I tried some unusual mods on my Marshall clone

philb

philb

New member
I said to myself: "Self, what the hell!"

I moved the EQ section from the last stage before the phase inverter to right after the first stage. I was expecting better tone shaping out of it.

It's cool and yes, the toen shaping is betetr somewhat but I think it's limited by the bandpass aspect of the couling caps so you end up with something similar than the original.
I also get a high noise level (a nice ssssssssssshhhhhhh)

The other one was to modify the typical Maarshall cathode follower stage to a regular circuit so I could get another gain stage. Man! I get a LOT of gain now but the tone too congested.

I just need to voice it better. The bass is still too flabby. I'd like to improve that aspect of it.

Sometimes, I'm really wondering if I'm just trying to mod my marshall into a Boogie.....
 
I'm pretty much done modding my Marshall. In the end, it's just going to sound like a Marshall, and not a Mesa. I just gotta wire up the effects loop and I'll be golden.
 
Yeah I know. I'm going to keep the idea of the extra gain stage but I'm going to work on the voicing and tune up the gain structure.

I find I play with the amp for a while, try something, play,mod,play etc.... :D
:D
 
I did a mod like that to an old traynor bassmaster that has a plexish circuit too, it came out ripping. If you haven't seen it already there's a layout posted by a guy over at the metro amp forum that is killer. Do a search for "rocco spec", I followed the layout and tweaked it to my liking and it sounds great. Lots of gain but it's not over the top, well it was at first when I tried to use the rich mod with it, the one wire master works much better with that circuit imo.
 
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Nigel Tufnel":c34cf said:
I did a mod like that to an old traynor bassmaster that has a plexish circuit too, it came out ripping. If you haven't seen it already there's a layout posted by a guy over at the metro amp forum that is killer. Do a search for "rocco spec", I followed the layout and tweaked it to my liking and it sounds great. Lots of gain but it's not over the top, well it was at first when I tried to use the rich mod with it, the one wire master works much better with that circuit imo.
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Will do, thanks !
 
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Nigel Tufnel":dba67 said:
I did a mod like that to an old traynor bassmaster that has a plexish circuit too, it came out ripping. If you haven't seen it already there's a layout posted by a guy over at the metro amp forum that is killer. Do a search for "rocco spec", I followed the layout and tweaked it to my liking and it sounds great. Lots of gain but it's not over the top, well it was at first when I tried to use the rich mod with it, the one wire master works much better with that circuit imo.
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Iv been thinking of trying that out on my JCM800 2204, but i have no idea how to hook it all up on the PCB board. Id have to take the PCB out and put in a PTP board to try it..
 
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MrDan666":f0807 said:
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Iv been thinking of trying that out on my JCM800 2204, but i have no idea how to hook it all up on the PCB board. Id have to take the PCB out and put in a PTP board to try it..
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I modded the stage right on the tube socket :eek:
Not pretty but only temporary until I figure out how to mount it on the board.
 
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philb":4e24e said:
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No I don't. I wouldn't want to post any. Like I said, it doesn't look good and is temporary for trying it out.
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Dont worry about it man, alot of us here are still learning about this stuff and building up our skills and knowledge. My Marshall is going to look awful at first, but i can get round to tiding up the wiring when iv decided im finished modding! :)
 
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MrDan666":c8623 said:
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Dont worry about it man, alot of us here are still learning about this stuff and building up our skills and knowledge. My Marshall is going to look awful at first, but i can get round to tiding up the wiring when iv decided im finished modding! :)
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Well, I can take a picture of it and post it, what the hell...
I'll post it when I get home tonight.
 
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philb":ceb9c said:
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Well, I can take a picture of it and post it, what the hell...
I'll post it when I get home tonight.
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Thanks man, that would be very cool! I enjoy looking at all kinds of amp work/mods, its interesting to see all the different possibilities of what can be done with such a simple circuit like most old Marshalls have!
 
I've got one more mod to do to my 18 watter. I miss not having an effects loop. I'm going to add this SS effect loop to mine.

http://www.ironsounds.com/

effectsloop_pic.jpg
 
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MrDan666":39a66 said:
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Thanks man, that would be very cool! I enjoy looking at all kinds of amp work/mods, its interesting to see all the different possibilities of what can be done with such a simple circuit like most old Marshalls have!
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Here's a pic of the mod.

mod1.jpg



You see the 2 100k plate resistor and the coupling cap between the two stages. The two resistor standing up is the cathode resistor and the grid resistor to ground.

I put the original EQ circuit in and it sounds better. WHat I have left to do now is balance the gain between stages. In Marshallits typically 470k/470k but I believe I need a lower value to ground so the gain stage doesn't work to hard and the effect is more gradual.

I'll probalby take a look at a SLO 100 circuit and see how the he did it with 4 gain stage.
 
If you've got a ptp board thats similar to a marshall or relatively close you can lay the rocco spec out on it. My traynor that I did it to was more of a fender style eyelet board with rows of turrets on each side, it took some planning but I made it work and it even came out lookin pretty clean. I think the guy Mark that posted it over at metro said that he had to add two turrets to his board but you could really make some connections without adding them at first just to see if you like it. It's a great circuit though, I tried all kinds of different mods and this one blows them all away. He posted some clips of his that sounded real nice. If you do it just make sure you use shielded wire where needed and watch your lead dress because there's a lot of gain on tap, I had to massage mine a bit before I tamed the feedback, it's not perfect yet, kind of on the verge of going nuts but still controllable, I like though, it's more of an animal that way.
 
Phil - one thing to consider as you start to gain your amp out - putting the tone caps and parts on the pots themselves. You'll save at least a foot or two of wire, and the amp will be quieter and less likely to oscillate. I did this on my last 18watt build and it worked great!

Pete
 
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stratotone":bbe41 said:
Phil - one thing to consider as you start to gain your amp out - putting the tone caps and parts on the pots themselves. You'll save at least a foot or two of wire, and the amp will be quieter and less likely to oscillate. I did this on my last 18watt build and it worked great!

Pete
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Yup - or twist all the wires for the three band eq going to the pots.
 
Thanks for the tip guys. The amp is more quiet now but the bass is flubby. it seems like no matter what I do with the gain, the bass remains flubby unless I turn the bass all the way down. Could it be because of the supply voltage to the preamp tubes?
 
ah HA!! Found the problem with the flubby bass. It was indeed the supply voltage. In the 1987x schematics, there's 2 resistors to regulate the supply and I changed those to a lower value but for some reason, it would not increase to the level I was expecting. I looked closely at the Weber schematic only to realize that there's a additional 22k resistor in series. Changed it to a lower value and voila, much tigher. Now the amp has an incredible amount of gain with somewhat tight bass (not as tight as other amps) but good enough to close the amp for now and play with it.
 
Here's some things that you can do to tighten the bass.
First you can try lowering the first 2 coupling caps, I find .022's to be too loose under high gain, try .0047's or .0022's, they will tighten the amp quite a bit, the lower you go the less bass you will get early in the preamp.
Also look at what negative feedback resistor value you have, 100k is gainy but it can be too loose 47k might seem a bit smoother and tighter.
Output coupling caps can be lowered to limit bass later in the circuit too, I personally like smaller tighter values around the first stage and bigger values in the pi so the preamp stays tight and you get your thump from the ouput section. For ideas on output coupling caps you can use these comparisons, Superleads used .022, Slo's use .047, and Superbass's used .1, Hope it helps.
 
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