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Discussion Starter #1 (Edited)
I bought one of those little Danelectro Hodad battery-powered amps off a fellow on Kijiji a year or two ago, for $25. It's a cute little thing, with a pair of 3" speakers, powered by a 1W chip (though I suspect it's more like 600mw) a headphone jack, a distortion option, plus "echo" and tremolo whose speed can be adjusted by a little accessible trimmer. You can see a reasonable demo below.

I got curious about it the other day and decided to explore the innards. Much as expected, it was a hybrid of mostly surface mount and some thru-hole, and used the ubiquitous PT2399 digital delay chip for echo. The "echo" is simply a very short delay with fixed level and repeats/feedback, operated with a pushbutton. It will take me a bit to see where on the board those parameters are set, but I *did* see that it used a fairly textbook arrangement to set delay time - a 6k8 resistor to ground from pin 6. I sweated out the teensy 6k8 resistor, and installed a small 50k pot in series with a 4k7 resistor. Popped a hole in the chassis for the little black plastic pot shaft, and crazy-glued the pot in place. Much to my delight, I am now able to get echoes in the old Memory Man range (around 350-400msec), as well as a slightly shorter "room reverb" delay than stock. I could have gone to a higher delay time, but, not knowing whether the filtering would be successful in keeping the audio grime out, I left it at a modest max delay time. The portion of the tremolo circuit that I was able to make out looks very familiar, and similar to a rather classic design found on many older solid-state amps. Hopefully, I'll be able to add on a tremolo-depth option, though surface-mount stuff can be harder to figure out and mod. I may also be able to add a second power-amp section to goose the output level a bit.

Not like I was hurting for delays, but being able to have overdrive, tremolo, and real echoes out of a 9v-battery-powered portable amp is kinda neat. Feels like a brand new amp. Beats the crap out of the little Marshall MS-2C battery-powered amp I fixed for a buddy this morning.

 
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