Mesa Dual Caliber series Output Level control mod/improvement PSA - The Gear Page
Originally Posted by jdonegan
Here are a list of mods you can easily do yourself.
- Change it to Series (change the Send jack to a Switchcraft 12A jack: Part # W-SC-12A at Antique Electronic Supply
) I remove the pot altogether and use the hole for a bias pot or switchable negative feedback, or whatever else I think the amp needs.
- Remove the 220k resistor that is across the input and the wiper of this pot. This will give you much more control of the volume of the amp. I have mine on a push pull pot so that I can pull it out for larger gigs.
- To change the speed of the Reverb (Dwell), experiment with the 1 M resistor tied to Pin 2 of V5A I like 680 K or 750 K, it slows the Reverb down just enough to warm it up.
There is a .002 cap from Pin 1 of V5A to ground. Move the side that goes to ground to Pin 3. This should make it a little stronger.
Change the 22 K resistor that feeds B+ to the Red wire of the Reverb transformer to a 10 K. You could probably replace this resistor with a jumper, but the transformer might fail early. You can go down to 5 K easily though.
Lead Channel - More Gain
Between V1B & V2A, there is a 150 K resistor going to ground. Change this resistor. I like 220 K. Anything larger will get a little mushy. The higher the value, the more gain. The higher the value, the spongier the crunch will sound too.
Right after V3A is the Tone Stack. The stock resistor is 82 K. This resistor is usually located underneath the .022 caps in the Tone Stack. You may have to remove these to get to it. Changing this resistor with greatly affect your tone. Lower value makes the amp sound darker and meaner. I like 56 K or 47 K. Higher value makes the amp brighter. This mod really depends on the speaker/s you are using. If you have a bright speaker, then you may not want to make the channel brighter.
- I really like using an NOS 12AX7 in V4 to sweeten up the cleans.
- You would definitely have to place a 10M resistor across the contacts of the switch to prevent popping. Look at most Mesa drawings, they will have a 10M resistor across anything that will make a pop. It wonít change the sound because the signal is like water. It will find the path of least resistance. The resistor simply keeps capacitive charges from building up and releasing (or decreases the difference of potential) when the switch contacts close. This is the Gain mod, so you could do low, medium, high. It wonít change the tone that much, mostly it will be the saturation that changes.
Look at the clean channelís Tone Stack and you will see a great example of a 10M resistor across switch contacts.
- I forgot about this one, but it makes a world of difference!
If you look at the Phase Inverter circuit (page 7), you will see an 82K & 100K resistor right after V6. Across these resistors are 2 120pf caps. The purpose of these caps is to limit high frequencies and prevent feedback. I remove them. This really opens the amp up like you would not believe! You might try this before you do any other mods. They are concerned with feedback. I play a JS1000, basswood body, and have no unwanted feedback. I have lots of ability to make the guitar feedback with this mod though! You should also notice more sustain after removing the caps!
Another great place to work with cutting the bass out is with the Tone Stack.
Try increasing the 82K resistor to 100K. 150K is about as high as I have seen them.
A great trick for that is to increase the Treble Cap. This is the 500pf cap in the Tone Stack, just after V3b.
A 750pf or even a .001mf should add tons more upper mids and make the amp less bass heavy. This is a great place to experiment.
You wonít notice much of an increase in mids until the treble is turned up above half way.
This should give you a bit more gain as well.
The Clean channel has this very same idea already in place.
When you pull the Gain pot out, it increases the treble cap.
It also bypasses the mid and bass pot, so you get a huge jump in volume.