Author Topic: Re: FeelElec New Arrival FY-6900 Signal Generator  (Read 19967 times)

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Offline yo3fhm

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Re: FeelElec New Arrival FY-6900 Signal Generator
« Reply #200 on: January 02, 2020, 11:54:41 am »
OK, while nobody posted any reply to my answer, I found the following information on a review from the FeelElec Store on AliExpress .
It is from a customer from USA (as the flag say there). Hope to be useful for other people :

Quote
The last 2 days I have been testing the functions of my FY6900 generator with a 12 bits oscilloscope. The instrument has lots of controls, and built-in functions, so serious testing took some time. I am very happy with the results. The specifications are fulfilled within the given limits. The generator came with software to control it through an USB connection. The computer control works fine. The software also allows you to draw your own waves, and to store them as arbitrary wave which works also well; another plus for the FY6900. The manual was a good help, not to long, but clear; that is the next plus. I am most satisfied with this instrument, its software and documentation, and its very reasonable price. Thank you FEELELEC for your balanced equipment, and documentation. I expect it to be highly useful for the next years in my workshop. 28 Sep 2019 14:17

Also, I mention that I contacted FeelElec and the response from their sales (on the E-mail) also included the serial communication protocol (Host Computer Communication Protocol Specification Rev 1.8 ), which contains the commands *and* all the necessary examples for programming !
I think this is a big plus for those who want to automate various measurements.
 

Offline wz5q

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Re: FeelElec New Arrival FY-6900 Signal Generator
« Reply #201 on: January 09, 2020, 02:00:59 pm »
I have a FY6900-60M (Serial Number 191169001053) Firmware rev 1.3.

It is working just fine and I am impressed with the device.
It works amazingly well for the cost.

The only bad thing I have found is an aggravating anomaly with the "SWEEP" function.

The following is an example:

The unit is set for running a Sine Wave, Linear Frequency Sweep from 1Hz to 100KHz at a time period of 500.00 seconds and the direction set to Forth. When the Sweep is engaged, it starts at 1Hz and starts to increase in frequency normally until it reaches 100KHz. This is normal function.

This is the anomaly:
If you stop the Sweep and then restart it, it does not start at the set beginning frequency.

For example, the Sweep is running from 1Hz to 100KHZ and you stop the sweep at 10KHz. If you start the sweep again it starts at 10KHz and continues to 100KHz. The sweep does not start again at 1Hz, it remembers where it stopped and starts at that point to continue. There is no option I can find to make it start again at 1Hz where the unit is set to begin, it will always remember where it stopped and starts at that point.

This anomaly also occurs when the direction is set for Forth, Back, and Forth to Back.

I sent Feeltech an email at service@feelelec.com explaining this, we shall see what they say.
Hopefully they can fix this in a future firmware upgrade.
 

Offline AlMuz

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Re: FeelElec New Arrival FY-6900 Signal Generator
« Reply #202 on: January 09, 2020, 09:39:47 pm »
Hi Everyone,

I've finally got my device and have a few questions to a group of experienced users.
 
But first few words about my experience trying to get it from China:
I was trying to get this device since September 2019. 
  • First ordered it from Banggood, the order never shipped, was in processing for like a month. So I've canceled it and asked for refund.
  • Decided to "upgrade" my pick to 3-channel FY8300S and re-order, from Banggood... Again,... almost the same story - in processing for 3 weeks, than marked as shipped but no tracking number provided. Waited for 6 weeks to arrive - then asked a question to Banggood. They have discovered that the package actually never made it to a postal office in China. Glad got my money back... again (not sure it was the same amount because of currency fluctuations).
  • For the thrid time decided to try my lack with AliExpress, they seem better than Banggood becuase the disclouse the seller/store name, so if you failed with one - you will try another.Got my device in 9!!! day after placing the order.
To be added - I am not trying to say that AliExpress better than Banggood. It is just hit or miss with these Chinese re-sellers. Had similar issues at AliExpress ordering T12 soldering iron from KSGER (however going to another seller helped).


So, back to device:

I am not an expert, but would recommend to everyone do tear-down immediately to check everything.
Say in my scenario I had a ground wire barely holding to solder joint on power connector. It fell of when I finished removing plastic panels.
Totally sure it would fell off by itself just from ambient vibrations in the room, with a risk of shorting device ground to power line.

I've got a Kkmoon 60Mhz version. Which looks have got slightly updated main board from what posted here previously (silckscreen says v.1.9 instead of v.1.8)
Major difference I see (from what I could figure out just by looking on videos and pictures posted by others) is that the newer board got a FAN connector under the power-lines plug.
Which is in fact complete nonsense -  it is simply a  JST connector footprint that is directly hooked to 5V power rail. You will not get any speed control. But 5V probably might be enough to spin 12V 40mm FAN at a lower RPM still getting away some heat without producing too much noise.

