Reasonable function generator - Page 1
Forum section: electronics / testgear

author: p2potter
author_rank: Contributor
timestamp: December 14, 2017, 04:04:57 am
content: Hi all,Newbie here who is getting back into a hobby that was cultured by my father 40 years ago. I haven't had the time or money until recently and since I emigrated to the US from the UK, most of my old equipment is unlikely to be functional here. I want to teach my son the basics of audio amplification, design and use of tube and SS preamps and amps, as well as some basic digital info (most of this is foreign to me as I have not kept up - hence a learning experience for both of us).I hope to get a Rigol 1054z as the bedrock for my lab, but would like a decent function generator. Used is fine and there are many choices on eBay. However, a couple of questions:1. There are a bunch of BK models that look ok, 4011, 4012, 4017, etc. I am not familiar with this brand so are these OK choices (really only need up to 1Mhz). Are there better options that would be in a reasonable price range, say up to $125?2. Do I need to worry about significant drift in signal on older models?3. I looked at the selection on Amazon and was very underwhelmed. I realize that this is not a great website to look over test equipment, but at least the reviews tend to be pretty honest. Are there any new, reasonable quality generators in my price range that you think would meet my criteria?Thanks in advance.

author: jgalak
author_rank: Regular Contributor
timestamp: December 14, 2017, 04:26:15 am
content: I'm looking for the same thing, so following along.I have an older Elenco FG500 kit, which will go to 1MHz, but I hooked it up to my new Rigol 1054z and was very unhappy with the quality of the waveform. May try to dig I to to see what the issue is - I seem to recall it working better ~10 years ago (though I looked at it then on a much worse scope).

author: ez24
author_rank: Super Contributor
timestamp: December 14, 2017, 04:58:53 am
content: Wavetek are respected. They were built in San Diego and are very good quality. I like the "retro" look on some of them. I think the 145 is a good starting point. Also a 135https://www.ebay.com/itm/Wavetek-Model-135-Lin-Log-Sweep-Generator-2Mhz-Used-Tests-OK/322924104829?hash=item4b2fc6cc7d:g:nV4AAOSwoVNZ78Bq

author: HalFET
author_rank: Frequent Contributor
timestamp: December 14, 2017, 06:39:10 am
content: You can significantly improve the output of the lower end signal generators by adding external filters. That being said, the noise and non-linearity of the signal generator should be too high in frequency to get past your amplifier's input filter.

author: Paul Moir
author_rank: Frequent Contributor
timestamp: December 14, 2017, 07:37:11 am
content: There should be at least a tonne of HP 3312a function generators on Ebay. They're just an analog 13 MHz generator with AM, FM and triangle modulation, but tough as nails and a pleasure to use. I use mine all the time.If you're going digital I think the cheap and cheerful candidate is Siglent, but that'll come in for more than twice what you're after I think.

author: jgalak
author_rank: Regular Contributor
timestamp: December 14, 2017, 01:14:35 pm
content: How's the HP 8111A? Seem some good prices on eBay for it. ~$150 for a 20 MHz unit...

author: Mr. Scram
author_rank: Super Contributor
timestamp: December 14, 2017, 01:25:18 pm
content: BK Precision is a fairly respectable brand. US based, as far as I know. I do understand that some of their cheaper offerings are rebranded units, but even Tektronix and Keithley do that now.

author: bd139
author_rank: Super Contributor
timestamp: December 14, 2017, 02:24:04 pm
content: Don't buy anything cheap and new in the function generator space. So many turds.I'd hit one of the following:HP 3312A. Rolls Royce. Sweep, modulation, built like a tank.Krohne Hite 1400 or 1600. sweep, nicely built, easy to use.heathkit IG-1275. Huge, but decent bit of kit.Thandar TG210. dead simple, reliable, easy to maintain. No modulation or sweep. I really like these. Not sure if available in 110v.All of the above have standard parts and decent service manuals so your investment isn't likely to result in something going in the bin.Stay away from any early HP synthesized or digital units. They are pretty much impossible to fix if they break and entry is horrible.You really want one with sweep to start with if you're on a learning curve. Visualising filter responses etc is an incredibly powerful learning tool.As for drift, they all drift slightly as they are RC oscillators. In practical use, this is not of much concern. My old TG210 drifted less than anything else and could sit at a spot frequency and not budge by more than 1Hz/minute.

