# JMP Master Volume



## smcgov

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


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## janarn

Why should you add a master volume?
Buy a Hot Plate or a Ultimate Attenuator.


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## smcgov

because they cost mucho $$$


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## janarn

To add a mastervolum is how mucho $$$?
And the amp will not sound like it is supposed to do.


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## ThreeTone

A master volume will allow you to control the volume while still driving the preamp as much as you want. But at low volumes you won't be pushing the power section, and that's where the really sweet tone comes from.

An attenuator is the best option to get power tube saturation, touch dynamics and power tube harmonics at low volume levels. A Ho's Electronics or Ultimate Attenuator is what I'd recommend.


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## The Mick

Weber


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## HAMPAMP TUBE AMP SERVICES

There is another option that I've yet to do myself, so I can't tell you if it is expensive. POWER SCALING is a mod that reduces your amps voltages internally, kind of like using a variac without destroying the amp. Like I said, I haven't tried this myself so I can't tell you how well it works, how it affects the sound or how costly it is but I've heard some good things about it. Might be worth checking in to. I've done some builds where I've kept the preamp B+ voltages at a lower level (which works well) but POWER SCALING deals with the power amp as well.


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## AtomicRob

As I understand it (which is not very well!!!) power scaling is fairly easy to implement on cathode biased amps, because the bias will scale automatically with the power. But on fixed bias amps like a JMP or most other Marshalls, it's a lot more difficult because you have to scale the bias circuit as well to keep it biased properly as the power level changes.


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## HAMPAMP TUBE AMP SERVICES

That is correct, everything is scaled except the filaments. More costly than a master volume also. I guess you could also try something like THD yellow jackets to tame it down but that's probably costly too. Let's face it, you're probably better off selling it.


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## smcgov

anybody have an idea what a mv install would cost??


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## HAMPAMP TUBE AMP SERVICES

Well, I can't speak for other techs cause everybody charges differently but if you were local to me, it would cost you about $35-$40 plus parts, I haven't priced parts for awhile but I'd say less than $75, but a lot of shops charge that for an hours worth of labor so I really couldn't give you any guess at all. Also depends on which master you want, most of them only require a standard pot, a couple require a dual-ganged pot. Check your local shop and see how much they charge for labor, multiply that by 3 and add another 15-30 for parts and you might be close.


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## PaoloJM

Ask the tech about the Lar Mar version of the post phase inverter master volume. These sound great in JMP type amps. Check out a guy called Rockstah on soundclick for some of his sound samples.

The sweet power amp distortion comes from driving the phase inverter hard, heavily overdriven power valves don't actually produce that great a tone.

A normal master volume limits the signal to the phase inverter so you don't get any of the PI tone. That's why people prefer attenuators.

The LarMar allows you to drive the PI hard and limit the signal to the power valves instead, which sounds great IMO.


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## janarn

You can't get the sound of EL34 distortion from a 12ax7 in V3 (PI).
The only way to get that is to play loud, or use an attenuator.


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## PaoloJM

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.


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## janarn

Well I have tried different master volums on Marshall modells,
and my ears tell me that they don't sound as good as an original Plexi.

I think mastervolum only works on amps with more gain stages in the preamp, 
than on the classic Marshall four holers.

That's why the early 2204 amps didn't sound good until they cascaded the preamp.

Models based on preamp distortion works well with MV, old Plexis don't.


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## PaoloJM

I agree with you, there a lot of very bad master volume mods out there.
For some reason some techs think you put a 2203/4 stlye master volume in a 1959 type circuit. As you point out, they do not sound good.
Many post phase inverter master volumes don't sound good in a plexi either.

Lots of people seem to think that a master volume is a master volume. This, however, is not the case.
There are an estimated 60 variations of master volume type out there today. Different types work well in different amps. Plexi amps definitley need the master volume to be installed after the phase inverter.
The guys over at Metroamp came up with PPIMV variation called the LarMar (mentioned in my previous post). When installed well properly in a '68 spec plexi it absolutley nails the early Van Halen tone, once it's turned up past three on the dial. I think most would agree that the tone on Van Halen I is thee cranked plexi tone.
When used with an attenuator you can approach bedroom volume this way.


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## HAMPAMP TUBE AMP SERVICES

The Metroamp PPIMV kit is nothing more than a Ken Fisher master volume circuit in a kit form, it's been around since the 70's and it is in my opinion the best master volume circuit to use. I've even taken the standard master out of 2203's/2204's and installed this one instead and they sound much better. Good advice and recommendation.


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## PaoloJM

It's a bit different than the Ken Fisher version. Fisher used a 100k dual pot.
The LarMar uses a 250k with a 2.2Meg between the wiper and V bias.
This has two advantages; the 250k with 2.2Meg = 220k when dialed right up. This is the exact same as the stock circuit without the mod. 
Secondly the 2.2M resistor keeps V bias on the grid even if the pot wiper fails, which prevents tube melt down.
It works on the same principle as Ken Fishers but with two important enhancements, isn't this how all great ideas come about!!