Also - the ground wire in my version goes directly to the main board, instead of power supply broad. This is probably better, avoiding the resistance of few additional wire-plug contact points on the way to BNC connectors. The wire still just cut-off from original 6 pin connector. Anyway, as a simplest safety improvement I would replace thin ground wire from JST plug with a proper thick and insulated ground wire that goes directly from GND TH-pad of the FAN plug (or any other massive GND pad at the bottom ground plane of the board).

Anyway, I did not go for FAN installation to this JST pad or ground wire fix just because I plan full replacement of power supply. I've noticed some spikes in output signal likely from swithing supply, so plan to rework it into decent full-linear regulator.

Just ordered nice fitting (D=3" x H=1") toroid transformer.  There are plenty of these available on eBay or AliExpress for $35 shipped. Designed for audio amplifiers some of them posses output windings of multiple voltage levels (+/-9 and +/-15).

In my case I've got a very good deal ($23) for 20VA toroid with just two 13V AC positive and negative windings.  Should be just right to power 12V (or actually 13.5V) DC rails. For that I plan to use widely available AC-DC supply module based on LM317, LM337 and LF353 (not sure what the last OpAmp serves, looking to schematic - likely for better output stabilization).

5V supply for digital circuitry will drop on positive winding (should have common ground with analog op-amp supply rails anyway).
And to somewhat even the load between positive and negative windings - will drop a separate full bridge rectifier with BUCK converter to power-up a temperature-regulated FAN speed controller. Total of all the parts I've already ordered (with some additional components) is under $60.

The question:
I've also noticed that main board has two new empty SMD pads for inductors, they were not there before in FY6800 version (to the right of power rails JST connector). Likely for additional filtering of +/- 12V rails. There is a narrow trace connecting two square pads on each inductor footprint (shorting them togather). Did anyone cut those and installed some chokes? What were the choke parameters (inductance and series resistance)? Did you notice any improvement in signal output (with original power supply or upgraded one)?
« Last Edit: January 09, 2020, 10:04:50 pm by AlMuz »
 

Offline excitedbox

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Re: FeelElec New Arrival FY-6900 Signal Generator
« Reply #203 on: January 13, 2020, 12:29:22 am »
I also had problems getting mine. I ordered on Ebay but it disappeard in Customs. The seller sent it again and same thing happened. Then I ordered from AliExpress from a seller that claimed to ship from Spain but really shipped from China and repackaged in Spain. This caused a long delay and the seller didn´t answer any emails until the last day of my dispute on AliExpress. It seems the repacking company doesn´t update the tracking number so the tracking shows it as delivered even though it only got to their warehouse in spain. After that it still took another 3 weeks until it arrived. I was pretty angry because the shipping guarantee was for less than 2 weeks total and it took over a month and a half. Plus no communication was just unacceptable. In addition to claiming to ship from inside of the EU. I would not have ordered there if I had known that. I even paid 12 Euros extra for shipping which I would have saved buying directly from China.


In the end it all worked though and I ordered an Amplifier board for ~26 Euros so I can output up to 32V 5A waveforms.
 

Offline rhb

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Re: FeelElec New Arrival FY-6900 Signal Generator
« Reply #204 on: January 14, 2020, 03:38:17 am »

In the end it all worked though and I ordered an Amplifier board for ~26 Euros so I can output up to 32V 5A waveforms.

32 V into a 50 ohm load is 0.64 A.  5 A through 50 ohms requires 250 V.

I think there is something wrong with this picture.

Reg
 

Offline nctnico

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Re: FeelElec New Arrival FY-6900 Signal Generator
« Reply #205 on: January 14, 2020, 08:22:29 am »
Those amplifier boards don't have 50 Ohm outputs; usually the output impedance is close to 0 Ohm.
There are small lies, big lies and then there is what is on the screen of your oscilloscope.
 

Offline teecelly2020

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Re: FeelElec New Arrival FY-6900 Signal Generator
« Reply #206 on: January 14, 2020, 02:15:30 pm »
Replaced the power supply in the FY6900 with this handy module from Jameco.  Meanwell PT-65B +5v, +12v, -12v switching supply.  https://www.jameco.com/Jameco/Products/ProdDS/216726.pdf

Fits perfectly.  has isolated ground, and lower noise than original unit.  Lowers noise floor and THD dramatically...especially below 4 volts.  (I use it for audio testing)  Also, higher current capability means it doesnt sag under load.
 

Offline rhb

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Re: FeelElec New Arrival FY-6900 Signal Generator
« Reply #207 on: January 14, 2020, 03:43:20 pm »
Those amplifier boards don't have 50 Ohm outputs; usually the output impedance is close to 0 Ohm.

6.4 ohms based on the numbers given.  Actually not a bad compromise if one wants to drive 4 & 8 ohm speakers for testing.  But really bad if one is trying to drive an RF power amplifier.  I just wanted to emphasize that you need to also state the load impedance not just voltage and current.

