diggy_dude
Now 169% diggier!
guts...somewhere in this mess that only NASA understands is the roadmap for tone.....
If Danny Partridge, legendary bass strummer of stage and screen, can figure it out, so can you.
New amp for Greg - Bladow! (lots of pics)
- Thread starter Greg_L
- Start date
If Danny Partridge, legendary bass strummer of stage and screen, can figure it out, so can you.
Playing the what?
No I really like the 900, this one is better though. I might start using the 900 for bass.
jonny deep
Disappointing Member
Oh man. There's someone in selling a mint condition JVM410H for £725. He says he got it as a backup amp when he was gigging lots, but never actually used it. So, it's been sitting in a flight case (occasionally let out for fresh air) and is totally like new.
It's a great price for mint condition, but not sure about any warranty or anything. It is in Swansea (Wales), though, and I really can't justify it right now. I would love to own a proper Marshall, but I'd need to upgrade speakers as well and I haven't really tested the full capacity of my current amp (and have yet to build an iso-box to be able to crank it properly).
I got serious GAS, though!!!
I won't be buying it, but if anyone in the UK is interested, it's on Gumtree, just search for JVM. Looks like he listed it for £750 a few weeks back and has dropped the price to £725 this week.
It's a great price for mint condition, but not sure about any warranty or anything. It is in Swansea (Wales), though, and I really can't justify it right now. I would love to own a proper Marshall, but I'd need to upgrade speakers as well and I haven't really tested the full capacity of my current amp (and have yet to build an iso-box to be able to crank it properly).
I got serious GAS, though!!!
I won't be buying it, but if anyone in the UK is interested, it's on Gumtree, just search for JVM. Looks like he listed it for £750 a few weeks back and has dropped the price to £725 this week.
ibleedburgundy
The Anti-Lambo
I am looking at the combo version. I can't think of any reason to get the half stack unless I wanted to record with the cab in an iso booth with the head outside but I don't have an iso booth although I might acquire one someday. I went to guitar center to play one but they didn't have it in stock.
You think a 100w 2x12 combo is gonna be that much quieter? Man up. I track sitting right next to a halfstack, and it's fucking exhilarating.
I played with the speaker emulated line out yesterday, and wow, that shit sounds pretty damn good. It really does sound natural. It sounds like the Marshall folks emulated a near speaker-edge mic placement. Good, but a little too dark for my liking. It was nice though. I tried it in conjunction with a mic'd cab, and phase issues reared their ugly head. I had to slide the line out track a little to line up with the mic'd speaker track. Then it was okay, but not worth the effort IMO. So....for late at night cranked sound, sure the speaker emulated out will do, but it doesn't beat a mic'd cab.
diggy_dude
Now 169% diggier!
This new guitar is gonna be 40 years old before the new wears off, isn't it? 
This new guitar is gonna be 40 years old before the new wears off, isn't it?
Hey, this is the new amp thread.
diggy_dude
Now 169% diggier!
Oh, sorry. Same question applies though.
Lol. I'm still feeling my way around. There's so much stuff this amp can do. One thing it can't do without being at blazing wide open volume is get that kind of squishy open power section sound like the JMP/2203's. This amp sounds awesome across the board, but it only hints at true vintage Marshall tones. I found an easy mod that reduces the negative feedback within the amp and allows it to act more like a 70's/80's circuit if you want it to. It's a resistor and an extra knob. You can dial it up to keep the stock high negative feedback power section behavior for tight metal sounds or sparkling cleans, or you can dial the negative feedback out to get the raw sound of a power section melting down like a JMP/2203. Some people wire it up as a switch (stock/JCM). With the knob you can go anywhere in between. I'm gonna do it.
diggy_dude
Now 169% diggier!
It's nice when the gear gives you options instead of obstacles. Try not to electrocute yourself. 
It's nice when the gear gives you options instead of obstacles. Try not to electrocute yourself.
Yes, well we'll see.
I can see why Marshall didn't include this option as the amp has to fill many roles. But damn, what's one more knob on an amp that already has 28 of them? If the mod is as easy as it seems, it should just come that way. Mesas do it somewhat with their "Raw" "Vintage" "Modern" settings.
This mod really seems to help with the mid gain settings. From what I'm reading it really helps the crunch channel and "green" modes on the OD channels. Those channels/modes sound great, but they're kind of "tight".
ido1957
9K Gold Member
Nice - My bass player (who also plays guitar) bought a JVM210 and I play it almost weekly when we get together. Even the 210 has a myriad of sounds but we usually stick to 2 or 3. And the line out is great (not at all like the fizzy shit out of my 900), a little bassy compared to using a 57 but he's a bass player so he loves it haha...