author: wn1fju
author_rank: Frequent Contributor
timestamp: December 14, 2017, 03:29:33 pm
content: While the previous poster recommended staying away from early HP synthesized/digital units, the analog function generators, like the HP 3312A, canalso have their share of problems with dirty/broken switches and pots. And both analog and digital units can also easily suffer from power supplyproblems (which is the cause of most repairs anyway).I really like the HP 3314A function generator which goes to 20 MHz, does the usual sine/triangle/square stuff and also has a rudimentary arbitrarywaveform generation capability. Yes, there are a couple of HP hybrid ICs, and if they go, you definitely have problems. But the rest of it is easilyfixable.It should be easy to find an HP 3314A on eBay in the $150 range for a working one and <$100 for a non-working one if you want to take a chance.

author: sprintcarfan
author_rank: Contributor
timestamp: December 14, 2017, 05:07:57 pm
content: +1 for the HP3312A since you're in the US and they're common on ebay. Mine was $86 shipped and it works beautifully. It was advertised as working and the auction showed a couple pictures of the output displayed on an oscilloscope, but most auctions don't do this. With that said, I don't think there is much to fail on these old units?

author: GreyWoolfe
author_rank: Unknown
timestamp: December 14, 2017, 05:55:05 pm
content: Another vote for the HP 3312A. I scored mine for $35 from my local surplus store. It needed a fuse and has a couple of broken button caps but ii is still quite usable. I scored that one right out from another members nose as he also frequents the same toy store.

author: p2potter
author_rank: Contributor
timestamp: December 14, 2017, 06:26:43 pm
content: All,Many thanks for the very helpful responses. I'm currently scouring the web and eBay for the 'perfect' instrument. Seriously, I know that the minute I buy one, the next link I find will have a better model at a cheaper price, but as long as it is functional, I'll be happy.Thanks again.

author: nctnico
author_rank: Super Contributor
timestamp: December 14, 2017, 07:16:24 pm
content: I'd forget about the old crap (with loud fans) and get a new Feeltech function generator if you are strapped for cash. They are cheap and have 2 channels.

author: jgalak
author_rank: Regular Contributor
timestamp: December 14, 2017, 07:32:16 pm
content: Welp, just pulled the trigger on a 3312A based on this thread.Now I just need to find a good RF-range signal generator to go with it.

author: bd139
author_rank: Super Contributor
timestamp: December 14, 2017, 07:51:08 pm
content: When you get the HP 3312A, open it up, look at it and marvel at the engineering

author: p2potter
author_rank: Contributor
timestamp: December 14, 2017, 07:53:33 pm
content: nctnico,I have seen the Feeltech 3224, but I am concerned about the lack of a polarized plug and linear power supply, such that 90V can appear on the BNC output ground depending upon the way the plug is inserted in the wall socket. I did consider building a new power supply for thsi device (nice video on you tube discussing this), and ultimately I will have an isolation transformer, but the last thing I want to do is trash my equipment/project with a dodgy piece of test gear. I guess they may have fixed the issue by now, but I have seen no reports to that effect.Thanks.

author: nctnico
author_rank: Super Contributor
timestamp: December 14, 2017, 08:03:41 pm
content: Quote from: p2potter on December 14, 2017, 07:53:33 pmThe solution is simple: mount a mains socket with earth connection and connect earth to the shield of the output. Every piece of ungrounded test equipment (no matter which brand) will have half the mains voltage on the case if it is not grounded because of the mains filter. The exception is equipment with isolated outputs ofcourse.The 3312A is an RC oscillator. These suck pretty bad if you want a really stable output frequency. Also no frequency readout and analog amplitude control

author: p2potter
author_rank: Contributor
timestamp: December 15, 2017, 03:44:36 am
content: Thanks for the tip, but I would rather spend $25 and add a new PSU for total piece of mind. Just hard to believe that such a device is being mass marketed to the relatively unsuspecting public. Might only take some damp hands to get a significantly jolt.

author: nctnico
author_rank: Super Contributor
timestamp: December 15, 2017, 09:26:44 am
content: Quote from: p2potter on December 15, 2017, 03:44:36 amThe current is very small so no danger or whatsoever. Lots of people have their PCs plugged into unearthed outlets with the metal case having half the mains voltage on it.

