FeelTech FY6600 60MHz 2-Ch VCO Function Arbitrary Waveform Signal Generator

[GregDunn]

On the 6600 the encoder has a push switch button ,this allows you to change the display to  uHz Hz Mhz etc , its the OK button on the 6800 does that ,I wasnt sure from your post if you had figured out how to toggle Mhz/hz in the display or not .
And yes do keep posting your thoughts or possible improvements here .

  Wow, do I feel like a numpty now.  You're absolutely right; I assumed that feature was missing because the encoder doesn't have a push switch (the manual is a hasty conversion from the FY6600 manual, and some things are confusing).  But "OK" cycles through the units very nicely with the decimal point shifting to accommodate and you can quickly enter the desired range/value.  Not necessarily the procedure I would have coded but easy to work with nonetheless!  Once I get accustomed to it there should be no problem.  Hopefully the manual will be updated eventually to make that and a few other small details clearer.

I'd like to see a platform-agnostic interface to upload arbitrary waveforms rather than a PC-only program; that's probably do-able and would allow you to use pretty much any tool to create the data list.  All my computers are Macs, but fortunately I can get by with the predefined waveforms so I'm not bothered by this for now.  FeelTech have provided a pretty thoughtful list of arbs already.

[soundtec]

Hz,khz etc was one of the  functions I needed to refer to the manual about when I first got the 6600 so nothing to be ashamed about .

Im still only managing 11.6 volts on the +/- with the switcher ,I see the rectifier diodes on the outputs are common In 400x ,could I get a few hundreds of milivolts by using low forward drop diodes here ? or are there easier ways to increase output voltage of switchers ?
Id like to seperate both 5 and +/- onto two different supplies , but the only way I can get the opamp  rails stable and with enough voltage is by using a large resistor to burn off current on the 5 volt line , in the case of a single unit ,could adding more load to the 5 volt line bring up the rail voltage ?

[svetlov]

 Hello Dear Friends    which operational amplifiers are installed at the output of the generator? they are different in the models 6600 and 6800?
Thank you 

[soundtec]

Hi Svet,
Here's a link to an old post ,theres lots on the output stage to be found if you try search in this topic.
https://www.eevblog.com/forum/testgear/feeltech-fy6600-60mhz-2-ch-vco-function-arbitrary-waveform-signal-generator/1150/

I havent lifted the heatsink on my 6800 yet ,there does at least seem to be a change in output op amp package style in the 6800 ,as you will see from my post ,in the original 6600 there was a mismatch in height between the two op amps under the heatsink ,so the heatsink wasnt very effective and was on crookedly .  A couple of layers of heat sink rubber pad fixes this in the 6600.

There is a brand new op amp (THS 3491)suitable for use in the 66/6800 ,only issue was compatibillity with the package/pinout ,I did read that even though its had a different package to the 3002/3095 it was still compatible .The THS 3491 can draw upto 350ma at full output ,so if you decide to try it you will need a bigger psu and output stage heatsink to get any benefits . The other possibility is to populate all three pads in the output section ,two single channel op amps and one dual ,this is easily do-able ,but output padding resistors would need to be re-arranged also.

[soundtec]

In the above zip you'll find some stuff on the 66/6800 in one place ,instead of having to scan the entire post .Fremens V .5,.6,.7,schematics ,and driver ch340.

Thurlby Thandar Wavemanager 4.10 is nice package thats compatible with Fremens software ,the functionality of the program isnt hampered by not having a TTI device connected ,and theres no nag screens . Requires NI Visa runtime installed . The waveform creation allows a much better range of math functionality,including adding subtracting and multiplying waveforms together .As you create each wave type a selection of parameters becomes available ,the 'heartbeat' wave having around 10 parameters to adjust . Ive created a few interesting paterns with stairstep  mixed with other waves . It will be interesting to hear how these waveforms end up sounding in the audio range . I really want to explore the possibilites of using my 66/6800 for sound and music creation in a modular type setup .

