Appropriate signal generator on a budget

[Noidzoid]

I have been using an app based generator (Keuwlsoft) just so I could see my hm605 working and get  a very basic understanding of amplitude & timebase and what some of the controls are for.

I have seen some very nice "looking" old analogue generators for not much cash that look really well built. Also some really new plastic (almost toy like in appearance) digital ones.

Bearing in mind my goal is to learn to diagnose/repair cd players, tuners, amplifiers etc could I get away with buying an older beautiful looking and solid to the touch machine or will I be needing something newer?

What I would like to hear is that one of the following would be suitable:

Farnell LFM2
Farnell LFM3

Both of these seem to be attainable below £60 and look like real equipment rather than what look like toys that can be bought new at this price point.

I have read of other respected analogue generators from the likes of HP and BK but they don't seem as prevalent in the UK.  Farnell also still list both the machines as serviceable on their site which I found impressive considering their age.

I would love to own either of these generators, but not at the cost of them being redundant.

I also quite like the old style red digits on some of the older machines, but as already mentioned, they must be usable for the intended work.

All opinions, thoughts and advice gratefully received.

[james_s]

I have an ancient analog signal generator which has been more than adequate for diagnosing audio equipment, I rarely even use it for that though, normally I just play some music from a known good source. I can't think of any reason you'd need a fancy modern instrument for that.

[nctnico]

Buy the newest Feeltech FY6900. It will serve you much better than an old RC generator. For starters the amplitude and frequency stability are much better. Try to test a narrow notch filter for example. IMHO getting an old RC signal generator is a waste of money.

[ferdieCX]

Repairability is also a point to consider. Modern equipment tend to be built to lower quality standards than the older ones, and to be full of unobtanium components.
If you don't need extreme stability or fancy bells and whistles, an old RC generator could be a good option. 

[james_s]

The FY6900 does look like it offers a lot of bang for the buck. I'm not really a fan of buying Chinese gear but some of it is not bad. I guess like most things it depends on what you plan to do with it and what you can find. Occasionally good quality old gear turns up for peanuts, other times it fetches far more than arguably superior modern gear costs new. Either way we're talking <$100 so not really a major life decision. Heck if you have space and budget you could buy both, sometimes it's handy to have a second signal generator.

[Noidzoid]

Is there anything that an old analogue generator such as the Farnells above could be better at compared to a modern cheap offering? (Besides the possibility of repair)

[tautech]

Is there anything that an old analogue generator such as the Farnells above could be better at compared to a modern cheap offering? (Besides the possibility of repair)

Sometimes p-p output but you need check specs.
Boot times might be faster but otherwise a modern AWG can do so much more.

I still have my old 2 MHz Phillips FG and never use it now, dodgy/tired switches and noisey pots I can’t be bothered with these days.

[Berni]

For just tracking signals around analog cirucitry any signal generators works just fine.

What you get in new ones is AWG capability, superior frequency stability since they all PLL from a crystal oscillator and the ease of setting the output frequency and voltage by just punching it in using buttons and getting it spot on every time.

[nctnico]

Is there anything that an old analogue generator such as the Farnells above could be better at compared to a modern cheap offering? (Besides the possibility of repair)

No, there isn't. Not even after replacing all the potmeters and switches which likely have issues after such a long time.

[Noidzoid]

It seems that maybe the FY6900 is the recommended and sensible choice here at just a few more £ than a beautiful to look at thing from yesteryear.  I must admit to trying to justify buying one of the Farnells or something similar as I have a weak spot for old well made things.

On that note, could the Juntek JDS2800 be a contender compared to the FY6900, as they seem to be in the same price range and aimed at the same market?

[bd139]

Quick solution. Just bought one of these for £35 (seller accepted offer) as I am dumping my AWG in favour of an RF signal generator: https://rover.ebay.com/rover/0/0/0?mpre=https%3A%2F%2Fwww.ebay.co.uk%2Fulk%2Fitm%2F264486669617

Dirt cheap, reliable, not made of poo, fully discrete, repairable and safe (!). Service manual available. Made in UK.

Has 0-2Mhz, 20dB attenuator, stable enough for audio usage, TTL out, sweep in. Can kick out a reasonably good sine, square and triangle.

