Mesa MarkV / Saturation 'mod'

[bandit2013]

If and when I get to it, sure, I can post it here as it is related. Not much of a difference in the circuit topography considering the tube chain. Drive circuit is identical but does not have a C39 counterpart on the V4 circuit (based on a IIC+ schematic). After owning and operating the JP-2C for a while, it seems like the fundamental tone still sits in the darker side of the Mark Series, very similar to the Mark III blue stripe I had. Huge difference on the channel volume, a setting at noon is like the Mark III set to "3 or 4". Sure the amp can be dialed it to be abusively bright but does lack the ice pick characteristic as I have yet to experience the broken glass effect in the eardrums like I was getting with the Mark V on CH3 before the 12AT7 discovery of this thread. Not exactly sure what the actual differences are in circuit design as I have not viewed my eyes on a JP-2C schematic (only reference is a an old IIC+ hand drawn sketch of the amp so I will not take that as a blue print for the JP-2C in its entirety.)

 

[Markageddon]

Again: Different amp that has its own forum..the vids would be a cool demonstrator of the mods commonality, like the AT7'd IIIs, IVS and stuff set with roughly the same config /actual same tubes due to relevance.

And remember you've gone at great length throughout this thread to state that yours was a bit different from the start somehow. And you've hard modded it. I think your statements regarding 'JP2c compared to The Mark V' must be viewed through that lense, for maximum usefulness. I know than mine doesn't behave or sound like yours, judging by your clips so far. Its a seemingly minor point, but its huge. As what you're really doing is JP2C vs your particular V'.

 

[bandit2013]

That is true, I was comparing the JP-2C to the Mark V in hopes to improve the characteristic of the Mark V so I would get more enjoyment out of the amp. Considering the circuit topography between the two (assuming the JP is based strictly on the IIC+) there is plenty of common ground between the two amps except for the tone stack, Power transformer, Power amp type, where the 5BGEQ is placed relative to the FX loop. Sure there are two extra tubes in the Mark V which basically provides one more gain stage to CH3 (6 gain stages) vs JP-2C (5 gain stages) for the high gain channels. Never really considered that the Mark V has an extra gain stage. V3 is no in the manual as being a gain stage for CH3 but it is (5th gain stage).

I will eventually experiment with the JP-2C and see how it can be tailored with the tubes I have on hand. Sort of need to bring it up a notch from the dark shadow it lives in tone wise. It is becoming almost as dark as the Roadster with stock tubes. So far I have yet to get any flub from the JP or even the Roadster. Mark V is a different story on its own account for that. Mark IV was also a flub maker with my old Recto 412 cab. In either case I feel the MC90 speaker is just not a good match for Mark IV or the Mark V.

Too soon to make any statments on the JP-2C tube rolling as I have not started it yet.

 

[Markageddon]

RE: C90 For Mark V:
Works great on mine. :twisted:
Sounds like some 'varied dialling' practice maybe be needed to find the sweetspots for that speaker? I know I have to boost the 240 and 2200s higher than the others to get "That" tone for me..mines in a 1x12 ported wide, if that helps explain further.

Again, most errors in your posts regarding this can be corrected by using the "my" V instead of the "the" V, as you're not comparing the un-modded JP2c (which is irrelevant here anyway) to a typical Mark V - modded of otherwise- according to your earlier testimony.
You can't pronounce definitive judgements about the V based on your amp that you claimed yourself (and that your vids have reasserted your position on) doesn't represent the model well.

And doing so despite that comes off a little like you just want the unmodded JP2C (which coincidentally you own one of) to be a constant reiterative focal point in the V thread for some reason whenever its pointed out that more joy is had by others with their Vs than you've had with yours...?

And when it was suggested that you AT7 mod the JP (making it semi-relevant here) you declined/shrugged it off to some point 'if and when" in the future, indicating that the comparison you make to the V (Exclusively in the JP's favour supposedly to help the V Mod thread, as you just claimed) is just all your verbal speculation as to it's potential..