Have fun!
Reg
 

Offline einfachprima

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Re: FeelElec New Arrival FY-6900 Signal Generator
« Reply #208 on: January 14, 2020, 06:05:36 pm »
I received my FY6900-60 last week (KKmoon, firmware 1.3). Based on the infos in this thread and on the website of Janusz (thanks a lot!) I was able to do the following modifications:
  • I replaced the rotary knob with a more finger friendly knob
  • I added four small rubber feet to avoid moving the unit on my table
  • I calibrated the frequency so it fits to the frequency counter of my oscilloscope
  • I replaced the tiny cable to mains ground with a solid one
  • I installed software 6.3, updated to 6.5 and installed firmware 1.4
The software is useless for me, there is also a major bug, if you enter a frequency the unit gets the wrong frequency (e.g. entering 60 MHz results in 6 MHz).

There is one thing I don't understand: Some of you replace the power supply with a better one. And  this is a lot of work. What's wrong with the Feeltech power supply? How can I measure the problems of this power supply?
 

Offline Johnny B Good

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Re: FeelElec New Arrival FY-6900 Signal Generator
« Reply #209 on: January 15, 2020, 12:51:21 am »
I received my FY6900-60 last week (KKmoon, firmware 1.3). Based on the infos in this thread and on the website of Janusz (thanks a lot!) I was able to do the following modifications:
  • I replaced the rotary knob with a more finger friendly knob
  • I added four small rubber feet to avoid moving the unit on my table
  • I calibrated the frequency so it fits to the frequency counter of my oscilloscope
  • I replaced the tiny cable to mains ground with a solid one
  • I installed software 6.3, updated to 6.5 and installed firmware 1.4
The software is useless for me, there is also a major bug, if you enter a frequency the unit gets the wrong frequency (e.g. entering 60 MHz results in 6 MHz).

There is one thing I don't understand: Some of you replace the power supply with a better one. And  this is a lot of work. What's wrong with the Feeltech power supply? How can I measure the problems of this power supply?

 As far as I'm aware, the FY6900's smpsu board is a slightly modified version of those used in the previous two models (6600 and 6800) and its main failing in this context is that of all cheap smpsus, high levels of conducted and directly radiated switching noise from the mains voltage HT switching module, not forgetting the related switching ripple noise riding on top of each voltage bus (+5, +12 and -12 volt rails - or, in this case the +5, +13.5 and -13.5 volt rails).

 The only good things about the psu board used in these signal/function generators are that they are class II psus which don't require a safety earth connection (and therefore neatly avoids the ground loop issues introduced by FeelTech's abuse of the LVDC 6 wire ribbon cable in the 6800 and 6900 models) and the design of this smpsu whereby the secondary 12 or 13.5 volt rails are inherently symmetric in output current rating to create a perfectly balanced bi-polar opamp supply which is something I've yet to see in any similarly rated 3 rail smpsu.

 Searching for a better quality smpsu to replace the existing unit with one that also offers identical current output ratings on the +/-12 or 15 volt rails has, so far, been on a par with searching for Unicorn droppings or Hens' teeth. Every single contender had this curious imbalance between the +/-12 or 15 volt rails, typically a 1A positive rail versus 330 to 500mA on the negative rail (a 3:1 to, at best, a 2:1 current rating ratio).

 Considering that the blindingly obvious, no-brainer use of +/-12 and 15 volt psus is to power opamps requiring balanced bi-polar supply rails, this lack of balanced output smpsus is quite contrary to all expectations where one might consider the 2:1 and 3:1 current rated psus to be speciality 'curios' manufactured for obscure off the wall applications rather than the almost ubiquitous pests of the smpsu world they appear to be. IOW, just WTF is going on!

 The only downside to the FY6600's floating ground rail was the troublesome half mains live 'touch voltage' courtesy of the EMC mandated use of the class Y capacitor bodge which creates an ESD hazard to the DUT. Many owners of the FY6600 replaced the C8 mains socket with a C14 in order to provide a ground connection to shunt this half live mains touch voltage directly to ground to suppress this ESD hazard. Some recognised the earth loop issues in using a hard connection so used a 100nF cap in series which eliminated any unwanted DC offsets from the mains earth wiring but did nothing for high frequency noise both being picked up by and sent out from the signal generator.

 In the end, after several weeks of looking for a solution that would allow me to retain the original C8 mains connection (an exercise in futility as I eventually proved), it turned out that the optimal solution was to upgrade the C8 to either a C6 or a C14 socket and simply use the protective earth terminal as a connection for a "static drain" resistor of sufficiently low value to reduce the 115vac 'touch voltage' down to just half a volt. In this case, a sufficiently low value of 'static drain' resistance turned out to be 10KR. Low enough to eliminate the ESD hazard but high enough to provide some 60 to 80 db attenuation to interference between the signal generator and the mains earth wiring.

 Some FY6600 owners tried upgrading the psu to a better quality smpsu and others chose to design and build an analogue psu based on a conventional mains transformer using 7805, 7812 and 7912 voltage regulators.

 Unless you can track down an ultra quiet smpsu designed for use in sensitive test gear, a seemingly better quality smpsu probably won't provide much, if any, improvement over the original in terms of noise reduction, Hence the decision by many to go the "analogue psu" route with a DIY design of their own.

