Products > Test Equipment
FeelTech FY6600 60MHz 2-Ch VCO Function Arbitrary Waveform Signal Generator
bugi:
The cleaning afterwards is quite easy, at least if the area is not tight, but it still needs to be done. Price is indeed high, so one needs to consider the price of the device being "fixed" (or modded) and prices of other solutions. However, I think in this case the device is valuable enough that using a bit of that alloy would be justifiable.
If one already has a nice hot air station, then that would likely be simpler solution.
Johnny B Good:
--- Quote from: DaveR on November 20, 2018, 01:52:13 pm ---Hi Johnny,
That's quite a tome you've just sent: forgive me for not replying in detail, but it sounds like you're an old-time tinkerer like myself. I started off on various bulletin boards in the very early days of the internet, before the likes of Compuserve and AOL appeared, and well before the WWWeb took off. Usenet served me well for years, but with everything being web-based now, you just have to accept the quirks and foibles that come with it. You soon grow into it!
Back to business, no-one has come up with anything better than the D75J TCXO so far. It's cheap, but the only place you can get one is Digikey (order in the UK, get it in a couple of days from the US, but postage doubles the cost unless your order is over £40), and it is a drop in replacement - but you'll need a hot air gun to remove the old one unless you can rig up a piece of wire on your soldering iron to melt the four contacts at once. I remember looking at those Chinese TCXOs a few months ago, but they are rather expensive to take a chance on, and they'll probably need mounting on stilts, or a daughterboard, as there'll be no room on the PCB for them.
On the subject of soldering irons, my 18W Antex bit the dust about 5 years ago and I had to continue with the 30W Antex I bought in the 1980s, using a bit that was too large for most modern needs. A couple of years ago I switched to Hakko T12 stuff - it was like driving a new Jag after getting out of a Ford Anglia. Even the Chinese clones are good, and the right tools make modding a breeze!
I need to have a read of the 3491 datasheet again, going by what you say, as I was sure they were a simple direct replacement for the 3091/3095 even with the floating pins.
Regards,
Dave
--- End quote ---
Hello Dave,
I didn't get started with the internet (and usenet) until around 1996 when I joined up via a dial up service to a small, highly recommended ISP (based in, of all places, the Shetland Islands!) known as zetnet. For the first 4 or 5 years, I was totally reliant on their dial up PoP until my teenage daughter paid NTL to install their cable TV service with 512Kbps broadband at the behest of her boyfriend / fiancée (now our SiL) who was/is a web developer with some expertise in Linux. I assembled a lowest power consumption PC and had him install a Linux based router/firewall/gateway OS so the BB could be shared to the Cheapernet(tm) cabled house LAN for all to access with a tenner a month towards their rental costs as the inducement.
This was just about the time when zetnet's resident wizard (Tim Cole, RIP) had added additional connectivity to the custom email/usenet client, ZIMACS to allow authenticated connections via other dial up access points provided by the likes of Freeserve et al, allowing me to connect via the NTL BB cable connection, neatly eliminating the cost of a dial up connection (zetnet had started offering ADSL packages by then to their customer base). I learned soon enough of the crapiness of ADSL compared to the real deal of a cabled broadband connection from all of the ADSL connection woes being endlesly reported in the zetnet groups for the next 5 or 6 years).
When my daughter left home, I took over the NTL account just at the time when they first offered broadband internet connectivity as a stand alone service sans what had been a mandatory pre-requisite of TV and broadband. Having discovered I was paying an extra 20 quid a month for an unnecessary TV and BB service, I ordered a cessation of the TV package and transfer to BB only (at the minimum speed of 128Kbps 15 quid a month service).
Unfortunately, their 'engineers' (two of them) turned up whilst I was in hospital as a result of an emergency admission and simply recovered the Pace STB without replacing it with the Ambit modem to effect the change-over to BB only. So through no fault of my own, when I finally got home after a fortnight or so's stay in hospital, I found myself without a connection and had to wait another month for NTL to schedule another visit to correct their cockup. However, I did receive compensation for not only the month or so I'd been without service but also another few months' worth for free. If I had been on hand at the time of the first 'engineers' visit, I would have stopped them taking the Pace box away until they'd returned with the required Ambit modem to complete the task as per my request.
