JMP Master Volume

[firego]

I used to use an electric fire element as a dummy load when I was repairing amps for a living. I used a small jubilee clip to hold the connection to the element and slide it up or down the element to adjust the impeadance(resistance). Make sure you put the element in series with the speaker and make sure the output setting on your amp is right eg 8ohm speaker 8ohm setting. This will cut the volume from your speaker. Be carefull the element will get very hot. Firegoblin.

 

[HAMPAMP TUBE AMP SERVICES]

That's it

 

[Ken]

Why would someone buy a clone of a plexi and then complain they have to play it loud to get distortion? What did you expect? That's like buying a vintage Les Paul and complainging it's too heavy.

Ken

 

[smcgov]

Why would someone buy a clone of a plexi and then complain they have to play it loud to get distortion? What did you expect? That's like buying a vintage Les Paul and complainging it's too heavy.

Ken

Gee, I think its my money?

Why would someone take the time to write a post like that, I thought this forum was about helping people out, not critizing them.

 

[Ken]

Gee, I think its my money?

Why would someone take the time to write a post like that, I thought this forum was about helping people out, not critizing them.

Well, you seem unhappy that the amp wasn't was you expected in spite of the fact it seems to be exactly what it should be. Maybe instead of changing the flavor of the amp with EQ, attenuators, master volumes mods...you should just buy a JCM 800?

Ken

 

[Viking62]

Good point Ken... besides isnt true that powerbrakes, attenuators and the like are working the tubes real hot and possibly overworking the whole rig unnecessarily?

 

[madmmx]

A post phase inverter master volume is what you want for that amp. It will get you what you want. Parts would be under $10 if you did it yourself. I couldnt see an amp tech charging more than $100. A good amp tech near me charges a $75 bench fee plus parts.

The PPIMV is pretty transparent and sounds ok at lower volumes but will sound alot better if you can get the volume up a little.I had a 1987 clone that I built and installed this master volume and I liked it alot...... And if you turn the master all the way up, the amp will sound the same as if no master was installed.

 

[Stu Blue]

Just bought a JMP hand wired clone 100 watt 1968 specs, and god damn it needs to be loud to get some good gain...any idea on how hard to add master volume and is it a good idea?

here it is....

100 watt Plexi hand wired - eBay (item 280337471754 end time Apr-28-09 08:27:29 PDT)

I might have to sell, the JTM 45 I have is much more versatile...

Thanks

With the ppimv type the only thing you'll miss is the sound of speakers being driven close to the edge of distruction. I have had one on my jtm45 since 1976, so I can use it as a practice amp. They work fine on JTMs and JMPs. BTW a JTM45 is only 30watts (80 watts for the JTM45/100) whereas the EL34 JMP is running 120 watts (60 for the 50watt).

Edit. You could try running the JMP "clean" and using a fuzz face (controlled with the guitar volume) like Jimi did.

 

[tolm]

I have a Bluesbreaker re-issue from 2007. Would the PPIMV mod mentioned here work for that? At the moment I'm happy using a decent OD pedal but it's always nice to have options

 

[rockstah]

I have a Bluesbreaker re-issue from 2007. Would the PPIMV mod mentioned here work for that? At the moment I'm happy using a decent OD pedal but it's always nice to have options

yes it would!
Mark

 

[peterichardz]

Power scaling kit here;

http://www.hallamplification.com/main.html#2,2

 

[CKCinMass]

Power scaling kit here;

http://www.hallamplification.com/main.html#2,2

That kit is for only for 50 Watt amplifiers. Has anyone used this kit before and if so, what are your thoughts? I am intrigued by it.

 

[GIBSON67]

I would yank 2 of the output tubes, and put a 5751 tube in V1. That would tame it a bit. I use a RCA 5751 with Black plates and it is the best I've tried.

I would try something simple and give the amp some time before going overboard and changing anything.

 

[Leif Johan I]

I have a JMP 69' Super Bass 100 watt, and I just bought the Ultimate Attenuator, and those two works great together, and the Ultimate Attenuator gives you the "bedroom" levels mentioned earlier in the thread.. You can find great used ones at Ebay.. ULTIMATE ATTENUATOR | eBay
Also the sound is awesome!

Good luck

 

[ElectricMagick]

I have the London Power Scale on my 1959SLP and it sounds amazing and I'm glad I did it.
http://www.londonpower.com/catalog/product_info.php?cPath=7&products_id=27

 

[yladrd61]

I have both Pre and Post PI MV's on my 1970 Super Lead and it sounds killer from bedroom levels up to too loud to stand next to without permanent hearing damage \m/> <\m/

 

[rockstah]

nice amp too!

 

[indeedido]

El34s don't produce distortion in a Marshall.
The more signal you give them the more sustain, warmth and responsiveness you get but you don't get more distortion. Power amp distortion is produced in the PI.
If you don't consider the PI to be part of the power amp then I agree with you, but traditionally it is considered to be and that is what people are refering to when they talk about power amp distortion.
The combination of PI distortion, power valve sustain/dynamics and a lot of air moving from the speakers is the cranked Marshall sound.
You get that same warmth and sustain even with less than full signal on the EL34s. Granted, a certain point you do start loosing it and you wont get it to bedroom levels. Attenuators don't do bedroom volume either.
A PPIMV let's you get the PI distortion and the sutain/dynamics at far reduced volumes and works great for gigging and even rehearsals with a drummer.
If you want to hear what EL34 distortion sounds like then disconnect the negative feedback from your Marshall and see. I doubt you'll like the results though. The presense control kinda does this for higher frequencies and most people find it a bit harsh after about 4 on the dial depending on the model we're talking about.

I had never heard this before about where the power amp distortion comes from, great information.

 

[61rocker]

@Threetone.....I'm a new member...glad to see all the useful advice and info.....Here's my question...I saw your post above about the master volume and how it affects the power section at low volumes....I have a '71 100w Super Lead that I had a tech put the master volume in the CH2 lower jack....I have to turn up the CH1 and CH2 volumes to drive it...it's beyond gutsy and I do get a lot of great comments on the sound....so....is this the same type of master volume mod that you are referring to or is mine wired differently....BTW I paid $25 for my mod.....about 7 years ago....and, I read different opinions about "Rosemary" signed amps....mine is and it's awesome.....anybody have any comments on "Rosemary".....?

 

[Vector]

Take Ultimate attenuator, and oll will be Ok ))) And it will be authentic!!!