1977 Jmp Non Master Volume "1 Wire Mod Help" I Know Im Sorry

[Pelvisbuster]

I KNOW ITS BEEN DONE TO DEATH AND IM SO SORRY TO ASK AGAIN BUT PLEASE PLEASE HELP ME. I have a 1977 Jmp non master volume 1987 model 50 watt plexi. I have installed the LAR/MAR MV mod,and cascaded the front end. I have searched and searched and searched for a component lay for THE PBC VERSION..and its nowhere to be found. It would be such a huge help. I cant seem to get the gain right. When volume 1 is all the way up..its really ugly sounding. it cant be raised higher than 8 or it just sound like bee's pissed off in a fart can.. like its over driving the preamp tube(s) or something similar. The treble is too much until its below 5-6. The bass doesnt do much except cause the sound to me muddy, or jumble the sound up..no seperation in the notes , but without the presence of actual bass.. as if there are no low mids in the sound. Is there cap/resister values to get this all in order? I need help.. Im new here,and Im not an amp builder. Im have extremely good soldering skills,and very mechanically inclined. I know what the compnents do,just dont know how the act or react in a circuit. I can take pictures..or list whatever is necessary to get the help I need.. Please be gentle guys.. Im sorry to ask this same stuff again..but everything Ive read so far, just seems so vague. Only part component layout that I can find is the point to point wiring.. having a horrible time trying to get the right information. by the way,my name is Ben,and thank you so much in advance

 

[Pelvisbuster]

Oh,also meant to say that it has KT88's in the power stage and are fresh. biased properly..also changed preamp tubes over and over with 7-8 that i have here to make sure its not a preamp tube.

 

[Pelvisbuster]

Help... Anyone? I have this amp tore down on my desk.. useless in all it's glory.:-(
I'd be very grateful for anyone's knowledge to help me clear this up.

 

[matttornado]

The PCB layout is basically the same as the point to point layout. look a both pictures side by side and you'll easily see what I mean.
I would try checking all of the preamp tubes.

Did work Ok before or, did you just install the mods and are having trouble? if you just installed these mods, I'd start with the Master fist and make sure it works properly before doing the one wire mod.

I never installed the one wire mod in my amp but from what I understand, there's more to it than just moving the wire. You need or should replace the V1a 220uF/820 with a 1 watt 10k resistor also.

And I have installed larmar master many times - know it well. That will kill your presence control until you turn it up pretty loud so there's the downside to that. Soundskiller at low bedroom volumes though. I'm not a fan of any master volume mods.

Sorry I probably wasn't much help.

 

[matttornado]

Just found this

 

[Pelvisbuster]

actually you were help.. It came to me in this state: the amp worked,but was VERY clean. when both volume knobs were dimed,super low breakup. Had zero tonal qualities of a mid 70's jmp. So as i said before, im not an amp builder but I do know some things about electronics.. so I searched for as many gut shot photos as possibe and realized that someone tried to mod it that had NO clue what they were doing. The amp sit in the guys closet for 20+ years because he wanted a HOT RODDED marshall sound and had no clue how to get it there. So I opened it up..got it back to stock spec,then modded it. The master volume Ive done is great,it does exactly what its supposed to do. Went over the instructions several time,checked my work with a fine tooth comb,and have convinced myself that its good. I have already done the ONE WIRE MOD,and it does work. I have swapped the caps as everyone has stated ( that Ive read) with .22 in place of .0022 and vice versa. the presence control isnt really what im worried about. I feel like once i can ge tthe core sound down,then Ill be able to remedy that situation as well.. just cant seem to get the lowend to sound like lowend..and I cant seem to get the highend to sound pleasing.. just really need some good info,and maybe a really good layout. I try to go off the point to point stuff..but what I find to be very difficult is,the fact that there are so many variations in these circuits.. so many part substitutions.. Its just super hard to know what "X" value will work better in "X" spot.. Does that make since? Also,I wanna say thank you so much Matt for your help.

 

[Pelvisbuster]

Holy Crap Matt!!! thank you brother!!! How Different is this '74 super lead gonna be from my '77 1987 model?

 

[matttornado]

Not sure. I'd have to take a look....

