JTM45 and Master Volume Options – Pros and Cons?

BenTobith

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Hi all,

As I start to enter the home stretch of my preparations for a JTM45-based build (starting point is the Valvestorm/Metro kit), I’m contemplating Master Volume.

My main “use case” for this amp will be as a Marshall voiced, clean platform for effects pedals. Not planning to use it much for cranked or power amp-induced distortion, as I have another Marshall build for that.

I’ve looked at the various Master Volume options, some of which are as simple as tying into the Treble pot, with others being post-Phase Inverter and more involved as far as the implementation goes. For example, this one has my attention as a good option: http://valvestorm.com/Amp Mods/PPIMV

However, I know some of the Master Volume approaches can have downsides, as well. Whether that is changing the tone or characteristic of the amp below a certain level, interfering with or even disabling the Presence control, and so forth.

For those that have experimented or tried a few MV options on a JTM45 or JTM50 style build or amp, what are your thoughts and suggestions? Pros and cons?
 

ToneWitch

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Ken Fischer Trainwreck #2 PPIMV

Hands down the absolute cleanest and most transparent master volume circuit I have used.

The full amp is still there if you want it. And you can get it quieter than the vibrations of the strings off your electric guitar. Quieter than bedroom level and doesn’t sacrifice any of the tone as far as I can tell.

It’s the MV I put in all my amps now. Can’t recommend it enough.

I use shielded cable for the leads and tie the ground of the shielded to the ground on the pot


E6FC64E8-AC53-43EB-B7E8-EB532D20D02D.jpeg
 
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BenTobith

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Ken Fischer Trainwreck #2 PPIMV

Hands down the absolute cleanest and most transparent master volume circuit I have used.

The full amp is still there if you want it. And you can get it quieter than the vibrations of the strings off your electric guitar. Quieter than bedroom level and doesn’t sacrifice any of the tone as far as I can tell.

It’s the MV I put in all my amps now. Can’t recommend it enough.

I use shielded cable for the leads and tie the ground of the shielded to the ground on the pot


View attachment 104627
Thanks!

So are you saying the grounds for the shielded wires you ground to lugs 1 or 4 in the diagram from Rob? Did you do shielded wire for both the 2/5 wires and the 3/6? Regular wire for 1/4 to the bias connection?
 

BenTobith

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You won’t need a MV if you’re not trying to drive the power tubes. It will have great cleans at a reasonable volume, unless you have a sleeping baby or live in an apartment.
Right, I think I’m going to build without one, but wanted to keep some options in mind in case I decide I need it. Would like to be able to play it at reasonable volumes in the evening (in a house), clean, which I think I should be able to do.
 

Chris-in-LA

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Right, I think I’m going to build without one, but wanted to keep some options in mind in case I decide I need it. Would like to be able to play it at reasonable volumes in the evening (in a house), clean, which I think I should be able to do.
The problem I had was the the cleans sounded so good I kept wanting to turn it up!
 

SLA

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Had an plexi build 100 watter before, worked great with an ppmiv.
Now I have the studio vintage 20c - even better, dont need an ppmiv as a volumebox into the effectloop does the same thing, both are after the phaseinverter-tube. I think a lot of the magic lies in the preamp and the phaseinvertertube (part av poweramp). Most of the poweramp distortion happens in the phaseinverter-tube anyway. You dont get that in the same way with say an jcm2204 with mastervolume. I also have an 2204 jmp.. the truth is in the ears, not some ol myth about the holy power-tube distortion..
 

themidnighter

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Go w/ a power attenuator. I've tried many master volumes (Post and Pre-PIMV, VVR, whatever). none one them ever pleased me as much as an attenuator. I use a power plate, but you can find some fancier ones (all directions points toward the toneking).
 

obx351

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Burke Hunn of Hunn Amplification, http://hunnamps.com/Site/Main.html, has built me four custom amps, '64 spec JTM45, '66 spec JTM50 (both made with vintage and spec correct custom parts) and two 18-22 watt combos based on his own specs. All of them have a PPIMV and I love the volume control. He puts the PPIMV dial in the back of the amp and for the most part it's set and forget for my use. But if I need to dial it back it works very well. I think it works as well and maybe better than my aracom attenuator that I use on my '73 JMP 50.

