Cheap pre-built (no kit) signal generator?

[YurkshireLad]

I've watched various videos of signal generator DIY kits, but is there a recommended cheap pre-built signal generator? Probably something with a frequency range that doesn't need to go above 1MHz. The XR2206 is a kit and seems to have various flaws, according to some YouTube videos. Or is it good enough for the price that a total noob wouldn't be affected by its foibles? Just curious and pondering.

[YurkshireLad]

I forgot there's also the FG-100 DDS, which I think is about C$60 or so. The next step up is the SainSmart MHS-5200A (C$120) or the JDS-6600 (C$120).

[bob91343]

It depends on your needs.  Output voltage, impedance, distortion, frequency range, stability, etc.

[Electro Fan]

Bandwidth, functions (types of signals generated), one vs. two channels, and accuracy might be some of the key considerations along with the budget.  If possible, try to anticipate what you are most likely to do with the signals you generate, and how much bandwidth you will need to do that. 

Another consideration is what you will use to measure or observe the signals.  Awhile back you were inquiring about oscilloscopes - did you select an oscilloscope or do you have one in mind?  Function generators can help you learn and do stuff, but they often work in concert with an oscilloscope (not always, but often). 

A kit might help you learn how a function generator is designed; an off the shelf assembled generator might give you somewhat more performance.  It kind of depends on whether you prefer to learn by building (and then use the completed kit to support other projects) or whether you prefer to learn (and further build) by using off the shelf assembled equipment.  Either way, it might be good to think about how the generator will be used with the projects you anticipate and how it will work alongside other test equipment that will go on your bench and that will need to fit within your overall budget.

Sometimes it's hard to know what you will do with test equipment until you have it on your bench.  If it's too difficult to anticipate where all this is going, I'd get a $9.99 XR2206 generator kit, have fun building it, and then see if it has any limitations as you use it for experiments and projects.  If it doesn't have any limitations, you are all set.  If it does have some limitations you will know what they are and this knowledge will help you select your next generator.  If on the other hand you can forecast your bandwidth and other likely needs, then spec out what you need and look for the best bang for the buck that will meet those specs. 

My guess is the first thing you will miss with the XR2206 is a BNC output, so you could skip the XR2066 and start with something like the ~$33 FG-100 DDS.  Probably the first thing you might miss with that is more bandwidth, so the next stop is probably something approaching or a little over $100 like a FY6900 or a UTG932.  Somewhere around there I'd be holding out for two channels because there is nothing like comparing two signals side by side when it comes to testing and learning.

Enjoy the journey, a generator can be an excellent tool for testing, learning, building, and repairing.

[bob91343]

One thing I have discovered about tools, whether they are hand tools, power tools, test equipment, or whatever, is that until you have one, you aren't sure what parameters it should have.  Once you acquire it, your mind buzzes with possibilities and limitations.  Soon (at least in my case) you "need" a different tool, one with wider jaws or higher voltage, and eventually it mushrooms into a vast collection.  One of the coolest things for me is to discover something I had forgotten I had.  That happened yesterday while trying to fix an antenna.  I looked on my patio and saw stuff I had forgotten about and, as it turned out, helped me solve the problem.

[YurkshireLad]

I'm not sure about most of the specs, but I'd use it for basic electronics, perhaps leading me to play around with the simplest of guitar effect pedals. So audio frequencies for sure, which the FG-100 DDS will do. Otherwise I don't really know where this will take me; I'm just playing around, learning the basics and trying to have fun with a small, not too serious hobby. It may not take me anywhere, hence my reluctance to spend a lot of money.

I was looking for an oscilloscope, but I didn't pick one up for that very reason. To be honest, the DSO150 would suffice for my most basic needs as a starting point (audio, basic electronics). I have some Amazon gift cards so I wouldn't be out of pocket if I bought something like the DSO150 and then picked up a decent Rigol later.

The same goes for a bench power supply; I'll most likely need one and I'll probably get the Korad (again, from Amazon) that people usually recommend here.

