Jason & Shea rescue a modded '79 Marshall JMP 2204 - SLO mod!!
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- เผยแพร่เมื่อ 28 ส.ค. 2024
- Fun real-time style video documenting the rescue of a JMP that was shipped to us for repair. The owner knew that I was visiting Shea and thought that this could be something we worked on together - our first 'at the bench' collaboration. The amp was dead on arrival - but ends up sounding pretty killer!!
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Oh man, what a hassle that amp was. Good work lads. Always a lot of fun working with another tech on a tricky amp. You guys nailed that tone in the end. :)
Great job rescuing the JMP! The bright cap on the SLO preamp gain pot is .0022 microfarad. Would be cool if 39k clipper stage cathode resistor could be changed to 10k when plugged into low input.
Christ....that sounds absolutely majestic. And, the best part is that it's not over-the-top gain. The tone retains bite, and articulation...no fizz whatsoever (that I could hear). That percussive, punch is exactly what people are after today. I don't know of any amps outside of these JMP's (usually modified), or an SLO that get's that percussive attack. GREAT video. The problem is that these JMP's are going for a tone of money online if you find one in good shape. And, even then, given the inconsistencies of these amps back in the day, you don't know how it's going to sound. So, Shea hit the lottery with this purchase. Then again, one always feels better about taking a chance on a piece of gear like this, when your brother is an amp genius....lol. Btw, Jason, I'm still gathering info on that online class we talked about, Jason. Putting together a couple ideas for you, along with some resources. Stay tuned!
Thanks Phil. The info will be great, especially as I’m about to be full time on headfirst.
@@HeadfirstAmps Wow....that's great news. Glad the amp biz has grown to that point. Congrats. That's gotta feel good. I'll see if I can't get you some info by this weekend.👍
This was a FUN video to watch!! Very cool guys!!
Thanks for taking us along for the ride. ; )
I think that "house of Frankenstein" poster on the wall, is quite appropriate 😂 as it seems like you guys are (awesome) mad scientists. Very interesting stuff. Thanks guys.
i've done exactly this mod to my 2204 clone. Put the entire SLO channel into it. You need to get the B+ correct and replace the 10k droppers with much lower ones.
What 2204 clone do you have? I have the Wangs 2204 from China and would be interested in a mod like this
@@dylanjastle mojotone. i'm sure what you have will work fine. the key to the slo circuit is the voltages. the Robinette site has a detailed schematic (and layout) with the voltages.
@@geezberry8889 thanks for the info. Down the rabbit hole I go
I hope you did a schematic of the mods. Sounds killer.
Yeah, we got the essence of it captured!
Nice work Jason and Shea.
It's a Marshall! Its good to see too tech's making that boy bad kick butt! It sounded really good! One thing for sure the guy who own that bad boy is going to be very happy! And if he is not them ship it me and i will be happy! Thanks guy's rock on!
Wow, so many little things adding up to a big mess. great job troubleshooting and fixing that amp. it does sound great!
Meant to say this before. LesPaul and Chopstick troubleshooting!! Like a boss
Tremendous work on solving all the issues on that one. At least it sounds like this amp was well worth the trouble, sounds great here!
What a mean sounding unit even with all its issues! Nice work guys!
Nailed it!
love your work as alwasy, that one was a PITA 😂
please please please give us the lowdown on that vintage modern in the background! :D
I immediately thought how the amplifier sounds in a special way. it turned out to be a new mic)))
Good job Jason, sounds great.
Great teamwork boys!
Glad to see you guys getting to work together, awesome!
Fantastic sound! 👌🏻
Awesome work guys !!!
Very nice video guys. U2 r amp geniuses. Excellent.
Great example of chopstick diagnostics!
Bangin now!
Yes!!
This is why I'd much rather build a jmp or.jcm on a turret board than buy an old marshall. Pcb poison. Your pcbs are intriguing, though!! I definitely see the benefits of pcb if they are robust enough
Shea & Jason! Great job, I learned a few things. Shea I was wondering where you are located, and if you would be interested in modding my MojoTone 2204? I live in NWI, Portage area.
2 techs! Double the charge?
Hey Jason. Shea needs to teach you how to speak English. Super fun video. If you want to get the amp tested live just send it to me and I will take it on the road. I will see if its fixed and buy it from your customer for 1000 dollars no problem.
Hey, at least we still spell English words correctly! Haha
👍👍
It looks like the first gain stage is fixed and the second is variable? Very cool sounds
Yeah, the gain pot is after the 2nd stage IIRC
Jebus those solder jobs before you two fixed her up were horrendous. I wonder if the board went microphonic?
Holy S! Is that the gain with no overdrive pedal? I want that mod for my 78 JMP100 : )
Everything on this channel is straight into the amp! It's a pedal free zone.
Nice!!@@HeadfirstAmps
Was this amp modded by Martin Golub (LA Sound Design)? Looks a lot like his style of work and the mod/circuit itself looks very similar to his Lead mod, sounds like it too!
