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Bellari RP220 + Tube swap = WTF ? Single-Channel Preamps
Old 11th September 2011
  #1
Gear Maniac
 
NothingTheory's Avatar
 

Bellari RP220 + Tube swap = WTF ?

So I had my rack out of it's niche and decided to mess with the tubes in the Bellari since it was accessible. It had 5751's in it because that's pretty much what is recommended to tame the gain from a 12AX7 a bit.. I think it sounds great in its sweet spot, but its not very flexible, and I would like it to be a bit more useful overall.

So I decided to try a 12AT7 and drop the gain a bit more to se if could be more manageable, or what that would do to the sound. 12AT7 inserted .. NO DIFFERENCE IN GAIN ! Wha ?

So .. hmm .. I pulled out an old Baldwin 12AU7 and inserted that ... NO DIFFERENCE IN GAIN ! WTF ?

Just to make sure I wasn't going crazy I tried the 12AT7 and 12AU7 in another pre .. and yea the gain dropped to almost unusable at the 12AU7 level for a pre designed for a 12AX7 ..

The Bellari sounds gorgeous at its extremely narrow sweet spot with the 12AU7's in it .. so I left that in there .. but Im still baffled ( and is it my imagination that the 12AU7 actually sounds better ) ... is this thing even using the tubes ? or using it in some what I'm not getting.

Anyone tried other tubes besides 12AX7 or 5751 ? Im starting to think all this talk about dropping the 5751 in as a must is BS since it doest seem to do anything to the gain .. .. or I have a seriously messed up unit or something. confused.

I know this is not a very popular unit, so Im not hell bent in getting info about it, maybe more of a heads up to anyone that has one.. as its kind of an oddity in my rack.. but I keep thinking it may come in useful someday.
Old 11th September 2011
  #2
Lives for gear
 
Jimsi's Avatar
 

my undersstanding of the Bellari's is it was both intergraded with Hybrid/transistors and a tube and the 250v plate voltage was higher than a 50v starved plate preamp like a $40-$50 dollar pre..

Sounds like this is designed on the same principal, pull the tubes and see if it works and if it does, the tube is just adding color not amplification...that 12au7 tube is less than 1/4 the gain of the 12ax7 tube....for the 70db gain it produces, the 12a*7 tubes wont deliver it without some help from transistors/fet ....

My UA 710 produces 70db of gain using 300v for plates and when I rolled lower gain tubes in it, the volume dropped and i know it has transistors/fets from input to output in it, even on the tube side...
Old 12th September 2011
  #3
Gear Head
 
djsmuv's Avatar
 

Bellari + Black Lion Audio mod book ?

dont know if this helps but , heres a collection of mods
Old 12th September 2011
  #4
Gear Maniac
 
NothingTheory's Avatar
 

Thanks

Thanks for those links, especially the BL pdf !! Sorry I missed your post by about a week and probably should have just posted this there instead. I'll poke around and report anything interesting.
Old 12th September 2011
  #5
Gear Maniac
 
NothingTheory's Avatar
 

Schematic

OK a quick 2 minutes with the schematic and it does appear that the signal can go direct to the opamps without the tubes, I can see that without pulling them.....so as Im lowering the tube gain I'm hearing more and more of the opamps. Well, I guess Im impressed with the opamps I'm using then, lol.

OK case closed on this one... I'll post further results on the other thread ( and sorry for splitting it ) .... I wonder if there's a better way to mod this than just replacing some parts.
Old 15th September 2011
  #6
Gear Head
 
djsmuv's Avatar
 

at this point in time
the rp 220 has been in production 15 + years
dont make apologies for the finest bass di in existence, an enduring
low end theory legend . this gear ranks as a top 20 mod in these forums .
**** on it if yOU WAnt , its still hot kit ftw wtf uak?
Old 15th September 2011
  #7
Gear Maniac
 
NothingTheory's Avatar
 

its good for me if it good for you

Sorry, I wasn't necessarily dissing the RP220. The tube in parallel rather than series took me by surprise for sure - and I base that on its excellent sound .. its not what I was expecting. It has put low cost OpAmps in a whole new light for me.

Set up in a certain way it can be the best sounding piece in my rack... my only issues is that its a pretty narrow parameter of what kind of mic, how loud the source is, etc, kind of thing and I really want to get it to a place where its more flexible across the board .. because i'd like to use it MORE actually.

Admittedly I have not tried it as a Bass DI .. I will do that for sure.
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