Of course its totally up to you man, just suggesting trying to keep it relevant and tidy here and free of too much unnecessarily TLDRish derailment.. and its great that you love your JP2c so much.
(Happy for you, but doesn't mean anyone else has to be unhappy with their amp... or that they have to GAS for yours.)
As if you'd google'd wanting to find out about this V mod, you'd be "whats all these pages and pages of non-modded JP2c stuff doing blocking your quest for sweet, sweet 12at7ish Saturation mod information...?"

You're an engineer, right? Would you -in your draws of screws- keep the 8mm screws in with the 7mm screws when the label on the drawer says '7mm'? or put 7mm screws of a subtly but crucially differing type in with them..? :shock:
My guess its that you'd be ejecting someone doing that to your well organised stock of screws from your worklab at near light speed, testing the surface resistance and tensile strength of the seat of their pants against the accelerative forces bestowed upon it by the end of your boot..! :lol:
I'd guess maybe you'd just not looked at threads this way before, so just a heads up/word to the wise..

Yes its too soon as you've not rolled: We don't roll to make statements. We make statements if the rolling did something worth reporting. And good dialling usually is requirement specific. Kind of like that "Good business is where you find it" line in Robocop. The rest is in the playing. Take the time, dive in and have much fun.

 

[bandit2013]

As for the MC90, to me it always had a ***** tone to it. What was shown in my video may have been my preference for the Vertical 212 cab I was running. I basically dialed in both amps to sound as close to each other. When I converted my Mark V head to a combo (yeah, sick I know, why would you do such a thing) it came with the MC90. Was not bad at reduced volume, actually sounded good in the Mark V. However, turning it up a bit just was not ideal sound for me. I have gone though many MC90 speakers. For some reason, the dust cap always seems to detach itself from the cone. Checked for deformity in the cone and could not see any, I am aware if you compress the seal too much you may end up with a warped cone. My combo sports an EVM12L Black Label speaker. I have also mounted the same in the open back widebody 112 cab so I can use it with the JP-2C or pair it up with the Mark V. The Mark IV was one amp that brought out the mud or farts in the MC90. I would much prefer the subtle breakup you get from the V30 over the MC90 speaker. I do know why I would go though speakers, especially with the Mark V. It was peaking out at 150W (it would peg the RMS meter on my Rivera Rock Crusher Recording attenuator). That was before I decided to make an important modification, raise the bias potential (more negative) by change in one resistor. After doing that I was able to run Mesa power tubes in the amp, before that I was red plating tubes left and right but the =C= 6L6GC tubes never failed. I should have sent the amp back when it had a valid warranty as it was a lemon from the start. I think I paid too much money for this amp (New). Now it is much better, I can run Mesa power tubes, I do not burn my hand if I touch the chassis or transformer. Amp was constantly overheating or heat soak (another reason to convert from head to combo as the speaker also provides more air movement). Enough said..... I sure hope others have not had to go through the trouble I have had with mine. Not just speaker issues either, screen resistors (had to replace after they split open) lost a few JFETS in the reverb circuit, and worse of all it had an improper bias issue from day one. I just assumed it was crappy tubes, but it was not limited to Mesa tubes either, only tubes that would last running a 6L6 was the =C=. EL34 seemed to be fine at full power (did not see the mandatory variac power mode until downloading the most recent Mark V manual).

 

[bandit2013]

As for the JP-2C, if you can get past the low frequency hum, Tung Sol, Mullard (12ax7 or CV4004) EHX, or other tubes from the same Saratov factory will be OK. Only preamp tubes I tried that did not become burdened with the low hum (and it is loud) were the stock tube, Chinese Sino (Ruby or Preferred 7025), or the NOS Chinese Beijing 12AX7 with square getter. I would have kept the JAN/GE 5751 tube in V1 as that had promise but the one I have seemed to be popping corn every once in a while ( I cooked that tube in a Stiletto as I do recall the getter flash was silver before I installed it, I even saw it turn black after running that amp for a short time, not a normal thing to see, tube still works but it has seen better days).