[DaveR]

I had a spot of trouble with my FY6600 over the weekend, when C82 blew and took the -12.5v rail down to -1.25v.  It happened while I left it running as I went into the garden for ten minutes, and I got back inside to find the scope display scrambled, and the mains transformer and LM337 regulator very hot instead of their usual slightly warm.  I can't see any reason for C82 going bad other than it  being just a faulty capacitor (which turned into a 63 ohm resistor), but fortunately it doesn't seem to have caused any damage to anything else, as all is fine again with a new cap in place.  Maybe it would have been a different story if I was still using the original power supply?

Whilst using Der_Kammi's schematic to trace the fault (C82 is one of the 100nF bypass caps to the IC5A/B op amp, half-under the heatsink on the main board), I noted that the schematic shows IC5 as a JRC 4558DD, whereas my v1.501 board has a JRC 4556A there.  From the datasheets it looks like the 4556 is something of an upgrade over the 4558.

Soundtec - thanks for the Wavemanager 4.1 tip: I've downloaded it, but haven't tried it out yet.

Regards,
Dave

[bugi]

... I can't see any reason for C82 going bad other than it  being just a faulty capacitor (which turned into a 63 ohm resistor), ...

... (C82 is one of the 100nF bypass caps to the IC5A/B op amp, half-under the heatsink on the main board), ...

Would that C82 happen to be an ordinary cheap ceramic SMD? Under a supposedly hot spot? Perhaps uneven thermal expansions, ceramic or its ends breaking, leading to a broken cap? (Certainly the cap could have been bad to start with, or partially damaged from e.g. soldering process, add some extra stress later...)

[DaveR]

Yes, the very same ultra cheap SMD, but it wasn't actually under the hot spot - which isn't that hot anyway - so thermal stresses would have been minimal.  Under the magnifier you can see that a groove has been burned across one face, and one end is brown and pitted (which is what caught my eye initially).  Just bad to start with, or a bad soldered joint, probably.  I'm waiting to see if its twin, C81, blows as well, as I've now got 49 spares to replace it with

[danco]

Hi guys, I,ve been reading this thread all from the start, in the meantime my fy-6600 has arrived, v.3.3. First thing, even before testing it thoroughly, I was swapping the 3002 with 2 pcs. 3091 I bought from aliexpress. All seemed fine until recently I got time to play a bit with it and found that over 5V level a relay made a "click" and the signal at the outputs vanishes. In fact, channel 1 outputs a -11.7V DC, channel 2 outputs 0 V. Consulting the schematic I see that the final stage is switched in by a relay (most likely over 5 V output amplitude) so I think both my aliexpress chips are dead. Switched back to the original 3002 and everything back to normal (in certain limits). Can anyone confirm all this is plausible or I could have made something wrong myself? The chips look genuine, came in original tape cut, but were only $2.79/piece. Any thoughts?

[bdivi]

The THS output is switched for signals over 5V so your assumptions is correct. Most probably the aliexpress parts are a dud.

I decided to go for the TI's original THS3491 which cost me $10 a peace direct order - $20 total with free shipping.
The have been working perfectly so far.

[danco]

Where did you buy in BG with free shipping, my suplyer of choice (TME) doesn't seem to stock it?

[soundtec]

Heres a comparison between the chips I have in my 6600 and the ths 3491, shows very much improved linearity and bandwidth ,I might order the 3491's for my 6800 ,upto 420ma of current x2 ,did you replace the power supply too Bdivi? looks like these new chips could signifgantly reduce harmonics by up to 10 db,the specs quote harmonics for the 3491@50mhz and the 3091@10mhz so if they were measured on a like for like basis you would expect very much improved performance from the 3491 .Which component package is the most appropriate for the upgrade?

Have you done any comparisons before and after the op amp upgrade Bdivi ,to confirm the much reduced distortion of the waveform ?

[DaveR]

Hi soundtec - I think you forgot to post the comparison you mentioned.

By coincidence, I've just received a 6800 which I ordered a week ago, just before C82 blew on the 6600.  It's got a KKMoon logo on the front instead of FE, but it's still a Feeltech instrument - just 20% cheaper!  I was just about to use the £20 saving to buy a D75J oscillator for it, and replace the THS3002 with 3095s as in the FY6600, but then I thought I may as well try the 3491s instead to see what happens.  They'll be a big improvement over the 3002, I know, but now I'll be able to do a comparison against the 3095s as well, where the difference might not be so visible.

