Mesa MarkV / Saturation 'mod'

bandit2013 said:

Has anyone tried the V4 or V6 mode with EL34 tubes?

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My "thing" is southern rock and I have always preferred winged c el34s in my mark v, mostly living in channel 2 crunch even though ch1 of course takes a hit on the cleans. I am now running an at7 in both v4 and v6 and now actually prefer channel two's mark 1 with thick after the swap. My Marshall JCM800 2203 is getting much less air time now.

Today I decided to compare the JP-2C to the Mark V again..... Now the V sounds thin as did before with the 12AX7 in V4. I cannot even dial it in for similar tone to the JP. (actually I think that amp is getting darker in tone but still amazing, definitely rivals the Roadster in some respects.) It could be the old tubes I have in the V as they are now beginning to ring out with the signal. Again down that spiral path again.... Keeps getting harder to climb back up. I think I may go capacitor hunting :roll:

Was not sure I was going to share this.... and probably should not.... but I found the capacitor :roll:

Well that changes everything. Makes me wonder if the more current Mark V are build with the 120pF installed or not. I would almost assume they do not as not many are complaining about the ice pick tone on CH3. Against any better judgement I decided to find the ceramic capacitor, confirm it was the correct one and remove it. (Warranty expired a while ago, no big deal for me). There is one on V5 but that is necessary, and one on V6, I left that as is. But I did remove the one on V4 which is one part missing on all the other Mark series amps.

:shock: I no longer need the 12AT7 to cut the ice out of CH3. I may try that tube again but so far I am impressed with the Mark V again with stock Mesa tubes. Now that is what a Mark amp should sound like. Sort of hard to do a before an after recording.... but the V sounds much better than it ever did.

https://www.flickr.com/photos/151502107@N03/shares/93gXt7
Full power, triode, 6L6's
Very low global master so probably wont sound too good cranked up but at this low volume i was loving it :twisted:

Jamming to Metallica and this got me pretty close. Proper heavy tone with lots of grunt. Plenty enough scoop for Master Of Puppets, for ...And Justice For All just drop the 750Hz slider to near the bottom and your good. Sounds great to me with my EMG equipped Schecter. Hopefully have a sound clip to post soon.

Never could have had the Presence, Treble, 6600Hz and 2200Hz sliders all this high before the AT7 mod. Would have been unbearable. Now just sounds thick and crunchy, heaven.

bandit2013 said:

Was not sure I was going to share this.... and probably should not.... but I found the capacitor :roll:

Well that changes everything. Makes me wonder if the more current Mark V are build with the 120pF installed or not. I would almost assume they do not as not many are complaining about the ice pick tone on CH3. Against any better judgement I decided to find the ceramic capacitor, confirm it was the correct one and remove it. (Warranty expired a while ago, no big deal for me). There is one on V5 but that is necessary, and one on V6, I left that as is. But I did remove the one on V4 which is one part missing on all the other Mark series amps.

:shock: I no longer need the 12AT7 to cut the ice out of CH3. I may try that tube again but so far I am impressed with the Mark V again with stock Mesa tubes. Now that is what a Mark amp should sound like. Sort of hard to do a before an after recording.... but the V sounds much better than it ever did.

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Very interesting this, doubt i'll have the time to try it yet and very happy with the AT7 in V4 so not in any rush either. Great to know that your initial observations and thoughts were correct though. Hope you have many years of fun with the Mark V and all yours other Boogies, and new mics!!!

I had JJ EL34ii's in my Mark V at the start of this thread and they sounded great with the mod. Switched back to the old 6L6's the amp came with to see how the mod responded and loved it so they've been in ever since. Had the EL34's in for a couple years until recently and loved them too. 6CA7's next when i get some spare cash, christmas approaching fast so doubt that will happen this year though. More than likely the EL34's will go back in soon now that you've sparked my tweaking bug again :lol:

Read your reply to my about the ribbon mics and your correct, i was confusing the sensitivity with the phantom power, i had read about it in a manual for my bands mixing desk years ago and time had clouded my memory. Thanks for the clarification.