Other than that major cockup of a simple change of service request, NTL (now Virgen Media) have provided a very reliable service that puts to shame the service typically experience by many relying on ADSL over their phone lines. Over the years, what had started out as the slowest basic broadband service (initially 128Kbps for 15 quid a month until they decided to bring it in line with the 600Kbps upgrade of their next higher level of 512Kbps service by increasing it to 150Kbps as a ruse to charge an inordinate 3 quid increase) has enjoyed "free upgrades" which have, so far, culminated in a speed boost to 80Mbps down, 5Mbps up. Mind you, inflation has just about doubled the monthly rental to £37.74. Still, I suppose a connection speed increase of 640 times for a mere doubling of cost is hardly a basis of complaint. :)
Mind you, I wasn't entirely new to the concept of Usenet since I'd been making use of the radioham BBS packet radio service since the mid 80s prior to gaining direct access to the internet. The transition to Usenet was a natural upgrade on the radioham BBS packet radio based setup. It's these web based forums that seem so alien and klunky by comparison. :(
Anyway, back to the topic. I took note of the D75J TCXO reference and googled it (I wasn't sure whether it was an actual part number or named after its proponent (like the classic G5RV antenna)). I see that it's merely a 1ppm part rather than the 0.1ppm ROJON TCXOs being offered by Chinese only sources (the cheapest option yet is a small PCB module containing a TCXO for approximately £15.59 now (yesterday, it had been approximately £15.42) available here: <https://www.ebay.co.uk/itm/1pcs-50MHZ-hifi-TCXO-0-1ppm-Ultra-precision-Golden-Oscillator-CLOCK-power-supply/132652757688?hash=item1ee2b872b8:g:zFoAAOSwlgNbGBqS:rk:5:pf:0> or https://tinyurl.com/y8he5bqa).
If it wasn't for the fact that I'd like to have a decent very low leakage high efficiency smpsu based PSU with a little more margin in hand, I'd have ordered it there and then. However, one step at a time - I don't want to find that by the time I'd received the TXCO, mid January 2019 (knowing my luck), my FY6600 had suffered a horrible infant mortality failure no longer insured by its warranty due to my modifications to date. An ultra low leakage three rail class II smpsu can always be found a use elsewhere, the 1 or 0.1 ppm 50MHz TCXO, otoh, is a rather more niche item to repurpose.
This leads me to the problem of tracking down an affordable 3 rail ultra low leakage class II smpsu PCB module. Try as I did last night - the reason I'm only replying just now - I couldn't find anything remotely suitable. Such low leakage class II smpsus are possible - I've actually got one in the form of a Nokia 5.7v 800mA "For LTE use only" phone charger 110 to 240vac wallwart which only shows as 12.5vac leakage voltage to ground with my DMM (presumably 10 or 11Mohm impedance) versus the more typical 75-79vac seen with the Feeltech and almost every other wallwart smpsu I have to hand. Better yet, its no load consumption is circa 50mW (barely perceptible when viewing the mirror backed 100 watt scale of my Metrawatt analogue wattmeter with a magnifying glass) which bodes well for its efficiency.
It looks like my best bet is to track down a low leakage class II 90 to 265vac 5v 3 or 4 amp smpsu and hang a couple of dc-dc 5v to 15v (one plus, the other minus) boost converter modules onto its output. Low leakage 3 rail PSUs seem to be about as rare as unicorn droppings. >:(
With regard to my soldering kit, I'll just carry on with my existing 18 and 24 watt Antex irons and copper wire adaptor bodges for now. I'll consider soldering tool upgrades when (and if ever) I get a decent workshop sorted out (we're considering moving from this large 6 bedroom, with basement, Victorian semi-detached house, to a decent sized 3 bed bungalow with an outhouse or two (or space to build a decent workshop)) so I'm in a bit of a Limbo situation right now.
Regarding the need to tie the Vref to ground or -Vs on the THS3095, I think the advice (emphasised so clearly in the THS3491 data sheet but overlooked in the THS3091/3095 data sheet) to NOT let the Vref float still applies. If you read the description on page 26 of the 3095's data sheet, you'll see the need to tie the Vref to ground or -Vs rail since this would otherwise float to the V+ rail, some 4 volts above its recommended voltage level. The /PD can be left floating since this also swings to the Vs+ rail. The /PD pin has to be 2v or more positive than the Vref pin in order to guarantee enabling of the amp. This condition is clearly impossible when both pins float to Vs+, hence (in the 3491 data sheet) the exhortation to NOT let the Vref float free.
The residual distortion shown in the DSO trace of the THS3095's output waveform at 20v P-P 20MHz may simply be a symptom of allowing the Vref pins to float. I chose to tie the Vref to Vs- rather than ground since it saved scraping through the solder resist to solder onto a groundplane and a handy VS- connection lay only three pins away from the pin 1 Vref on pin4 of the chip (also if I must rely on just letting the /PD pin float in a vulnerable hiZ state to the VS+ rail, the extra voltage margin wouldn't hurt).
