Sometimes I get a little nostalgic for the "old times" and when I'm at the local electronics store, I'll just pick up what I know, because it worked for Forrest Mims right? In the guitar pedal world, some of the best sounding guitar pedals were made with the scarce LM308 and the closest thing I could find on my last jaunt to the store was a batch of LM307s (good name for a band). I bought a fistful because I was making a bunch of guitar gadgets. If you're interested they sound great because of the awful slew rate which creates even-order harmonics which are apparently pleasing to the ear.

The main problem was that I wanted to run this project off of a single supply voltage and I knew this op amp wouldn't get too close to ground. You see, the 555 timer needs a minimum of 0.4v in order to hold in reset and these old op amps can only get within a couple of volts of the supply rails. I could have used an actual comparator like the LM339, but I'd have to wait for another shipment and I'm far too impatient for that. I could use some transistors and just bias them to get what I want or I could reevaluate the circuit itself. After another cup of coffee, instead going through a peak detector, x10 amp, then a comparator... I found that I could just amplify the heck out of the transformer voltage (x80), then use the peak detector, and use a proper op amp like the LM358 that gets closer to the rails. The '358 does a fantastic job of keeping it in reset (at least I think so. I never checked on the scope :)   )

So at this point it seems that everything is in working order. When the detected voltage gets through the peak detector, it runs through the comparator and saturates as expected. The values involved are heavily load-dependent at this point and there is definitely room for improvement, but for now it'll work for me.

I think its about time to turn on the video camera and document where I'm at so I can release the next YouTube video.

Thanks and look forward to the video!

Derek