Bode Plots?

Rpschultz13

Well-known member
A few years ago I bought a good scope for troubleshooting, a Siglent SDS 804X HD, which is a pretty nice beginner scope for $350-450 (2 vs 4 channels). Probably way more features than I'll ever figure out, but I'm learning. One of the reasons I needed a scope, I'm designing an acoustic preamp & EQ pedal... you can only do so much with a DMM.

At some point I realized I needed to prove it's design, frequency wise... I needed to do Bode plots. I had a crappy signal generator. But the guys over on AllAboutCircuits.com showed me a real easy way, by getting a Siglent SDG1022X Plus AWG (Arbitrary Waveform Generator). You can connect the AWG and the scope (since they are both Siglent), and it does all the work for you.

You tell the scope the frequencies you want (starting freq, ending freq, points/decade, etc) and the scope tells the AWG what to do, then measures and plots the results. Plot below is the Preamp with a HPF and a mid cut at 265 Hz (look at cursors). This is a tutorial on how to set it up, it's a bit tricky the first time but after that it's super easy.

SDS804X_HD_PNG_36.png

Two questions:
  • Does anyone here use or have the need for Bode plots?
  • If so, how do you create them?
My method wasn't so easy even 5 years ago. I remember in college (early 90's), creating Bode plots in my circuits class, by HAND! It was so tedious. Measuring the output of each frequency and then plotting. Times have changed!
 
Congrats on the expanded bench!

I use BODE plots all the time. It's great for confirming designs and seeing tolerance (when it's bad). I also find it useful for measuring other pedals.

You can do pre and post drive EQ as well by controlling the gain and amplitude in.

I sweep my work through my audio interface using REW (room eq wizard) as a signal generator/measurement software. REW has a couple extra bells and whistles like THD vs frequency. I highly recommend as a secondary tool.
 
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