Members newholland Posted February 3, 2009 Members Share Posted February 3, 2009 Thanks for the update. Is there any way you could post up the schematic? PM'ed-- i don't wanna mess with the copyright po-po... last thing i need is a lawsuit, which i doubt would happen... but better safe than sorry! anybody wants-- i'll send it to you! Link to comment Share on other sites More sharing options...
Members newholland Posted February 3, 2009 Members Share Posted February 3, 2009 thanks fred-- yeah i tried that first-- still too much gain-- i tried an au and a 5751.. still too much gain! Link to comment Share on other sites More sharing options...
Members shepherdspy Posted February 3, 2009 Members Share Posted February 3, 2009 the 470k resistor (r292) isn't just REMOVED-- in fact, it's swapped out for a 1 meg resistor. oddly-- that's MISSING from potatoes' amp! i dunno if they changed it somewhere along the way-- but it seems to not be there!Well that kinda makes sense. If Potaetoes removed the 470k and then replaced it with a 500k pot, then it would be the same as the Mesa version of two 1 Megs in parallel(the pot and the replaced resistor). But I'm sure Mesa has a reason for doing it their way. This gain pot mod seems great for this amp, but I'm not sure I could mod my baby. And few people talk about the cleans on this thing, but they are awesome. Better than a Deluxe Reverb and more compact. Thanks for the pics, potaetoes! Thanks for the mod info, newholland! Link to comment Share on other sites More sharing options...
Members newholland Posted February 3, 2009 Members Share Posted February 3, 2009 hell yeah-- as much as i've struggled with the .22 and getting it figgered out-- it really is an awesome amp-- and this can only serve to make it MORE usable! i'm gonna get into the mod this week if i can-- so i'll report back with a photoessay! Link to comment Share on other sites More sharing options...
Members chris_d Posted February 3, 2009 Members Share Posted February 3, 2009 Well that kinda makes sense. If Potaetoes removed the 470k and then replaced it with a 500k pot, then it would be the same as the Mesa version of two 1 Megs in parallel(the pot and the replaced resistor). But I'm sure Mesa has a reason for doing it their way. I think maybe their reason has to do with current handling? Considering that an amp usually specs 1/2w resistors or so, and that a normal 24mm Alpha pot in audio taper is rated for 1/4w, putting a 1M 1/2w resistor in parallel with a 1/4w 1M-A pot, should give 3/4w power rating for the final circuit, right? As i was saying to newholland, lots of folks build with the 1/4w pots or even worse, anyhow... But being that this was a factory mod, it makes some sense that they might have considered current rating and that is why they chose the method they did? Or perhaps they just had an awful lot of 1M-A potentiometers and 1M resistors lying around, and not so many 500k-A? Who knows? -chris Link to comment Share on other sites More sharing options...
Members McQuinn Posted March 3, 2009 Members Share Posted March 3, 2009 Newholland,Thanks for your hard work. Waiting to see the photo essay. Also, thanks again for the help on boogie board (Zuga). McQuinn Link to comment Share on other sites More sharing options...
Members jj2k123 Posted March 24, 2009 Members Share Posted March 24, 2009 Has anyone done this to their cal 50 +. Not sure where to find it because all the only schematic i've found from the cal 50 + is drawn by hand and has different values then the cal 50. Link to comment Share on other sites More sharing options...
Members guitarbilly74 Posted March 24, 2009 Members Share Posted March 24, 2009 maybe I should do that to my .50 Cal.. that would definitely add some versatily, although I am able to balance the channels well with the stock amp Link to comment Share on other sites More sharing options...
Members potaetoes Posted March 24, 2009 Author Members Share Posted March 24, 2009 I think maybe their reason has to do with current handling? Considering that an amp usually specs 1/2w resistors or so, and that a normal 24mm Alpha pot in audio taper is rated for 1/4w, putting a 1M 1/2w resistor in parallel with a 1/4w 1M-A pot, should give 3/4w power rating for the final circuit, right? As i was saying to newholland, lots of folks build with the 1/4w pots or even worse, anyhow... But being that this was a factory mod, it makes some sense that they might have considered current rating and that is why they chose the method they did? Or perhaps they just had an awful lot of 1M-A potentiometers and 1M resistors lying around, and not so many 500k-A? Who knows? -chris that's a plausible explanation. i think having the resistor in parallel also makes the taper a bit better. Link to comment Share on other sites More sharing options...
