Beginners Function Generator / Signal Generator? - Page 1
Forum section: electronics / beginners

author: cincin
author_rank: Regular Contributor
timestamp: February 04, 2023, 01:23:27 am
content: I'm looking into buying my first function generator, and I have no idea what to get.My needs are very simple, I think. I'm a beginner at electronics repairs, I'm mostly working on vintage synthesizers, guitar amps, drum machines, audio effect units, right now; but I'm interested in learning more about it all and expanding my skills.What I need out of a function generator at the moment is simply a clean signal that I can then trace around audio circuits to find the source of noise, distortion, etc. I don't yet know why I might later need a 100Mhz signal, or an am/fm modulated signal, or a really strong amplitude.So a little guidance would be appreciated.In my shopping so far I've found:- A used 1987 Dick Smith Function Generator $40cad10 Hz to 170kHz in three ranges2 .5 volts peak 10 peakamplitude stability of .1 dBSine, square, and triangle wave forms- A new KKMoon Chinese AliExpress special $140Comes in 20Mhz, 60Mhz, and 100Mhz, which one?Specs here:https://rb.gy/iriuxeI'm trying to do this on the cheap, but not if I will invariably have to buy again later.Any advice for a signal noob?

author: james_s
author_rank: Super Contributor
timestamp: February 04, 2023, 01:35:35 am
content: For the needs you mention, one of the many different brands of analog function generators from the 70s-80s would probably serve you well. I haven't looked lately but it used to be easy to find them for around $50 or less. BK Precision, Protek, HP, etc, loads of different companies made them, most had similar capabilities.If you want to spend a bit more and don't mind Chinese stuff, I've heard good things about the FY6900.

author: MathWizard
author_rank: Super Contributor
timestamp: February 04, 2023, 01:44:00 am
content: Hi there, if you aren't too concerned about nice perfect sine/triangle/square waves, and are just doing low power audio signal tracing, I'd have no problem using 1 of the $15-20 sig. gen's on ebay. They use chips like the IC8038.Even if you only had 1 of the $15-20 oscilloscopes to go with it, someone could find a lot of audio circuit problems with the 2 of them. Maybe they would not be great at really seeing what op-amps are doing, but as small pocket sized tools, they would do great in a jam.The sig.gen can be used as a driver to get all kinds of power levels. They work pretty good up to 50-100kHz, but my goes up to 1MHz iirc. I don't know how "digital" they are inside, but they have a lot of steps from Vmin to Vmax. I should look at mine on my real scope, and compare it to my real sig.gen.I have both above mini-scope and mini-sig. gen., if they weren't so fiddly, I'd probably using them more often, like a DMM.But yeah if you have a few more dollars, something non-pocket sized might be better.

author: BillyO
author_rank: Super Contributor
timestamp: February 04, 2023, 01:48:06 am
content: I recently picked up a BK Precision 3010 function generator for only $35 CDN. Works a charm. 0.1 Hz to 1 MHz, sine, square and triangle waveforms. Adjustable offset and both TTL and variable level outputs. Nice true isolation via a linear power supply. Simple to operate and no funky noise or stray voltages caused by SMPS.

author: themadhippy
author_rank: Super Contributor
timestamp: February 04, 2023, 02:00:34 am
content: QuoteLike being the operative word,there sorta close,but not the genuine thing.The genuine 8038 does a pretty good job,at least the one ive been using for a number of years does .Might be worth trying to get a peek inside the tricky dicky unit to see if its using one,if you dont use its a signal generator you could repurpose it in an fx pedal

author: MathWizard
author_rank: Super Contributor
timestamp: February 04, 2023, 03:12:47 am
content: Some of the hobby $100-200 ones sound pretty good on paper. There's a few that are around 250MHz and use like an MCU I think, plus whatever all else ADC/DAC.I got myself a 25MHz Siglent AWG, and hacked it to the 125MHz version. It's great for everything I've tried so far. I just wish it remembered some settings.