Cheers,

Wayno.

One rule, never use a passive ribbon mic with phantom power, unless you want to replace it. the Cloudlifter does require phantom power so it will also protect the ribbon mic only if it is connected to it. I never thought the EVRE320 would sound so good as I tried that with the ribbon mic. One new mic which is the sE Voodoo VR1. Had to get a rear shield to cut back on room noise. Also I need to run the attenuator with the JP-2C as that amp is just too loud for mics. I was pegging the preamp with just an SM57 with the amp set to 60W power driving the 212. I need to figure out what I need to get two amps in stereo (another attenuator and another mic would do it, ouch). Too bad the TC-50 is out for service......

I decided to put in the 12AT7 into V4, now that is total harmonic bliss. I could not stop playing but I got hungry..... Now that is JP-2C territory all the way but with more harmonic sensitivity. When I took out the EVM12L speaker I went with the MC90, sounded great but for some but it started sounding like the voice coil was jamming (had this problem with the Mark IV combo). Had to swap the MC90 with the Celestion Redback. Now I am really digging the change even more. Since I had jumped into removing a part that I felt was not essential (it may actually be needed but is it? ) I felt like the amp had a boost in volume levels. Presence control was very influential so I had to back that off a bit than normal. This Mark V has become a beast...... I would not say this is a must thing to do but if you hated your mark v prior to this thread, it may be something to consider. Perhaps wait and see if I caused any unforeseen damage. **** this amp sounds awesome now. (please note my interpretation of awesome may not be the same as yours..... if you do not like the JP-2C this simple modification may not be for you, also not an easy task as care is required not to cut the other cap next to it as that one is essential as it is part of an RC filter network on the grid circuit. Also it you do not like it, it will take more effort to restore it than just swapping a tube. Best you have a tech to perform this task if you feel it is necessary.

Bandit: Do you happen to have a photo of the capcitor you removed which shows where it is on the circuit board? Just curious that next time I open take the amp out of chassis I will look around to see what version I have. That being said, the Mark V has been sounding amazing after the AT7 in V4 mod.

Thanks,

Mace

mace said:

Bandit: Do you happen to have a photo of the capcitor you removed which shows where it is on the circuit board? Just curious that next time I open take the amp out of chassis I will look around to see what version I have. That being said, the Mark V has been sounding amazing after the AT7 in V4 mod.

Thanks,

Mace

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Indeed it does. Mines still kicking all sorts of *** too. Played with the 90w again this weekend. Thick, juicy and vintage sounding. Ive also noticed that the amp is set to triode as it was for the open air clip. The universe only knows only how savage and in massive it will be in Pentode at that volume..

The more I hear about the early model, more glad I am of the fact that I changed to a 2011 head in 2012, from the original combo I had (which was in the late 800s). Hope you thats sorted it out for you Bandit, you've worked hard on this stuff and you deserve your happiness..

I can open it up and take a picture but will not do me any good... photobucket has prevented me from sharing pictures. Need to find an alternate source for hosting photos. Any recommendations?

The capacitor sits very close to the V4 socket, close enough that the reference designator is covered by the plastic base. The cap is blobbed over with silicone glue, and is in-line with a molded axial leaded tantalum capacitor (used for the bright switch controlled by a JFET). Note: if this mod had failed to impress me or if it was a mistake, I would not have posted it. I know someone else is looking into doing something similar but may or may not do it. There is a similar cap on V6 and that should be left alone. Only one part. If you love the amp as is, do nothing and be happy. If your amp does not have the component from the start and you think you are removing the suspect part, you may be removing the wrong thing. I was not very happy with the Mark V so it made no difference to me if it became better or worse, went up in smoke or just stopped working. (surely I jest).