Preamp tuning, it seems that the hum was too annoying for me to continue. However I did manage to get a JAN/Phillips 12AT7 in to V5 (phase inverter). Not bad at all. It did not seem to alter the volume or punch of the amp. Actually it provided a slight bit of clarity to the gain stages. Tone wise, it is not as rich as the Stock tube and it seemed to filter out some midrange but not in a bad way either. Decided to hit with a dropped tune guitar, sweet. I put the original back in and liked that too. Did not do any recordings or video as it was not much of a dramatic change but just enough to differentiate one from the other. My preference is the stock preamp tubes in the JP-2C. I did like the Chinese 7025 for the clean channel but that was about it. Still the JAN 5751 was a better choice, too bad the one I have should be tossed out. Bummer.


I will not disagree that I need to dial in the amp better (Mark V that is). I do often change the sliders on the JP-2C as well as the simple tone controls. I just did not demonstrate that in any video as that would take way too long.

 

[Jfriley]

I made the V2 mod to my Mark V 35 back in Jan, with some tweaking here and there it really opened the amp up for me. For the longest time, I liked the amp, but didn't love it. Now it has the tone I've been chasing (with some help from my pedal board as well).

Question for someone who understands the circuitry, does this mod only affect Channel two, or does it change the tone of channel one as well.

 

[Markageddon]

According to the manual: 2nd gain stage on 'crunch', and 4th gain stage on channel 2.

You may need to target both channels with Tungsol in V1, and another 12AT7 in the Phase inverter slot to get the best pan channel effect. My 25 is a demon with that config.

As for any shared circuitry, I'd bet on them being seperate. Good question though.

 

[jnoel64]

FWIW, TubeDepot is offering the JAN Phillips 12AT7WTC for 9.95 each for a few days.

 

[bandit2013]

Since I have the day off, I was contemplating on modifying the V4b circuit just to see what the effect would be. Was considering a change in the 270K plate resistance and possibly a change in the cathode resistance but without having to remove the original parts. I have a few resistors of the same type used in the amp. 1M, 221k and 39.2k. Parallel combination of the 1M and 270K would result in 212k. Ran the gain calculator to see what the end result would be with and without the 0.22uF cap. 221k in parallel to the 270k would result in 121k ohms. and the 39.2K in parallel to the 3.3K resistor would end up as a 3k. In order to keep the low frequency gain the same, I would have to use the 1M and 39.2k resistors. Hope to use the 12AX7 vs the 12AT7. A modified circuit would result in 82Hz gain at 33 and 10KHz at 73 compared to the original 82Hz at 36 and 10K at 77. The 12AT7 in the original circuit provides gain at 82Hz at 31 and 10KHz at 57. Always best to run simulation using calculators that have a bode plot of the gain over frequency. I think that just swapping the 12AX7 with the 12AT7 is the best way to go. I also installed new speakers in my extension cab and Mark V combo (EV Classics) and love the end result with the 12AT7. I must be bored since I am not at work. Not going to change anything even if I cannot get the thought out of my head. Considering I am enjoying the V more than I was before all of this.... I don't see any point in making further changes. It is almost tempting to get another Mark V..... not... would rather wait and see if something else pops up in the next few years. Tempted to get a Mark V 35 though or even the Mark V 25.

Took the jumper out coupling the two caps on V6A circuit. It was not a bad mod but I like the Extreme mode without it. Still have the 3.3K resistor fix on the GEQ caps. That is staying. As for the Mark V, I keep wondering if I can make it better. The new cones did it for me. Was comparing the Mark V combo with 12AT7 in V4 to the JP-2C driving the extension cab and damn near equivalent. I doubt it can bet better than this. Perhaps I will swap in a Mullard long plate in V4 and experiment without making any hard mods. What has been done is done in that aspect. C39 still absent, no more ***** tone.