Most of the cheap (and expensive) ones these days can’t kick out much voltage. The TTi one does 20v pp full whack.

I’ve had three over the years and can vouch for quality.

As for Farnell stuff, it’s not always well designed. A lot of their stuff blows up if you look at it funny and the designs are marginal.

[nctnico]

Most of the cheap (and expensive) ones these days can’t kick out much voltage.

Not true. Most function generators (including the ones from Feeltech) can do 20Vpp (into a high impedance load). Only the built-in function generators in oscilloscopes have a limited amplitude.

[bd139]

It's frequency dependent on all of them although looking at the spec it'll do 24v p-p to 5MHz which is pretty good actually and a lot better than some of them for sure.

But here it's 3x the price of a TG210, completely no support or warranty and you can't repair half of what goes wrong with it without specialist gear. I wouldn't buy one myself. I've got a DG1022Z which is arguably a considerably better generator and it has some seriously shitty problems with it, particularly at low frequencies (try a very low frequency pulse on one and it generates a double step) and bugs galore. It is cracked to 60MHz though which is some compensation. I'd rather have the cash and an analogue function generator and a separate RF signal generator these days.

[nctnico]

What else do you expect from a Rigol... And I don't really get the fixation on being able to repair things. The modern generators have far less parts so much less can go wrong (and hence they are easier to fix). The most sensitive parts are typically the power supply and the output amplifiers. Both are not hard to repair and use standard components. Besides that Ebay and Aliexpress have a warranty period as well so if the unit turns out to be DOA then it can be exchanged.

[bd139]

People do stupid things with signal sources. I know I have. And they’re not that trivial to repair. For experienced engineers with the right tools yes but that’s not most people.

[nctnico]

People do stupid things with signal sources. I know I have. And they’re not that trivial to repair. For experienced engineers with the right tools yes but that’s not most people.

On a Feeltech generator you can replace the output amplifier with a standard soldering iron. You don't need any special gear for that.

[Mr. Scram]

On a Feeltech generator you can replace the output amplifier with a standard soldering iron. You don't need any special gear for that.

Too bad Feeltech won't supply the corrupt chip so many people are dealing with. Well they say they will from now on but seeing is believing. The Feeltech is not a good example of repairability.

[Berni]

Its not only signal generators built into scopes that give you pretty limited output voltage range.

For example my Tek AWG2041 dinosaur of a digital signal generator can only do +/- 2V into 50Ohm. That's pretty pathetic and makes it barely able to drive the input of 5V digital logic when open cirucit. But at least in return you get very speedy 1.5ns rise time on the output, 1GS/s, 1Mpts of sequenceable memory and a 7 digit resolution in its PLL clock source to ensure there is no digital interpolation used. I been meaning to make a little amplifier box for it to get its output swing to the usual +/- 15V.

The thing has been one of the most unreliable piece of gear i had. I had to re-seat some connectors because it would spit out errors and not give output. At one point the PFC circuit in its switching PSU it died and blew up the softstart circuit, no service manual for that huge complicated 3rd party PSU but i got it fixed since it was a simple fault. Then some time later the errors came back and re-seating connectors didn't help, leading me to the root cause of this issue that the OCXO reference oscillator is not giving any output. Being a weird obsolete no longer made OCXO module (With a weird frequency of 16.77721MHz for some reason) i opened it up and after soldering all the joints in there it came back to life. Hopefully it keeps working because i had enough of fixing the thing, but its the best signal generator i have.

[Fungus]

On a Feeltech generator you can replace the output amplifier with a standard soldering iron.

Is there enough space to fit a standard size soldering iron inside and still close the lid?

[Performa01]

On a Feeltech generator you can replace the output amplifier with a standard soldering iron.

Is there enough space to fit a standard size soldering iron inside and still close the lid?

Probably not, but the soldering iron yields much more output power. You always have to compromise somewhere…

[bd139]

Meant to post this earlier.

This is the inside of a TTi TG210 with the LCD frequency readout:



Versus Feeltech (typical sample from their line):



Note the lack of firmware and software in the former  (and proper grounding)

Some more feeltech including a noisy little switcher hot snotted in and dubious mains wiring...



You get what you pay for.

