taking a very close look at the 'arrow' buttons with a view to 'upgrading them (or at least the RHS one) into a properly working condition. I don't know what awaits such a close examination so there's a chance that nothing short of a replacement front panel will resolve this issue. Since the FY6800 model appears to be an FY6600 with an upgraded front panel, I might, in that eventuality, land up buying a 60MHz version from which I may elect to cannibalise its front panel as a replacement for the FY6600 in view of all the work that's already been invested thus far. However, that does rather depend on just how similar the main boards actually are between the two models. If the front panel transplant proves to be impractical, that just means I'll be treading a well worn upgrade path to bring the FY6800 up to scratch.
I'm not quite ready to 'throw in the towel' and splurge 700 quid on a Siglent SDG2122X just yet! :)
Regards, Johnny B Good
Noy:
Ist it worth to get a FY6800 if you already have a Toellner 7401 and the build in AWG from Rigol MSO5000?
Or better a old wavetek Model 275? I think the wavetek is to old or? Waveform has to be tipped in over the buttons because i don't have a GPIB..
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