Members jj2k123 Posted March 24, 2009 Members Share Posted March 24, 2009 I've just completed this mod on a 50 + and it works perfectly. one thing its not r292 on the caliber 50 + i believe it was r281. but its in the same place as the pic from the first page. Link to comment Share on other sites More sharing options...
Members Hephaestus Posted October 20, 2009 Members Share Posted October 20, 2009 I know its asking a lot, but did anyone ever write up a walk-through or pictorial walk-through? The shared gain knob on this thing is killing me, both channels are amazing, but they really can't co-exist on one gain pot. I'm good with solder and de-soldering irons but really have no clue what I'm doing come time to read a schematic. Sorry to bump a 7 month old thread haha. Link to comment Share on other sites More sharing options...
Members newholland Posted October 20, 2009 Members Share Posted October 20, 2009 sorry from my point of view--- i sold the amp-- but i never did the step by step. potatoes has some GREAT photos that outline it, and i can PM you the mesa/boogie schematic. Link to comment Share on other sites More sharing options...
Members Hephaestus Posted October 20, 2009 Members Share Posted October 20, 2009 Well I've got the original schematics, or are you talking about a post-mod schematic?I guess what I'm really wondering is if someone was able to detail what needs to be done, could the average Joe with little circuit board modding experience and a steady soldering hand do the mod? Or am I better off taking this to a tech to have it done? Link to comment Share on other sites More sharing options...
Members potaetoes Posted October 20, 2009 Author Members Share Posted October 20, 2009 Well I've got the original schematics, or are you talking about a post-mod schematic?I guess what I'm really wondering is if someone was able to detail what needs to be done, could the average Joe with little circuit board modding experience and a steady soldering hand do the mod? Or am I better off taking this to a tech to have it done? the hardest part is getting access to the board - not super hard: take out the tubes, unfasten all the pots and jacks from the front of the chassis, unsolder the yellow wire that goes to the speaker jack, unclip the plastic standoffs, and carefully tilt the whole board 90 Link to comment Share on other sites More sharing options...
Members Hephaestus Posted October 21, 2009 Members Share Posted October 21, 2009 Awesome, seems easy enough. What specs do you recommend on the pot i'll be adding on this mod? Appreciate this so much. Link to comment Share on other sites More sharing options...
Members potaetoes Posted October 21, 2009 Author Members Share Posted October 21, 2009 Awesome, seems easy enough. What specs do you recommend on the pot i'll be adding on this mod? Appreciate this so much. either a nice 500k pot or a 1M with a 1M resistor across it. mine's just the 500k pot without the resistor, been working fine that way for years. audio taper is probably best, but taper likely isn't critical. btw, i don't remember whether anything has to be done about the reverb leads... one of those might also have to be unsoldered to flip the board. been a while since i had mine opened up. Link to comment Share on other sites More sharing options...
Members mxr2000 Posted August 21, 2010 Members Share Posted August 21, 2010 disclaimer: i'm a dumbass and forgot to check the value and taper of the pot. BUT, it should be somewhat higher than the resistor it replaces. anyway, here's the amp here's the knob here are the three wires that connect it to the PCB here's a shot of the other side of the PCB, taken through the V1 cutout, where you can see R292 is missing. also (important), you can see the trace is cut between the solder points for the yellow and orange wires. you could probably perform this mod without even removing the PCB from the chassis... anyway... anyone who was interested in this mod, there ya go! hello could this mod be done to a caliber .50 plus too? Link to comment Share on other sites More sharing options...
Members mxr2000 Posted February 5, 2011 Members Share Posted February 5, 2011 Bump. Nice thread please more info about this mod Link to comment Share on other sites More sharing options...
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