Potential New JP2C Owner

[bandit2013]

@Doug Doppler

That was great response. Enjoy your travels.

 

[bandit2013]

I probably spent too much time trying to understand the differences between the mark models, what changed how it was addressed and what makes it better or worse.

There was a lead drive circuit that set the Mark amps from the rest that sort of became the standard since the IIC or IIC+ (uncertain if there were any copies out there, not like there is a patent on that dual triode circuit). However, it was only found in the Mark series amps. ED, RA, TC, Dual/triple Rec, Roadster/King or any of the lunch box versions except the mini marks. Sure, Mesa has changed it a few times from a circuit using that pair of triodes from two separate tubes. To my understanding the Mark III was the version that used both triodes in one tube. Mark IV, V and VII have that circuit separated like the original. Now there is another amp that uses that same lead drive circuit, the Badlander. Not a cold clipper overdrive circuit but a cascaded gain stage forced into distortion than boosted by the second stage. That is not my point. What separates them is where the actual gain control is located, how many volume controls does it have and then what is going on before or after the FX loop. Sure, it is an interesting Hybrid of sorts. When it comes to the several versions of the Mark amps, there are a few things that set them apart from each other. Regardless if they used volume1 or gain, they are located on the V1B circuit. That listed as lead drive is the second gain control when using the lead mode. That pre-gain volume 1 or that labeled as gain on IIC+ through the Mark IVA or IVB was omitted in the JP2C. It was replaced with a voltage divider circuit instead so it is a fixed parameter that is not adjustable. Not exactly sure what the gain control is on the clean channel of the JP2C. It could be a gain control following the tone stack like the original and may switch to a voltage divider circuit when using CH2 or CH3. The control labeled as "gain" in this case is the "lead drive" control from the older models. All three channel masters sit after the FX loop.
This is the IIC+ circuit also used in the JP2C (assumed) : V1A -> tone stack -> V1B -> V3B -> V4A -> V2B (fx loop) V2A ->GEQ -> PI. Sure the V2 triodes were reversed in this case based on the tube task chart in the manual. It is as close to the original IIC+ but using JFETS and relays instead of LDR circuits along with a midi implementation to control the channels vs the other methods of the past. Starting with the Mark IV, the switching matrix got complex.


The following may contain errors, miss-interpreted fuzzy prints that are difficult to see any details.

The basic Mark circuit with lead drive turned on. This is the IIC+ circuit: V1A -> tone stack -> V1B -> V3B -> V4A -> V2A (fx loop) V2B ->GEQ -> PI . Sure some may have altered what tube position is used, the basic design remains much the same. This does not reveal where the volumes and gain controls are located. In respect to the lead drive use, volume 1 is a pre-gain volume control that is part of the tone stack to set the signal level on the second gain stage V1B. The lead drive is the gain control to set the signal strength on the control grid of V3B, signal is supplied by the plate of V1B. The lead master is on the plate side of the V2A circuit before the FX loop and the Master 1 control sits after the FX loop in front of the GEQ if it has one and slams the PI with GOD like goodness. Below is the short chassis version. Image from Reverb.

Mark III comes out with an added channel called R2 or RH2. It is an impedance change on the bypass circuit that alters the signal strength on the V2A control grid. It does not make use of the lead drive circuit. This is where Mesa combined the lead drive triodes into one tube. This is the stripped series as it was either a no stripe, black, red, green, blue or purple made by a marker on the back of the chassis to indicate a mod or revision of sorts. Not sure what the various stripes reference, mine was a blue stripe simul-Class from 1989 as I bought it when I got a band together.
Lead mode of the Mark III: V1A -> tone stack -> V1B -> V3A -> V3B -> V2A (fx loop) V2B ->GEQ -> PI. Very similar to the IIC+ as it has a pre-gain volume control on the control grid of V1B. Lead drive is the gain control for the lead drive circuit on the control grid of V3A. Lead master is in the same location as it is for the IIC+ on the plate side of V2A before the FX loop. Master is on the plate side of the V2B circuit before the GEQ and the PI. This is a longer chassis version. More common with the Coliseum or KRG. Not sure if the K was available in the short head version. The Mark III combo I had was a short chassis version, reverb and the power switch were on the back side. I got this from Reverb and it was not as beat up as the rest.

Now the Mark IVA or IVB short or medium chassis (aka wide body) Somewhat similar but different based on what was done with the FX loop. This time around, it was more or less a modified Mark III but with the lead drive circuit back to separate preamp tubes. RH2 basically shorts out the bypass circuit used with the RH1 (clean) to push the V2A circuit a bit harder. The Mark III and Mark IVB had a common lead drive circuit using a single tube for both overdrive and boost circuits.