Yeah the line out on the JVM is a speaker emulated line out, which is suitable for going straight into an interface. I agree it sounds bass heavy, but it's okay. The line out on your 900 (and mine) is just straight pre-amp line out and is meant for live use going straight into the board. The other says "recording" but it's useless unless you use a speaker cab simulator, and even then it's crap.
But back to the JVM, I did my first mod on this thing today. I did the "negative feedback" mod. I don't know the exact inner workings, but this is how I understand it in a very paraphrased generic layman's nutshell. Someone else please chime in with better details or to correct whatever I get wrong. Caution, long post ahead:
The JVM, like most amps on the planet, uses negative feedback (not the squeal kind of feedback) to keep the power section sounding clean and tidy. The power section is kept tight by re-introducing the signal and certain frequencies and noise gets cancelled out. The stock resistance in the feedback circuit is relatively low, so that makes it hard for the power tubes to crunch up and add that rich juicy power tube saturation even at really high volumes. Eventually when the volume is loud enough the feedback circuit collapses and lets the signal through unfiltered, and that's when the goodness happens, but in stock form it's more like an on/off and it has to be really super loud. That's where this mod comes in. The JVM is basically a super hot-rodded JCM 800. What made the JMP and JCM800s such monstrosities is that they supposedly had the least amount of negative feedback of any of the classic Marshalls and the power tubes got involved very fast and with a very natural and linear type feel. So what this mod does is reduce the amount of negative feedback in the JVM and let's the power tubes get involved sooner and more smoothly. The result is a really rich, harmonic overdrive that crunches up with less preamp gain yielding a thicker, more full-bodied sound, and the amp is more responsive to pick attack. Pick lightly, it stays cleaner, hit it hard and it goes berserk. Overall having the negative feedback reduced makes the amp a little louder and more open/dynamic sounding.
All that was involved is snipping a wire in the feedback circuit and soldering in an adjustable pot. I used a 1 meg audio taper pot, which keeps it stock at 0, turn it up to about 3 and you get into EVH modded Plexi range, and around 5 is full JCM 800 style openness. After that you get into even less negative feedback wide open "Vox" style ranges. The difference is considerably noticeable as you turn the knob. Marshall should have this option come stock on these mega amps. It's so easy and sounds so good. I can't possibly understand why they wouldn't include something like this. The amp already has 2000 knobs on it, what's one more? Anyway, it works great and sounds in-fucking-credible!
Here's a couple action shots:
Marking tubes so they go back in in the same spots
The guts
This is the heart of the negative feedback circuit. R58 is the resistor. One method involves snipping it out and replacing it. No way I'm doing that, so I used a different method I found online, and followed the blue wires of that connector...:
Here's the other end of those blue wires connected to the speaker out board:
This is the wire that will be snipped:
Here goes nothing....
Checking the pot. Pot on 0 - this will give stock JVM negative feedback
JCM 800 range pot value about halfway. The stock resistor will provide the rest.
Pot at max - this will yield the least amount of negative feedback
Wires to pot soldered in
Wires tucked away and zip tied back into place
Attached to pot
Doing a successful mocked-up test run. I'm gonna get a better pot and a Marshall knob before I drill the chassis and mount it. I don't want to drill the front of the amp, so it will go on the back. There's a really nice open spot near the power chord for a knob.
And that's it! A little nerve-wracking, but very easy overall. This badass amp just got badasser!
Lol. Hell no. I still don't really know how electricity works. I just follow someone else's instructions. Monkey see, monkey do. I would love to know more about what all those resistors and capacitors in there do though.
Okay, drilled the chassis (gasp!) today and mounted in a new pot. The 1 meg audio taper worked great like it should, but it didn't really change anything past halfway. So I had a 250k linear pot laying around, measured it up to check it out, and in it went. This gives a little finer detail and doesn't have a bunch of "wasted" pot range not really doing anything.
New pot wired in
This was a nice, clean, empty spot on the back and easy to get to. The amp is ruined!
Pot installed with a Marshall knob I swiped off the 900. Looks like it belongs there, yeah?
Now I need to make a little label to go around the knob. Maybe something that goes to 11.
Works fantastic! Sounds great!
New pot wired in
This was a nice, clean, empty spot on the back and easy to get to. The amp is ruined!
Pot installed with a Marshall knob I swiped off the 900. Looks like it belongs there, yeah?
Now I need to make a little label to go around the knob. Maybe something that goes to 11.
Works fantastic! Sounds great!