Function Generator Output Distortion - Need Advice

[Richard P]

I picked up a cheap VIZ WR-550B function generator so i can learn to use one properly. I hooked it up to my scope and noticed some distortion on the output that I would like to eliminate if possible. My primary concern is the distorted shape of the sine wave and the two ripples at 1 MHz - it's similar at lower frequencies but the distortion isn't quite as pronounced. Square and triangle (at 10kHz) look pretty good, but have some overshoot at the peaks. Any thoughts on what to look at? I tested the caps in circuit with a DER DE-5000 and they appear to be good for dissipation and ESR. The only thing i noticed on the board is that Q5 appears to have some rust at the base . . . doesn't seem like that would cause a problem, though.

I'm open to any and all recommendations.

 

[sregor]

Without a schematic and calibration information, my only suggestion is to change out the opamp - guessing dual but ??. Also check supply voltages, but I wouldn't suspect those given the other wave forms. My 2 cents.

 

[Watthour]

The DC power supply of the unit may have some imbalance. If there is an adjustment for the +/- rail voltages, that might be something to try.

 

[gadget73]

some of these use a series of diodes to convert triangles into sine waves. If one of those diodes is leaky or the biasing resistor feeding it is off value it will create some odd shapes.

 

[avionic]

Function generators usually really suck for generating sine wave. Audio signal generators are quite a bit better.

 

[Richard P]

Thanks for all the feedback. I'll look into the OpAmp, power supply and diodes/resistors a bit. All of that makes sense. Eventually i'll get a proper signal generator to replace this, but as bad as this one is, it's a step up from the app i've been using on my phone. Worked great for centering the voice coil on a speaker i was refoaming . . . pretty high tech, eh?