Mesa MarkV / Saturation 'mod'

[bandit2013]

Sorry Bandit, I need clarification. You posted "one more thing to boast about.... I believe the second IIC+ mod (GEQ fix) had improved CH2 and CH1". Is this referring to the 3.3k across C49 and C99 mod? Is this a mod that helped in your amp?

My amp was assembled in May of 2010 and I have a feeling we share the same design and problems, and I would hope to get to the point of satisfaction you are at. Thanks again for your patience and excellent help with this matter!

It is possible that the IIC+ correction has improved the other two channels as this will always be active on all channels and or voice selections. However how much of a change is hard to tell. I can remove it and see what happens. So far I like what I am hearing and feel no need to explore any more changes, would hate to loose what I have obtained.

I was boasting about the end result of my mods was amazing..... and that I was not making other changes to correct this or that and the amp is too bright. (MACE was waiting for me to add another change or mod because I keep struggling with the amp). I am actually impressed with the end result. I wish I had done this long ago but opted just to settle with the amp as is. The 12AT7 is one of the key factors. Still I am puzzled as to why this is necessary. It just sounds better to my ear than it did with the 12AX7. I may have to try the 12AX7 and hear for myself how it compares. I tried to make the brittleness come out and could not manage to coax it. Even with the EV speaker or the V30 speaker. I can now feel that the Mark V is on the same level as the JP-2C. Still they do sound a bit different but definitely closed the gap and have a useable amp that I can actually enjoy playing though. Dynamics are there, Harmonics are there, more punch form the amp than expected and now this thing is a beast, no flub that I can squeeze out. I can definitely push the bass a bit harder. It is not a miracle mod or anything like that. It does make the amp more musical and enjoyable to play through without ear fatigue. What is also cool with the Mark V is how it responds to different preamp tubes. I basically have all Mesa tubes in it but have one that is not a Mesa tube other than V4. I am using a 7025 in V2 which kept the Mark 1 mode out of the mud. I even discovered edge mode was not all that bad (like the Mark I voice you need to adjust the tone controls to make it sound good, could not do that before). Crunch is like an excited IIC+ voice, still sounds the same but with the gain maxed out it gets nasty. Perfect for Metal chugging. I never really had much of an issue with the Crunch but I think it sounds a bit better. Had the same preamp tube in there when I started with mods so there was a minor change overall.

It is possible that the IIC+ correction has improved the other two channels as this will always be active on all channels and or voice selections. Yes, I believe the change in the GEQ pull down resistance (11.7k for IIC+) and (9k for all others) is not a dramatic change from the 10k pull down on the normal mode. It is different for the IIC+ but this also couples the 0.22uF with the 10uF cap. I have not noticed any ill effects of the FX loop. I have been using the amp with the FX loop active. I have not tried it with it turned off yet.

 

[bandit2013]

Please note, my last post was not an April fools day joke. I really love the Mark V. Seriously. 8)

 

[Wayno]

Please note, my last post was not an April fools day joke. I really love the Mark V. Seriously. 8)

:lol: :lol: :lol:

 

[mace]

Please note, my last post was not an April fools day joke. I really love the Mark V. Seriously. 8)

haha Glad you can enjoy playing more (guitar) now.

I’m curiuos where Apeman and Wayno ended up? They also liked the AT7 V6 and V4 mods but also did some additional circuitry mods later. I’ve been sitting tight with the easy AT7 mod in V4 only in my 2012 Mark. I think before I’d do any surgery on my Mark I’d A/B with a new Mark V and see if there was any difference and if so, opt for the new one.

 

[Wayno]

Please note, my last post was not an April fools day joke. I really love the Mark V. Seriously. 8)

haha Glad you can enjoy playing more (guitar) now.

I’m curiuos where Apeman and Wayno ended up? They also liked the AT7 V6 and V4 mods but also did some additional circuitry mods later. I’ve been sitting tight with the easy AT7 mod in V4 only in my 2012 Mark. I think before I’d do any surgery on my Mark I’d A/B with a new Mark V and see if there was any difference and if so, opt for the new one.

Hi Mace,

I am running AT7 in V4, C39 mod and the V6a cathode bypass mod currently. My soldering iron crapped out on me the other day and I'm currently skint so I'm taking stock for a few weeks with where the Mark V is now. Maybe I'll stop here, who knows. I'll see.

