Express gain mods?
Moderators: pompeiisneaks, Colossal
Express gain mods?
Hey everyone, Love the forum. A good friend of mine (and a talented amp builder) built me an Express and its an incredible amp, however, when you really crank on it, it sounds like a fuzz pedal. I saw a while back a mod to reduce the gain without changing the tone. I get to play really loud so I would like to be able to turn it up without fuzzing out. What do you guys recomend? BTW I have several cabs. Mostly 2-12 w/v-30/h-30 speakers. A greenback loaded 4-12 also.
Re: Express gain mods?
try a 12at7 in the PI. And or a 5751 in the V1 and or V2 position.
Re: Express gain mods?
+1 on the 12AT7 in the PI. I love what this did to my amps.
Also, I have a pot on one of my Express amps (the UniWreck - a Univox to TW conversion) which replaces the 1M resistor on the grid of V1. When I turn down that pot to 3/4, the amp cleans up a bit in a nice way. So you might try replacing that resistor with a few different lower values to see if you like the results.
Finally, I also have a split plate load resistor on the UniWreck, and it also does really nice things by reducing the signal fed to the PI. I didn't invent it - someone here posted about it. My diagram is attached. You can play with the values of the two resistors, as long as they add up to about 100K.
Also, I have a pot on one of my Express amps (the UniWreck - a Univox to TW conversion) which replaces the 1M resistor on the grid of V1. When I turn down that pot to 3/4, the amp cleans up a bit in a nice way. So you might try replacing that resistor with a few different lower values to see if you like the results.
Finally, I also have a split plate load resistor on the UniWreck, and it also does really nice things by reducing the signal fed to the PI. I didn't invent it - someone here posted about it. My diagram is attached. You can play with the values of the two resistors, as long as they add up to about 100K.
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Re: Express gain mods?
Thanks for your replies. I have already tried several different tube options. NOS, expensive, cheap etc. I'm looking more for an internal gain reduction that won't change the spirit of the amp. Any help is appreciated.
Re: Express gain mods?
If you want internal mods then I would recommend the split plate load mod already mentioned. It preserves the tone and character best. I used the 82/22K split on V1b. never tried the V2. It appears "sliberty" did and likes it there as well.
Another area to mod is the 150K resistor to ground labeled R7 in UR12's schematic revision. Lower the value to taste. I have tried a 250K pot in place. Some like it around 68K .
The other common mod is the feedback resistor, changing from 100k down to 68K seems to be popular. Resistor # R22.
Another area to mod is the 150K resistor to ground labeled R7 in UR12's schematic revision. Lower the value to taste. I have tried a 250K pot in place. Some like it around 68K .
The other common mod is the feedback resistor, changing from 100k down to 68K seems to be popular. Resistor # R22.
Re: Express gain mods?
R7/C8 seems to be the generally accepted place to tune the Express and Liverpool. Changing the values of C8 and R7 together can help you keep the frequency response of the amp the same. Altering one of the other will shift it.
68k for R7 is still gainy but more managable. Doubling the value of C8 hould keep your response similar.
68k for R7 is still gainy but more managable. Doubling the value of C8 hould keep your response similar.