27-11-2016, 07:08 AM
Yep, sorry, 7915 instead of 7815. Before reading your last post I wasn't happy with the excess voltage situation, I'll definately do something about after reading your post. the regs arn't on a HS, but there's a big ground plane underneath them. I could retrofit HS's or I thought about putting resistors in parallel with C45/6, these are smoothing caps after the bridge rectifier. I temporarily put two 470u/35v caps in place of the 220u/25v original's.
After a test with music, one channel is overloading/getting hot, I need to do more work here. The original mains toroid's AFAIK had 63v secs, giving +/-84v rails loaded. The new tfmr's have 67v secs giving 96v loaded. I've looked at all components specs and can get away with this xtra voltage, EG OP Q's have a max Vcbo and Vceo of 200v. I replaced the original's (63v 0v 63v and 15v ov 15v 0v 625VA) because one had already been replaced with a 50v 0v 50v 500VA and the one original had OC 63v secs. It must have took something catastrophic to blow open a copper winding of 1.4mm dia. I spoke to a bloke at Stage Accompany, he said they did have a bad batch of tfmr's. Not having much cash I was a bit restricted in what I could get.
After lots of thought and advice, though very reluctant, I'm going to have to unwind a few turns off both secondaries. It doesn't feel right trying to retrofit HS's and it really doesn't feel right winging it with 96v rails. The mains smoothing caps are rated for 100v and though they're big hefty Sprague's built like a brick bog, I'd be happier if the amp was running as originally designed.
I'm not an advocate of wonder amps, I,ve found changing speakers have far more "effect" on the music. Listening to the amp yesterday I was pleasently surprised. I heard passages in music I hadn't heard before and the stereo separation is very good, it should be as the amplifier is really two separate amps in one. I'll do some testing today, then bite the bullet and take the amp apart AGAIN! Out with the tfmr's and lose a few turns, best to do the job right.
Andy.
After a test with music, one channel is overloading/getting hot, I need to do more work here. The original mains toroid's AFAIK had 63v secs, giving +/-84v rails loaded. The new tfmr's have 67v secs giving 96v loaded. I've looked at all components specs and can get away with this xtra voltage, EG OP Q's have a max Vcbo and Vceo of 200v. I replaced the original's (63v 0v 63v and 15v ov 15v 0v 625VA) because one had already been replaced with a 50v 0v 50v 500VA and the one original had OC 63v secs. It must have took something catastrophic to blow open a copper winding of 1.4mm dia. I spoke to a bloke at Stage Accompany, he said they did have a bad batch of tfmr's. Not having much cash I was a bit restricted in what I could get.
After lots of thought and advice, though very reluctant, I'm going to have to unwind a few turns off both secondaries. It doesn't feel right trying to retrofit HS's and it really doesn't feel right winging it with 96v rails. The mains smoothing caps are rated for 100v and though they're big hefty Sprague's built like a brick bog, I'd be happier if the amp was running as originally designed.
I'm not an advocate of wonder amps, I,ve found changing speakers have far more "effect" on the music. Listening to the amp yesterday I was pleasently surprised. I heard passages in music I hadn't heard before and the stereo separation is very good, it should be as the amplifier is really two separate amps in one. I'll do some testing today, then bite the bullet and take the amp apart AGAIN! Out with the tfmr's and lose a few turns, best to do the job right.
Andy.
