ฝัง
- เผยแพร่เมื่อ 30 ก.ค. 2024
- A review and teardown of an inexpensive MHS-5200A function generator, including the reverse engineering of its analog front end and troubleshooting to track down the source of some nasty harmonic distortion.
The schematic for the analog front end can be found in the blog post at: www.analogzoo.com/?p=916 - วิทยาศาสตร์และเทคโนโลยี
(A voice from the past!)
Nicely done, sir.
Another smoking gun on the AD812 is "Figure 15. Large Signal Frequency Response". It looks like we should expect output amplitude issues from about 1MHz and up, pretty bad at 10MHz, and atrocious above that. Quite disingenuous of them to give the generator those specs without identifying the limitations due to the parts that implement them. As the wicked witch said, "What a world, what a world!"
Brilliant and fascinating! Does this suffer from voltage leakage that flows through the BNC connectors? Or is that just the cheap Feeltech signal generators?
Thank you for the very interesting review. Cheers!
Hello,
I find your videos very interesting. Thanks.
Great review, thanks for sharing. If using sweep mode is there a way to get a trigger output that you know of? Thanks.
Good video! Classic example of "you get what you pay for". But this unit might have a redeeming feature in its hackability. Since the digital stuff is ok, one could design a replacement front end for the output.... Or perhaps there is a pin compatible part to replace the AD812.
Very well presented. Thanks
Nice work! Looks like that output stage was under engineered. Maybe they were cheaping out on that chip?
can you build these ciruits on just breadboards?
Nice review - just ordered one. I'll put up with the distortion for now as it fits my budget and is better than no generator. Hobby / Ham work, should get me started. I assume that if you don't drive the amplitude too high the signal is usable in most cases? (Sine waves that is)
+Digger D Yes, as long as you keep the amplitude low then the slew rate distortion won't rear its head.
Thanks for the reply. Just checked out your mods and they look doable even for me (with patience and magnification). Once it arrives (ordered one today) and I get a chance to play with it on my scope I will order the parts and do the mod. Great work! New subscriber :)
Hi there... I know this is an old review and a "cheap" product. I was just wondering if you would check the counter function on this ? I was trying it and it was behaving utterly erratically. Cheers and TIA.
I'm assuming this would be a ok start for a generator to use at home until you can afford a better one. Also to use on basic circuits.
+str8ng3r It's...OK. The problem is that as I use it, I find more and more little bugs; this can be particularly bad for beginners since they might think there is something wrong with their circuit, when really it's their signal source!
Well done maybe you can make a trip to China as a consultant and show the manufacturer how to fix this.
Thanks for the review Jack and a good adjunct to the “devtty0” review (and improvement!) of a similar but more capable function generator import (th-cam.com/video/WfC0h8XhA4w/w-d-xo.html). Are you a ham by the way? (the HP8640B may be a clue). 73 - Dino KL0S (long time lurker!)
I really can't watch this. Why are you using a screwdriver as a pointer??? It will scratch the screen of your Agilent. Aaaaargh.
رايد البرنامج مالته للكمبيوتر
This review convinced me NOT to buy this function generator. So my question is; which function generator for under $150 is good for beginning experimenters?
Slew rate is causing problem.
rapsod1911 Ah, that could very well be it. The AD812 has a high slew rate, but it seems to be dramatically reduced when used in an inverting configuration (there's not much info on inverting gain affects in the datasheet, since it's a CFA). The slew rate also increases a bit with supply voltage, so that could account for the improvement seen at slightly higher supply voltages.
rapsod1911 Actually I've been doing some testing, and even configuring the AD812 as a non-inverting amplifier (which, according to the datasheet, should provide a substantially higher slew rate), I'm getting the exact same harmonic distortion. And the distortion starts happening exactly where the datasheet predicts the Vpp output cutoff should be for the given supply voltage. So it does appear that the supply voltage is the limiting factor; perhaps I'll do a follow-up video on it.
I see now that on page 9 of ad812 datasheet there is Maximum Slew Rate vs. Supply Voltage diagram.
Maybe ICs are not getting enough current due to bad decoupling and long traces and there are 2 in one package.
devttys0 MHS-2300A appears to be nearly identical to this. and MHS-2300A has some interesting issues - square wave experiences jitter at all frequencies (sine and triangle are fine), and ch1/ch2 experience phase shift. if you set ch1 and ch2 to e.g. 10khz they are perfectly locked - lissajous is solid, but if you set ch1 to 10khz and ch2 to 20khz, you get a slow phase shift (lissajous slowly rotates). this should not happen.wondering if it happens on the MHS-5200A as well.
ms3bani I wouldn't be surprised to find that they're very similar. The MHS-2300A looks physically smaller, but the MHS-5200A board only takes up 1/2 the case!
I haven't noticed significant phase differences between the two channels on the MHS-5200A, but I haven't really tested that properly either. I have noticed amplitude differences between the two channels at the same frequency though.
I'm hoping to do some hardware mods to address some of these issues in future videos, so stay tuned!
The AD812 is being overload, output being influenced by the feedback current in the AD603. Really crap design. Don't get me started at the SEVERE overload of the output AD812!
Nice work! Looks like that output stage was under engineered. Maybe they were cheaping out on that chip?