We’re Back on Track

Despite facing some unexpected challenges (S@#t Happens), we are now back on track. We received the revised boards last week. I must say that PCB manufacturing and assembly have come a long way. The turnaround time for printed circuit board assembly is now just about a week, including shipping time. With the new boards in hand, I wasted no time and got straight to work.

The sustain driver amplifiers are fantastic! Four TCA0372 power op amps in a dual bridged configuration are powered by an 18V source. There is plenty of headroom. The microcontroller drives the op amps to roughly 10V peak-to-peak at maximum sustain, occasionally peaking at 15V peak-to-peak. On one hand, the low-E string is the easiest to drive, requiring only 3V peak-to-peak (seen in the scope above) at maximum sustain. On the other hand, the thinnest E-string is the most difficult to push due to its low magnetic mass. The high-E string is driven at roughly 6.6V peak-to-peak at full sustain.

As mentioned previously, I decided to use analog class AB power op amps instead of more efficient class-D amplifiers because I wanted to avoid high current, high-frequency switching components. The power op amps have a current driving rating of 1A. To protect against inductive kickback from the driver coils, diode clamps are installed at the amplifier outputs. The actual coils are not included in the schematic. The coil assembly includes an RC Zobel network to prevent ringing and provides stability under normal operating conditions.

I took the opportunity to conduct some fine-tuning sessions to ensure everything was perfect. Infinity, the brains behind Thor, has been upgraded to the latest firmware version. This process resulted in several enhancements, bug fixes, and performance improvements. I’m doing per-sample processing at 48,000 samples per second for 6 (and up to 8) channels. If time allows, I’ll provide some sound clips.

Oh, and BTW, the final board will be all black.

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9 months ago

Looks cool! Since you’re playing with guitars, you may be interested in this (now expired) patent I submitted when I worked at Phillips:
Device, method and system for the visualization of stringed instrument playing
US 6350942
Basically the idea was to attach strain gauges to the strings so you could measure the force being applied directly to the instrument and use this to drive a visual display. By measuring the string forces directly, you can easily visualize things like use of the whammy bar and so-on.
Phillips was just interested in puffing up their patent portfolio, so we never built one or did anything beyond the filing, but I always wanted to see someone run with the idea.
— Richard

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