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In Reply to: RE: Bi-amping issue posted by carcass93 on January 14, 2015 at 12:22:51
what to try?
I've used bi-amping successfully for several years with a pair of Quad 303s so upgraded they give 'Trigger's Broom’ Paradox' a run for its money. The difference between one amp and two is, in my case at least, very marked with SQ distinctly improved.
I use one amp per channel (not one for HF and the other for LF as you do) so the only link between the two is a common power connection. It's not, for obvious reasons, a permanent solution but the first thing I'd try is the one-amp-per-channel scenario. At least you might discover (or perhaps already have discovered) something.
I also ensured that the crossover circuits in each speaker (LF and HF) were electrically separate as it seemed a sensible precaution and was easy to do.
Could your DC-at-the-pre-amp hypothesis not at least be tested by putting a suitable capacitor between the pre-amp OP and the tube amp IP (correcting for phase reversal by swapping one pair of speaker leads)?
BTW, are you still using a Lampizator pre-amp?
Follow Ups:
A single cap will shift the phase 90 degrees so swapping polarity will not correct this. Best to use caps for both amps. Assuming the input impedance is 50k, then a 0.47 mF cap will block the dc without interfering with the bass. Caveat: A lot of amplifiers have a input cap already so this may not be a solution.
A single cap will shift the phase 90 degrees so swapping polarity will not correct this . . .
This is true (I checked later but the OP had already moved on so I let it go) but the suggestion was explicitly for a quick fault-finding test, not a permanent mod.
A lot of amplifiers have a input cap already so this may not be a solution.
It's an "interesting" design that doesn't but, since suspected DC on the DUT's input blew a fuse, my hunch was that it might just be such a one.
So far, DC on the input seems the most realistic assumption, and designer of SS amp, whom I contacted, confirmed that the consequences could be indeed blown rail fuse, if that was the case.
For the time being, I'm just going to watch my power-off sequence carefully. Tube amp is going to its manufacturer anyway, for a fix and couple of upgrades, so I'll raise that issue too.
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