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## HAMPAMP TUBE AMP SERVICES

Yea ,I always used the 250k instead of the 100k because I've always installed them on EL34 Marshall's and the early problems with this circuit was with pot failure.


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## smcgov

this??

Metroamp Parts Store

is all I need? I am so confused....


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## 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.


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## HAMPAMP TUBE AMP SERVICES

That's it


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## 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


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## smcgov

Ken said:


> 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.


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## Ken

smcgov said:


> 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


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## 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?


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## 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.


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## Stu Blue

smcgov said:


> 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.


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## 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


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## rockstah

tolm said:


> 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


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## peterichardz

*Power scaling kit here;*

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


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## CKCinMass

peterichardz said:


> *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.


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## 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.


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## 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


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## 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


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## 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/


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## rockstah

nice amp too!


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## indeedido

PaoloJM said:


> 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.


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## 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".....?


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## Vector

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


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## yladrd61

smcgov said:


> 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



I have both a Pre and Post PI Master Volume on my 1970 Super Lead I can get the sound I want from talking volume up to Permanent Hearing Loss and my Power Tubes last a long time


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## AlvisX

I would think a 1959 CLONE to be the perfect candidate for a ppmv.
I mean you wouldn't wanna put one in a real one ...? I mean I guess most folks wouldn't 

I could kinda care less. I think at least 4 of my "vintage" amps have a ppmvv, 2 of 'em Marshalls and I bet if I didn't tell you they were there, you'd be none the wiser . I probably dont use it below 70% of full volume anyway , BUT I believe the 30% is probably keeping me employed just a little bit more than before. The people that hire you to play gigs dont give a damn about my tubes
And a ppmv is cheap & easy ...you can use common household items...common around my household anyway

preamp distortion , pwr amp distortion...tone comes from the fingers...tone comes from the gear 

I know noTHING , my name is M'Fckn Schultz....Im just a guy makin a living with this sh*t that alst 16 yrs or so

@ Rockstah, your amps sound killah !!


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## Pleximan

PaoloJM said:


> It's a bit different than the Ken Fisher version. Fisher used a 100k dual pot.
> The LarMar uses a 250k with a 2.2Meg between the wiper and V bias.
> This has two advantages; the 250k with 2.2Meg = 220k when dialed right up. This is the exact same as the stock circuit without the mod.
> Secondly the 2.2M resistor keeps V bias on the grid even if the pot wiper fails, which prevents tube melt down.
> It works on the same principle as Ken Fishers but with two important enhancements, isn't this how all great ideas come about!! [/QUOTE
> 
> 
> Question...How does the LARMAR work with a FX loop? Does delay get distorted? What loop design works well with LARMAR?


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## slide222

well i'm old school and believe that a tube amp should be driven naturally to get the sound you require , and have never been keen on master volume. maybe get a 20 watt-


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## Viking62

HAMPAMP TUBE AMP SERVICES said:


> That is correct, everything is scaled except the filaments. More costly than a master volume also. I guess you could also try something like THD yellow jackets to tame it down but that's probably costly too. Let's face it, you're probably better off selling it.



Naaa tried the Yellow Jackets on my 1959SLP, makes fuck all difference to the volume control and I'm pretty sure it changed the tone a bit too which I didn't like.
I took em out and just have to live with a very very loud amp if I want the "Crunch". and get it down to a manageable volume, I generally run a Fulltone OCD pedal through it as it doesn't tend to change the sound too much.. Dosent worry too much though as I've got 4 of the Bastards to run between.. ha ha


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## Goatroper

Viking62 said:


> Naaa tried the Yellow Jackets on my 1959SLP, makes fuck all difference to the volume control and I'm pretty sure it changed the tone a bit too which I didn't like.
> I took em out and just have to live with a very very loud amp if I want the "Crunch". and get it down to a manageable volume, I generally run a Fulltone OCD pedal through it as it doesn't tend to change the sound too much.. Dosent worry too much though as I've got 4 of the Bastards to run between.. ha ha


 
I was always curious about the Yellow Jackets but never tried them. Can you explain further why you didn't like them? Im not catching your dialect.


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## sct13

I just did an amp build of a 1959 (Metroamp), I tried it at full tilt and and WOW! What a tone, but of course it is too loud, since it was a kit build I had no problem putting in the LARMAR, and that works very well. I am taking it to band practice on Friday, I will see then.
It was easy to build and install the LARMAR parts are available at "valvestorm" 

It wasn't until I installed this that I found out about the Variable Variac switch....But... it was then I discovered that the kit I did get, had the transformer option that does not allow this. The variable variac put less Voltage to the plates and therefore a closer approximation to the "Brown Sound" So a second 80% tap on the Power Transformer is required. 

maybe the next build....


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