Gain Stage Addition

ironskull · Post by **ironskull** » Tue Nov 22, 2005 3:56 am

Does anyone have a schematic or any other info on how to add a gain stage to a 2204-type amp? I am considering this, yet was unable to find any useful information on my own in the short time I spent.

I am also thinking about adding an fx loop that uses one gain stage to boost at the end, rather than a true buffered loop. Any thoughts or criticisms? This would also be convienient for the above-mentioned gain stage addition, taking care of the other half of the tube.

Bainzy · Post by **Bainzy** » Tue Nov 22, 2005 12:36 pm

The hoffman gain stage mod should work great in a 2204 - just don't go cutting any holes in it to fit the DPDT switch, use a push pull pot as it's much cleaner and won't devalue the amp at all if you keep the old pot.

http://www.hoffmanamps.com/charts/hotswitch.htm

Billy Batz · Post by **Billy Batz** » Tue Nov 22, 2005 1:03 pm

Before you go adding tubes, there is a huge amount of untaped gain in 800s if you havent tried yet. The user Brent recently experimented with that and he was able to find quite a lot of gain to play with and different sounds mainly by playing with the cathodes. For instance having all the cathodes with 1.5k/.68u will give you a pretty large amount of gain compared to a stock 2204. As it is the first stage is 1.5k/.68, I think, and the other 2 are 10k then 820k unbypassed. Just watch your lead dress and use sheilded cable. I dont think its super high gain like a Bogner or SLO though but its a lot more gain then a stock 2204. He said playing with the cathode values also changed the vibe of the amp a lot (820R, 1.5k, 2.7k).

If I was going to have anything it would be a send buffer for a loop. But to each his own. My preference would also be to not build it inside the amp but to have a set of passive loop jacks and use an external buffer when I wanted to use the loop. That way when I only have to remove cables form the loop to make the amp back to stock. There are good non-tube buffer designs that are a lot less coloring that you can fit in small pedals. Or you could buy a pedal or tube buffer. Just a few ideas to think about other then installing a return boost gain stage. The problem with your thought taht your adding a tube for a gain boost anyway so why not a return boost stage is they would probably be ont he opposite sides of the preamp (unless you plan on adding that stage after the loop?). Theres yet another option for adding a gain stage without adding a tube. Thats to make the cathode follower (V2b which powers the tone stack) a cathode biased gain stage. Youd have to add a few parts to the board but youd have to do that to add tubes anyway.

jerryd · Post by **jerryd** » Wed Nov 23, 2005 11:43 am

you could duplicate instead of just v1a having the standard 2.7k/.68 you duplicate that on v1b instead of the 10k. or first try removing the 470k/470pg between the two change it to a 68k. look at the groove tube trio preamp Scream channel schematic

gldtp99 · Post by **gldtp99** » Sat Dec 10, 2005 3:08 am

i've been playing with some of the ideas from this site lately--- my heavy-droptuned playing friends say the amps (Bogen 50 w/EL 34's and Gibson Atlas/6L6GC) i've installed modded JCM 800-style preamps into sound like "almost-Mesa"--- i'm not sure about that but it's fun messing around with "gainy" mods sometimes--- anyway it's a break from the bluesy/classic rock type amps i usually do-----http://www.tone-lizard.com/Ultimate_JCM800.htm............gldtp99

Flames1950 · Post by **Flames1950** » Sat Dec 10, 2005 8:04 am

Yeah, those mods will get you into Mesa territory if that's what you really want to do............