I have noticed the amp is a bit louder without the 120pF capacitor, not by much but definitely louder, bottom end is tight and the response of the pick attack is on par with the JP-2C. Before the capacitor removal, the bottom was a bit muddy, lower midrange was minimal and the upper mids and top end dominated the signal. (OK in tone and character, just not very impressive and becomes tiring after a few minutes of playing) The 12AT7 before the component removal did improve signal characteristics but did not correct for the mud in the bottom as much as I would have preferred. After the component removal, the amp was more lively, responsive to pick attack and bottom end was tight. With the 12AX7 it was much brighter but no ice. With the 12AT7 installed it was heaven. It is like a new amp, different but similar. Lower mid range is thick as is the upper midrange. The amp is still bright with the 12AX7 or the 12AT7 but not brittle at all. The 12AT7 is better in terms of gain control and saturation levels. No compression as I found note definition has been improved. I can take a picture of where the capacitor was..... Body of the cap is round ceramic, school bus yellow in color, 121 (120pF) and 1kV (1000V) is printed on it (when I found the part, the printing was facing the other capacitor that it was glued too. I had to use process of elimination to find it by checking continuity to pin 8 on V4 and component leads, as well as pin 7 to component leads. It was the only part that shares electrical connections to both terminals. I believe the Reference Designator is C39. It is a tight squeeze to get in but manageable. Small tools are needed to remove it. I originally was going to just cut one leg but opted to remove it completely as it would be easier to install a new one rather than trying to solder the cut leg together if the side effect was not desired. There is no guarantee your amp even has the part, I was uncertain if it was there as it is common to see components on the schematics and not on the assembled PCB if it was omitted on purpose based on revisions. Also the schematics were based on the 2009 version but so far has held up to reference designators being actual. However it does not include the switch logic and some other features that would be helpful in repair if needed.

Thanks for the info! I will absolutely not be soldering on this amp but I was just curious to someday take a peek at which version it is. (early 2012/late 2011 model).

Mace

I did notice one side effect after removal of the capacitor, the presence control as a bit more aggressive than it was or just seems to be. I probably will have to pop out the chassis anyway. Not sure if it is related or not as the presence control is only a feed back from output to the phase inverter and is not actually part of the preamp circuit in question.

Actually to remove the part, no soldering required. just cut the leads and it is done...... but you better know it is the correct part or you will be soldering something.....

Never mind, presence is still the same..... The pick attack is not however which made me think it was different.

Finally the amp just sounds pissed off, very aggressive and way better than it was. No chocking off on the lower midrange. Now Mark IV mode is more articulate. The Mark IIC sound more like the JP-2C. The bright switch seems more like the gain pull on the JP gain control. If my assumptions are correct that this part may not be populated on the more recent versions then I now know what you are hearing..... Now I am overjoyed with the Mark V. Now I have to question is the JP-2C redundant or is the Mark V? Since I swapped in the Red back speaker back into the combo it even sounds better. Will have to work on capturing a recording and I will use the capacitor location as the image if that will work. I could always try facebook, that may work.

My only comment.... if you are uncertain or in doubt, don't do it! I am unsure if this part has been populated on every amp over the years. Mine is a 2012.

You don't need to solder or do anything tricky. You could just clip one leg of the cap. But if for some reason you don't like it, you'd then have to replace it since it would probably be ruined (the cap you clipped the leg on). But it's super easy. Or should be.

Well, right now I'm 99% happy with the amp (who is ever 100% happy??). But I am really curious if the dual capacitors are in there or not. Someday I'll look.

Wasn't there a serial number breakdown of when the production changed to the single capacitor?

