irky

Sounds a touch discouraging ... but I salute your persistence & hope that you get there in the end (& hope you share if you do!!)

Recently got my hands on a scope. My circuit as is has a problem with parasitic oscillation on the virtual ground. To fix this I swapped out the LM324 quad op-amp with a TL074cn. The LM324 cannot sink enough current at it's output to provide a stable virtual ground, the TL074cn seems ok. TL074cn might not be the best chip for the job - it was just what I had in my box - I guess any that can handle 40mA at the output will do. FWIW, this fix didn't have any noticable effect on the functionality! It worked fine with the oscillations (they were at about 1Mhz). Might improve the efficiency a little, but I doubt it as most of the juice is used by the LM386 which doesn't use the virtual ground. cheers Col Thanks for the update. Hmm sustainers, I arrived here thinking there'd be a coherent detailed tutorial for a complete system (nope - just the driver apparently), & it seems the whole genre is still beset with issuettes/quirks, niggles and 'oh so nears'! I'm used to the luxury of confirmed builds (often built by many before I venture that way), so being time 'light' wrt my electronics hobby, I think I'll park this one up & look back in a few years ...there might even be a schematic to accompany the ubiquitous DIY driver coil by then. Cheers.

On the contrary, if someone says something erroneous ...then the associated correction is *very* relevant. BTW I've absolutely no idea what you're going on about ....my response was not in response to the OP's request, but instead your mistake saying the LED doesn't conduct until the forward voltage is breached, here you go... ... yes a spec sheet is essential for establishing the actual parameters are, but clearly you didn't follow your own advice! Now what was all that about jump leads and microphones? (that could be quite useful for singers late for a winter gig due to a flat car battery - they'd have to sing loudly though, LOL).