 

[Wayno]

Good work Bandit. I'm still loving mine :twisted:

 

[bandit2013]

The problem starts when I run the JP-2C with the Mark V... I know the bottom end will never be the same as the JP but still had the box tone thing going on. C39 removal helped with that.... somewhat. I really was considering doing the circuit mod on V4 but mulled it over. Decided to review some history of the Mark lineage to find the missing link. Mark IIC+, sure that is a different beast but the stage after the lead circuit is very similar to V6. Mark III, Mark IV similar. Compared all of the components on the cathodes, plates, and feedback circuits. Very much the same except for the other 120pF grid to cathode cap. The only other difference is a 500pF cab across the 270 plate resistor on the equivalent V4B circuit. That bypass cap will reduce the higher frequency of that given stage. Not present on the Class A/B IIC+ but indicates its installed for the simul-class version. MKIV also has the plate resistor bypass cap. Mark V does not. May thing about that for a while. However the other grid to cathode cap C44 sort of made its way out of the amp while I had the chassis out. Bingo. sure the amp got a bit brighter but lacks that boxy tone. I contemplated its removal for a long time since it was the second thing that was different. May have to try the 12AT7 in V6 now that I have stuck my clippers into the circuit. Now I am in debate which amp wins. I am almost liking the Mark V a bit more than the JP-2C. For some reason it seems much louder than the JP. I currently have the Mark V combo loaded with an EV classic and stuffed the same into the widebody 112 open back cab so I can pair it up with the V or use it with the JP. Mark V became more aggressive than it was. Sure I had to dial in the preamp section a bit differently but at least now it sounds much better. Odd that I was loving the V before this running the two EV speakers but since the tone changes a bit using the 4 ohm taps that would explain it. Bottom end is a bit bolder too, not louder or drowning just seems a bit tighter. The other differences are where the reverb is captured from. Whoever said the TC has more gain is mistaken. I believe the Mark V probably has the most gain (or distortion characteristic). I think I better recheck to see where the send level is on the amp as I did not look at that after installing the chassis. The amp seems much louder than it was before I trimmed out the cap. I did run the 12AX7 in V4 for a bit but went back to the 12AT7 (or at least I think I did, could have easily put the 12AX7 back in since the dog was begging for attention when I was trying to get the tube in, dropped the bloody tube shield into the speaker basket and struggled a bit to get it out. What ever the case may be, I think it is gold now. Now I want to tube roll and see what happens. How can I tune it even further ? I see a Mullard long plate re-issue coming to mind, then the JAN/GE 5751 has been cold for too long. Wonder what the RFT 12AT7 will sound like, it is a bit darker tone wise than the JAN/Phillips 12AT7. I am more excited about this new change I want to play with it some more. Loving what I am getting more than what I had before. First time for everything, and first time I thought the Mark V sounded better than the JP-2C. :roll: Oh yeah, if you do this simple mod, you have to remove a ribbon cable, do not forget to put it back into place before you power it up !

 

[bandit2013]

Dang it, taking the amp apart again. I recently got a new speaker, EVM12L classic, so I can run that with the one I have in the extension cab. Well, since the last mod smoothed out the ***** tone and added more brilliance to the amp, by no means has it gone back to being brittle, that battle is long over. The EV classic sounds great but I feel the OTR is a better choice. I just plugged a cable up to the OTR and inverted it in the EV carton with the cardboard ring and made a poor man's speaker cab out of it. That sounded much better. Hopefully I will have better results with the speaker installed in the combo than in the cardboard box. I can always run the OTR with the EV as that does sound good together. JP-2C was too dark to use the OTR but the Mark V is not. It would be similar to connecting up to the 4ohm jack with an 8 ohm load. I need to go to work as I end up tearing into the Mark V when I have a few days off due to holidays.

 

[bandit2013]

Here I can express in words until I can get a video or recording of this.....
C39 removal, done that a while back. Corrected GEQ with 3.3k jumper, still have it. Jumper on V6A circuit, removed that a while back. Stock tubes except for V4, hard to get away from that mod, JAN/Philips 12AT7. OTR speaker installed in Mark V combo. :shock: OMFG is this unreal. Run an EV classic loaded in open back widebody 112 cab in parallel with the OTR, :twisted: I think I am in love with the Mark V. Will have to find the cover for the JP-2C as it may get some cool down tome.