If I were you, I'd be inclined to strap pins 1 and 4 on each of those 3095s and repeat the waveform tests at 20Mz 20v P-P both in HiZ and 50 ohm terminated conditions to compare against the earlier tests. You might not need to upgrade to the 3491s (unless you're planning on doing a mod that over-rides the crafty relay switching designed to mask the 3002's shortcomings).
For anyone who might be contemplating some of the modifications that have successfully been applied by members of this discussion thread, It seems to me that the best order to follow is firstly to modify the existing PSU to improve its efficiency on the +/- 12v rails by replacing the shoddy RF1007 diodes with proper 20 or 30 amp 40v PIVr rated dual shottky TO220 rectifiers and fit a 100K or 47K resistor across the lower arm of the 10K+10K divider network to raise the 5v line from 4.95 to 5.25 or 5.49 volts to take the 12v rails another half to one volt higher again.
It's a simple and effective mod but it doesn't address the HiZ half mains voltage leakage issue. The solution to that problem needs a better class of class II PSU, analogue if you must but preferably a good quality smpsu which uses an HF ferrite transformer with the required shielding foil layer between the high voltage primary and the low voltage secondary windings to obviate the need to bodge an EMC countermeasure in the form of that 1nF class Y cap.
Secondly, upgrade the existing dual opamp setup to a pair of single opamps using either THS 3091, 3095 or 3491 SOT8 chips, remembering to strap pins 1 and 4 together in the case of the 3095 and 3491 chips.
Thirdly, if you feel the need to match the existing 50MHz 100ppm frequency reference to the counter's display resolution, then install a 50MHz 0.1ppm TCXO (if you're going to bother at all, why only take half measures with a mere 1ppm rated TCXO when you can get hold of a 0.1ppm ROJON part from a Chinese supplier on Ebay for as little as 15 or 16 quid? :)).
Fourthly, if the issue of mains leakage still troubles you, replace the PSU board with a class II unit (analogue or smpsu) that only has a few pF's worth of half mains voltage leakage (mains transformer 50/60Hz leakage of analogue PSUs or ditto for the foil layer screen connection via a 10nF capacitor to the half mains voltage virtual ground in a high quality ferrite transformer used in properly designed smpsus free of the need to include that abomination of the classic 1nF EMC bodge capacitor).
The classic analogue mains PSU has the charm that such low leakage is inherent without having to specify it explicitly whereas the smpsu needs to have this requirement clearly spelled out in its specifications - good luck in finding such smpsus by design. :(
[EDIT 2021-11-25] Please disregard my rather pompous advice above :-[ and take note of the edit below. ::)
Regards, Johnny B Good
[EDIT 20190425] I eventually changed my mind about replacing the PS board with a medical grade low leakage smpsu just to avoid having to upgrade to a 3 pin socket and thicker, "Tail wagging dog" mains lead some two or three months later.
I eventually realised that even with such low leakage, there'd still be enough residual leakage voltage with a potential to destroy the more electrically fragile DUTs I might land up testing. In the end, the pragmatic solution also proved to be the most optimal. However, I used an 11KR resistor (three 33KR resistor in parallel) as a low impedance static drain which knocks the 90vac down to a mere 500mV without introducing earth loop effects which the 100nF capacitor option used by others would introduce at high frequencies.
All the PE connection was doing was to provide a convenient way to automatically connect an 11KR static drain between the zero volt reference and ground. The PS board is still a class II double insulated smpsu so a 'hard' protective ground connection is not needed (nor desired). Leakage voltage risk suppressed without the introduction of a troublesome grounding loop as per Feeltech's bodgery with the FY6800.
The details of this are in my later posts - I'm mentioning it here for anyone who may be plodding their way through this thread for the very first time. :-)
soundtec:
Hi Johny ,welcome.
Wow a three day read through , and then a re read .
I probably read each post at least twice by now , but in small chunks ,
I have both 66 and 68 hunderd , the 68 was a won in a competition held by Feeltech itself , there was several other people very worthy of a free machine for their contributions ,but if your not in you cant win .
Ive recently got myself a pair of Hewlett Packard HP200cd tube sine oscillators , in the 50's these were state of the art and in fact the product line lasted well into the mid 80's tubes and all , they did drop the tube rectifier in the later models though ,about .5 % thd was as good as they do normally , now with the Feeltech I can easily get very very low distortion audio frequency sine waves ,the key to this is to use an external attenuator and run the unit full throttle ,thus minimising any digital artifacts and using up the full bit rate of the unit . Theres no doubt the original power supply would be marginal with higher powered op amps and under volted too .Any offset dialed in at 20v pk-pk instantly clips the outputs , theres no margin .
