the McGrath Mini amplifier

  Here's my basic design for a 555-based audio signal generator.  I will need this for troubleshooting the McGrath Mini amplifier prototype.  In particular, the issue of lower-than-expected gain in the effects loop. I carefully traced my wiring in this section of the circuitry, hoping to find some obvious error, but there was none that I could find.  The circuit appears to match the schematic.  This is only partly reassuring, because the design embodied in the schematic is my own, never before tested, based purely on theory and my speculative understanding of tube circuits with feedback.  However, I researched triode feedback stages in several different trusted sources online, and this seemed to confirm that I'm on the right track and the gain should be approximately as I have calculated. So, my plan is to send a test tone into the input of the amp, using the circuit shown above, and disconnect the top of the master volume pot from the circuit, then use a t...

I have now completed initial work on the electronics of the v2 prototype, and have given it its first audio test: https://youtu.be/cYrF3rC199E On my youtube channel (Industrial Baroque), you'll also find a number of other videos documenting the build process leading up to this point. The photos show the unit in "testing mode", with the electronics assembly hanging out of the top of the chassis, with the upper chassis box stacked on top of the lower chassis (power supply), and the speaker connected via an extension cable.  (Enabling this configuration -- which of course makes it much easier to take measurements, make changes, and debug problems -- is the reason I used tube sockets which mount from the inside of the chassis, rather than from the outside.) My initial impressions: the clean sound is good, and output is strong, seemingly exactly the same as the v1 prototype.  However, each of the circuit sections beyond the basic clean signal path seem to need work.  This is a...