Variances in modded Marshalls JMP/JCM 800...

[michiganmusicalcraze]

Hi guys,

I was wondering if anyone else has noticed variances between a mod on a JMP/800 and the same mod on another amp that *should* be the same? I've noticed this and I believe i've read a couple of posts of others finding the same thing... although this has never really been discussed it seems? Some may sound thicker or brighter... etc. A weird thing I also notice is also that the Presence controls can really vary for some reason? Some of these sound best with Presence really low, some sound best with it around half or even more. I think the output transformer may have something to do with these variances too? I was wondering if anyone here has noticed this also? It's an interesting topic, IMO. Thanks

 

[boost]

Marshall's are like snowflakes. Modded or not.

 

[severinsteel]

I think a lot has to do with certain components being no longer available and Marshall having to use a different make for certain parts. I assume that tolerances are much tighter as far as electronics go now than they used to be, so there is that.

 

[michiganmusicalcraze]

I was just refering to the 70's JMP Master vol. and early/mid 80s 800's as those are the most commonly modded. No newer Marshalls.

About the snowflakes comparison from boost--- Very interesting. I've heard some modded JMP/800s back to back with the same mod and they do definitely sound different with the same settings. The Presence seems to vary alot--some heads liking it set higher, some very low (Presence works in the power section right? So that could make sense related to the output transformer). Has anybody looked into the impact of Output transformers in these things? Not different model (since most are the same Dagnall C2668 for the 100 watters) but the reasons each one may sound different? Interesting, odd, intriguing... hmmmm

 

[LP Freak]

Friedman always said that they all come out a little different.

 

[JTyson]

Even stock Marshalls from that era (and before and after) sound a bit different from head to head, seems to be logical that the modded heads would be the same end result. Some are better than others. I'm sure the trannys are at least part of the equation, but even the caps and other stuff can be slightly different sounding
Welcome aboard, BTW

 

[Meathead]

Marshall's are like snowflakes. Modded or not.

Yup...even the same strat made the serial number after will sound different.
Lots of pieces fitting together.

 

[Kapo_Polenton]

I've got an 82 800 and a home made 800... set them up the exact same way modelled after the 82 which just sounds great. They don't sound identical... bias them the same, same tubes, same circuit tweaks... DIFFERENT.

A lot of it has to do with components that were available but also variance in tolerance (what the components actually measure rather than what they say on the side of the resistor or cap).

Iron - these old Drakes are bitchin! But I don't think anything is 100% alike so there are prob some combinations of all of the above that make "the sound" or the one and only..

It's always going to be a gamble until you have the amp in front of you to judge for yourself.

 

[michiganmusicalcraze]

LP Freak - That's legit! I'd love to talk to Dave about that more. Since I guess he would be speaking of using the same components in his mod, but each amp still turning out different. Thanks for that info!

JTyson - I appreciate the welcome! I have noticed that with stock also. What's interesting is like LP Freak said above about a mod that would use the same components, but still turn out different head to head. That would then seem to lean toward that transformer alot... hmmmm

Randy Van Sykes - I have experienced that also! Both of my old strats, same era-same wood sound TOTALLY different.

Kapo_Polenton - Variance in tolerance makes sense for sure. I just have a hunch that those big ass chunks of iron are crucial. The best modded Marshalls I've heard have had a Dagnall C2668, but i've heard some also w/ that transformer that have been average. The Presence variance also triggers my interest, especially it's correlation to the output section (output transformer specifically)

Thanks everyone.

 

[Bloodrock]

Supposedly this was one of the reasons Cameron Mods were so great. He didn't just throw a generic set of mod components at any amp, but tailored every mod to sound the best that it possibly could, so they all came out different. I've never owned a Cameron but I'm sure some guys here could attest to this.

 

[michiganmusicalcraze]

Supposedly this was one of the reasons Cameron Mods were so great. He didn't just throw a generic set of mod components at any amp, but tailored every mod to sound the best that it possibly could, so they all came out different. I've never owned a Cameron but I'm sure some guys here could attest to this.

Yeah, I imagine that would be the way to approach it. But there's a reason that's even necessary, know what I mean? That's what's most interesting. Thanks

 

[O'Rourke]

It's almost impossible to build two amps that sound exactly the same.

Those old carbon comp resistors were 10% tolerance plus they drift with age. A 10k resistor could be 9k or 11k and still be within spec for example. The film caps were 10%-20% and the electrolytics are usually -10% to +30% tolerance. Add that up throughout the whole amp and there you go and that's not even factoring in inconsistent transformers and different components being used through the years by Marshall. Also there were two different presence control designs used, the earlier 5k pot one has a more even sweep.

 

[michiganmusicalcraze]

It's almost impossible to build two amps that sound exactly the same.

Those old carbon comp resistors were 10% tolerance plus they drift with age. A 10k resistor could be 9k or 11k and still be within spec for example. The film caps were 10%-20% and the electrolytics are usually -10% to +30% tolerance. Add that up throughout the whole amp and there you go and that's not even factoring in inconsistent transformers and different components being used through the years by Marshall. Also there were two different presence control designs used, the earlier 5k pot one has a more even sweep.

I didn't realize there were two different types of Presence pots used depedning on year. I did research after seeing your comment, apparently they switched around late 1978 from the 5K to the 22K pot. So that would contribute to differences in a modded JMP year 77/78 compared to a 79-- With the 5K you said it would have a better sweep, so you mean the 5K at a lower settings, would be the same as a 22K at a setting of noon or more? Thanks

 

[boost]

In addition to the above mentioned tolerance issue, you have to remember these amps were made on a production line. If they ran out of 220K resistors and the next shipment wasn't for two weeks, did they shut down the line? No, they may have been able to use a 230K and that would have been acceptable. Keep the line moving. Add all the variances up and they will all sound slightly different.

When I bought my first Marshall cab many years ago, the guy had a stock JMP that I played through. George Lynch in a box. It wasn't for sale. He and his friend ordered one at the same time, same model. He said his friends sounded like a distortion pedal. You just never know.

Guitars are the same way.