Thanks,

Mace

As for the drive circuit, the Mark series amps generally had a 120pF cap between the grid to cathode on the first stage. The Mark V is the only mark amp that has the 120pF on the second drive triode. The topography is essentially the same from the Mark IIC+ on up. If I recall correctly there was a slight difference between the Mark IVa and the Mark IVb such that the drive circuit did not use the same tube for both triodes on the drive circuit and was similar to the Mark V circuit. The feedback circuit paths are also different between the models too. The Mark V is using a tuned feedback loop with a low pass or notch filter network. The big advantage of not using the same tube for both gain stages is evident since the 12AT7 can be used to alter only part of the drive section. The gain factor of the 12AT7 does play an important role just as much as the impedance of the tube as that will effect the frequency response considerably. I took a gamble on removing the 120pF from the second drive stage just to see what would happen. Still I do not know what changes may have been made over the years if in fact the capacitor is even present on current production or if there has been a board change. I had decided not to make any changes except for the 12AT7 and that was fun for a while but I still had the same tone and character that I found tiring after a while. If I went to play the JP-2C it was like a magnet that was hard to put down. Sure there is more at play when the entire drive circuit is looked at in its entirety including the overlooked feedback loop. The historic feedback loop was just a 10pF or 20pF in parallel to a 3.3Meg resistor that coupled the output of the drive circuit to the input. The Mark V is quite different in that regard. However I would not recommend making any dramatic changes as this would result in poor performance with some of the three voice selections. I will work on a recording of the end result and compare that to the JP-2C, will even run all three voices on CH3 on the Mark V with also demonstrating the bright switch on and off. I still need to find a host for posting a picture of the area in question.

Dreamtheaterrules is correct, you can simply cut one leg (opposite the relay) and you could solder it back together as this is not a high current circuit path. I opted to remove the cap completely as it would be easier to install a replacement with the part out of the way as well as removing leads. I am not one who would promote modifying an amp circuit. If you love what you have now with just the 12AT7, leave it as is. I was just not getting the desired results. I have tried the 12AT7 in V6 and the original tone seemed to creep up and the bottom end lost its composure. At least with the capacitor removed I can run 12AX7 or even better the 12AT7 and I am loving the change in character, actually more than I expected.

I had some difficulty getting the chassis out as the dog was trying to be as close as possible, storm was rolling in. Thunder.... I did manage to get a picture in focus and marked it up. Arrows are pointing to where the 120pF used to be. Note that it was glued to the other ceramic disc cap that is also glued to the large orange metalized film capacitor. It is a tight space between the V4 tube socket and relay. Had to cut the white silicone rubber goop to free it from the other parts. I will try to get a recording this weekend. For your reference...... For me something like this is an easy task, I would not do it if you are not familiar with working on this type of electronics as it is easy to make a mistake (including electric shock potential). If your amp only has the one ceramic capacitor you do not need to remove anything. Also my amp dates to July 16, 2012. Unknown if later models have this component or if the value of the part has changed. Also, if you like the way your amp sounds as is... do not remove it as it will be more difficult to put back. 8)


https://www.flickr.com/photos/159449305@N05/36542222983/in/album-72157686850818214/

I will try to run some simulations on PSpice to see if the capacitor is even relevant or has any effects on frequency response. I am curious to is purpose as it may just be for parasitic oscillations if that is an issue. So far I have not had any problems after its removal on V4B. I actually like the change but is it related to the capacitor removal? Having a grid to cathode capacitor is not very common, the question: is it really necessary and does it really affect the tone or gain characteristic.... I way I think it does have a tone effect. The gain characteristic has not changed that I can tell. More data please.....too much on theory and not enough (ah, what does that do? and why is it there?).

The 12AT7 or 12AX7 sound great so either way it is a win-win (assuming the cap actually has any influence at all considering its location in the circuit).

Wanted to chime in and give some feedback about the C39 and 12at7 mods. I've been lurking this entire thread to see what it would produce. I have always been a little unhappy with ch. 3 on my Mark V. I was always fidgeting with it and could never quite get what I wanted out of it. I have a Soldano SLO (depth control, KT66s, FX loop mod) that sounds heavenly. Wanted the Mark V to be the versatile gigging amp...especially since I don't want my SLO ripped off.

It is my second Boogie over the years, but was struggling with it. Many humble thanks to bandit2013 (especially!) and to everyone in this thread.