I actually have a photo (gut shot) of this exact amp I found online, from before it had the filter and bias caps replaced. Everything checks out like the scorch mark over the 500p position to the way the presence cap lead is bent, must be the same amp. Jack ground wire is still attached in my photo, let me know if you want it and I can send it over to you
Interesting! Yes please send. Headfirst.amplification@gmail.com
Killer
I chopstick an amp just like this lol
hahaha, that 4x12 was up LOUD!!
Sushi afterwards 😂🎉
NGL, as f**ked as the solder/board mod work was, I’m definitely gonna take some screenshots and have a look at that pre amp voicing!
390V?!?? Which taps are you using?? If this is a 1979, it should have the serial number on the FRONT also and on the left-hand side and I can see this at 10:04 in!
Which color taps are you using?? Some were wired off-board and some to the turrets, like the one you have, and the all-original one I recently purchase out of England and recently serviced at Marshall to ensure 100%!
I haven't reviewed the video in entirety. I will after this posting, but noted you saying 390V. These amps are NOT the low-voltage ones and plates should be around 460VDC, UNLESS it's actually running different input taps, or something wrong with it!! The lower-voltage ones are typically around 1983-ish.
I've had a few 1979s and later 70s....1977-1979 in the shop and these sound Amazing to typical Marshall and suggest people purchase them if interest!
However, I will note there are different Power Transformers in them also and have had BOTH T2562's and T4074!!
Let me/us know what PT is in this, but again, I'll review the video in it's entirety, but wanted to note this. I'll also comment on the taps after reviewing the video and let you know what was/should have been used.
It’s a 2204, I’ve worked on other 1979 50w JMPs that also had the lower plate voltage.
Good observation Rob, the chassis was only sent in but this could very well have originally been a combo amp, I’ve done other amps from the late 70s and the lower voltage ones have been that.
Ok, just finished watching the video in it's entirety! Yeah, right away, I saw all of the hack work by someone and gray shielded cable, different bright cap, and they fucked up and put in the 470k incorrectly into the NFB instead of was supposed to be 47k on the 8 ohm tap! A lot of backyard tech hacks will use poor wire that does not flow well as they think wire is wire and the net result is poor connections!!
I noted you guys went from the 82k to 33k in parallel with the 470k finalizing on 33k which is going to net about 30.8k on the 8 ohm tap. 82k would have gotten you about 70k. Typically for the folks out there on an 8 ohm tap, you want 47k or 56k, which if you didn't install outright, would use a 52k or 64k in parallel to that 470k, so with the 33k, your applying a little more NFB.
As far as the bright cap, typical for a 2-whole or JCM is 470p. My 100w JMPs had the very right 4700p, like in Randy Rhoads amp, which is pretty aggressive! When I saw the blue cap, I figured probably had been replaced as they are usually the sand-color.
What Voltages are you getting on the PI?? I note one of the dropping resistors is bypassed, so only 10k of total resistance! Typically on the 100w units, you have 2 10k in series and 20k. On some this can lead to too low voltage, say 280V on the PI, so I will typically change this to a 10k + 4.7k to balance out the preamp.
I typically do NOT like Soldano's tone, BUT the tone of modified Marshall's to Soldano-spec actually sound very juicy to me!! Not sure what the difference is and may be in the B+ filtering and voltages if all things being equal. This amp sounds very good and you or the customer should be happy, though only one channel.
Is Shae in Australia or you in the states?? I know you (Jason) are down under and though Shae in the states and in Indiana!! So wondering if someone is visiting someone?!? Hopefully we will hook up soon. This year's vacation plans are booked, but maybe next year we will. I know my wife wants to visit Australia! So if and when we do, I'll hit you up!!
Jason's PT:
BLK - COMMON
BRN - 240V
RED - 220V
ORG - 200V
YEL - 110V
BLK - 120V
BLU jumped from BLK to BLK. which is common to 120V typical to the Power SW and if your taps are in the same order as mine. My ST1 actually has the labels, such as "220" or "240" written on the PCB, but other board, like yours do NOT!
Mine with the PT taps to the turret were as follows:
BLK - COMMON
VIO - 240V
BLU - 220V
GRY - 200V
RED - 110V
PNK - 120V
I've had BOTH T2562 and T4074, but the recent one and with taps identified on PCB and above is the later T4074 PT. The T2562 did not go to the PCB and turret, nor taps identified on PCB!!
Oh, wait, I noted your cap can setup and this is a 2-input 50W amp! Mine were ALL 100w version! So maybe why different!!
Let me know what PT part number this is and if original or been replaced.
@@Monomythamplification the lowest I've had come across the bench was a 4210 1x12 50w combo. It's actually one of the best sounding (MODded) amps at the house with the low voltage!! I don't see the voltages in my folder, so maybe I'll go out to the shop and pull the chassis and document where it's at, but as I remember, yeah, it's about 400V! I'll check it out a little later, find out, and document it (can't believe I didn't have this already as I'm a stupid organized person! lol).
Hey Robb, yeah I was in Indiana…first time ever! I plan to be back next year too, where are you located?
Great post by the way, thanks for writing this!