This is not what you were asking for but it's a great alternative as stated above by ToneWitch. Reach out to Burke if you have any questions. He can be hard to reach but is a great guy.
 

lespaul339

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I have a PPIMV in my JTM45 that I built. I love it. I use it all the time for low volume playing. I'd put one in if I were you. If you don't want to use it you don't have to, but that way it's there if you decide you do want one.
 

pjd3

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I suppose a PPIMV is good if you want to get a little more preamp overdrive effect. I installed one in my 20 watt plexi build. Most of the time it is all the way up as I use the amp as a clean and pedal platform at this time. But, if I wanted some crispy bacon grease, I could turn the PPIVM down and crank the input volumes, or use a drive pedal for that response. My PPIMV is very well behaved but it needs to be installed well. I used a PEC dual ganged pot for better tracking and wiper action, plus, applied the -50volt bias voltage onto the shields of the board-to-pot connecting wires for an extra level of noise reduction. I spent 3-4 hours just on the wiring of the pot to make sure everything was done to the best standards I could muster. And it is a very well behaved and transparent addition to the amp. I'd say it doesn't hurt to have it even if I never used it.
Best,
Phil D
 

Pete Farrington

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Most of the poweramp distortion happens in the phaseinverter-tube
That idea seems to get widely repeated on Internet forums, but it’s almost invariably incorrect.
As the signal level fed to a valve power amp is increased from 0, the first stage where clipping occurs is the output valves. If the amp is ever to put out full power, how could it be otherwise?
For class AB1 amps such as the JTM45, the first clipping point is typically the control grids of the output valves. It’s exactly the same mechanism as described by Merlin in section 1.14 Grid Current Clipping, see http://www.valvewizard.co.uk/Common_Gain_Stage.pdf
However, with its 8k OT primary impedance, the JTM45 is unusual, and this high value of load impedance generally causes anode current cut off clipping to occur first, see the preceding section of the above link, 1.13 Cut Off Clipping.
Of course, as the signal level is increased past the point of cut off clipping, grid current clipping still occurs, it’s just that the output valves are already being overdriven.


I fitted a type 4 master vol to my JTM45 type build, 2204 style. 6k OT.
Plugged straight in, there’s not much depth of preamp overdrive available. But with a pedal, even just a treble booster, that situation changes.
With the channel and master vols cranked, and a booster etc pedal, as the master is turned down, I can’t hear the tonal / response change; it just gets quieter. Which surprised me, I thought it would be obvious when the output valves stopped being the primary clipping mechanism.

I’ve tried a LarMar style type 2 master vol on previous builds, and that’s pretty good too. I didn’t like it on JTM45 type amps because I use its presence up full, and type 1, 2 and 3 master vols lose the presence boost and high degree of damping factor, which is an unusual characteristic of that amp.
 
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SuperFleeky

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Hi all,

As I start to enter the home stretch of my preparations for a JTM45-based build (starting point is the Valvestorm/Metro kit), I’m contemplating Master Volume.

My main “use case” for this amp will be as a Marshall voiced, clean platform for effects pedals. Not planning to use it much for cranked or power amp-induced distortion, as I have another Marshall build for that.

I’ve looked at the various Master Volume options, some of which are as simple as tying into the Treble pot, with others being post-Phase Inverter and more involved as far as the implementation goes. For example, this one has my attention as a good option: http://valvestorm.com/Amp Mods/PPIMV

However, I know some of the Master Volume approaches can have downsides, as well. Whether that is changing the tone or characteristic of the amp below a certain level, interfering with or even disabling the Presence control, and so forth.

For those that have experimented or tried a few MV options on a JTM45 or JTM50 style build or amp, what are your thoughts and suggestions? Pros and cons?

I second the mention of the Ken Fischer Trainwreck #2 PPIMV. I know you wrote about your JTM45 being used for a pedal platform, but once you hear how great that amp sounds in the crunch zone, you may want to use that from time to time, and that's where the Master volume will obviously come in handy. I've put in PPIMVs on both of my JTM45 and 1987... in fact, I've put in two that are foot switchable. Now I can use them live, crank em up to get that killer crunch tone, but control the volume. I like having two levels for solo boosts; hence the two master volumes (there are no effects loops to boost with these guys). At any rate, I think these PPIMV work really well with preserving the tone at lower volumes.
 

sackvilledan

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Go w/ a power attenuator. I've tried many master volumes (Post and Pre-PIMV, VVR, whatever). none one them ever pleased me as much as an attenuator. I use a power plate, but you can find some fancier ones (all directions points toward the toneking).

This is what I came here to say. Big fan of the Alex Attenuator, which I think was purchased and is now marketed by another company. The only thing that does my Bluesbreaker justice when I want to crank it without losing my hearing.
 

Gene Ballzz

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Had an plexi build 100 watter before, worked great with an ppmiv.
Now I have the studio vintage 20c - even better, dont need an ppmiv as a volumebox into the effectloop does the same thing, both are after the phaseinverter-tube. I think a lot of the magic lies in the preamp and the phaseinvertertube (part av poweramp). Most of the poweramp distortion happens in the phaseinverter-tube anyway. You dont get that in the same way with say an jcm2204 with mastervolume. I also have an 2204 jmp.. the truth is in the ears, not some ol myth about the holy power-tube distortion..