 Many of these were successful but others fell foul of the additional heat produced by the voltage regulator ICs which, despite the manufacturers' claims for overheat protection, burnt themselves out anyway, taking out an opamp in at least one such case.

 I've been considering a psu upgrade for some time now and I've reached the conclusion that the best cost effective solution would be to use an R type mains transformer (24 to 30VA with two separate 16 to 18 v secondaries) and use dc-dc buck converters with ldo voltage regulators to get the best of both worlds (switching and analogue).

 However, before I even start such an upgrade, I have yet to test the potential improvement using battery power (a 12v SLA for the +12v and +5v rails (7805) with a couple of 6v lantern batteries to provide the -12v rail) to completely eliminate the smpsu switching noise which currently pollutes the generator's output. Once I've seen the effect of eliminating such switching noise for myself, I'm sure I'll have all the motivation I'll need to design and build my own replacement psu. At the moment though, my 'Basic GPSDO' project has priority and such battery testing remains on the back burner for the time being.

 As for "measuring the problems of the psu", the best way to quantify the 'problem' is to substitute it with 'battery power" as I described above and check the generator's output using an HF radio to tune into and around the carrier frequencies chosen for this test. You can, of course, use a spectrum analyser if you are so blessed but an HF radio can be just as effective a way to discern any improvement.

 Trying to quantify noise and ripple of any power supply using an oscilloscope is fraught with many problems as explained in the following YT video https://youtu.be/Edel3eduRj4 (I just put "measuring psu noise and ripple" into YT's search box and this, unsurprisingly, was the first hit).

JBG
« Last Edit: January 15, 2020, 01:07:34 pm by Johnny B Good »
 

Offline einfachprima

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Re: FeelElec New Arrival FY-6900 Signal Generator
« Reply #210 on: January 15, 2020, 09:40:09 pm »
Thanks for your detailed answer!

I had mixed up some information for 6600/6800/6900 in the past. Let me summarize what I now understand. Basically there are two independent problems:

Ground connection / ground loop / ESD hazard

FY6600 has a C8 mains connector without PE. That's ok because it's a class II power supply. And it has an advantage: no ground loops etc. Disadvantage: A voltage between PE and BNC ground can be measured (ESD hazard).
Possible solutions:
  • Replace C8 with C14, connect PE to BNC/PCB ground
  • To avoid ground loop a 100nF capacitor can be used (in serial)
  • To avoid ground loop a 10k drain resistor can be used (in serial)
FY6900 has a C14 mains connector, PE is connected to PCB ground (with an inappropriate wire ...).
If I want to separate PE and BNC ground I have three possibilities (similar to FY6600):
  • Remove wire between PE and PCB ground
  • Add a 100nF capacitor (in serial)
  • Add a 10k drain resistor (in serial)
Do you suggest to use option 3 (drain resistor)? Or is it better to use an isolation transformer?

Signal noise introduced by smps ripple/noise

It's a good idea to do a short test with a battery powered FY6900. If the signal is significantly better a new power supply (linear regulator, ...) is an option (this probably solves the ground problem as well). Currently I doubt that justifies the effort. At least for me and my oscilloscope. The ripple/noise of the function generator output is currently no problem for me (between 5 mVpp and 20 mVpp with a visible 60 kHz signal).


 

Offline Johnny B Good

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Re: FeelElec New Arrival FY-6900 Signal Generator
« Reply #211 on: January 16, 2020, 05:33:17 am »
Thanks for your detailed answer!

I had mixed up some information for 6600/6800/6900 in the past. Let me summarize what I now understand. Basically there are two independent problems:

Ground connection / ground loop / ESD hazard

FY6600 has a C8 mains connector without PE. That's ok because it's a class II power supply. And it has an advantage: no ground loops etc. Disadvantage: A voltage between PE and BNC ground can be measured (ESD hazard).
Possible solutions:
  • Replace C8 with C14, connect PE to BNC/PCB ground
  • To avoid ground loop a 100nF capacitor can be used (in serial)
  • To avoid ground loop a 10k drain resistor can be used (in serial)
FY6900 has a C14 mains connector, PE is connected to PCB ground (with an inappropriate wire ...).
If I want to separate PE and BNC ground I have three possibilities (similar to FY6600):
  • Remove wire between PE and PCB ground
  • Add a 100nF capacitor (in serial)
  • Add a 10k drain resistor (in serial)
Do you suggest to use option 3 (drain resistor)? Or is it better to use an isolation transformer?

Signal noise introduced by smps ripple/noise

It's a good idea to do a short test with a battery powered FY6900. If the signal is significantly better a new power supply (linear regulator, ...) is an option (this probably solves the ground problem as well). Currently I doubt that justifies the effort. At least for me and my oscilloscope. The ripple/noise of the function generator output is currently no problem for me (between 5 mVpp and 20 mVpp with a visible 60 kHz signal).

 I'm not surprised you were mixing up the information between those three topic threads. The FY6600 one has been going for some two and a half years and is now 86 pages long with a total of 2149 replies as of the 2nd of this month!