Mark IVA lead circuit: V1A -> tone stack -> V1B -> V3A -> V3B -> V2A (fx loop) V2B ->GEQ -> PI.

Mesa changed the Mark IV and called it the Mark IVB, also introduced the wide body format. Here they separated the lead drive circuit into separate preamp tubes. Similar to the IIC+ but slightly different pairing. This eliminated the cross-talk issue between the two cascaded gain stages.

Mark IVB lead circuit: V1A -> tone stack -> V1B -> V3A -> V4A -> V2A (fx loop) V2B ->GEQ -> PI .

What may be different would be a slight change in the cathode bypass resistors used on the boost stage, changed from 1.5k to 3.3k along with the voltage divider circuit following the boosting stage.
I had the Mark IVB wide body combo amp loaded with the MC90. Sort of a boxy tone compared to the Mark III blue striper combo with the black shadow EV speaker.

What was labeled differently as there are now three gain controls for the three channels. From the original design, that gain control would be the same as the volume 1 control from the IIC+ as they are associated with the signal level on the control grid of the V1B circuit. Lead drive is the same. Now there are three master volumes in front of the FX loop and the output level is the after the loop.

Continued....

 

[bandit2013]

Continued from previous post...

The Mark V:90 Still in current production? Perhaps, I can still find it on Mesa's product offering page so I assume it is. Mesa made a radical change when they came out with this amp. Swiss army knife that sort of has other models listed like the Mark IIC+, Mark I, Mark IV and a few other modes like crunch and extreme. Keeping it short, we will stick with the lead drive channel only, CH3. Since they made some gross modifications to the amp design, the tube positions have changed. Instead of just 5 preamp tubes, the Mark V90 has 7.

Here is a gut shot if you really want to look inside.

Mark V90 CH3: V1A -> tone stack -> V1B -> V5A -> V4B -> V3A -> V6A -> GEQ (fx loop) V6B -> PI

Sure, looks like you get two more gain stages since the V6A triode is not used to set the FX loop send level as that is created by the GEQ circuit. Considering the CH1 and CH2, the gain controls are tied into the V1B circuit. For CH3 it is a fixed voltage divider circuit. Similar to the JP2C in a way. With this signal path, V5A is the overdrive stage that has the CH3 gain control, and V4B is the boosting stage. V3A is similar to the V2 of the previous versions. It is where all of the channels merge. However, since there is one more gain stage here on the lead drive circuit V6A, the signal level is cut in half before it gets to V6A. There is no additional overdrive signal strength to hammer into V6A. The V6A triode is used as a voicing gain stage that defines IIC+, IV, and Extreme modes. The Mark V90 also has a weakness, it is how the FX loop send level is derived by the GEQ circuit. This sort of creates a high impedance output for the FX loop and may not work well with most FX units. Some say this is a boxy toned amp, Depends, mine was a 2012 head that kept overheating and red plating power tubes, Converted it to a combo and tried the MC90 but kept blowing out the speaker. Not very compatible with the EVM12L as I tried that too. My least favorite Mark amp. Some I have tried sounded really good, mine was just not to par with what it should be.

Now for the JP2C, we all know what it looks like but will post a picture here anyways.

Finally back to the original as close as you can get or much closer to the IIC+ than the Mark V will ever manage to be. Some do not like the JP2C as those that favor the Mark V as it has a borrowed feature from the Rectifier line, global master control. So there is a pre FX loop volume control and a global volume control after the FX loop. The thing here is, the JP2C has three channel master controls after the FX loop, not one. To emulate that with the Mark V above can be done by turning off the FX loop on the back of the amp (hard bypass). I blame the Mark V for discovering Strymon as those products were the only units that would work in the V's loop without any signal issues (tone suck or over driven buffers). The JP2C has no such issues and I can use the fx units that did not work in the Mark V loop without issue. Found I prefer the Strymon stuff so I barely ever use the other fx units anymore.

A cool feature for the JP2C is the dual GEQ. Note that I do like using the clean channel with the EQ circuit. No rule that says you cannot do so. No more kitchen sink with the garbage disposal modes. Simple and easy to set up. Has a few throw backs from the older models with the gain and presence pull switches. They do come in handy, and sometimes it helps depending on the cabinet choice. When using one of the newer boogie cabs like the open back 410, that presence control is what is needed to get that cab to sing properly. Sure best served hot with the standard 412 cab but this amp rocks the Vertical 212 cab just as well. Both being a Rectifier cabinet loaded with the Mesa proprietary voice coil Celestion V30 made in the UK (not made in China). Oh yes, this amp is very compatible with the EVM12L speaker, black label or classic. Push that as hard as you want, it just sounds really good from low volume to gig levels. I bought mine in 2016, had the FX loop mod memo in with the literature pack. First release had issue with volume levels between clean and the two lead drive circuits. They made the mod to mine. Would not doubt they revised the board to have the components so there are no extra parts soldered to the gain control except for the wire leads.