Who knows.

Thanks all.

[ledtester]

I forgot there's also the FG-100 DDS, which I think is about C$60 or so. The next step up is the SainSmart MHS-5200A (C$120) or the JDS-6600 (C$120).

I wouldn't consider any of these.

For the latest offerings have a look at the Uni-T UTG962 or for more money the Juntek PSG9080. You can find a number of recent youtube reviews and posts here on them.

There is also a lot of discussion here on the FY-6900.

[MathWizard]

The average pre-made xr2206 AWG is still just fine for lots of stuff. It's just a matter of precision/accuracy. The kits probably cost about the same as the knock-off chips on ebay.

I bought 1, and used it hardly ever, but it was fine for radio Freq electronics. Now I have a nice Siglentsdg2042 hacked, but I could still get by with the XR2206 or the IC80??? something similar.

IDk what current they can drive, but for basic breadboard stuff, they can do a lot. They have quite a few transistors inside, try making that on the BB.

The chip itself, is way better than anything I'd make out of BJT's, and they are cheap

GET SOME

[ledtester]

I forgot there's also the FG-100 DDS, which I think is about C$60 or so. The next step up is the SainSmart MHS-5200A (C$120) or the JDS-6600 (C$120).

I wouldn't consider any of these.
...

Some elaboration on this remark...

The FG-100 is just an Atmel AVR microcontroller. As such it has at most a 10 MHz sample rate. The sample rate of the Uni-T and Juntek units is 20 times that. The design is based on "Jesper's MiniDDS" project from the early 2000's:

http://www.radanpro.com/Radan2400/mikrokontroleri/Jesper's%20AVR%20pages%20-%20MiniDDS.htm

The MHS-5200A is one of the original low-cost DDS units to come out of China. As far as I know the company never came out with a successor product and I don't think they are in (the DDS) business anymore. In fact, I seem to recall reading that some of their engineers quit and formed or were lured to a rival company (perhaps FeelTech?).

Having read a lot of forum posts here on these low-cost DDS function generators one of the main impression I get is that these products exhibit a lot of "rookie" mistakes and for that reason I would just stay clear of older designs. Moreover, consider that a lot of the usefulness of these DDS generators is contained in the firmware and computer software support, and companies are not as likely to continue improving the software of their older models as they would for their most recent offerings.

[YurkshireLad]

I see what you're getting at. I think for now a max of 10 MHz would be enough for a starting point for me.

[ledtester]

I see what you're getting at. I think for now a max of 10 MHz would be enough for a starting point for me.

Just want to make sure you are aware of the relationship between DDS sample rate and max output frequency...

To output a reasonable sine wave the DDS sample rate needs to be at least 2.5 times more than the sine wave frequency. For square waves I've heard that a ratio of at least 5 is desirable.

The sample rate of the FG-100 is probably closer to 1 MHz. That corresponds well with its stated max output frequency of 500 KHz.

[Kleinstein]

Those cheap FPGA based DDS generators from Chinea like the MHS5200 or feeltech are not that bad for the price.

They have there limitations caused by cost cutting. One is a limited BW and power BW of the output amplifier. Essentially all the low cost ones use a OP to drive the ouput and this a limited amplitude (some 20 Vss with high Z and 10V_ss with 50 Ohms termination. The maximum amplitude is also only availabel for lower frequencies (e.g. 1/3 the maximum), due to a slew rate limit.  A square wave is also limited by the same output amplifier - so not really square anymore at the higher frequencies.

The other point is often using a SMPs for the supply and thus the required Y caps and thus some residual hum current from half the supply.

I would not count very much on higher amplitude resolution - they often use just a simple R2R chain and this limited accuracy/distortion no matter if the FPGA calculates 10 or 16 bits.

[wizard69]

You might want to consider that you are jumping the gun here.  If your current interests are audio, there are lots of ways to generate suitable signals and frankly a lot of used equipment out there.    If you develop your interest a bit more you should be able to nail down the required specs better.   You might also justify a higher end signal generator.