 If that 5 to 20 mV ripple with a visible 60KHz signal you mentioned is a reference to the 60KHz switching noise, you might see some reduction if you try it with a 10KR in series with the earth connection.

 My own concern over the noise and ripple stems from my experience when generating a 30MHz carrier using a Kenwood TS140S HF transceiver to monitor it where there did seem to be some ripple and noise modulation on what should in theory have been a perfectly quiet carrier wave. Other than that, such ripple noise hasn't proved to be a major problem so far but then I am still working on modifications to enhance its frequency accuracy and stability so haven't been using it very much other than for testing those modifications and researching the workings of a DIY GPSDO I've been working on for almost a year along with discoveries of the GPS system's own deficiencies (nanosecond phase shift modulation due to ionospheric propagation conditions being the major problem for a basic pll driven GPSDO such as the one I'm trying to rebuild into a screened metal enclosure onto veroboard).

 The FY6600 has been a project in its own right for just over a year now and was what had spawned the basic GPSDO project I'm trying to box up as a workable frequency reference. These two 'projects' feed off each other so I'm dividing my time between the two. What doesn't help is my reliance on Banggood and Ebay to supply the components needed for these and other ancillary projects which have created additional delays to these long drawn out projects. I might eventually get around to fitting the four long screws that secure the FY6600's case halves together and have my GPSDO up and running in maybe as little as 6 months time with a bit of luck.

 When I was looking at the half mains live touch voltage issue with my own FY6600, I was a little reluctant to convert from the C8 connector and the very flexible 2 wire 6A mains cord to a C14 connector with its much stiffer 3 wire 10A rated mains cord in order to avoid the "Tail Wags Dog" effect with such a lightweight piece of test gear (only 700 grammes with no grippy rubber feet to stop it sliding all around the bench, especially true when propped up on its bail stand which left the rear hard rubber faced feet dangling in mid air as the rear edge grounded onto the bench top).

 I tried all sorts of inventive schemes to eliminate the touch voltage including mostly ways to cleverly null it out, overlooking the fact that you had to at least detect which way round the neutral and live wires of the non-polarised cord were plugged into the C8 socket so as to connect your nulling out circuit's reference to the neutral.

 Several doomed experiments with 1:1 mains transformers to create my anti-phase mains voltage source finally convinced me that, whilst in principle such a scheme could be made to work given a clever enough polarity detection system to control an automatic mains reversing switch, my "clever cure" was far more trouble than it was worth and still contained a risk of doubling the touch voltage if it went faulty for any reason.

 Since I've already suffered way too much at the hands of the Lord Murphy (of "Murphy's Law" fame), I decided that discretion in this case was most definitely the better part of valour and gave up the whole idea of nulling out the problem and looked to the more prosaic solution of using a polarised 3 pin mains socket to provide a convenient earthing point for attaching a 10KR drain resistor to kill off the touch voltage without introducing a low impedance earthing loop into the circuit.

 By way of a compromise in regard of the "Tail Wags Dog" effect, I chose a C6 (trefoil - clover leaf) mains inlet socket instead of the big butch C14 sockets other FY6600 owners (and Feeltech in the case of their 6800 and 6900 models) had elected to use. I'd noticed that a few of my C6 mains cables had been made up using thinner lightweight mains flex than typically used with C14 cords which would mitigate the "Tail Wags Dog" effect (as indeed this proved to be case).

 It might be argued by some that by not directly connecting the protective earth to the zero volt rail (BNC grounding point), I have compromised the generator's electrical safety. However, since it uses a class II smpsu board which does not require the use of a safety earth anyway, I don't see this as an issue of safety in this (plastic) case. The mains socket upgrade is merely to provide a reliable earthing point to automatically shunt the Y cap's half mains leakage touch voltage safely to ground via a 10KR resistor.

 It seems that Feeltech had been reading the FY6600 topic thread and taken note of the stream of complaints over this half mains live voltage issue and in a half assed ill thought out bout of unthinking pragmatic knee jerk response, decided to "upgrade" to a C14 mains socket, vandalising the 6 wire psu to mainboard ribbon cable to divert one of the only two ground return wires directly to the protective earth tag. Not only had they introduced an unwanted low impedance earth loop issue, they'd also aggravated the psu noise and ripple by stealing one of the ground return wires linking the psu to the mainboard into the bargain.

 Judging by the fact that the ill fated FY6900 was also given the very same (identical in fact) treatment, it looks as though Feeltech must have given up monitoring the FY6600 thread once they'd sprung their "Improved FY6800" upon an unsuspecting world otherwise they'd have used a more elegant solution for the FY6900.

 Basically, when it comes to fixing the earthing sins of the FY6800 and 6900 models, the optimum solution of using a 10KR (or even a 3k3R if you prefer) to link the ground rail to the protective earth as described for the FY6600 remains the same since these later models still use a cheap and cheerful class II smpsu board inside of their plastic cases which don't require a low resistance earth connection to meet electrical safety requirements.