author: montemcguire
author_rank: Regular Contributor
timestamp: December 15, 2017, 09:49:27 am
content: QuoteI haven't used a 3312A, but I have a 3314A, and one evening I put an HP 3314A and an HP 3325B on an XY display and watched them chase each other around. While the 3314A (also an RC oscillator) has a static calibration error, after about an hour, trimming the 3314A error with the 3325's high res frequency entry, the two could chase each other to around 10-50ppm. I was actually shocked, since the 3325B is a synthesized generator, locked to an internal 10MHz, and it's dead on all the time. So, while an RC oscillator won't be that accurate, they can be very stable once warmed up, and their waveforms are fairly clean too. FWIW, the 3314 has a nice knob to control F or amplitude, whereas the 3325 is a keypad numeric entry device, making it more precisely controllable, especially in a GPIB system, but more cumbersome to use on a bench. So, each generator will have different strengths and different weaknesses.I see no problem with having several generators for different uses, and sometimes you need a few at the same time, so one alone isn't always sufficient. As was stated before, the older HP stuff is built like a tank, is generally pleasant to use, and if you're lucky, can be found surplus for low $. No shame in having a few of them!

author: bd139
author_rank: Super Contributor
timestamp: December 15, 2017, 10:06:02 am
content: 3312A is pretty stable when it has warmed up. At around 1MHz mine was only showing +/- 20Hz drift over an hour. It might be an RC oscillator but it's not any old RC oscillatorReally 90% of the time, precision isn't actually that important both in frequency and amplitude. I have built for example, 600Hz high Q audio filters using 10% capacitors, 5% resistors and a analogue function generator and a VTVM and the 600Hz passband is bang on when I stick it on a "homebrew SNA" with a DDS + digital scope.

author: nctnico
author_rank: Super Contributor
timestamp: December 15, 2017, 04:00:08 pm
content: Quote from: montemcguire on December 15, 2017, 09:49:27 amThe 3314A is a different beast (AFAIK it uses a PLL to stabilise the frequency) and cannot be compared to a simple RC oscillator. I'd very much prefer a generator from Feeltech over the 3314A. I used to own a 3314A but it just isn't that versatile especially when taking the size and fan noise into account.

author: p2potter
author_rank: Contributor
timestamp: December 15, 2017, 06:26:54 pm
content: Sorry, but when folks are reporting being shocked by the instrument, three things come to mind:1. Sloppy design;2. Cutting corners to save cost;3. Poor or no beta testing (or worse they new about the issue before they relased it and just tried to mitigate the current to keep it 'safe').I'd rather have an older, well designed instrument, that isn't doing its darndest to deliver unwanted current into me!

author: bd139
author_rank: Super Contributor
timestamp: December 15, 2017, 06:34:38 pm
content: Indeed.The HP 3312A has no corners cut. None at all.Compared to:

author: nctnico
author_rank: Super Contributor
timestamp: December 15, 2017, 07:05:03 pm
content: Quote from: p2potter on December 15, 2017, 06:26:54 pmIn my experience old HP gear is rather notorious for wires which are soldered into the PCB directly getting loose either because the solder joint gets brittle or the strands break. This includes mains wires! Pick your poison!As stated before the current is very small (by design) and you have many devices in your home already which have the same issue. Ground yourself and touch every switching mains adapter you have. 9 out of 10 will shock you. Don't make a big fuss out of something which is super easy to fix. Otherwise spend the money on a more expensive new generator which has the ground wire already installed. No matter how much you may like the old boat anchors because the way they look on the inside a modern function generator (including the ones from Feeltech) runs circles around the old clunkers when it comes to operating them and the features they provide.

author: p2potter
author_rank: Contributor
timestamp: December 15, 2017, 09:28:38 pm
content: bd139,Thanks for the images. Clearly a picture paints a thousand words!

author: rhb
author_rank: Super Contributor
timestamp: December 15, 2017, 10:15:54 pm
content: The signal quality from the FeelTech FY-6600 is very good. But the UI has serious problems which FeelTech has not resolved. Some people have been trying to get theirs fixed for over a month. Mine crapped on itself right after I finished adding the ground. Check the forum threads about the unit. Mine looks *exactly* like the one shown at the start of the reflashing thread.If and when they take care of existing customers it's worth considering. Otherwise I don't recommend it. In any case, if you get one, make sure you buy it with Paypal from a US ship location so you're not held hostage by overseas shipping costs which are $30. I'd also stipulate that it *not* be version 3.0 or 3.1 FW if you buy one. Even if FeelTech replaces the front panel, it's a hassle. It *will* fail.I added a ground to mine, but the 3 wire receptacle I used had the mounting screws to the side. As a result I had to reinforce the back panel. A receptacle with mounting screws above and below will be easier to mount.