Bottom line, bass is very punchy, way better than it has been. Amp did get a bit brighter as well as more musical but I have not been able to get CH3 to run brittle, even before I swapped out the EV for the OTR. This amp is actually putting the TC-100 to shame, JP-2C still a great amp but I will give it a rest for a while. The revised changes could easily mop the floor with the Roadster. I did some tube rolling but wound up with the same tubes I started with. Considering how many other issues I had and mostly with the overall tone, that has been eliminated. For some reason I believe this amp has become louder than the JP. Perhaps further investigation is needed to confirm. I am still overjoyed with the change.

 

[Wayno]

Here I can express in words until I can get a video or recording of this.....
C39 removal, done that a while back. Corrected GEQ with 3.3k jumper, still have it. Jumper on V6A circuit, removed that a while back. Stock tubes except for V4, hard to get away from that mod, JAN/Philips 12AT7. OTR speaker installed in Mark V combo. :shock: OMFG is this unreal. Run an EV classic loaded in open back widebody 112 cab in parallel with the OTR, :twisted: I think I am in love with the Mark V. Will have to find the cover for the JP-2C as it may get some cool down tome.

Bottom line, bass is very punchy, way better than it has been. Amp did get a bit brighter as well as more musical but I have not been able to get CH3 to run brittle, even before I swapped out the EV for the OTR. This amp is actually putting the TC-100 to shame, JP-2C still a great amp but I will give it a rest for a while. The revised changes could easily mop the floor with the Roadster. I did some tube rolling but wound up with the same tubes I started with. Considering how many other issues I had and mostly with the overall tone, that has been eliminated. For some reason I believe this amp has become louder than the JP. Perhaps further investigation is needed to confirm. I am still overjoyed with the change.

C44 still out Bandit?

Knew you'd finally fall in love with the V. Like any relationship, the ones you have to work for are ultimately the most rewarding! Loving mine still too. Forget exactly what tube line-up I've got going on but i know it's V4 and V7 AT7's. There's 2 x Sylvanias and a Tungsol somewhere in there too. V6a bypass cap jumper still in. 3k3 GEQ fix and C39 still gone. Amp absolutely rips you face off.

 

[bandit2013]

Yes the C44 is still out. Please note: removal of this component may not be to your liking. The tone of CH3 will change as a result. The gain characteristics will remain the same. I shold have not made this contribution to the thread as it is irrelavant and should have not been posted.

 

[Wayno]

I believe all contributions are relevant at this stage. No plans to mod my amp any further as of yet. Loving it too much as is. Was just curious as to yours.

 

[bandit2013]

I am really enjoying it much more. Had to dig out my manuals so I can revisit the sample settings again. Things are looking good and sounding great.

 

[bandit2013]

I need some time to live with the change, It may not be a good idea to remove the C44. I was trying out a few of my other guitars and feel the amp may be too bright. I did try to delete the post where I suggested such but cannot seem to do that. The more playing time I get the more I realize this is part of the voice of the Mark V. Please remember that my amp is not normal. The change is not all that bad but it definitely changes the sound. The louder you play the brighter it gets. I should have left this to myself and not make haste in saying this is a good thing. Most of all, do not remove parts on your amp. The purpose of the original post is to gain some additional characteristics with just a tube swap. So I failed in maintaining this concept.

The 12AT7 mod is something to enjoy and you can always go back to stock by changing a tube. Try not to be tempted in making other changes as this is a fools errand and may end up going in the wrong direction.

 

[bandit2013]

After some review of the one mod, I restored C44. I am beginning to understand the grid to cathode cap's purpose as it is used. It will do a similar task if the cap was bypassing the plate resistor however a smaller value can be used on the grid to cathode method vs applying it as a plate resistor bypass to have the same effect. I only whish I withheld my excitement and experimented before posting. Please do not make changes as I had suggested. Any other mods I may or may not do will no longer be discussed here.