# Help picking a Master Volume (PPIMV) mod to install in my vintage amp



## traynor_garnet

Looking for some informed advice if anyone could be so kind to help a layperson out.

I have a very early Traynor Bassmaster (7027s and tube rectified) which is very close to a Tweed Bassman/JTM 45 circuit. The amp is amazing but it is also very loud. Before I try yet another attenuator, I was thinking of having a Master volume installed. Of course, the question then becomes, "_what type_ of master volume" will work best in this particular circuit?

In doing some research it seems that post phase inverter master volume (PPIMV) controls are often lauded as the best. Yet there are different types of PPIMVs with supporters for lar mar style and supporters for the Ritch style. These discussions are quite technical, however, and they quickly go way above my head.

So, in my particular amp, what would you recommend?

Any advice would me much appreciated.

TG


----------



## JHarasym

Following this with interest. Would power scaling work in this amp?


----------



## traynor_garnet

JHarasym said:


> Following this with interest. Would power scaling work in this amp?


Power scaling is quite invasive so I am not too interested in doing it on a vintage amp. It is also much more expensive than a MV so I would probably go attenuator before power scaling (no mods, same price).

TG


----------



## mhammer

I did a PPIMV on a blackface Tremolux some 25 years back, and I rather liked it. I had converted it to use 6CA7 power tubes (same as EL34) so the comparison to Marshalls is moderate. This is the PPIMV that uses a dual-ganged 250k-1M pot and the extra series cap. I sold the amp a while later, so I have no idea what the impact on tube life was, but it sounded good.


----------



## WCGill

Lar Mar PPIMV is best for Marshall style circuits. It's my go-to.


----------



## traynor_garnet

WCGill said:


> Lar Mar PPIMV is best for Marshall style circuits. It's my go-to.


Thanks for the input. Since this amp is as much Bassman as it is JTM 45, would you still classify this a 'marshall circuit' and go with the Lar Mar?

Thanks so much,
TG


----------



## WCGill

To me, they're identical circuits, just component values being different so there should be no problem.


----------



## dcole

I believe the Lar/Mar mod replaces the grid bias resistors with potentiometers on the power tubes.

The Rich mod adds potentiometers in between the phase inverter and power section using capacitors to feed into the pot and out of the pot to eliminate dc voltage on the pot.

I have done the Lar/Mar succesfully on a Marshall JCM800 and a Traynor YBA1. They both worked well. I think a power scalling system is just as invasive as PPIMV unless you are removing one of the speaker cabinet connectors to put the potentiometer in.


----------



## High/Deaf

Don't know if you really want to compare an old one to a re-issue, but both the Tribute and the Mod1 use a Rich-type MV, although it is a stepped attenuator rather than a variable pot. But you may be able to see if you like what it does if you test one at LM. You could borrow their values for resistance and capacitance, but use a pot instead. 

I don't know if the originals and the re-issues use the same component values around the PI and output tubes though. So I may be talking out my arse. Just a thought.


----------



## jb welder

High/Deaf said:


> Don't know if you really want to compare an old one to a re-issue, but both the Tribute and the Mod1 use a Rich-type MV, although it is a stepped attenuator rather than a variable pot.


Yes, I guess if you use a pot, you can't pretend it's a power attenuator and call out the steps in numbers of "watts" :congratulatory:

But the mod1 circuit is a little different from the rich as the pot is only being used as a rheostat, so a pot there would have the third leg floating, rather than having a ground reference.


----------



## High/Deaf

Yea, that 'attenuator' label is a bit libelous. But not the most misdirected information I've seen from an amp manufacturer. The more I read about a few of the boooteeek builders, the more I wonder what planet their from, and how sound works there. What exactly are haunting mids? Or crystal lattices? And I thought the hi-fi business was goofy with artsy-fartsy terminology. These guys could show Monster Cables a thing or two.