[nctnico]

Well... these pictures are from the first model from a few years ago. The newer FY6900 looks completely different on the inside and has a nice graphic screen showing the shape and parameters from the output waveform. So 'close but no sigar'. I don't get your obsession with the TG210. From a functional point of view it is worse in every aspect and I spot a whole bunch of potmeters which can be worn/gone bad on a used / aged unit.

[bd139]

Yeah that's fair enough but the point is you're buying to a price point and some of the short cuts to get there are not good.

If the FY6900 is like the FY6800, the mains side is still dodgy as fuck.

The TG210 obsession fulfills the poster's original requirements, is available locally, is cheap (less than half the price of the FY6900 here), repairable, has full service data available and arguably better than the Farnell units they were suggesting. Also they're safe, well engineered, reliable and have no surprises or edge cases and were not engineered to a price point. Also the pots on the things are like £2 a pop and I've never seen a worn one because they use half decent Alps / Omeg ones. Now Chinese encoders - let's not go there 

[nctnico]

If the FY6900 is like the FY6800, the mains side is still dodgy as fuck.

But it isn't...

[TERRA Operative]

What about an old HP boat anchor?

3325A units go for a good price here all the time for example.

[Noidzoid]

What about an old HP boat anchor?

3325A units go for a good price here all the time for example.

Nice, but not cheap here 

[Noidzoid]

This is the inside of a TTi TG210 with the LCD 

I see from pictures on the internet that the TG210 was available with and without the LCD display although I didn't notice any difference in the model name, am I missing something (quite likely)?
I assume having the screen version is an advantage but how much and why?

Also, is the TG315 similar in the way it is put together and repairable as the other TTI machines already mentioned in this thread?

[bd139]

They're all based on a similar design. It roughly goes:

TG2xx = 2MHz series
TG3xx = 3MHz series (this replaced the TG2xx)
TGxx5 = +display
TGx2x = +sweep
TGx3x = +modulation

Ergo TG315 is 3MHz + display

There is no service manual for the TG300 series AFAIK and the thing is likely surface mount as all devices they ship in that chassis seem to be now.

There's a tear down of a TF930 here which is same chassis and era to illustrate their design changes: https://www.eevblog.com/forum/testgear/test-equipment-anonymous-(tea)-group-therapy-thread/msg1373109/

TBH most of the TTi stuff never breaks though. I've never had a bad item other than some of their very early Thandar branded power supplies but they complete reengineered them since.

[Noidzoid]

Regarding the little screen vs no little screen. Is it a big disadvantage not having one?

[bd139]

The ones with screens allow you to set accurate frequency, amplitude and offset. That certainly is an advantage. Big vs small depends what’s on it. Big one shows two parameters at once.

[nctnico]

Regarding the little screen vs no little screen. Is it a big disadvantage not having one?

Yes. I have an RC based function generator like the TTI one and a Feeltech FY3200 generator. Actually I'm not sure whether I even have the RC based function generator or that I have thrown it away. The FY3200 generator OTOH is in the stack with equipment I use regulary. To me the FY6900 seems to be even more convenient to use because it has a graphical display.

[Noidzoid]

The ones with screens allow you to set accurate frequency, amplitude and offset. That certainly is an advantage. Big vs small depends what’s on it. Big one shows two parameters at once.

So, if using a generator with no screen/readout, does this mean that a separate frequency counter would have to be used to generate a frequency accurately?

[bd139]

Yes but the dial is good within 3-5% usually and that’s mostly good enough unless you’re doing RF or analogue synthesis or digital clocking. If I’m designing band pass filters for example when I measure the resulting circuit I will peak the output of the filter by sweeping it with the function generator control until the amplifier output peaks on my scope. Then it’s advantageous to have a counter connected to the sync port in the generator to work out the frequency.

To note though it’s generally better to have two separate instruments for this as the standalone counters are way more sensitive and have more useful features. I have separate HP 5316A and 5334B counters.

Edit: another vote against encoders here: they’re horrid for sweeping things (and the sweep function is awful for finding peaks etc being suited to plotting trends)

[Kleinstein]

The cheap RC type generators may need an external counter (could be the scope) to get an accurate frequency reading. It may still drift quite a bit even if there is a digital reading (and still set the frequency via pot). How accurate the analog scale is, depends, but often it's more like +-5 or 10%, with switches for the decade and a pot inside the decade.