I'm interested in the C18 mod and iic+ (geq) correction mod so it's actually good that the soldering irons broken. Otherwise I'm pretty sure I would have just done them. This way I might decide I don't need to after a little time with what I have. Very happy so far, but I know what I'm like so I probably will end up taking her to bits again.

 

[barryswanson]

Excuse me for being a simpleton but out of these mods witch one is going to give me the iic+ with the larger coupling capacitor like the original?

 

[Wayno]

The credit goes to APEMAN on this one but I added a few things so you can remove the mod if you wish to do so. To correct the GEQ or the IIC+ mode, one trick is to add a 3.3k resistor to C99 and C49. There will be some cutting here though, but though the silicone adhesive blob that prevents C99 from vibration and is glued to the inductor array next to V5. The resistor should be soldered to the negative terminal of the 10uF cap (located out of view and is under the C99 cap, reason to cut the clue to get to the C49 terminal). The other end of the resistor needs to be soldered to the C99. Once you have the resistor soldered into place, confirm the body of the resistor is not touching the metal twist tab on the V5 tube socket. I placed a dab of silicone adhesive to isolate the resistor body from the sharp metal tab. Then move the C99 back into its original position and secured it with some more silicone adhesive. clear adhesive only. This helps regain some of that beef the IIC+ has, just as much as the JP-2C.

Fix for GEQ capacitor:

This is the coupling cap mod.

I've not done this (yet) myself so I can't vouch for it but I believe it works. Bandit knows his Sh!t

 

[bandit2013]

I believe you need both the jumper mod and the GEQ mod. The simple jumper mod really makes a difference on the IIC+ mode bottom end. As for the GEQ mod, I am not sure that really matters much since the Mark V GEQ is completely different than that of the IIC+, III and IV models. Also there is not much of a change with just the GEQ mod. Note that IIC+, MKIV and Extreme will still have their own characteristics. However, I do believe the GEQ mod does enhance the other channels just a bit.

The last gain stage of the IIC+ has a 15uF as well as a 0.47uF cap on the cathode circuit. There is a pull switch that engages the 15uF cap on that circuit. (in the MKIII which is basically the same to some extent has that labeled as pull deep). The V6A mod using a resistive jumper does simulate this part fo the circuit. MKIV and Extreme use the 15uF where as the IIC+ only uses the 4.4uF (2.2uF in parallel). With the small value resistor (15ohm to 150ohm) this ties in both capacitors but adds a pole to the circuit since the two ground points will not be connected together with a solid jumper wire. This in itself does not seem to cause any low end flub, it actually sounds much tighter and has more punch that mine was lacking. (my amp was on the flubby side before I did this.) I did the V6A mod first and thought that was a huge improvement. The GEQ mod did not seem to have much of an effect since I did that mod following the V6A trick.

The 6VA trick: Following three images shows the same mod, either use a jumper wire or a resistor to make the connection.

Another view of the 6Va trick:

Jumper wire version (without using the small via on the board):

Wayno showed the GEQ correction.

 

[barryswanson]

Very cool thanks for clearing that up. Just to be a pain in the arse, is there something we could do to channel 2 Crunch to give it more gain/saturation ?

 

[bandit2013]

No..... that channel is a difficult one to work out. Best advice is to tube roll in V2. I much prefer the Chinese 7025 (preferred series or the Ruby 12AX7AC7 HG+ ) in V2. That is all subjective just like everything in this post. Since the gain control for CH2 is pre tone stack through V2A circuit, that stage basically sets the character of CH2. Sure V1 is part of it as V1A feeds into V2A then it all jumps back to V1B before V3. Since the gain configuration of V2 is not much different than most of the gain stages, a lower gain tube like a 12AT7 would not be a favorable result. The trick of the 12AT7 in V4 is that it cuts the high frequency gain (audible and beyond) but leaves the bass and midrange gain about the same as a 12AX7. This is due to the 270k plate resistor on V4b circuit. The GEQ mod does add a small change to the other two channels. It is not dramatic but slight change. You will get more from what you select to use in V2. Even a Mullard CV4004 will alter the CH2 character in V2.