author: cincin
author_rank: Regular Contributor
timestamp: February 04, 2023, 03:41:49 am
content: Thank you all for the great advice.So, if I was to go with the Chinese FY6900, are there any reasons I'm not foreseeing to get the 100Mhz (or 60Mhz) over the 20Mhz?This is all well above audio frequencies, my main area of interest, but still for potential future expansion (and I do realize how naive this question is): In what situation would you need a 100Mhz signal, where a 20Mhz signal wouldn't cut it?Cheers!

author: jonpaul
author_rank: Super Contributor
timestamp: February 04, 2023, 04:56:42 am
content: voilà my 1973 Popular Electronics Super Audio SweeperIntersil ICL8038, 1 Hz..100 khz sin/trisq sweep,Was an MITS kit. Am sure many people the Chinese F are using similar.Recently restored this 50 years old analog to 100% in calCan still be built...Bon SoiréeJon

author: james_s
author_rank: Super Contributor
timestamp: February 04, 2023, 05:12:46 am
content: Quote from: cincin on February 04, 2023, 03:41:49 amIf you were working with an RF circuit you'd need a signal source capable of operating in the range of that circuit. If you're working with audio gear then 20MHz is already orders of magnitude higher than you need. If the cost difference is small you might consider getting the higher frequency model just in case, but if you take good care of it you can probably sell it for close to what you paid and upgrade later if you do end up needing more. The budget priced gear is so cheap to begin with that it tends to hold its value really well.

author: cincin
author_rank: Regular Contributor
timestamp: February 04, 2023, 05:17:41 am
content: Thanks! Yeah, you never know, I might end up in radio. Fun!

author: donlisms
author_rank: Frequent Contributor
timestamp: February 04, 2023, 06:47:42 am
content: My first thoughts were "Just pick one; doesn't matter which!" I tend to think you can't really know what features you want until you're using it for a while and say "Gee, I wish I had ...", and when you say that three times, you have permission to upgrade!I like used gear. If I want to fix things, the test gear itself is a good exercise. Replace capacitors as necessary, clean EVERYTHING including all the pots and trimmers and switches and all that might be hidden for calibration and such, because flaky unstable test gear is no fun (but often and easy fix).I have a nice old Interstate analog generator with lots of features. I like being able to sync it to another single-channel generator, and trigger the scope, and such. So for me syncing in and out is desirable. Effectively a dual channel generator, kinda. I don't care about speed, which keeps the cost down and makes room in the budget for the other goodies.

author: shapirus
author_rank: Super Contributor
timestamp: February 04, 2023, 11:53:38 am
content: Quote from: cincin on February 04, 2023, 03:41:49 amHaving experienced a similar situation not so long ago, I think I won't be very wrong guessing that something likehttps://www.aliexpress.com/item/1005004618727924.html, or evenhttps://www.aliexpress.com/item/32862689682.htmlis going to serve you well for your immediate needs at a very low cost.When you outgrow them and will need something more advancedQuote from: cincin on February 04, 2023, 03:41:49 amyou will very likely know more or less precisely what you need by that time to justify a bigger spending.I personally bought a little more advanced generator, this one:https://www.aliexpress.com/item/32885128317.html, but only because I needed it to be capable of frequencies beyond audio, up to probably 10 MHz, other features being only a nice bonus.

author: jasonRF
author_rank: Regular Contributor
timestamp: February 04, 2023, 03:00:47 pm
content: Since you want a 'clean' signal, I would be wary of the super-cheap options from aliexpress and similar places, unless you have found legit reviews of the exact model from the exact vendor that show clean signals.I agree with others here that a great option is to find a good deal on used equipment, as long as the seller has a scope and can send photos of the unit working correctly. That is what I did when I bought my stand-alone function generator. I think it worth your time to check what you find on ebay, etc.The Dick Smith option would probably suit your current needs just fine, but only 2.5V peak-to-peak (at least I think that is what you were trying to say?) means that you might not be able to tell if something is clipping early. A lot of audio sources generate more like 2Vrms or 5.6V peak-to-peak. I know that from personal experience - my first signal generator (built into my first scope - a Picoscope 2204a) was limited to 4Vpp and at times it was not enough for testing limits of audio gear I was building. My solution was to build a 6 dB amplifier for it, which can also be a fun project. An amp for the 170 kHz bandwidth generator can be simply made with an inexpensive opamp that is easy to keep stable on perfboard.jason