The under-load voltages from the SMPS are 4.958, +11.792 and -11.953, so pretty good except for the +ve rail being a bit low.  I'll see how it gets on before I consider any mods to the PS this time.

The D75J is an essential though - I did a frequency stabilty test starting them both from cold, and the FY6800 took over 50 minutes to settle down, compared with just 10 minutes (probably less) for the FY6600.  The total deviation was 41ppm for the FY6800 and just 1.5ppm for the FY6600, so it was a no-contest.

Amusingly, the FY6800 came with a non-UK mains lead and an adapter plug - which has a plastic earth pin!!  I suppose the seller would claim he just sells them, and doesn't have to know anything about them?!

Dave

[soundtec]

http://www.ti.com/product/ths3491#

Thats the link to the comparison chart with the 3095 , I forgot to post it
Thats a night and day difference with the DJ75J too ,I might get a pair of them in .
I swapped out the diodes in the switcher I use on my 6800 ,with low forward drop diodes on the outputs of the rails +/- ,I instantly got a much better voltage balance across the rails ,the difference now is only a few tens of millivolts ,and I also gained a couple of hundred millivolts bringing my rails to 11.9 volts , might be a simple worthwhile mod for others too .,
In the case of the ths 3491 I fairly sure the heatsink will need attention ,even with the 3095 with both channels flat out into 50 ohms ,quite a bit of heat is generated ,with 3491 its almost double the current and the heat.

It is a bit funny that the cost of the upgrades ,2x3491 and DJ75J arent too far off the cost of the unit itself maybe the 15mhz model at least ,still very much worth the effort for me though . My guess is the upgraded 66 or 68 measures up well against even machines at multiples of price ,you'd probably need to get a sig gen with variable clocking to get much better performance and they usually cost 1000$'s.

[Mr. Scram]

Is this thread about the FY6800 now too? Maybe it's a good idea to change the title to represent this.

[bitseeker]

Unfortunately, the thread was started by someone not actually interested in being a forum member.

[Mr. Scram]

Unfortunately, the thread was started by someone not actually interested in being a forum member.

Nothing a moderator can't fix.

[bitseeker]

It'd be ideal to re-assign the ownership of the OP to one of the members actively working on the 6600/6800.

A less-elegant alternative would be to start a new thread and cross-link them.

[DaveR]

It was decided a while ago to keep the same thread going as the FY6600 and FY6800 are essentially the same item, and anything discussed about one applies to the other.  A new thread for the FY6800 alone would potentially result in masses of accumulated information being missed by new searchers who aren't aware of the history of the two devices.  Likewise, questions posted in an FY6800 thread would get missed by knowledgeable FY6600 owners who could otherwise provide help and answers.

If this was a car forum, would you have one thread discussing the engine performance of a blue version of a certain car, and another thread discussing the same thing about the red coloured version of the same car?

[Mr. Scram]

It was decided a while ago to keep the same thread going as the FY6600 and FY6800 are essentially the same item, and anything discussed about one applies to the other.  A new thread for the FY6800 alone would potentially result in masses of accumulated information being missed by new searchers who aren't aware of the history of the two devices.  Likewise, questions posted in an FY6800 thread would get missed by knowledgeable FY6600 owners who could otherwise provide help and answers.

If this was a car forum, would you have one thread discussing the engine performance of a blue version of a certain car, and another thread discussing the same thing about the red coloured version of the same car?

We can decide all we want, but the thread isn't going to be found by people interested in the FY6800 very quickly if they weren't already familiar with the thread. I've asked a moderator to rename the thread.

[GregDunn]

I've been using my FY6800 pretty much as the generic test signal source for my troubleshooting and repair efforts; it's nice to be able to check gear with swept frequency and amplitude as well as single frequency input. 