 However, for those of a nervous disposition over the use of unearthed test equipment, there are ways to provide a low impedance path for fault currents to flow to the protective earth which under normal, non-fault conditions, can still provide a high resistance drain path for the unwanted half mains touch voltage. Basically it amounts to shunting the 10KR (or 3k3R) drain resistor with a couple of high current silicon diodes in series in anti-parallel with a second such pair (four diodes in total). In this case, you can get away with just a single pair of anti-parallel high current rated silicon diodes by using a 3k3R resistor (the ground loop noise margin will only drop 10dB in this case).

 This is a method I'd used some forty years ago to eliminate mains earth loop induced hum on a turntable with built in RIAA amplifier which blessed it with line out level signals that already gave it considerable immunity to such mains earth loop induced hum. In this case, since it was essentially only the 50Hz and the first few harmonics I was concerned with, I recall putting a 100nF cap across the two back to back diodes to guard against the possibility of high frequency harmonics should the diodes start to conduct and generate any distortion products (I can't remember whether or not I'd included a 1 or 10 k resistor across the diodes). I think the diodes I'd used had an Irr rating of 6A.

 In this case, I wouldn't add any capacitance across the diodes, just a 10 or 3.3 k resistor. If you're only guarding against the risk of a mains fault internal to the generator itself, I should think 6A rated diodes would suffice. If you're more concerned over an attached DUT injecting mains voltage, you'll probably want to fit 20 to 50 amp rated diodes (in which case you're likely to see the mains flex burst into flames with that level of fault current). For such current ratings, it's probably best to parallel up several 6 or 10 amp rated diodes to improve the chances that at least one will fail short circuit in the event of any such catastrophic fault current events.

 That, of course is a very simple solution and I'm sure there are better alternatives based on a pair of heavy duty thyristors (or triacs for some redundancy) where you can trigger them from a higher volt drop such as 10 to 30 volts to avoid any false triggering. Of course, triacs and thyristors have minimum sustaining current specs which will need to be considered in such a paranoid protection scheme. The one thing I wouldn't rely solely upon in such protection is any form of electromechanical relay to switch the high resistance drain circuit into its low resistance safety earthing state.

 TBH, after proof reading this, it does seem a rather over the top solution to a problem that may never ever arise but If I'd seen the need forty odd years ago to provide a safety earth connection that would avoid the hum loop issue, there may well be purpose designed devices available for just such protection by now but it hasn't occurred to me to go searching for any. A quick internet search failed to reveal any such ground loop isolating devices. My perception of the quality of human ingenuity has just gone down yet another notch or two. :(

  After having another go at tracking down a diode based 'hum eliminator' I came across this Youtube video https://youtu.be/qNQX8jyxRrs where the guy mentioned a 70 dollar hum eliminator, the "Ebtech Hum X Ground Loop Hum Exterminator" which he'd suspected was also based on the two anti-parallel diodes device he was building. I had already come across this item which I'd also had the same sneaking suspicion that it was quite likely based on the same principle (possibly utilising triacs rather than diodes).

 The youtuber mentioned that he'd seen the circuit he was building in other internet sources but failed to mention where. It would have been nice to track down other mentions of a circuit I'd invented for my own use over forty years ago. It seems I'm not the only person on the planet to have come up with the blindingly obvious solution to safely overcome the issue of hum loops in domestic audio systems where the short runs of screened interconnects are able to short out the modest voltage drops involved to keep the diodes in the high impedance state as in the case of the Feeltech signal generator's connections to the DUT and any other test gear located on the test bench.

 Two final observations I have in regard of that youtube video and the "Ebtech Hum X Ground Loop Hum Exterminator", is that I think the safety concerns that were expressed in the comments are entirely valid. The only safe place for such a circuit is inside the device rather than as an external add on adapter. Also, the need for 500v PIV rated diodes is a spurious one where the anti-parallel connection of the two diode (strings) means they'll never have to face more than one or two diode forward volt drops worth of reverse bias anyway.

 If one of the diode strings fails open circuit under a fault event, the 500v PIV rating won't help the situation and it would be far better to give a 50v PIV diode every opportunity to fail short circuit in such a circumstance. Indeed the lower the PIV rating, the better the chance of it failing short circuit rather than being blown to smithereens like a glass fuse by a high energy 300+ volts avalanche breakdown transient.

 If a semiconductor manufacturer could be persuaded to integrate this diode or triac based ground loop hum eliminator into a dedicated device, it could be optimised to reliably fail safe and meet electrical safety standards so I'm a little disappointed that there seems to be no such device commercially available. Presumably there isn't sufficient demand to justify the required investment.

JBG

 
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Offline einfachprima

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Re: FeelElec New Arrival FY-6900 Signal Generator
« Reply #212 on: January 16, 2020, 11:42:30 pm »
Today I compared the noise of the FY6900 (DC 1.0 V & DC 1.1 V because the amplifier changes above 1 V) with the different PE options (disconnected, connected, 100nF, 10KR). I found no or only minor differences, so this has no real influence.

I will keep the 10KR (or the cap) to suppress the half mains leaking voltage between BNC GND and PE and to avoid ground loops. I'm fine with that solution.
Further (paranoid) protection with several diodes or triacs is an interesting thought experiment, but I don't think I need it.