author: shapirus
author_rank: Super Contributor
timestamp: February 04, 2023, 03:13:56 pm
content: Quote from: jasonRF on February 04, 2023, 03:00:47 pmGood point, but it's also worth noting that adding a narrow bandpass filter at the output of a signal that's not as clean as you want will turn it into a much cleaner sine wave.But yeah, unless you're desperate, it's generally best to avoid the cheapest options. Starting at ~$20-$30 however, it's possible to find something quite decent, especially if all you need is an audio-frequency sine wave.

author: Bud
author_rank: Super Contributor
timestamp: February 04, 2023, 03:28:52 pm
content: Building a tracking bandpass filter that follows the input signal frequency is difficult and nobody does this. For DDS based signal sources usually a low pass filter is used with cut off frequency of about 0.45 F clock, to utilize max DDS range.

author: shapirus
author_rank: Super Contributor
timestamp: February 04, 2023, 03:39:42 pm
content: Quote from: Bud on February 04, 2023, 03:28:52 pmCan you please elaborate on this? Is it to reduce the DAC artifacts?

author: Bud
author_rank: Super Contributor
timestamp: February 04, 2023, 03:41:08 pm
content: That is right.

author: Doctorandus_P
author_rank: Super Contributor
timestamp: February 04, 2023, 07:10:24 pm
content: I bought a JDS6600 which is very similar to the other 6600 clones from Ali. I bought the lowest frequency version, It think it goes upto 10MHz, and bought it for around EUR60 to EUR80 a few years ago.These DDS things have two channels and a gazzilion amount of functions. It's not a great function generator, but it is very good for it's price.It's got a few limitations, but that's t be expected at that price point.The power adapter that was delivered with it was utter garbage to that ended in the bin, but it only needs 5Vdc and there is plenty of room in the box so it's easy to do a bit of tinkering and put in something decent.Another (mayor) limitation is the R-2R DAC used. The resistors are not very balanced, which leads to visible steps and some non linearity in some settings, but it's quite usable. I have been thinking about replacing all those resistors with hand sorted ones, but I'm mostly to lazy to do it. If you plan on doing so, then first make sure you've got the skill to replace those small resistors. I think they're 0402 or smaller. (It's been a while since I last opened it).

author: shapirus
author_rank: Super Contributor
timestamp: February 04, 2023, 07:54:00 pm
content: Quote from: Doctorandus_P on February 04, 2023, 07:10:24 pmI believe my JDS2800 is pretty much the same inside, and yeah, I second all of this. Very decent tool, especially for its price. Yes, it's not exactly a precision instrument: for example, there is some slight (of the order of millivolts) DC offset when the setting is zero, but if some application requires it to be precisely zero, a simple capacitor in series will solve the problem. Similar simple workarounds can be used for other little issues.At the same time, it has no trouble outputting a 0.01 Hz wave, for example, and can even output arbitrary waveforms that you can draw by hand using some PC software (I didn't try it though).