Want a gut shot of this? Here it is. Just note it was much easier to remove the chassis than to get it back in. Mostly had difficulty with getting the power cord plugged in. in the lower left corner, you can see the Mesa installed mod on the gain control pot.

The JP2C is a reach to its roots and I love this amp for what it is. After I got it, I never wanted another Simul-Class amp again. Well, that thought did not last very long. After my despair with the Mark V90, call it dread, or disappointment, I waited too long for the next version to come out. To me the JP2C was it. Had to have it and happy I got it. That sort of erased the regrets of selling the Mark III and Mark IVb.

The last newcomer on the block is the Mark VII. Just looking at the chassis layout from the tube side, it is practically identical to the JP2C. Preamp tubes are in the same location, huge transformers, etc. OK there is one feature that sticks out on the bottom of the chassis that was not evident on the JP2C, the internal load resistor is now external and split into two resistors vs one huge one. Head shell is the same size. Sort of makes me wonder if the JP2C chassis would fit into the Mark VII combo shell. And if it does, would you actually want a JP2C combo? I would if they offered it with the EVM12L speaker but MC90, nope. I personally do not care much for that speaker due to the issues I had in the past, mostly the dust cap separating from the cone once you try to get to gig level with it.

Anyhow, the Mark VII model is much on par with the JP2C, it seems that Mesa held true to the traditional circuit but with a few twists without sacrifice to the lead channel. Sure the lead drive circuit is fixed in its location, however it is introduced into different locations by means of using relays. That was smart on design as it retained a minimum preamp tube count. Not sure if the IIB is close to the real deal. Based on a readable schematic of that amp, it appears to be making the assumption that the lead drive circuit is using the same or similar components. The IIB mode just bypasses the overdrive gain stage. It still runs through the booster stage and will have a more clean character in its driven state. Not quite sure if the gain control is connected to the control grid of the boost circuit by relay magic. No schematics to review to see how it is done. Only assumptions from this point. The tube task chart in the manual is somewhat helpful but may not always reveal what may be helpful.

There are 5 modes that make use of the lead drive circuit. The traditional modes are the IIC+ and IV settings on CH3. IIB as I mentioned removed one of the gain stages from the circuit. Mark VII mode on CH2 uses the full lead drive circuit but may have some changes to parts. I feel it has a closer drive or grind characteristic to the IV mode. Crunch is the opposite of the IIB, as it makes use of the overdrive gain stage but bypasses the booster stage. Since this is all arranged by relays, traditional circuit is retained on IIC+ and IV modes as the tone stack is still sandwiched between V1A and V1B. When using crunch or VII modes, the tone stack gets pushed out so it becomes a post gain tone stack and the lead drive circuit gets inserted between V1A and V1B. The gain control of the lead drive circuit I assume remains on the overdrive stage. What makes the Mark VII a bit different other than the simul-class power and the 7 modes, it has a dual volume control circuit on each channel. Dual pots on one shaft. I would assume one is associated to volume control after the FX loop but it is unclear what the other pot is controlling. Here is the gut shot of the VII.

I am not sure if these amps share the same power transformer as they are basically the same size in the iron dimensions. Not quite sure about the OT as those may be different. The one on the right is the JP2C, those are the STR415 tubes, the blue inked logo rubbed off due to handling. I got them direct from Mesa. The Mark VII may look like it has a larger PT but dims are about the same as I measured them both. Hard to tell what the windings look like as the laminated steel plates can vary. Also have to consider the perspective of the image, the black plates look bigger than the varnished steel plates. Also different manufacturers of the transformers.

 

[ntotoro]

Maybe I need a III... and a IV... and a VII... and a JP2C...

 

[bandit2013]

I tried to stay out of the weeds as I am not much of an expert on the IIB, IIC, IIC+ or even the Mark III. What also worked its way into the mix were the power transformers. Some operated at 510VDC plate voltage which translates to : you must use the STR415 tube, not always but that was the general case.
I am sure the output transformers may have changed or were different. It was a changing mix of stuff. Not even sure the IIC or IIC+ had serial numbers, If you were lucky to get a Prune Boogie (modified Fender Prinston or what ever that was) you got the embossed tape treatment. So while the business was evolving, so were the designs and how they were made. It is all good. I just wanted to cover the basics and not dig into the weeds. Some IIC+ amps varied as some have said. I was ignorant on the subject matter and did not know what I was buying when I got the Mark III in the first place. It just sounded good and took it home the first day I tried it.

