22-07-2017, 11:56 AM
(This post was last modified: 22-07-2017, 12:00 PM by Diabolical Artificer.)
Hi Mike, yep am nearly half way there, as, as you say I have to build another one. I have most of the parts but need to wind another toroidal mains tfmr. I test into a dummy load most of the time or use a cap for square wave testing. It works well into a speaker. I use a 100w G15 15" Celestion woofer, 10" Celestion as the mid and two fane 70w horns for HF. They all go through an old Kef Xover.
I havn't reallly cranked it all the way up in the workshop as the windows rattle and I don't want to freak the guinea pigs out. But at some point I'll put the speaker outside and crank it up to 11. For a short while only, don't want to freak the neighbors out....much. Video here of it playing music - https://www.youtube.com/watch?v=MZTTpBLvRCw. You can't really hear how it sounds though as it overloads the camera mic. At some point I'll get a proper cardioid out.
That's pretty much what I've done Trevor.
Applied NFB through a 20k pot with 820p cap in parallel = 0.3 THD at 50w 0.8 at 100w 1khz sine in. Pot off, measured it, 4k. Pot off, 2 x 2k fixed R's in place of pot = weird low frequency stability issue. Maybe the pot being wirewound had a bit of inductance that influenced things? Put a ferrite bead on NFB wire, no improvement. I'm used to this now, fix one issue another pops up.
Another video on it's way soon. Andy.
I havn't reallly cranked it all the way up in the workshop as the windows rattle and I don't want to freak the guinea pigs out. But at some point I'll put the speaker outside and crank it up to 11. For a short while only, don't want to freak the neighbors out....much. Video here of it playing music - https://www.youtube.com/watch?v=MZTTpBLvRCw. You can't really hear how it sounds though as it overloads the camera mic. At some point I'll get a proper cardioid out.
That's pretty much what I've done Trevor.
Applied NFB through a 20k pot with 820p cap in parallel = 0.3 THD at 50w 0.8 at 100w 1khz sine in. Pot off, measured it, 4k. Pot off, 2 x 2k fixed R's in place of pot = weird low frequency stability issue. Maybe the pot being wirewound had a bit of inductance that influenced things? Put a ferrite bead on NFB wire, no improvement. I'm used to this now, fix one issue another pops up.
Another video on it's way soon. Andy.