There is still one point where an analog generator may be better than the cheap modern DDS type ones: this is the triangle waveform, especially if use in a kind of differentiating circuit. The DDS type triangle is usually just some stair steps - sometimes visible in the cheap (e.g. < $60) ones.
The user interface also depends on the use - sometimes adjustment with a pot is more suitable than digital adjustment.

There may be a few other point's that an old analog generator may offer and some cheap DDS one miss, like the option to use it as an VCO, do sweeps (wobble) , maybe more powerful output or parallel sine and square outputs.
Generally even the simple DDS Generators are not that bad and can do most things better. Especially the frequency is more stable and accurate.

[Berni]

Well with encoders its depends on how good the encoder implementation is. There is a huge amount of variability from barely usable to amazing.

A example of good encoder implementation are the low end Agilent/Keysight scopes. The excellent velocity control lets you slowly tweak it in fine steps or quickly flicking it across half its range. Some old boatnahcors also have pretty nice optical encoder knobs, but the encoders on a lot of the modern lower cost gear are indeed really bad.

But when working with filters and similar i like to use frequency sweeps from a signal generator. If you can trigger your scope on the sweep start and tune your scope settings so that the sweep fills the screen you essentially get a poor mans network analyzer. The scope screen now shows amplitude versus frequency and you can pan and zoom around it by tweaking the signal generator controls for the sweep start and sweep width. This is the one reason why i miss my old scopes having a built in signal gen as i really like using this trick on the MSOX3000 at work.

[bd139]

Yeah the ones in the Rigol units are total shit. I’ve got a high end Bourns optical encoder in my radio. That thing is pretty excellent. But they are £68 a go.

I use my DG1022Z and DS1054Z to do filter sweeps for a long time. But honestly I usually just want to know when it’s 3dB down and 20dB down etc and that’s easier to find by manual sweeping after you’ve referenced the thing to the insertion loss in the pass band.

[Kosmic]

Seriously I'm not sure why someone would recommend or buy Feeltech / Feelelec products. There's a thread on the forum full of peoples complaining about their units. It's not necessarily cheap and everything they have been making is super suspect.

https://www.eevblog.com/forum/buysellwanted/re-feelelec-new-arrival-fy-6900-signal-generator/

Also I'm not sure why but they have been banned from this forum …

[nctnico]

Seriously I'm not sure why someone would recommend or buy Feeltech / Feelelec products. There's a thread on the forum full of peoples complaining about their units. It's not necessarily cheap and everything they have been making is super suspect.

The reason is simple: the price is unbeatable where it comes to value for money. Just set the China bashing and boat-anchor blues aside (*).  Sure some Feeltech models have more problems than the others but AFAIK the older FY3200 and the FY6900 just work. The forum has plenty of detailed information so it is clear what to expect from each model. The FY3200 needs a grounded inlet and a wire to connect 0V to ground and the FY6900 could do with a thicker ground wire but the wire used is not outright unsafe. However some people make minor problems much larger than they are and turn these generators into projects of their own. That is their right but don't go around saying it is a bad buy. I'd take a Feeltech any time over an old RC function generator or an old HP unit with their own set of problems and a loud fan (been there, done that). If you want to go a step up then you'd need to look at Siglent's SDG2000 series for example but then you end up in US $500 territory.

* Some people just seem to be hung up on build quality from the old days but forget that old equipment does get affected by time and safety and built standards have not always been what they are today. I also fall into that trap every once in a while. I've had various bits of HP gear through my hands in which I could pull the mains wires straight from the solder joints on the circuit boards. Talking about an accident waiting to happen... Or look at the original shoddy mains wiring of the Dynaload DC load I bought nearly 2 years ago: https://www.eevblog.com/forum/testgear/dynaload-dlf-100-100-1500-(100v-100a-1500w-dc-load)-teardown-repair/msg1381740/#msg1381740

The bottom line is: there are some great pieces of cheap Chinese gear out there which offer excellent value for money. Don't dismiss those off-the-bat with less than solid arguments. I have a few and they serve me well.