I like it!
Thanks Dave for this and so many fascinating videos!
As it happens, I was doing just this same experiment last weekend: making a bode plot to measure frequency response of an 30+ year-old Nakamichi cassette recorder. (It was out of spec over the full audio range, but amazingly good up to 10Khz. TDH measured < 1%, too!)
I ran into a problem, though. The deck has 3 heads--one for erase, one for record and one for playback. The tape is pulled across the three in that order, so when you record, the input signal is recorded to freshly erased tape and is immediately available for real-time monitoring. Very neat.
But, there's a small delay between these actions because the tape travels across them at a rate of 1 7/8 inches/sec. This caused me some grief: the playback head was picking up up the sweep, alright, but it was delayed from the signal generator sync by the time it takes for the tape to move from the record head to the playback head.
I could find no way to adjust my analog oscilloscope to compensate for this, so I had bode plots that "wrapped" around the screen and looked pretty lame.
Any ideas of how--with a plain-old function general/sweep and plain-old analog scope--to get the nice end-to-end bode plot in a situation like this, where the filter introduces significant delay between the input and output?
And, while I'm at it, let me ask you if you have any ideas of how to measure wow and flutter with simple instruments like this. There I was totally stumped! (And this is where the old tape deck probably has the most trouble, in fact.) That would be a very interesting topic for another video. (Forgive me if you already did this years ago and I missed it!)
Thanks again for the cool tutorial, Dave!
- Ken