author: jasonRF
author_rank: Regular Contributor
timestamp: February 05, 2023, 07:08:49 pm
content: Quote from: Doctorandus_P on February 04, 2023, 07:10:24 pmThe JDS6600/FY6900 and the like do have high bang-per-buck, and can do anything many of us hobbyists would ever need.I would just recommend the OP read the relevant threads in the Test Equipment forum to know whether they are buying one that will need modifications to the grounding to keep high voltages off of the output grounds. Many probably don't, but some do (or at least used to).When I finally purchased a stand-alone function generator I went with a used BK Precision precisely because I did not want the hassle of modifying the grounding on one of those units, or any of the associated safety issues that might arise if I did it incorrectly. The BK precision is well built and properly grounded, but has waaay less capability and fewer features than a JDS6600 and the like. For my simple work it is sufficient.But I was probably too paranoid about this stuff...jason

author: cincin
author_rank: Regular Contributor
timestamp: February 05, 2023, 07:37:12 pm
content: I went with the JDS6600. Now searching to see if I need to modify the grounding.

author: shapirus
author_rank: Super Contributor
timestamp: February 05, 2023, 07:53:08 pm
content: Quote from: cincin on February 05, 2023, 07:37:12 pmI have just checked my JDS2800's AC/DC power supply unit with my DMM (and looking at the photos, JDS6600 most likely has the same PSU). It measures infinite resistance between the output and input terminals and there is no connection to mains earth too, which means the generator's outputs are floating.YMMV of course.

author: cincin
author_rank: Regular Contributor
timestamp: February 05, 2023, 07:59:00 pm
content: Quote from: shapirus on February 05, 2023, 07:53:08 pmAnd that's a good thing, right? None of those grounding issues, though potential for floating....potential. No funny ground business with my precious TDS 340.So now I'm looking for a way to upgrade that power supply, which every singe post says is trash.

author: shapirus
author_rank: Super Contributor
timestamp: February 05, 2023, 08:16:06 pm
content: Quote from: cincin on February 05, 2023, 07:59:00 pmI somewhat hesitate at saying a definite yes on this, becase there may be possible scenarios where it would be undesired, however I can't think of any. Are there any?Quote from: cincin on February 05, 2023, 07:59:00 pmFor the JDS? I wonder what they mean. I have nothing to blame mine for. Seems to be as good a small switching PSU as any (mine is EU version though, maybe it's different in this regard).

author: cincin
author_rank: Regular Contributor
timestamp: February 05, 2023, 08:32:02 pm
content: Quote from: shapirus on February 05, 2023, 08:16:06 pmOh, good to hear. I'll wait and see what shows up then. Arriving tomorrow.Cheers!

author: BillyO
author_rank: Super Contributor
timestamp: February 05, 2023, 08:44:33 pm
content: Quote from: cincin on February 05, 2023, 07:59:00 pmYour TDS340 will be grounded if it's attached to a proper outlet.The power supplies that come with cheap and cheerful AWGs leave a bit to be desired. They are noisy and can produce leakage voltages. Measure between the outputs and your house ground. The last one I saw had about 30V AC leakage voltage and a few uA current. We ended up putting in a switch to ground the negative lead on the DC side of the supply to eliminate the leakage for using it with ground referenced DUTs. We will eventually replace the power supply altogether with one that creates less noise. Unfortunately it looks like there is not enough room inside for a suitable linear supply. That would be best, but these things can draw nearly 2 amps @ 5V when driving both channels as hard as they can into 50 ohms.

author: bdunham7
author_rank: Super Contributor
timestamp: February 05, 2023, 08:57:19 pm
content: Quote from: shapirus on February 05, 2023, 07:53:08 pmThe problem with that method is that any link between primary and secondary is likely to be capactive, so it would measure open on an ohmmeter. You would need to measure the voltage between the secondary and earth ground with an AC voltmeter.