Best positions for the Stock Mesa tube: V1, V5 and V6. 12AT7 in V4, 7025 in V2. As for V3 you can use any tube. I find the Beijing to be the most quiet and I use that in V3 and V7 but other tubes to suit your taste will work. The Beijing tube is what Mesa used in 1990 I have a few of the Mesa branded versions that I kept when I had the Mark III. I also got a few of them from Doug's Tubes. Those work great in the Roadster.

 

[Wayno]

Gotta agree with Bandit here. There's a hell of a lot of switching going on with ch2. Looking through the schematic there's a switching network after the tone stack of ch2, maybe if you could find it on the board, R17 330k could be reduced by adding a parralel resister to drop the value. That would increase the gain of the next stage a little in crunch mode. Or doing similar to R15 33k could add gain to both edge and Crunch. Doubt it would be worth the effort though, especially with the risk of unbalancing the ch2 circuit. I'd recommend like Bandit, tube roll V2.

 

[bandit2013]

I would think a change in the CH2 circuit would render one voice useless, Mark I mode may be at risk of getting much darker. Actually I like CH2 as it is (except for Edge mode, but it sounds better after I did the IIC+ GEQ fix but not by much). CH2 is one of those channels that you need to dial in your tone when changing the voice. It is not as universal as CH3 with the same settings can be used with all voices. So tempted to parallel V2A and V2B. Not sure what would happen if that was done. May not even be a good idea..... never mind. :x

 

[Wayno]

I would think a change in the CH2 circuit would render one voice useless, Mark I mode may be at risk of getting much darker. Actually I like CH2 as it is (except for Edge mode, but it sounds better after I did the IIC+ GEQ fix but not by much). CH2 is one of those channels that you need to dial in your tone when changing the voice. It is not as universal as CH3 with the same settings can be used with all voices. So tempted to parallel V2A and V2B. Not sure what would happen if that was done. May not even be a good idea..... never mind. :x

That's funny as I was just thinking the exact same thing about paralleling V2a and b. Wouldn't necessarily increase gain that much but would drive the tone stack with more current you would think?

 

[bandit2013]

I am not sure what it would do..... If there was any reason to do so it would have been done. An unused triode is ok as it does not draw power. That added stage made active may be enough to swap supply down too much. Have not considered it really, just thought if there was something to gain by using it.

 

[Wayno]

I guess the extra power consumption would depend mainly on whether or not v2's second triode heater is already powered or not. I may well be wrong but Isn't the heater draw in the range of 150 - 300 mA depending on 6.3v or 12v operation where as the anode (or plate) draw is around 0.6 mA at max dissipation. If it's already heated the current draw increase would be negligible. Is tempting just to connect v2's cathode to cathode, grid to grid and anode to anode just to see what happens. You are right though Bandit, if any serious advantage was to be had, boogie would've done that already more than likely. Then again though, they did opt to not include pull deep on the iiC+ mode which both of us agree is much better now we've modded that.

 

[mace]

It’d be interesting to know Boogie’s thoughts on these different variety of mods here. I mean, they chose what they chose for good reasons, I’m sure. But, no one thinks of absolutely everything. And it would be interesting for them to say “that’s an interesting idea” or “we thought about that but did not do it because of X”. I’m sure there will not be official Boogie comments, but they are likely reading.

 

[Wayno]

Yeah I'd be very interested in their thoughts too Mace. Like you said, I believe they have very good reasons for making the decisions they did with regards to voicing the modes on the Mark V. In its stock form you do get the full spectrum of the options available from the iiC+ up to the iV. However, I can also see why lots of people where a bit disappointed with the iiC+ mode, being that it's modelled after the non EQ and non pull deep setup. Those looking for that particular sound where not going to be that impressed. But you can use iV mode for that though. For me, I find the iV mode a bit too smooth and slightly over saturated after a while playing through it. I always find myself prefering the slightly more raw sounding iiC+ mode but then struggling to get the depth out of it that I'm after. With the pull deep mod I can get that easily so I'm very happy now. With the AT7 in V4 as well I'm over the moon!