I went linear ,with a transformer and regulators ,just like a conventional op amp audio set up .
I did fool around with a few other switchers as well , I tried to run the original psu with the 5 volt unloaded but the +/- rails dropped way low .
Deriving the three voltages from one switch psu I dont like , you'll find that under load the original psu droops under high voltage swing on the +/- rails , thats no good at all for fidelity. There have been a handfull hoping to make further improvements , including the custom software from Fremens, he ironed out some of the waveform compatibility issues for us in the Feeltech package , and of course allowed further tweaks if you used a programed STM32 microcontroller . I guess everyone's just settled into using their units now and are happy with the improvements they made , I would seriously think about a larger heatsink for the newer TI op amps though maybe even extra wings of aluminium extrusion screwed into the original .
Johnny B Good:
--- Quote from: soundtec on November 21, 2018, 10:32:06 pm ---Hi Johny ,welcome.
Wow a three day read through , and then a re read .
I probably read each post at least twice by now , but in small chunks ,
I have both 66 and 68 hunderd , the 68 was a won in a competition held by Feeltech itself , there was several other people very worthy of a free machine for their contributions ,but if your not in you cant win .
Ive recently got myself a pair of Hewlett Packard HP200cd tube sine oscillators , in the 50's these were state of the art and in fact the product line lasted well into the mid 80's tubes and all , they did drop the tube rectifier in the later models though ,about .5 % thd was as good as they do normally , now with the Feeltech I can easily get very very low distortion audio frequency sine waves ,the key to this is to use an external attenuator and run the unit full throttle ,thus minimising any digital artifacts and using up the full bit rate of the unit . Theres no doubt the original power supply would be marginal with higher powered op amps and under volted too .Any offset dialed in at 20v pk-pk instantly clips the outputs , theres no margin .
I went linear ,with a transformer and regulators ,just like a conventional op amp audio set up .
I did fool around with a few other switchers as well , I tried to run the original psu with the 5 volt unloaded but the +/- rails dropped way low .
Deriving the three voltages from one switch psu I dont like , you'll find that under load the original psu droops under high voltage swing on the +/- rails , thats no good at all for fidelity. There have been a handfull hoping to make further improvements , including the custom software from Fremens, he ironed out some of the waveform compatibility issues for us in the Feeltech package , and of course allowed further tweaks if you used a programed STM32 microcontroller . I guess everyone's just settled into using their units now and are happy with the improvements they made , I would seriously think about a larger heatsink for the newer TI op amps though maybe even extra wings of aluminium extrusion screwed into the original .
--- End quote ---
Thanks for persevering. :)
I had a lot of material to work with (69 pages!) and a lot of points I wanted to address. Sorry for unloading it all in two large lumps, so to speak. Hopefully, I can dial my post lengths back to more manageable portions now that I've got most of the comments and observations I've had bottled up over the past couple of weeks since I read through the whole thread off my chest.
Congratulations on winning the 6800 btw. I guess that makes you our "Go to Guy" for comparing these two Feeltech products. :) It's an interesting point you've made about the HP200CD only managing a half percent THD. Considering the revived interest in all things tubed (valved) by the HiFi fraternity, that must come as a bit of a disappointment for the more extreme proponents of tubed kit. TBH, it's a bit of surprise to me that valved test gear couldn't do much better.
Understand about the point of setting the output level to the 'sweet spot' and applying attenuation to get the required level (and minimise amplifier noise into the bargain as well). As you (and everyone else) have observed, the PSU in the FY6600 is barely up to the job even with the modifications suggested here (does the FY6800 suffer the same deficiency I wonder?). Reducing the loading on the +5v doesn't do the +/-12 volt rails any favours.
It's an old problem with multi-rail power supplies. The original PC and XT then the AT and now the ATX psus suffer exactly the same effect but in the case of desktop PC supplies, the variation on the 12 rails was never an issue, they just had to remain within the wider +/-10% tolerance that was allowed on those rails. In this case, it's the +/-12 rails that are the more critical rather than the 5v which seems to be used to power the 3.3v and 2.5v (and 1.5v?) regulators on the main board. Hopefully, the 3.3v regulator is a low dropout version (I haven't checked but it doesn't matter so much to me since I raised the 5v to 5.49 volts purely to increase the 12v rail voltages).
