Bypassing Bugera Infinium auto bias? (Clip Added) Crashing distortion

Kapo_Polenton

Kapo_Polenton

Well-known member
Got a 1960 Infinium, sounds pretty good if you don't crank it. If you try the VH everything on 10, the sound is horrible. Like a crashing on the high notes which I now know is not my attenuator. Clearly the auto bias function biases everything cold to be on the safe side so you can mix and match tubes without blowing your amp. Anyone have any experience with this circuit and bypassing it? My next stop will be bugera but what a pain in the ass they are with registering for some music network thing they are pushing. I just want an email and an answer from someone in China or India. Too bad, it is a cool amp but I can see now why the guy I got it from moved it along. For one it is loud. 2, if you open it up, the cold bias works against you. (I've changed preamp tubes as well to rule that out) I'm guessing mine is just a lemon because of component drift which likely resulted than colder than the norm or maybe someone screwed something up in the factory.
 
I'm not a tech and can't help you so this may be worthless but the Infinium technology is a known bust. Worthless crap. What was designed to protect tubes has turned out to be a PITA. I was originally thinking the circuit could be bypassed in a way similar to reversing what people do when they mod a 5150/6505 to be manually biased. I think the 1960 is based on a legacy Marshall circuit but that concept would be the same. Not sure if that is worth it or not. Too bad too because I know people that have the non-Infinium version of these and were pretty happy IIRC. Good luck.
 
Thanks. It really is a bummer because the features are cool enough and the idea is right but the execution is shiite. Why wouldn't they have a bypass for that either? As it is I can only think bias or maybe that crashing sound is what can happen with NMV circuits when the treble is on 10. DF mentioned that in the Deep Dive they did on VH tone but as there are no clips I can't compare it.
 
Does it do that even when you lower the volume? A lot of amps can sound like shit when totally dimed out
 
No, if I bring the volume down some and the tone controls down it def goes down but I will have another good go at it tonight taking it up in 4ths and then bringing up all the tone controls and gain to see if it is one pot/frequency causing that. Thing is, this circuit is essentially a superlead and those things were designed so that they sound right everything almost on 10. It shouldn't do that..
 
eeeesh.... ya that's not cool.
If the tube sockets aren't mounted directly to the pcb board, try adding 68k grid stop resistors to the PI tube ( both grids ).
Not all Plexi's sound great with everything dime'd ( as Dave Friedman will attest )
Blocking distortion at the PI can be a problem.
The 68k's will help.
 
fusedbrain said:
eeeesh.... ya that's not cool.
If the tube sockets aren't mounted directly to the pcb board, try adding 68k grid stop resistors to the PI tube ( both grids ).
Not all Plexi's sound great with everything dime'd ( as Dave Friedman will attest )
Blocking distortion at the PI can be a problem.
The 68k's will help.
Click to expand...

I'll have to try it. It is def. the treble pot. Was playing with it tonight and the treble past 7 when everything is on 10 creates that crash. I guess it is just too much signal. Alternatively, When I have everything else on 10 and I have the treble on 7, if I hit it with a clean boost, it will bring that crashing back in somewhat. An EQ boost won't. It is interesting but I guess in the old days would just be considered this particular amps characteristic and you would just dial back the treb. The flip side of this amp is that the cascaded input with the Randy Rhoads Marshall factory mod is really cool if you dial it in properly. Some nice crunchy meat there which you can hit with an OD and EQ like Randy did and get some awesome heavy tones. For the price, pretty damn good sounding if it holds up.
 
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