Re: New Amp Day! Marshall Content
Yup I'm a member there. Looks like you added 2 pots? Can you list the mods you competed? Thanks.
Ok, cool. I go by the same screen name over there.
I added 5 pots (one is around back), and the mods I've done are:
Plexi cap. I wish I would've left the switch out of the mod, because I never shut it off. I also may go with a bigger cap in the future, or make the existing cap permanent with an extra cap being switchable.
Mid sweep mod on the Clean, OD1 and OD2 channels. This just turns the slope resistor into a variable resistor and it's well worth it. The pots for the OD channels are over by the JVM logo, and I had to use 16mm pots in order to squeeze them in between the front panel board and the power switches. The clean channel pot is on the top right, by the input.
This is probably my favorite mod, because it allows you to dial in a lot of different tones. You can go from Tweed to Blackface on the clean channel and go from classic rock tones to absolutely brutal modern tones on the OD channels with this mod.
Blackface clean channel.
1959 crunch channel.
Recto OD2 mod minus the faux presence circuit. I decided to leave the faux presence circuit out of this mod because the JVM is plenty bright as it is, and it seems to have worked out quite well.
JCM800 OD1. Not too fond of this one. It made the channel sound too tubby for my tastes. I plan on modding this channel to OD2 specs along with the Recto mod minus the faux presence circuit because OD2 has become my go-to distortion channel, and it would allow to have two different settings without having to mess with the knobs.
3rd gain stage bias control/plexi one wire. Love this mod. It let's me dial in gobs if extra gain if I want it. The knob is located on the bottom right, by the input.
Negative Feedback mod. Love this one too. It let's you adjust how much negative feedback you have in the phase inverter, thus adjusting how much headroom you have in the poweramp. I originally had it's pot over by the input, but it caused the amp to squeal so I moved it around back.
Later on I may add a mid sweep control to the crunch channel, and plan on adding a choke. I also plan on modding the poweramp to run KT88/6550 power tubes and will probably upgrade the transformers when i do it. The stock transformers will run KT88s & 6550s, because they're identical to the transformers used in the Kerry King JCM800, but I would still feel more comfortable with bigger transformers. Besides, it'll give me a perfectly good set of Dagnalls to use for an amp build.