 

[bandit2013]

Maybe I need a III... and a IV... and a VII... and a JP2C...

If you collect them all, you may win a prize. Not sure what it is but you need the original box tops to send in to request your prize. NOT

 

[ntotoro]

By all means, get in the weeds!!! Anyone can benefit from it! I've always wanted to get a MkIII to unleash my inner John Sykes LOL! No stranger to amps that run stupid voltages and require specific tubes... the EL34 Shiva has been a mainstay of mine since 2005.

 

[bandit2013]

Some of the IIC+ and a few of the Mark III had a PV of 510VDC. That is no fun when the only tube that will take that is the STR415. The PV is what others have stated, I am no expert when it comes to the vintage Mesa amps.

The weeds would be including schematics and stuff. Not sure if that is taboo, but to my wallet it is if I get a cease and desist notice from the owner of the design.

However, the basic construction of the lead drive circuit looks like this: This is fro the Mark IVB schematic. At one point the schematics were drawn in a right to left format. Not exactly conventional in a USA sense as we tend to think left to right. The key ingredient of the Lead Drive circuit is the overdrive triode stage with the 82k plate resistor, 1.5k cathode resistor, followed by the high gain boost stage having a 270k plate and 3.3k cathode resistor. What is missing is the bridge circuit used by the clean channel that bypasses this part. When using the lead drive it appears that the high impedance bridge or coupling circuit forms a positive feedback loop. There is no disconnect for that bridge or coupling circuit from the tone stack recovery stage usually V1B to the V2A or V2B circuit (depends on the designed triode used for the gain stage before it is attenuated to the FX send jack). There are small tweaks that occur from model to model. In just about all of them, they have the coupling capacitor on the control grid to the cathode 100pf or may be of different values. Not all of the boost stages have the grid to cathode capacitor. What may also differ from model to model is the plate voltage defined by the "C" node. The Mark IVA version does not have the 250pF cap from the control grid to cathode on the boost stage, here represented as V4A. That amp would have V3B as the boosting stage.

To be honest, I can only assume the JP2C or the Mark VII has this same circuit but may be different tube triodes. Some of the resistor and capacitors may be different but the basic 82k/1.5k and 270k/3.3k is consistent for the Mark amps. I thought about poking around the circuits to confirm the circuits are the same.

I did poke around the Badlander out of curiosity. Wanted to identify if this amp has any cathode follower circuits, what is the value of the cathode resistor on the cold clipper. I was under the impression this was a Rectifier amp so the assumptions that the amp would have such was valid. No schematics out there so my curiosity took over. Considering I do like to experiment with tube rolling, knowing where the cathode follower circuits were was needed so I do not use the wrong tube and wonder why the amp shut down or sounded bad the next day. It does have two cathode circuits. One is the typical Rectifier FX send cathode follower used on V4. The other was the tone stack driver V2 as I discovered the tube socket had a direct connection of the control grid to the plate. While poking around on V1 and V3, I was seeing a pattern of plate and cathode resistors that were identical to the Mark Lead drive circuit. Cool. I sort of wonder when they were developing the next Mark amp, some of that design may have resulted in the Badlander. Since the crunch and VII modes are similarly used, tone stack is post gain in both cases, one is plate driven and the BAD uses a low impedance tone stack driver circuit more common to Rectifier amps. No cold clipper either. So the BAD is closely related to the Mark series in many ways as it is to the Rectifier series. This board is a Rev 5. The second BAD I bought is Rev 7 and has different transformers. They basically sound the same.

Interesting to note that the BAD runs a DC coupled tone stack driver circuit, the treble, mid and bass controls work very well and do not seem to be limited or dependent on the gain control like you get with the DR (Roadster or MWDR). The setting up of the controls will be more straight forward than the Mark amp as there are some tricks you can use to increase the amount of gain and tone density. That is the boosting of the gain and treble controls and dropping out the midrange and bass, then use the GEQ to tailor the low end. That only works with a plate driven high impedance tone stack driver as well as having the tone stack located as a pre-gain layout on a Mark amp. The exception would be the crunch and VII modes of the Mark VII as the tone stack is moved to post gain. Not like the BAD as that is still a low impedance source to drive the tone stack.

