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In Reply to: RE: Bryston comes through... posted by Jim Pearce on June 26, 2016 at 16:56:11:
I know, my amp ain't right!But it sounds fine. I like hot SS actually (to a point), so complaining about it is a bit twisty for me. The thing about the hot is it's enough to (indirectly) make the toroidals buzz a bit, that's what's been making me think it's "too much".
"Bryston" said when the trannies buzz, it means to back off on the bias. So it's not like they haven't heard of this, though very few web mentions. There is some temp sensor apparently involved in the biasing too, but I don't see an obvious one in the schematic...maybe he meant on the larger/non-modular amps.
The 6s have very substantially larger heatsinks than the 9s, whose HSs are really quite small. Obviously not *too* small...
I replaced my original 4/9B-ST combo in the HT with the SST2 equivalents. I honestly don't remember how hot the STs got. I had a 3B-ST before that driving Maggies and it did get quite hot. That's the only time I've ever seen clipping indicators on one of their amps, so went to the 4B-SST and have never seen since. Which reminds me: the LEDs of the 6/9 go orange when in thermal overload? I've never seen that either.
Edit: FWIW I played the John Wick BD (don't necessarily recommend the *movie* itself...) at reference level (about 3-4dB louder than I prefer) yesterday and the 9B-SST2 heat sinks were "untouchable" for more than 2 seconds, that hot, I'd guess in the 60s degC. Then I played the Mad Max BD at a similar level. Both these movies have "boisterous" surround levels, so give the 9 a bit of a workout for a change. No problem sonically, no smoke...
More: got the 9 on the kitchen table now (too heavy/awkward to carry downstairs to the bench) and warming it up for 1.5 hours to reach its typical temp. Top removed (lots of T8s, no need to remove modules to check/adjust bias), heat sinks are bigger than I suggested after all, things look much larger out of the rack...bias values appear ~normal so far, but when the amp is "cold" isn't the issue so we shall see.
Just to finish the story: bias is fine after 3-hr warm-up, pretty much within spec considering my Fluke is only within 2mV down there (0-5mV variation), but I barely touched them so they looked "correct" on the meter anyway. So then: that's the temp the amp is designed to run at, in rack or in open air it's the same. I think I figured that already... :)
But one thing I found: the *extremely* tiny trannie buzz I can hear out of the rack seems to be amplified by where the amp is in the rack in the room (corner-ish). The amp was on an isolation platform, which I've removed for now. Also there were two screws on the bottom of the amp case that were loose (haven't moved the amp in >7 years) and rattling, that's how I found them. Weird, all the other T8s were extremely tight; vibrated loose??
Edits: 06/27/16 06/27/16 06/27/16
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- RE: Bryston comes through... - cfraser 13:48:50 06/27/16 (0)
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