Putting my FY6600 into standby mode only saves just under 4W - it drops from a high of a gnat's dick shy of 10W to similarly just over the 6W mark. I'd say at least half the power supplied by its tiny PSU must be via the 12v rails when it's driving 50 ohm loads at the 20v p-p limit. Like yourself, I did observe quite bit of sag on the 12v rails between the zero and the maximum output levels. It could certainly do with a better quality PSU, preferably a higher efficiency smpsu to minimise the heat load. Small smpsus like the one used here by Feeltech, typically have an efficiency of 80% at full output so I figure the PSU is contributing a bad two watts to the heat loading inside that not very well vented case.
With only half a watt total being accounted for in the 50 ohm dummy loads, that leaves a balance of a further 7.5 watts of waste heat being generated by the front panel and main board. Going by the noticeably hotter feel of the underside of the case compared to the two 'Hot Spots' (fsvo 'Hot') on the topside, I'd guess a good (or bad if you prefer) 6 watts or so must be coming from the main board. I think drilling holes in the underside of the case below the main board would be the best place to make a start if you want to improve the ventilation.
From my experience of running a 24 hour heat soak test, drilling vent holes in the underside of the case will likely be enough to save the opamps from cooking themselves to death. Allowing some airflow round the underside of the main board will likely reduce the board and the heatsink temperatures by a noticeable amount. You might not need to add any extra metal to the existing heatsink.
BTW, from what further research I've managed to do into this question of mains leakage currents in class II smpsus, it seems the problem isn't an easy one to fix without increasing the level of common mode conducted switching noise on the output wiring. One treatise (see attached pdf) did note that the use of a screening foil layer between the primary and the secondary windings was the most cost effective way to deal with this 'conflict of interest' between mains leakage and EMC requirements.
The Y cap is simply a means to press the secondary into service as a shield against the high frequency switching transient voltage capacitively coupling into the output as a common mode conducted interference signal. Unfortunately, since the 'ground reference' is tied to a source of half mains voltage, the half to 2 nF class Y cap also provides a Hi Z leakage path for this voltage to manifest itself on the output terminals. Using a separate shielding foil between the primary and secondary windings as a dedicated screen where the capacitive coupling to the secondary windings is reduced to a mere 40 or 50 pF instead of the 500 to 2200 pF of a Y cap reduces the half mains voltage coupling considerably without compromising the EMC requirements.
As I see it now, I think my best approach may be to get hold of a low leakage class II 3 or 4 amp rated 5v smpsu and add a couple of DC-DC converters to generate the 14 or 15 volt rails. However, I'm still mulling over alternative solutions to this conflicting requirement of EMC and low mains voltage leakage.
Regards, Johnny B Good
DaveR:
Hi Johnny,
Have you seen these SMPSUs?
https://www.ebay.co.uk/itm/SMPSU-Switched-Mode-Chassis-Power-Supply-12v-0-3A-12v-0-2A-5v-2A-SMPS1-432-/141117111577?var=&hash=item667e84f884
https://www.ebay.co.uk/itm/SMPSU-Switched-Mode-Chassis-Power-Supply-5v-2A-15v-300mA-15v-200mA-Toko-783-/361575419603?hash=item542f930ed3
They look the part, if nothing else, but the seller is an anus - so caveat emptor!! See the negative feedback on him (which I can corroborate from personal experience.)
That TCXO module you found must be a new one, and it's cheaper than the oscillator by itself from other suppliers. There's also a Rojon mini TCXO for £22 if you want to be really extravagant:
https://www.ebay.co.uk/itm/Mini-TCXO-50-000MHz-50MHZ-0-1ppm-Ultra-precision-Oscillator-audio-DIY-GQ1-XH/382556866867?hash=item59122a8933:g:nIwAAOSwA3dYL7Cj:rk:3:pf:0
I can't see a problem with leaving pins 1 and 4 floating in the case of the 3095: both pins are unconnected on the PCB, so both will float to Vs+ and the device will be permanently enabled (no differential just means no power down control, but the default state is enabled, as would be expected). In the case of the 3491, although the datasheet doesn't recommend leaving PD floating, the device will still be permanently enabled if it is (subject to a probably unlikely stray signal event :)). I wasn't intending to upgrade the 3095s in my FY6600 to 3491s - I was planning to install them in my FY6800 (when I get round to it!) to get a direct comparison between them and the 3095s, more for curiosity and experimentation than anything else. If there happens to be a problem with them I've got spare 3095s I can drop back to as the upgrade from the single 3022.
Regards,
Dave
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