author: shapirus
author_rank: Super Contributor
timestamp: February 05, 2023, 09:33:36 pm
content: Quote from: bdunham7 on February 05, 2023, 08:57:19 pmGood point.Tested this: it measures 96 V AC between mains earth and any of the DC output terminals (230V being the nominal mains voltage). The generator's DC negative is common with the output ground. Capacitive coupling, yeah.Unfortunately, my DMM doesn't have a Low-Z mode, it would be interesting to measure that.However, I have also tested 4 (whatever I could grab around) other PSUs, some with a 2-wire mains connection, some with 3-wire (with earth). One was a cheap(ish) noname, one was a genuine Japanese laptop PSU, other came with usual devices like any other.*All of them* measured 93..115 V AC between any of the output terminals and the mains earth, just like the one in question. I measured them all without load.I don't know what to make of it. It looks like any PSU will be the same in this regard.Yes it can be a problem if you touch a small MOSFET's (such as 2N7000) gate with the generator's ground (maybe the signal wire as well) -- it may (or may not, or may partially) kill it, I did experience this in the past.My oscilloscope measures about +/- 36 Vpp if I touch the generator's ground with a 10:1 probe (ground clip being disconnected), which may be just enough to damage small transistors.But is there a PSU that won't be capacitor-coupled to mains? Sounds like this can be only solved by making the generator's output ground connected to mains earth, which will create its own set of well known problems.

author: bdunham7
author_rank: Super Contributor
timestamp: February 05, 2023, 10:44:20 pm
content: Quote from: shapirus on February 05, 2023, 09:33:36 pmJust put a 10K resistor in parallel with the DMM, measure the voltage and do the math to get the leakage current.QuoteWell, there's batteries for one! Also it is fairly easy to make a low voltage linear supply with a double-bobbin transformer that will have very, very little leakage.

author: shapirus
author_rank: Super Contributor
timestamp: February 05, 2023, 11:10:47 pm
content: Quote from: bdunham7 on February 05, 2023, 10:44:20 pmThat'll be for the others feeling adventurous, I have hidden those PSUs already for now.Quote from: bdunham7 on February 05, 2023, 10:44:20 pmThis is actually another interesting topic. I am seeing a significant leakage, or rather capacitive coupling (between the windings themselves), or maybe it should better be called "mains interference" on the output terminals of my DIY lab PSU that is powered from a toroidal transformer -> bridge + caps -> Chinese DC/DC adjustable module. Not usually a problem, but can kill small MOSFETs if I'm not careful enough. I wonder if there's a way to get rid of it somehow except for connecting one of the terminals to mains earth. Hmm.

author: .RC.
author_rank: Frequent Contributor
timestamp: May 26, 2023, 08:50:08 am
content: I am in the same boat as the OP in this thread. I would like a simple function generator that can put out basic waveforms. Square, Triangle and Sine. So I thought I would start with one of the cheap ICL8038 kits. Well the sine wave it puts out barely resembles a sine wave.So I looked at what is cheap and popular, and that is the FY6900, 20MHz, but it is $135 delivered. Then you read about fixing the issues it has. To fix them adds to the price, so then you think about the UTG932 which is about $100 more. Reading on them some say it is fine, other say it has it's own issues.Then you think. Do you want to spend more on something that may be not suitable, then down the track you have to replace it anyway.So I went back cheaper and foundthis cheap onehttps://www.aliexpress.com/item/1005004618727924.htmlThen a bit more expensive and not even a casehttps://www.aliexpress.com/item/1005004826478755.htmlThen before long you are up to this sort of price pointhttps://www.aliexpress.com/item/1005005295374464.htmlAnd I am not sure I want to spend more then that at this point in time and how do I know any of them can put out a decent sine wave.

author: coromonadalix
author_rank: Super Contributor
timestamp: May 26, 2023, 10:39:47 am
content: i use 3x Juntek JDS2900 at my job, the 40Mhz variantswork on 5vdc adapter and or usb ports with thoses woh as enough power ... control software for them toopaid 125$ CAD shipped at the time, gone up a bit, and they are easy to control, interface not hard to learnworks well for what i need ... and have Siglents and a TTI or serious stuff

author: .RC.
author_rank: Frequent Contributor
timestamp: May 27, 2023, 02:56:25 am
content: Thanks. In a moment of weak mindedness I ordered a FY6900. Knowing full well it's issues. With such a long thread on here about it with modifications and so on, it will be way overkill, but should do the job.