I first tried the 12at7 in both v4 and v6...didn't do so much for me and I was still struggling to get the saturation to feel better. Today I finally opened it up and clipped one leg of the C39 cap. I've played it only about 15 minutes, but so far I am really happy! Channel 3 is more what I expected/wanted it to be. Plays easier and the EQ is less finicky. I also tried a JJ ECC81 in v4 which tightened it a bit on highs and lows, but will go back to the 12ax7. With the 12ax7 the gain range for me was a little more versatile and in Mark IV mode it does that liquid lead thing better. I played with the Variac and Pentode/Triode settings and was very happy.

All warnings that bandit2013 gave apply...do not open up your amp unless you know what you are doing. Be safe and understand the high voltage risk!

I'm going to put it back together and play so more! btw, my Mark V is from January 2014 and it did have the c39 cap, bandit. I played it at moderate home volumes, but no parasitic oscillations.

That is great as I thought I was loosing my mind or hearing.... was it in my head because I think I hear a difference as a result of removing the part or did it do nothing at all. Thanks for the confirmation.

I generally play as loud as I can tolerate. Did you notice a volume difference after clipping the capacitor leg? I feel that CH3 gained a little bit of boost. Perhaps it added a bit of headroom to the cascaded gain stage. I was thinking of installing a cap in that position to get a "before removal" recording and then remove it for an "after removal" recording. For some reason I do not want to go to that trouble as I am finally happy with the result. Not even sure if that change can be captured from a mic.

Parasitic oscillations were the only explanation that Fender used on the explanation for the cathode biased 6V6 tube circuit. There were examples of a capacitor connecting grid to cathode and some had a capacitor from anode to cathode. They did have issues with the early models.

There is a form of positive feedback on CH3 which actually feeds back from the output of V4 to the input of V5 (this is needed but is quite different than the typical mark feedback circuit as it is a tuned feedback circuit. The other Mark amps may have some filter networks on the plate circuit but do not appear as part of the feedback circuit but may have similar affect on the tone. ) just for S&G I did look though the schematics that are available on-line for other use of this grid to cathode capacitor other than the Mark series amps used on the driver circuit. What I did find was something similar, a 0.005uF capacitor in series with a 3.3k resistor. This can be found in the early gain stages on the Express 5:50 as well as the Blue Angel (this one uses a switch to pull it in and was labeled as "DRY". I looked at the manual and there was no reference to "dry" . The Express had it hard wired and no switch. The Mark Series uses a 120pf on the first drive stage (only the Mark V has it on the second drive stage, and on the CH3 master volume circuit, I have no plans on removing any other capacitors.) Keep in mind that the 12AX7 as well as the 12AT7 do have intrinsic capacitance between grid and cathode, between grid and anode, and anode to cathode, and perhaps between cathode to heater. Based on small signal studies by Miller, the Miller effect is also called Miller capacitance. (more so studied with BJT and other silicon devices but the actual study emerged from tube circuits.) I am however, a bit rusty on theory and audio circuitry as it has been 24+ years or more since I had studied in detail and at the time had a better understanding (now it is just fragments or cobwebs and I keep thinking about the Laplace and Fourier transforms and bloody equations that filled a notebook for a single problem. sorry to bring back bad memories, somehow I understood all that stuff and I do remember the challenge was fun to some extent, do I use it now? No. Should I? probably.... :roll:

Really pleased you've found your happy place on this.
The way you describe the amp's changes is what my experience was too with mine.
Shame we cant directly compare for ascertaining this, but the posts above ring true over here. And if if thats what clipping the leg did for you, then i'm really chuffed for you both.

Nice work on the tech side too. You rule, Bandit.
Always something new to learn in this epic thread.

This amp has to be one of the finest created by the hand of man. And when the community can participate to enhance that even further, what a beast of a classic it is.
Its why the Amiga was king of the 16bits in the 80s. A thinktank that went about making a machine adaptable, accessible and open to future augmentation, at a realistic price. The public embraced this open feel vibe and had a huge underground scene as a result. (Then the company changed, and hung itself due to costcutting and dodgy management.) But Jay Miner's dream was beautiful. This all reminds me of the best of that time.
Very rarely have I bought anything that has consistantly brought me this much joy. (more and more as time goes on)

Heres to the dreamers.