I believe that most do not understand the circuits all that much, they think it is all high gain that creates the distortion. Sure, if you get the signal level high enough to force an amplifier circuit to clip it will cut the waveform and create distortion. Is it cutting at positive swing which is clipping or is it cutting at the negative swing which is a cut-off form of distortion. With a tube amp, clipping at the max will introduce more odd harmonics that sound like crap. Clipping at the cut-off region of the triode tends to force it into its diode region which results in even harmonics (this includes the sub harmonic content). The Cold clipper does all its work at the cut-off region and will not clip the positive going signal since that circuit will have too much head room based on the operating point where the DC load line intersects the AC load line of that gain stage. So what is interesting about the Mark Lead drive circuit, you get both forms of clipping. That results in an asymmetrical waveform that is more pleasing to hear than if it was all distorted by clipping at the top end.

This is the JP2C signal at the FX loop running through CH2. I ran a single frequency at 750Hz at a 700mV signal level into the front end of the amp. Not the asymmetrical waveform on the oscilloscope. Hard to tell in this image but the green trace is the output and the yellow is the input (sinusoidal). The green trace reveals a sharp top but the bottom portion is rounded and shows a harmonic due to the wave of the bottom. The rounded portion is created by the overdrive circuit with the lowest gain, the boost stage results in the sharper clipping of the signal. Note that the input signal was purposely inverted so it appears out of phase. In reality it is in phase so the display has the one signal inverted. This made it easier to see what was going on.

What I was really after was to find out what the signal output was on the FX loop as I was not trying to analyze the distortion effect here. Note that when a sinusoid is clipped, that creates some high order harmonics, the sharper the edges the higher the frequency content. Also note that the top portion is not perfectly flat it has ripple and a slope to it. Below is the capturing of the clean channel, note the difference in amplitude of the green trace, it has higher gain than the lead channel in relative terms to what gain is. Has nothing to do with distortion like many believe. The effect pedal was only used as a coupling point to I can attach the scope leads. It was in Hard bypass mode so influence on the signal. That orange box is a Lehel P-split II. I was using the isolated output to drive the amp's input as I did not wany any DC content from the signal generator or any DC ground coupling to occur.

Comparing that to the Mark V90 Ice Pick queen, not sure if the spike was related to the GEQ circuit as it is what generates the send signal. Note that I did not invert the input signal on the scope as they are in phase as they should be. I believe I started with the Mark V90 first and moved to the other amps following.

I zoomed in on the scope for this image, same picture. I put some yellow arrows indicating the spikes. This is the ice pick effect. Also had all Mesa 12AX7 tubes in the amp. It is unclear if the issue is from the GEQ circuit or if there is a bad coupling capacitor resulting in the upper portion having that shape. This was before removal of the capacitor that connected the control grid to the cathode. I have not borrowed the oscilloscope from work in a while. I got what I wanted, data to determine the FX send levels. I even measured the TC50, that amp ran much higher than the Mark V. The JP2C was much lower in signal strength. Forgot what the results were but I did post a findings report on it in the forums.

 

[ntotoro]

I'm definitely no stranger to bizarre tube requirements. The Shiva runs about 600v. The only tube that could handle that originally was the SED EL34. The JJ E34L can and is available, but sounded like roasted ass in my amp. I was happier once Ruby came out with the BHT. It didn't sound like the SEE, but was much, much, much closer than the JJ.

Does Mesa give a new revision number to every small tweak or are there often numerous circuit tweaks that occur even intra-revision?

I can believe that the BAD is more closely related to the Mark series. Sounds more like it. When it was advertised originally, it was as a "modern Recto" kind of amp, so the first thing I thought was a Mark V was extra high mids or something sounding like an Engl LOL!!!

You're a brave soul, poking around in your own amps like that LOL!

I know there is a lot of controversy surrounding the Roadster. How does its circuit differ so much from other Recto amps or even the Road King? The RK sounds much more "Recto" to my layman's ears.

 

[bandit2013]

• In most cases, Revisions are mostly a running change and not announced. That generally occurs when there are several added parts that are soldered onto existing circuits to correct an issue or missing part of the circuit. May be due to change in component to improve reliability. Hard to say. There were to revisions to the Mark V I am aware of but that does not mean there were no others. 2009 had ice pick issues with the tone stack so they changed it 2010 is the year the used the new design but may have the 2009 year on it.

I did a pre-order on the Badlander so I got one of the first 100 built. Rev 5 is on the main board. One of the large power caps is literally soldered onto the diodes. I guess they missed it but still made use of the boards on hand. Then there was a change in transformer manufacturer so that also had a board revision change. The latest BAD 100 I have is marked with Rev 7. Diodes were replaced with higher ampacity versions (much larger size) and the large capacitor actually has a place on the board for it vs soldering it on after the assembly.