 

Offline Johnny B Good

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Re: FeelElec New Arrival FY-6900 Signal Generator
« Reply #213 on: January 17, 2020, 07:08:51 pm »
Today I compared the noise of the FY6900 (DC 1.0 V & DC 1.1 V because the amplifier changes above 1 V) with the different PE options (disconnected, connected, 100nF, 10KR). I found no or only minor differences, so this has no real influence.

I will keep the 10KR (or the cap) to suppress the half mains leaking voltage between BNC GND and PE and to avoid ground loops. I'm fine with that solution.
Further (paranoid) protection with several diodes or triacs is an interesting thought experiment, but I don't think I need it.

 Your results with the varied earthing arrangements suggest that the common mode choke in the mains input filter on the psu board is doing a pretty effective job in attenuating switching transient noise leaking into the mains supply.

 Like yourself, I don't think there's any real need in this case (class II appliance) for the anti-parallel diode measure I'd offered for the benefit of anyone worried that inserting a 10k or 3k3 ohm resistor in series with the grounding wire would compromise the electrical safety of the signal generator in any way.

 The Thorens record deck however, being a class I appliance, was earthed for electrical safety so I wanted to avoid the risk of lifting the earth connection to rely solely upon the phono interconnect leads to the grounded inputs of the attached amplifier as was common practice in the audiophile community, hence my thinking laterally about the problem and the anti-parallel diode solution I'd concocted to fix both safety and ground loop issues at a single stroke.

 In this case, should the BNC grounds go fully live for any reason, I suspect the worst that would happen would be the operator receiving a "nasty jolt" through a fingertip rather than suffer electrocution (assuming said operator fails to notice a stronger than usual mains voltage tingle and take the hint that further careful investigation with a test meter should  be instigated to pinpoint and remedy such a potentially fatal fault condition).

 The risk of electrocution in this case seems such a vanishingly small one that I personally feel comfortable enough to live with (and I'll stake my life on that! :)).

 However, in the light of the above statements, it has just occurred to me that a better way to detect whenever a dangerous mains potential from whatever source is present on the BNC ground circuit of the signal generator (aside from the emission of magic smoke from a half watt 10k resistor) is to wire up a pair of blue leds (chosen for best luminous efficiency and brightness) in anti-parallel (for redundancy) in series with a 150k half watt or higher rated resistor across the 10k resistor (effectively a modern solid state version of the classic neon mains indicator lamp).

 This can be added to the front panel as a "Dangerous Earth Potential!" warning lamp to remove reliance on the operator managing to safely notice the resulting mains tingle touch voltage by pure dumb good luck alone. This offers the benefit of not only indicating a live to earth fault in the signal generator itself but also that of similar faults within any other connected test kit.

 Of course, one would need some means to verify that this warning lamp is in good working order. At the very least, it would need to be tested after its initial installation and at regular intervals thereafter (perhaps monthly or annually). In the case of 220/240v mains voltage, assuming a half watt rated 10k "drain" resistor has been installed, a 2W rated 27k resistor probe connected to mains live could be used to probe the BNC grounds whilst the generator is isolated from any other grounded kit ( in 120v regions, an 8k2 ohm 1W resistor could be used for this test). This should result in some 60 to 70 volts rms across the drain resistor, sufficient to light up the warning LEDs without risk of it burning out.

 Even better would be to incorporate this test resistor into the circuit with a test button that could be located out of the way on the rear panel. In this case, one might elect to use a 27k resistor regardless of the mains voltage standard. This will result in a 0.3mA lamp current on a 120v supply which is still more than sufficient to light up a blue LED quite nicely.

 Adding a  "Dangerous Earth Potential" warning lamp to the signal generator makes a lot more sense as a safety measure than my original anti-parallel diode idea which introduced the risk of overloading its mains flex earth conductor with fault current (quite possibly a hundred amps or more) from any other connected equipment that happens to suffer a live to earth contact fault. It's a feature that certainly merits further consideration but for now, I'll park that idea on the back burner until I've completed my current and more pressing list of planned upgrades.

JBG

« Last Edit: January 17, 2020, 07:14:33 pm by Johnny B Good »
 

Offline BeeJee

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Re: FeelElec New Arrival FY-6900 Signal Generator
« Reply #214 on: January 19, 2020, 12:11:14 am »
did you see the high quality solution by SDG Electronics on Youtube for the better psu in his FY6900 ? his video's # 029, 077, 080 & 081
 are very elaborate & usefull about that..
 

Offline rhb

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Re: FeelElec New Arrival FY-6900 Signal Generator
« Reply #215 on: January 19, 2020, 02:31:31 am »
Johhny,

Your are, as always, a bit over the top in detail.  But a huge pleasure to read.  Someone once remarked about me that if you asked me the time, I'd tell you how to build a watch.  You go a step farther and explain how to build the machines to make the watch parts. :-)

Have Fun!
Reg
 
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Offline stcoso

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Re: FeelElec New Arrival FY-6900 Signal Generator
« Reply #216 on: January 19, 2020, 02:40:34 pm »
Hi, I've got this func gen and I'm looking for a way to control it from PC without using the software from feeltech. Is the communication protocol known?
 