----------



## JHarasym

traynor_garnet said:


> Power scaling is quite invasive so I am not too interested in doing it on a vintage amp. It is also much more expensive than a MV so I would probably go attenuator before power scaling (no mods, same price).
> 
> TG


I put one in a deluxe with little invasiveness. Trinity has their Voltage Regulation Module for about $50 shipped: http://www.trinityamps.com/phpbb/viewtopic.php?p=16812
It lowers the B+ and reduces stress on the output tubes. I'm just not clear whether it's suitable for a YBA-1


----------



## traynor_garnet

Hello again,

I am sending my amp to my tech for a cap job so I thought I might have the PPIMV installed while he is at it. I just found this video and it sounds good. Not sure "what type" of PPIMV this is:

[video=youtube;mJ_bxZhbMik]https://www.youtube.com/watch?v=mJ_bxZhbMik[/video]


----------



## Vostre Roy

Looks like a LarMar type, but its hard to judge withtout a proper closeup of the pot, but from afar it seems like a dual pot.

I've added a LarMar type PPIMV in my '72 Bassmaster (exactly the same model that is shown in that video), its pretty great as it allow you to get a nice tone even at low volume. In fact, I've added those PPIMV in three amps and a slightly different type of PPIMV in my JCM800 clone and so far, I'm way more pleased with the LarMar.


----------



## traynor_garnet

Thanks for the post. Does the LarMar make your hi range expander (presence) ineffective when you have the master low?

Are you a tech?

TG



Vostre Roy said:


> Looks like a LarMar type, but its hard to judge withtout a proper closeup of the pot, but from afar it seems like a dual pot.
> 
> I've added a LarMar type PPIMV in my '72 Bassmaster (exactly the same model that is shown in that video), its pretty great as it allow you to get a nice tone even at low volume. In fact, I've added those PPIMV in three amps and a slightly different type of PPIMV in my JCM800 clone and so far, I'm way more pleased with the LarMar.


----------



## Church-Audio

Check out this link it explains some of the basic master volumes and how they work. Ken Fischer now deceased from Train Wreck amps was a genious when it came to amp building mods and repairs. 
http://www.blueguitar.org/new/schem/trainwreck/the_trainwreck_pages.pdf this is an extreamly good source of info on amps in general. This guy had forgotten more about amps than most techs could ever remember. He was and still is a legend.


----------



## Vostre Roy

traynor_garnet said:


> Thanks for the post. Does the LarMar make your hi range expander (presence) ineffective when you have the master low?
> 
> Are you a tech?
> 
> TG


The presence pot still works at low volume, maybe not as well as when the amp is getting driven but it still does.

And no, I'm no tech lol. Just a passionate dude who's dwelving into amp builds and mods. I don't get into very technical stuff for that reason, I leave that to people like Church-Audio who seems to have both experience and knowledge on the subject. I try to share what I know and gather more information on what I don,t know


----------



## Church-Audio

Vostre Roy said:


> The presence pot still works at low volume, maybe not as well as when the amp is getting driven but it still does.
> 
> And no, I'm no tech lol. Just a passionate dude who's dwelving into amp builds and mods. I don't get into very technical stuff for that reason, I leave that to people like Church-Audio who seems to have both experience and knowledge on the subject. I try to share what I know and gather more information on what I don,t know


most of us learned the subject of amp repairs by doing what your doing gathering information. Most of us started long before the Internet  it's avgreat ressource I still use daily. But there is good information and very bad information out there. Aiken amplification is a great resource if you want to learn more.


----------



## stormbringer

A Lar/Mar is easy to install and works pretty well. It does replace the stock grid leak resistors that are important components of the outputs section - pots aren't as reliable as fixed resistors, so it is possible to have a problem down the line.

Some famous techs prefer a type of PPIMV that is available online if you a google-image search for Bruce Collins Mission Amps PPIMV. It is also very good. 

Miscellaneous notes: 
- most PPIMVs use a dual-gang pot (except a cross-line master); they differ in other ways.
- the Lar/Mar was in use before Larry and Mark re-invented it on the Metro amps forum. It shows up as a 'bad PPIMV' in one or two of Kevin O'Connor's TUT books.


----------