When it comes to the old Rectos, there are those who seek the pre-500 (based on the serial number) and some are call it a Rev G or Rev F. the Rev ID is on the main PCB and not on the outside. Perhaps the SN may indicate what revision of board is in there but that is not as accurate as looking at the innards itself. As for poking around in the amp with a multi-meter, I know what I am doing. I generally test for high voltage first before sticking my fingers into the circuit. I can even poke around on a live amp too but that is a planned analysis to determine where I am going to measure and what I am looking at. Sure, the supply caps will store potentially lethal voltages after removing power. Knowing where to place a resistor shunt to relieve that stored energy helps. I may not be an amp tech or designer of such equipment. However when it is live, I am very careful and only using one hand with an isolated probe and will be very careful not to be a conductor of current.

What is different on the Rectifiers

• Considering the Roadster and Road King II are related not sure if there is any difference. Comparing the schematic of both they are identical except for the extra features and progressive linkage along with a pair of EL34 in combination of the 4 6L6GC tubes. Obviously, the transformers would not be the same, 6 power tubes vs 4 and the output transformer is different too. Other than the extra features like the dual FX loop, the Roadster and Road King share the same preamp design. The Roadster is the more affordable version of the Road King II flagship model.

The three Recto amps I have: Badlander, MWDR and Roadster. The Roadster is the one without the grill on the front face.

• Both the MWDR and Roadster are dark toned amps, The Roadster having the darkest tone of them all. Sub low harmonic bliss but can become a hindrance when palm muting. 4 channels to mess with. It seems that CH1 and CH3 are much brighter toned. almost like the MWDR and CH2 and CH4 are darker toned. Both Dual rectifiers were equipped with the STR440 tubes. The Road had all yellows and the MWDR had greys. Tried the green and grey matched tubes in the Roadster and it was too much early gain and got muddy. Best match color is the red which is what I got in it now.

• In other words, CH3 and CH4 are not exactly clones of each other, they may have the same modes and control labels but are voiced differently. Same with CH1 and CH2. Some of the 3 CH rectos also had differences in voicing. Often you hear of the red or orange channel When it comes to the MWDR, the two gain channels CH2 and CH3 are basically clones, I cannot tell the difference assuming I can dial them in the same. Both are considered to be Multi-watt. The Roadster and Road King were the first Rectifier amps to have that feature. The MWDR or New-Born came out after the Road and King were in production. Early Rectos I am not all that versed in were fixed power, 50W, 100W or 150W and the only way to reduce the power was to remove pairs of tubes.

The Roaster has a different layout than the MWDR or other Rectifier amps before it. The clean channels are similar to that of the Mark series, gain stage, tone stack gain stage one more boost and it is off to the FX loop or is bypassed by the control on the back panel. CH3 and CH3 get funneled into a cold clipper then a DC coupled tone stack driver with tone stack at the back end of gain circuits. Modern mode is a disconnect on the negative feedback circuit from the output. I had originally though it was just a circuit path change and still retained the connection from the output but was wrong due to how the schematics were labeled. Easy to miss-read when they are just not linked to the actual layout which is what most engineers use for creating PCB designs, CAD program where you start with the schematic that creates a net list to connect the pins on the parts with lines but not actual copper traces, that is done by the designer and is called routing. I do this all day, actually it is a process that only takes a few days if that, firmware and mechanical design takes a bit longer for the balance of projects I work on. I made the assumption that Mesa upgraded their method. Nope. I bet they are still using tape on film for the board layout.

Due to the 39k cathode resistor in the cold clipper circuit, they generate some serious sub-harmonics. Thought the JP2C was heavy on the low end, MWDR and Roadster had that amp beat. I got the MWDR after I bought the JP2C, I believe it was 2018. The Roadster was bought they year it was discontinued. At first, I was only trying to find the cathode follower circuits so I knew if there were any by cathode resistor or if the grid and plate had a common connection (tone stack driver). I had assumed the BAD had a cold clipper as my mind took 1.5k and thought it was 15k on the last gain stage of V3B. Thought I could tack on a parallel resistor in the Roadster to get a lower resistance and behold I neutered the gain and it was too clean, utterly no distortion at all. If I were to alter that cold clipper cathode resistor of 39k, I would also have to address the input circuit and possibly the plate resistor as the operating point shifted away from the cut-off region that made the distortion in the first place. After I looked at the BAD a bit closer by measuring the plate resistance and cathode resistance is when I realized it was a hybrid of a Mark and Recto combined. If you have no knowledge of what you are looking at, keep your hands out and you will not have any surprises.