Offline nctnico

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Re: FeelElec New Arrival FY-6900 Signal Generator
« Reply #217 on: January 19, 2020, 06:39:33 pm »
did you see the high quality solution by SDG Electronics on Youtube for the better psu in his FY6900 ? his video's # 029, 077, 080 & 081
 are very elaborate & usefull about that..
I've seen those too but I have doubts about the clearances (a 3.5mm screw terminal doesn't have the clearance for 230V mains) and the design seems to be over complicated without getting to really low supply voltage noise levels.
There are small lies, big lies and then there is what is on the screen of your oscilloscope.
 

Offline Johnny B Good

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Re: FeelElec New Arrival FY-6900 Signal Generator
« Reply #218 on: January 20, 2020, 10:28:32 pm »
did you see the high quality solution by SDG Electronics on Youtube for the better psu in his FY6900 ? his video's # 029, 077, 080 & 081
 are very elaborate & usefull about that..

 I found #077 and just 6 1/2 minutes in I see he's elected to choose a 1.5A -13.5v dc-dc converter which is 3 times the actual half amp requirement worst case loading with a -12vDC on both channels feeding 50 ohm loads  :wtf:

[EDIT] see the edit below - it's more like a factor of 6!

 I haven't watched the rest of the video just yet but I thought I'd post a quick response to his initial miscalculated requirements for the +/- 13.5 volt rails before viewing the rest to see how he's going to keep HF switching noise from leaking onto the output rails of the LDOs he was considering - I've done some more research into this subject since my last posting and am fully aware of the pitfalls in just slapping LDOs onto the output of buck/boost converters to get noise free DC rail voltages.

[EDIT]

 I finished watching that video and managed to track down the rest (I think!) from his home page which actually took ages to show up. I noticed he'd taken additional measures to keep the switching noise out of the LDO regulators and made provision to deal with the effect of the Y cap in his 24v mains smpsu module. I have to say I disagree with the use of a 10 ohm resistor to suppress the half live mains touch voltage issue since even a 10K ohm resistor is a low enough shunt impedance to hold this leakage voltage down to a mere half volt (at least in the case of the original smpsu board - it might need the use of a 4k7R for this higher power replacement) more than low enough to keep even the most delicate of ancient mosfets safe from harm.

 As for the 8mV of noise on the outputs of the generator being residual random noise in the opamps themselves, I'm not entirely convinced that that is the case, especially as he'd set the output to zero with no dc offset. That final test didn't seem thorough enough to my mind - ok as an initial check to confirm his psu wasn't radiating/conducting switching noise into the main board circuitry perhaps.

 A more thorough test would involve selecting the DC "waveform" set to 10 or 12v into 50 ohm loads on both channels. This the worst case psu loading of circa half an amp when both channels are generating +12 or -12 volt dc outputs simultaneously into short circuits - actually, it's a mere quarter of an amp when driving 50 ohm loads - even I was out on my initial psu amperage estimate! :palm: A CMOS waveform at 99% duty cycle would come a close second worst case as far as the positive 13.5 rail is concerned.

 I'm wondering if he actually did any similar noise checks with the original smpsu board in place before embarking on this psu upgrade. It's quite possible that most of the improvement might have arisen simply from the use of a well shielded mains voltage to 24VDC smpsu module replacing the original RFI radiating smpsu board.

 Putting the original psu board into a metal enclosure of similar volume to his replacement PSU assembly might possibly have proved just as effective a solution. We'd be looking at a large and airy enough full metal jacket to keep things cool and shielded whilst also providing containment of any possible fire hazard posed by the original board - it's just a thought.  ;)

JBG
« Last Edit: January 21, 2020, 02:13:03 am by Johnny B Good »
 
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Offline nctnico

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Re: FeelElec New Arrival FY-6900 Signal Generator
« Reply #219 on: January 21, 2020, 02:14:49 pm »
Try to set the PSU on fire. I'm quite sure it won't burn at all. It is a typical standard consumer PSU which has likely been sold to power millions of pieces of household electronics.
There are small lies, big lies and then there is what is on the screen of your oscilloscope.
 
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Online beanflying

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Re: FeelElec New Arrival FY-6900 Signal Generator
« Reply #220 on: January 21, 2020, 11:45:28 pm »
Other than the floating Neutral/Earth issues the power supply is no more or less horrid than the average to poor cheap ones sold in a bunch of items. Going to massive efforts to replace it with a relatively costly solution in this cheap box makes little to no sense. By the time you weigh up the cost of bits and even a bit for the time spent you are pushing toward some of the 'better' other Chinese made alternates.

That is not to say don't complain about it but it should be made clear AGAIN to the manufacturer that it is sub par and poorly engineered from the factory and unacceptable.
Coffee, Food, R/C and electronics nerd in no particular order :)
 
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