@SLA ,
You may be mistaken on the location of the EFFECTS LOOP in the circuit of the SV20, although that matters little if the solution you've described works well for you! Remembering of course, that the sound actually coming from your amp matters little to the audience, but is most important to enhancing your comfort and inspiration level while playing! The audience won't notice your sound as much as they will notice a stellar performance!



Go w/ a power attenuator. I've tried many master volumes (Post and Pre-PIMV, VVR, whatever). none one them ever pleased me as much as an attenuator. I use a power plate, but you can find some fancier ones (all directions points toward the toneking).


Yes, a good attenuator is the best solution, by far! Sure, attenuators get a bad name because of all the junk units that have been put out since the early '70s and/or the fact that really good ones have enough added features to make them quite pricey. The hands down best and most transparent "simple, passive" attenuator for under the +$500 is the @JohnH design (linked below), with material costs between $75 & $125, depending on added features and/or parts sourcing. Even if someone needs to be hired to build it, the cost will still come in much lower than any of the commercially available units and testing has shown the JohnH design to actually perform even better that most (if not all) other passive units.

All the important info is in post #1 of this huge thread and tips for layouts and packaging suggestions show up up throughout this very informative thread, but especially around page # 110 and beyond. There is a lot of great testing info throughout the thread, making it a very worthwhile read and any useless chaff is easily skimmed past.

These units well retain all tone, response and feel throughout the full range of attenuation. One small disclaimer is that at maximum (baby sleeping in the next room) attenuation, you can't really avoid the loss of the effect of air movement by the speaker!


With all that said, there is certainly nothing wrong at all with a well implemented MASTER VOLUME! Having multiple options (with varying plusses and minuses) for taming the volume is always a good thing.

Still Attenuatin'
Gene
 
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neikeel

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Like a lot of people here I have tried various MV types (stock pre-PI MV, Rich mod, Fischer as proposed above, and crossline). I also have x3 attenuators (Hotplate, Sequis Motherload Elemental and and Alex).
The Rich mod (as used on a lot of Metro builds is pretty good but does add a smidge of distortion). The Fischer Type 2 is ok on bigger amps (100w plexis) and only down side is the diminished effectiveness of the presence. I did not really like it on 18w or on JTM45s unless it was in 75% or higher. I no longer use PPIMV on my amps and much prefer the Alex. The Elemental has been stolen by my son (because of its recording tweaking abilities) and the Hotplate is for testing and minimal attenuation.
YMMV and you may have to go this road of discovery for yourself as your conclusions may be different and you may decide to go with the expensive all singing attenuators/reampers although I prefer simple and the Alex works for me.
 

dro

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With A JTM45, using as pedal platform. No need for MV, and no need for attenuator.
If you don't want it loud, don't turn it up.
 

mike_lawyer

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Is there a tonal difference at lower volumes with a Type 2 PPIMV due to the lack of negative feedback? I have always wanted to try a PPIMV on a Plexi. I have a 20 watt 6v6 Plexi with a regular pre-phase inverter master, it works well and if I need more grit, I just use a boost pedal.
 

Pete Farrington

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Is there a tonal difference at lower volumes with a Type 2 PPIMV due to the lack of negative feedback?
Yes. The power amp frequency response changes as a type 1-3 master vol is turned down, and the presence control will become less and less effective.
But details matter, and your amp will probably have a lower degree of negative feedback than a typical JTM45.
 
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pedecamp

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Hi all,

As I start to enter the home stretch of my preparations for a JTM45-based build (starting point is the Valvestorm/Metro kit), I’m contemplating Master Volume.

My main “use case” for this amp will be as a Marshall voiced, clean platform for effects pedals. Not planning to use it much for cranked or power amp-induced distortion, as I have another Marshall build for that.

I’ve looked at the various Master Volume options, some of which are as simple as tying into the Treble pot, with others being post-Phase Inverter and more involved as far as the implementation goes. For example, this one has my attention as a good option: http://valvestorm.com/Amp Mods/PPIMV

However, I know some of the Master Volume approaches can have downsides, as well. Whether that is changing the tone or characteristic of the amp below a certain level, interfering with or even disabling the Presence control, and so forth.

For those that have experimented or tried a few MV options on a JTM45 or JTM50 style build or amp, what are your thoughts and suggestions? Pros and cons?
I have a LarMar PPIMV in my 1959 and it works great. :yesway:
 

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