I use mine almost exclusively for audio.  Running it into my HP331A I see that the distortion in the range under 100KHz is moderate - about 0.25% or so.  Honestly I'm not interested in extending the bandwidth or output level of my generator per se; but has anyone seen or tested a mod which will reduce the distortion at audio frequencies into normal 10K-100KΩ loads?  That's about the only thing which would be handy for the work I do. 

[JS]

I've been using my FY6800 pretty much as the generic test signal source for my troubleshooting and repair efforts; it's nice to be able to check gear with swept frequency and amplitude as well as single frequency input. 

I use mine almost exclusively for audio.  Running it into my HP331A I see that the distortion in the range under 100KHz is moderate - about 0.25% or so.  Honestly I'm not interested in extending the bandwidth or output level of my generator per se; but has anyone seen or tested a mod which will reduce the distortion at audio frequencies into normal 10K-100KΩ loads?  That's about the only thing which would be handy for the work I do.

How low do you want? I guess your only option is filtering, if you are interested in a particular frequency a fixed filter would do. Otherwise, you are likely better to use a sound card or a dedicated sinewave generator but sweeping is hard-ish for an easy DIY project. The best option could be a tracking filter, which you could do. There is an article of a THD analyzer by Robert Cordell from '81 with a residual THD down to 0.0003% for a certain condition where you could find a few useful blocks. I don't attach it here as it weights about 5MB and I don't have a link but google will help you I guess.

JS

[GregDunn]

I don't really want to kludge a filter or other device on the generator that isn't transparent to its basic operation.  If I want low distortion at a single frequency, I guarantee my Heathkit will outperform most anything that isn't a professional series oscillator (somewhere around 0.01% over its operating range).  I was just curious whether someone had investigated a mod which would improve the audio band distortion of the FY6x00 series.  If no one has, that's OK; I just didn't want to overlook an easy mod.

[bitseeker]

It was decided a while ago to keep the same thread going as the FY6600 and FY6800 are essentially the same item, and anything discussed about one applies to the other.  A new thread for the FY6800 alone would potentially result in masses of accumulated information being missed by new searchers who aren't aware of the history of the two devices.  Likewise, questions posted in an FY6800 thread would get missed by knowledgeable FY6600 owners who could otherwise provide help and answers.

Certainly, a new thread for the 6800 alone wouldn't make sense and that isn't being suggested here.

A common way to handle it is to have an active member create a new thread (correctly labeled for both models, unlike this one), link from this one to the new one (and vice versa so that people know where older info is located), and continue in the new thread (locking this one as archival).

Another option is if one of the primary contributors to this thread messages gnif or Dave to rename the thread so that it's more accurate. It's the most elegant solution.

[soundtec]

Its a good plan to include the Fy6800 in the title somehow ,but now when I search FY6600 this post and this forum come up top everytime . I guess we dont want to loose top billing in browser search for our thread ,so how would we make sure our search priority wasnt affected by a thread namechange ,maybe leaving the main name of the thread unchanged and adding (including FY6800 model) in brackets ,really we need to find out the implications it might have before changing the name .

Im wondering is the limits in terms of distortion in the FY 66/6800 due to the dac/filter and the bits , in which case Im not sure if theres much benefit in distortion terms from changing out the op amps , surely though if you wanted the highest quality signal from the unit ,say for audio testing which often will require smaller signal voltages ,you'd be better off using the sig gen to make a large amplitude signal ,then using a passive attenuator network to attenuate that to a level suitable for your purpose , in otherwords does producing a smaller output voltage in the FY limit the bit rate of the output signal ?. Could a specially made switched attenuator, optimised for 50 ohms, used after the generator  allow an improvement in distortion ? I know that in the case of using a sound card for audio testing a couple of the smarter people in another forum I visit made up a special attenuator allowing attenuation in Db ,the signal generator is then run at 0db Fs digital for minimum digital artifacts. If at higher levels in the 66/6800distortion of the output stage is the limiting factor then power supply and op amp upgrades are worthwhile. For most audio testing the small distortion in the output signal of this unit is of no consequence ,it only comes into play really if its distortion  your trying to measure . I guess a computer and high quality dac /attenuator is a better option for producing signals in the audio range with very low distortion in any case .