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Blocking in THD Bivalve

7/16/2004 2:21 AM
Bob Clear
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Blocking in THD Bivalve
Any Bivalve owners here? I've had one for a little over a year, but haven't played it much in favor of its quieter Univalve brother.  
 
Recently I've dusted it off and discovered that it blocks in many situations. I started off with everything dimed; as you back the bass off 10, blocking starts (the 'pumping' variety). If you back off the treble in equal or greater increments, everything is fine. If you reduce the volume or 'attitude' (big bypass cap on driver), that'll clean it up too.  
 
It's got 4.7K grid stoppers; I went up to 20K and it got no better. I emailed Andy Marshall and he basically said "yeah, that can happen" in some situations (he was very polite about it, not a "take it or leave it" deal). I've noticed that it is worst with EL84s but all tubes will do it if I try. What freaks me out is why does it NOT happen with the bass full-up? I'd think it would be WORST there.  
 
The Univalve doesn't have this problem, BTW.  
 
Any thoughts?

 
Replies:
Chris - CMW amps Hi BobWhat's the topology (... -- 7/16/2004 9:43 AM