 

[matttornado]

Try removing the 5000pF bright cap on V1's pot. I did that and it tames the high end.

You know, it's kind of funny. I tried just about every mod imaginable for a plexi / metal panel circuit except the one wire mod & I'm back to basically a stock amp. My amp has all the distortion I could ever want with the stock circuit. I use a Marshall Powerbreak attenuator and sound great.

 

[SpHj]

Holy Crap Matt!!! thank you brother!!! How Different is this '74 super lead gonna be from my '77 1987 model?

The preamp section (where you’re working from) will be identical.

 

[Pelvisbuster]

SPHJ,see thats the thing..its not identical.. looking at the picture,and comparing them to the actual board in this amp..there are definite differences. I just wish I knew more about values,and what value changes what in the tone area..

Matt, the reason i want more gain is for the ability to use this in a gigging situation..where that EVH tone area falls.. this amp has never been a gain monster. from what i have read though,these amps were cascaded from the factory at some point ( in later years..thats how they ended up with the 800 series?)..this one was just not one of them.. kinda shooting for the 80's hot rodded Marshall sound.. slash..appetite record sound.. I guess, Im just really asking for someones expertise,and experience ...with just a dash of patience lol.. i wanna learn this so bad, but its super easy to get discourages very quickly.

Thanks for the replies guys, and help.. its definitely appreciated..

Ben

 

[SpHj]

Ok I should clarify. It’s the same “layout” so what does what is the same in that area. As for values, that’ll just be trial and error.

Cascading the gain on a 1959/1987 with its stock values will make it super gainy/buzzy what have you. That’s just the design of the amp. It’s not meant to be cascaded.

If you want help taming the gain, either keep your volumes off of max so you’re not pushing the preamp tubes into oblivion, or look at gravitating the circuit more in line with a 2203/2204.

Also. If you have a PPIMV installed it has to be turned up. If it’s not approx 1/2 way on, you’ll notice that the Tone stack can sound quite thin.

 

[Pelvisbuster]

It's sound better turned up.. but still harsh.. I'd like to be able to use the gain on tap.. some how.. also.. would like to have more low mids.. the useable kind..

 

[Pelvisbuster]

Hey by any chance can either of you put me in touch with some other guys here that have done what im doing thats had success? Maybe I could pick their brains,or get their input on this particular thing.. That would be crazy awesome.. Ive talked to Micheal R/T, but not super sure he wants to gimme his secret formula..

 

[Pelvisbuster]

Oh and wanted to say thank you also SPHJ for your help on this as well.

 

[neikeel]

 

[Pelvisbuster]

OK, so do I follow these values? or do I make this 1987 model a 2204? Where can I find this complete layout? Also my preamp Filter Cap is 50UF+50UF, will this matter? Does this layout make it so you can still keep the 4 holer kinda stock with the push pull switch? Please explain..sorry man.. I'm sure you've talked about this stuff till you guys are blue in the face..I really appreciate the help for sure!

 

[NewReligion]

I recommend if you are doing the One Wire Mod to omit the often suggested 1meg added resistor. Michael R/T and have discussed this on the phone a couple times. Michael agrees on the 1Meg. He also likes the PostPIMV.

I'm not such a fan of the PPIMV, I use the Lee Jackson Pre PIMV and some other stuff. I use a different method as I install Metro Zero Loss Loops in all of my work.

Anyhow here is a cool video Mike made to help guys out. He has the OWM buffed out at this point...Dig ♫



Demonstration Video here by Michael...

 

[NewReligion]

I started with the One Wire Mod and ended up on another Plexi planet lol...♫

 

[Pelvisbuster]

R/T's amps sound great.. yours sounds pretty damn awesome too.. I can get that amount of overdrive no problem.. but it still sounds like ass.. I have to roll treble knob ALL THE WAY OFF , other wise it's so shrill I can't stand it. The bass is so farty.. it sounds like the bass is to much going in.. but I've changed so many values in that area..just can't seem to the find the magic combo.. also, when I turn the volume all the way up on channel two it just goes completely out.. when I back off a bit it comes back. When I get them both to " wide open" it's just one of the ugliest " shitty BigMuff stomp box" fuzzy tone I've ever heard.. I want this thing to be bad ass.. just having a hard time getting the hang of it..