I too doubt you'll see anything official from them here. No doubt they have been watching the thread, any good company would be. But I wouldn't expect them to come on here and admit they made a mistake with the voicing of the iiC+ mode, that would just open the flood gates justifying the complaints. Nor would I expect them to feel they have to defend their voicing decision. The choices they made are made, and many, many people are more than happy with them as is.

 

[bandit2013]

I would not call it a mistake. Perhaps some of the voices on CH2 were created from the Mark I circuit. As for CH3, the same structure is there if you review the entire circuit of the Mark V to the old designs starting from the IIC+ on up to the MKIV. The only difference from the original IIC+ on up to the MKIV is the position of the GEQ in the signal chain and its topography. Mark V is the first one to place the GEQ in front of the FX loop. That in itself is one reason for the FX loop issues due to source impedance. Other than the obvious, there is reason to why the Mark V has a distinctive voice. Compared to the previous models, those were on the dark side where as the Mark V has more of a shift on the bright side. Much of this voice is the difference in the CH3 tone stack, some of the bypass capacitors on the late gain stages and the negative feedback of the presence control. In addition, there is also a change in the Simul Class power amp. Mark IV, Mark III both can use EL34 in the class A positions (actually it is recommended to use the EL34 in the Mark III vs all 6L6GC tubes). Mark IV is the only amp that can use 6V6 (I never tried this but if you do you need to only run tweed power). I have not looked into the plate voltage differences on the preamp circuits but that will also affect tone since this relates to the load line to some respect based on the plate resistor value. There are some tone similarities to the previous models that the Mark V is capable of creating but the fundamental tone of the amp defeats that in most respects. Most of this is due to the difference in the tone stack design.

As for V2, both heaters are in use. I have done many tube rolls in the Mark V with the chassis removed and I see both heaters lighting up on that tube. If you do attempt to tie in the grid, cathode and plate, I would recommend not making direct connections. You would literally have to add additional parts, plate resistor to set gain of that stage, cathode resistor to self bias that triode, and a coupling cap to the grid along with grid stopper resistor, etc..... If you do not, expect to replace the components used on V2A with higher capacity (2W resistors vs the 1W resistors that are used note that the parts are 1/2 rated but spec indicates they are suitable as 1W, I have a few of those resistors I bought to repair the TC-50 when it went dead but opted to send the amp in vs doing the repair myself as it was a TRIAC that failed.

For now, what ever I did to my Mark V, I am finally happy with it. I am using the amp with an EV speaker as it is a combo. I never noticed the immediate pick attack. That was never there before the mods. It is more forward with the circuit changes. Before the mod, I always felt the EV was the cause for the lag in response so I spend money and time to seek a better choice of driver to use (celestion Crème 90W ALNICO was a favorite but that was with stock preamp and stock tubes). The Mark V has turned into a beast I thought it was not capable of becoming. Still the JP-2C has the edge over the Mark V but it has been rewarding to discover it is not that far off. I would not doubt that the IIC+ GEQ mod has improved the other channels a small amount. When it comes to tone and characteristics, you do not need to make a huge change, the .22uF and 10uF capacitor coupled with a 3.3k resistor is a big change in GEQ output. I not sure if I can believe my ears but I can definitely feel the difference.

 

[bandit2013]

I think I know what happened to the gremlin once I released it from the Mark V. Since I made the mods all hell broke loose in my home. First discovered I had termites as I found a swarm of them in the garage coming out of an inside wall, adjacent to the studio where all of my gear is :shock: Drum set is now on the dining room table (broken down of course), amps were moved to the other side of the home into the spare bedroom, guitars all moved into the master bedroom. Just when I am ready for a win so I can begin recording again.... It gets better, when the termite inspector came I was crawling under the house with him to see how extensive the damage was only to discover the main sewer line was broken. Not just cracked but separated. Odd that I did not smell anything. And yes, my **** does stink. Oh just having fun with all of this. This will be one crappy weekend for me as I need to have the sewer line repaired before the exterminators come to treat the termites. Then the home repair will be needed to replace or strengthen the damaged wood. I guess I will not be buying any more amps or guitars in a long while, may have to sell most of it off to pay for damages and repair. Just my luck. Now I have something to complain about. Notice it was not about the Mark V. It may not have transformed into a multi voiced JP-2C but it does sound really good.

 

[jnoel64]

Well.... it IS Friday the 13th....