Author Topic: Beginners Function Generator / Signal Generator?  (Read 4027 times)

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Offline cincinTopic starter

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Beginners Function Generator / Signal Generator?
« on: February 04, 2023, 01:23:27 am »
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 $40cad
10 Hz to 170kHz in three ranges
2 .5 volts peak 10 peak
amplitude stability of .1 dB
Sine, square, and triangle wave forms

- A new KKMoon Chinese AliExpress special $140
Comes in 20Mhz, 60Mhz, and 100Mhz, which one?
Specs here: https://rb.gy/iriuxe

I'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?
 

Offline james_s

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Re: Beginners Function Generator / Signal Generator?
« Reply #1 on: February 04, 2023, 01:35:35 am »
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.
 
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Online MathWizard

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Re: Beginners Function Generator / Signal Generator?
« Reply #2 on: February 04, 2023, 01:44:00 am »
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.
« Last Edit: February 04, 2023, 01:47:41 am by MathWizard »
 
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Offline BillyO

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Re: Beginners Function Generator / Signal Generator?
« Reply #3 on: February 04, 2023, 01:48:06 am »
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. :-+
« Last Edit: February 04, 2023, 01:50:01 am by BillyO »
Bill  (Currently a Siglent fanboy)
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Want to see an old guy fumble around re-learning a career left 40 years ago?  Well, look no further .. https://www.youtube.com/@uni-byte
 
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Online themadhippy

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Re: Beginners Function Generator / Signal Generator?
« Reply #4 on: February 04, 2023, 02:00:34 am »
Quote
They use chips like the IC8038.
Like 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
 
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Online MathWizard

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Re: Beginners Function Generator / Signal Generator?
« Reply #5 on: February 04, 2023, 03:12:47 am »
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.
 
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Offline cincinTopic starter

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Re: Beginners Function Generator / Signal Generator?
« Reply #6 on: February 04, 2023, 03:41:49 am »
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!
 

Offline jonpaul

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Re: Beginners Function Generator / Signal Generator?
« Reply #7 on: February 04, 2023, 04:56:42 am »
voilà my 1973 Popular Electronics Super Audio Sweeper

Intersil 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 cal

Can still be built...

Bon Soirée
Jon
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Offline james_s

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Re: Beginners Function Generator / Signal Generator?
« Reply #8 on: February 04, 2023, 05:12:46 am »
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!

If 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.
 
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Offline cincinTopic starter

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Re: Beginners Function Generator / Signal Generator?
« Reply #9 on: February 04, 2023, 05:17:41 am »
Thanks! Yeah, you never know, I might end up in radio. Fun!
 

Offline donlisms

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Re: Beginners Function Generator / Signal Generator?
« Reply #10 on: February 04, 2023, 06:47:42 am »
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.
 
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Offline shapirus

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Re: Beginners Function Generator / Signal Generator?
« Reply #11 on: February 04, 2023, 11:53:38 am »
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?
Having experienced a similar situation not so long ago, I think I won't be very wrong guessing that something like https://www.aliexpress.com/item/1005004618727924.html, or even https://www.aliexpress.com/item/32862689682.html is going to serve you well for your immediate needs at a very low cost.

When you outgrow them and will need something more advanced

for potential future expansion

you 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.
« Last Edit: February 04, 2023, 07:39:28 pm by shapirus »
 
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Offline jasonRF

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Re: Beginners Function Generator / Signal Generator?
« Reply #12 on: February 04, 2023, 03:00:47 pm »
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
« Last Edit: February 04, 2023, 03:07:32 pm by jasonRF »
 
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Offline shapirus

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Re: Beginners Function Generator / Signal Generator?
« Reply #13 on: February 04, 2023, 03:13:56 pm »
Since you want a 'clean' signal, I would be wary of the super-cheap options from aliexpress and similar places. 
Good 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.
 
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Offline Bud

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Re: Beginners Function Generator / Signal Generator?
« Reply #14 on: February 04, 2023, 03:28:52 pm »
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.
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Offline shapirus

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Re: Beginners Function Generator / Signal Generator?
« Reply #15 on: February 04, 2023, 03:39:42 pm »
about 0.45 F clock, to utilize max DDS range.
Can you please elaborate on this? Is it to reduce the DAC artifacts?
 

Offline Bud

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Re: Beginners Function Generator / Signal Generator?
« Reply #16 on: February 04, 2023, 03:41:08 pm »
That is right.
Facebook-free life and Rigol-free shack.
 

Offline Doctorandus_P

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Re: Beginners Function Generator / Signal Generator?
« Reply #17 on: February 04, 2023, 07:10:24 pm »
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).

 
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Offline shapirus

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Re: Beginners Function Generator / Signal Generator?
« Reply #18 on: February 04, 2023, 07:54:00 pm »
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 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).
 
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Offline jasonRF

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Re: Beginners Function Generator / Signal Generator?
« Reply #19 on: February 05, 2023, 07:08:49 pm »
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).
The 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
 
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Offline cincinTopic starter

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Re: Beginners Function Generator / Signal Generator?
« Reply #20 on: February 05, 2023, 07:37:12 pm »
I went with the JDS6600. Now searching to see if I need to modify the grounding.
 

Offline shapirus

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Re: Beginners Function Generator / Signal Generator?
« Reply #21 on: February 05, 2023, 07:53:08 pm »
I went with the JDS6600. Now searching to see if I need to modify the grounding.
I 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.
 
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Offline cincinTopic starter

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Re: Beginners Function Generator / Signal Generator?
« Reply #22 on: February 05, 2023, 07:59:00 pm »
which means the generator's outputs are floating.

And 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.
 

Offline shapirus

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Re: Beginners Function Generator / Signal Generator?
« Reply #23 on: February 05, 2023, 08:16:06 pm »
And that's a good thing, right?
I 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? :)

So now I'm looking for a way to upgrade that power supply, which every singe post says is trash.
For 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).
 

Offline cincinTopic starter

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Re: Beginners Function Generator / Signal Generator?
« Reply #24 on: February 05, 2023, 08:32:02 pm »
For 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).

Oh, good to hear. I'll wait and see what shows up then. Arriving tomorrow.

Cheers!
 


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