The Roaster is accurate slur of the name Roadster. Some may even call it a Toaster. Many who run the Rectos like to push them with boost/OD stuff. To me that sounds like , tried it and was not for me. That is why I have a Mesa grid slammer and the flux drive.

The best mod I ever did to the Roaster required tubes only. No hard wiring or circuit mutilation required. The old Mesa Chinese 6N4-J military grade 12AX7, aka Beijing Square Foil Getter tubes. I call them unobtanium as they are difficult to find these days. I bought a dozen from Doug's tubes, I think I cleaned out his inventory as those tubes work really good in some Mark amps, they also rip in the Roadster. I also have about a dozen lightly used Mesa 1990 tubes of the same type. I did not try them until a year ago in the Roadster. I was curious how that would work out. Could not use the 7 string in the Roadster or the MWDR as you drown out with mud fest. However, those 1990 Mesa tubes cured that issue and now the Roadster is amazing with the 7 string. Badlander is compatible right out of the box, so no need to chase down any hard to find preamp tubes.

Have not worked out what preamp tubes to use in the MWDR to tighten it up for 7 string use. Probably will just leave it as is.

Sure, there are many who want to run an OD or distortion pedal on the front end. It probably would not matter what amp they end up with, they will still make use of the artificial gain. I am not into the hair band thinned out sound that gets on the fizzy size or too dang bright it becomes an ice pick. I do like aggressive grind and the level of distortion I can get just from the amp itself. Add in some reverb chamber or hall effect with some delay and it only gets better. I cannot say I am against using any boost up front, the grid slammer and or flux drive so sound good pushing the front of a Mark amp but not something I go for most of the time.

Sorry, about any personal information. It is not about me, but the amp and I did not make them. I do admire the work done by Mesa. They make some really innovative products.

 

[ntotoro]

Ok, so basically I need a Road King and a BAD to go along with the JP2C LOL!!!

 

[bandit2013]

No need to go overboard. I believe the Road King is still classified as a Dual Rectifier. I was wrong, max power is only 120W when using all 6 power tubes. It was the Tripple Rectifier that runs at 150W.

Whatever tricks I figure out with the Roadster should work equally well with the Road King II (but that is just an assumption). Blending of the EL34 with the 6L6 tubes sort of has me wondering about that.

Wonder what the Road Kings are selling for on the used market. Now I am curious but not willing to roll out the 412 cabs. Not much room as it is. But, I could run that with the Roadster in stereo. Interesting idea. I have two of these things so I can run a full quad of amps. I tend to go nuts with the stereo stuff.

In terms of Dynamics the Roadster as well as the MWDR have a wide range so you can easily run in modern mode and clean it up by rolling back on the guitar volume (passive pickups only, active pickups like EMG or similar do not do that very well).

The thing with the Roadster and I am sure the Road King II has the same characteristic, there will be a huge volume difference between modern on the gain channels and any mode used on the clean channel. Just the nature of the beast. Perhaps when using raw or vintage you have a better balance. I much prefer the modern mode so I will never be happy dropping to a clean channel. The guitar roll back trick does work so running a moderate amount of gain still cleans up as an alternate clean with the guitar volume trick. That is basically what I do with the Royal Atlantic RA100s. No need to change channels, just roll back volume to clean it up. That actually sounds better than the clean channel. Perhaps it has a hair of compression but so be it.

Mark VII cleans up quite well too. That is when I discovered it was more difficult to run that with the Badlander the way the guitarist dialed it in. We had a guest drummer one time, so I got to play guitar with the group. I could not match the same volume level with the Mark VII to get that same amount of gain. I tried and but should have switch the power down to 25W but still that would have been too loud with the guitar volume all the way up. Sure, the BAD can be loud as F-k, just as stage ready for big venues as the Roaster, Road King and MWDR. However, it can also be dialed down at 100W to keep the blue flashing lights away (depends on what state you live in, here in NC they only use blue lights, in PA they were red, white and blue or just red and blue, depends on if you get the local or state police wanting to join in on the fun of the party.) That never happened yet. It may have something to do with not playing the bass or drums after 1am. I have played the guitar past that point at gig level and never had any guests arriving with their lights on. Brick house and old neighbors helps, as long as they do not hear it while they are inside their homes, fine with me. I tend not to play loud past 11pm most of the time anyhow. If I am running the 4 amp rig, it is overkill and loud. No blue lights in my driveway yet.

