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Output stage

3/17/2005 11:30 AM
Albert Kreuzer
Output stage
Hi Pete,  
if the power amp is loading down your output stage, you can try to lower R23 (2M2 or 1M instead of 3M3). In most cases this seems to help.  
3/18/2005 2:33 AM
I went back to tech :) and looked up the text on FETs, and they're voltage sources not current sources, like the input on this power amp, so I think it's because the opamps in the mixer are supplying current to the input of the PA to drive it.  
Maybe you've got an idea - the input impedence of the amp is 4K7 in parallel with the signal and ground, then 3.9K in series, .001uf to an offset adjust, then 4k7 to BC547 base with 680pf to ground.  
A unity gain opamp seems to drive it to full rails, but I think the output voltage is somewhere around 2vpp. What I was going to do was put a buffer stage of 1:2 and increase it slightly and see what that does  
I think I might try changing R23, because of the current sourcing which might be an issue. 1M probably still wouldn't allow too much current to feed the bi polars.  
3/5/2005 6:01 AM
rubberlips Re: Bass preamp schematic
Dr Photon and Albert  
Cheers for the reply. I actually did look at Alberts preamp and I'm going to have a whirl at it this weekend. I've etched the board, but I'll probably wack in an EQ circuit as well.  
It looked about the most simplest designs I've seen and basically bass amps are clean anyway - a little grind doesn't go astray either. I'm a guitarist primarily, but I play a bit of bass when the need arises. I've got a cab, but no bass amp as such yet.  
The preamp will be going into a 300W poweramp that has more than enough volume to knock off my marshall TSL or Laney LC50. Those laneys are one seriously loud 50W  
It's a bit of a rarity for a drummer to tell you to play softy :)  
3/11/2005 1:45 AM
Albert Kreuzer

"It's a bit of a rarity for a drummer to tell you to play softy"
Why, that's what they tell me all the time :D  
Many guitarists like my preamp for clean sounds and for recording (warms it up a bit for going directly into the console).  
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