Still not sure about some JVM mods

Ken Ops

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So I’ve been considering doing the choke mod, and maybe OD2->OD1 (I have the 210H, so if OD1 is “better” it will be worthwhile). Been looking into various info, like this: http://www.valvewizard.co.uk/smoothing.html - must admit, some of it’s still a bit beyond me.

First of all, I don’t want to damage the amp, cause any issues, reduce its life, or add any noise, etc.

What I do want is slightly cleaner power, so the choke makes sense to me. Regarding “feel”, how does the choke affect that, vs. the resistor? And maybe a bit more “classic” OD tone, though I don’t know exactly how this alters the EQ(?). So the OD2->OD1 mod is a maybe.

In general, I like the JVM, and have got used to dialing in the sounds that work for me, just as any guitarist will do with any amp. But if there’s a couple of minor mods that will change it for the better, why not.
 

Ken Ops

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Isn’t that the whole idea of adding a choke to a guitar amp - cleaner (i.e., less ripple) power?

Clearly, I ain’t no tech. Just trying to understand these mods, their purpose, and what is likely to actually happen if they’re done.
 

Pete Farrington

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Ok, I wasn’t clear whether you meant the HT power supply, or the amp’s max audio power output, or something else.
The lower ripple, potentially stiffer HT provided by a choke is only really going to affect the screen grid’s HT supply node, and is only really going to make much difference at very high power outputs, especially overdriven.
Under such conditions, it may be worth pointing out that the stiffer, slightly higher voltage screen grid node will put more stress on the output valves.
Unless you’re pushing the power amp hard like that, I’m not sure that there’d be much effect / benefit in fitting a choke.
The amp is mainly about generating a monster tone in the preamp, then making it louder with the power amp (plus adding some spice with the presence and resonance).
 

Moony

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I’m not sure that there’d be much effect / benefit in fitting a choke.

Thank you so much for pointing that out!
I said it all the years that I never got the rave about adding a choke to the JVM from all the people who claimed "it turned the JVM into a whole different amp".

I suppose most of them thought so because they did a couple of mods the same time like reducing the plate resistors to get less compression or lowering the NFB.
The choke alone wouldn't alter the sound noticeably, it's more kind of a feel thing.

And to be honest, I don't think that Marshall left out the choke with this amp just to save production costs. It's Marshall's flagship amp and they even added a choke to the small 20W Mini Jubilee which is way less expensive (at least in the US).
They built in a choke for the JVM HJS Satriani version but that one isn't as much a modern high gain amp, less compressed sounding (100k plates) and less tight with the classic 100k at 4 ohms NFB (the regular JVM has 82k at 16 ohms).

Here's a video before and after adding a choke at a Peavey 6505MH (small version of the big one with a mosfet phase inverter):

 

saxon68

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Marshalls flagship amp were and will
forever be the triade of JTM45/1959/2203.

Or the 200W MAJOR.

Jvm.Please.:hmm::lol::iough:
Can’t take this comment seriously. The JVM has been the flagship since it came out.

The others are classics for sure. But they’re not current.
 

Whiteknuckle

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The OD2 to OD1i wouldn’t really bother with, as I can make the OD2 sound exactly like OD1 just by gunning the bass up 3, and the mids 2 notches higher than what I have set on OD1.
I find that OD2 is good for my down tuned guitars. I’d do all my leads in OD1 Red, as it’s the fattest, with EQ controls closer to 12 o’clock. If you don’t mind the knobs being at “extremes”, then I wouldn’t bother with that mod.
 

jagrenet

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So I’ve been considering doing the choke mod, and maybe OD2->OD1 (I have the 210H, so if OD1 is “better” it will be worthwhile). Been looking into various info, like this: http://www.valvewizard.co.uk/smoothing.html - must admit, some of it’s still a bit beyond me.

First of all, I don’t want to damage the amp, cause any issues, reduce its life, or add any noise, etc.

What I do want is slightly cleaner power, so the choke makes sense to me. Regarding “feel”, how does the choke affect that, vs. the resistor? And maybe a bit more “classic” OD tone, though I don’t know exactly how this alters the EQ(?). So the OD2->OD1 mod is a maybe.

In general, I like the JVM, and have got used to dialing in the sounds that work for me, just as any guitarist will do with any amp. But if there’s a couple of minor mods that will change it for the better, why not.
My JVM410H has a 10H choke and let me tell you, ....... It makes a great difference, regardless of volume setting. I would definitely suggest adding one.
 

Ken Ops

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My JVM410H has a 10H choke and let me tell you, ....... It makes a great difference, regardless of volume setting. I would definitely suggest adding one.

Interesting. What kind of difference has it made, to your ears?
 

jagrenet

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Interesting. What kind of difference has it made, to your ears?
To me it sounds tighter, ...... with a little extra "oomph" or punch overall. There are several mods in mine however, the choke is definitely distinguishable to the others.
 

South Park

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The choke and filter caps are like a back up power supply when the voltage drops on the tube plates the transformer does not see it . It can make a difference in tone and feel
 

Karl Brake

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Kruse Kontrol in LA does great JVM mods that clear up and beef up all channels without adding a choke, with switches to take any channel to stock when desired. Really fine work....made a great stage amp out of my 215c and 410h....I can pretty much leave the noise gate off, unlike with stock JVMs. Onstage they can be a pain. Unless you're Neil Schon and have an incredible sound team/front of house rig. He leaves the beast at conversational volumes on stage and lets the sound engineers worry about everything else.
 

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