Go ahead, if you play it, like it, then buy it. If they are out of production, those opportunities usually do not stick around for a long time. Every time I walked away only to return the next day and that amp was sold. I was interested in an Electra Dyne combo. Liked it. but thought about it that night and went back and it was sold shortly after I was playing through it. Oh well. that will happen.

 

[ntotoro]

So they have a master volume and separate channel volumes... ? I kind of had my fill of that with the Shiva. I love the separate masters with the JP2C. Is that typical of Marks?

 

[bandit2013]

Yes, Most marks have a main master control. JP2C just has three of them. ( I keep forgetting it has a clean channel). Same with the Mark VII. The Mark V90 was the only one that had a global master/solo boost function and mute. That circuit was borrowed from the Rectifier amps and it also includes a hard bypass that takes out the recovery tube and global/solo controls from the circuit and the individual channel masters are final masters in the circuit.

Mark IV was the first to separate the channel masters but still had a main master after the FX loop for final output.

I guess it varies from year to year or model to model. It just got easier to dial in a clean, crunch and high gain and make use of that without having to touch the controls. The IIC+, III, and IV used shared controls (IV was RH1 and RH2 so the lead was completely isolated). No happy medium for good sounds if you wanted to use all of the channels. Mark V took care of that and the JP2C and VII retired the kitchen sink to provide more usable modes that sound as close to the real deal. IIC mode and JP2C are dead nuts the same. the Mark VII mark4 mode is very slick too. At least the label used for the mode is an accurate representation and not just a label to name the switch position. The Mark V IIC+ mode is weak sauce, sounds nothing like the JP2C but some say that sounds nothing like the IIC+ and yet not all IIC+ amps are identical so does it really matter? You either like it or hate it. I think the Mark VII mode does a good representation of the Mark VII, oh wait, never mind. Too bad there is no extreme or perhaps that is a good thing. Not sure. I do not miss the Mark V90 at all. Too bad I still have it though.

 

[ntotoro]

Does the Mark VII mode seem to be more Recto-ish?

 

[bandit2013]

Only when you compare it to the Badlander, then yes it is similar but still different.

VII mode is so close to the IV mode with a slight bit of temperament change. Different attitude if an amp was capable of having emotions. What makes it Recto-ish is the tone stack gets pushed into a post-gain format, same with the crunch mode. All of the other modes the tone stack is pre-gain (before the gain control and what creates the distortion). If you think of mark settings, they will not work out but if you think Recto it will. In other words, pushing the gain all the way up along with the treble and dialing out the mids and bass does not create that "Ola Englund Tone of Death" sound. That only works for the IIC and IV modes since the tone stack is pre-gain like a standard IIC or mark should be.

For some reason, I believe the Badlander was spawned from the development of the Mark VI or VII since it is practcially the same circuit as the crunch and VII modes but tone stack being driven by a DC coupled cathode follower circuit (low impedance) vs a plate driven tone stack (high impedance).

Mark VII crunch, VII modes may be similar to the Badlander but not quite the same thing. The BAD crunch is much closer to a MWDR modern mode character and is more convincing when using the Variac power mode. Still, it lacks a cold clipper like a true Recto so the sub harmonics are not as swampy, they are more Mark like but at the same time not. Hard to describe it after getting used to the amp.

I do not believe the Ola tone of Death or what ever it is called may not be credited to him. Many have done this before but matters not. I felt the Mark VII in IIC or IV mode sounded better than the JP2C. Will have to change out the preamp tubes in the JP to confirm. They have more hours on them than the either of the Mark VII amps I have. Just did not get around to it over the weekend. Too many things to do so not much time spent on playing.

 

[ntotoro]

Makes sense. I didn't think of the differences in the tone stack originally, or how they work in one amp versus the other.

Are you saying those modes in those amps sounded better to you than the JP2C in-general or just with Ola's tone? I've never cared for that kind of sound and can't figure how that works in a band. Sounded especially harsh to me with leads. The same time, having the mids too high (more than noon or 1:00) seems to make the sound more dirty than I like... even with gain LOL!

 

[bandit2013]

There are several comparable properties of the Mark VII and JP2C. Some video's are out running sort of a side by side comparison. Some say that Mesa added more low end to the JP to compensate for the shred mode, I doubt it. There is a sonic difference between a Simul-Class amp vs Class A/B. Different level of power tube distortion effect. The Class A/B will sound deeper as all of the tubes are running at the same bias and plate current (depending on how well they are matched). As for Simul-Class such as the design of the Mark VII, it will be driving only one pair of tubes comparable to the JP2C but the other pair will have a different bias voltage thus creating more power tube saturation. It is that pair of power tubes that set the voice of the amp more so than the other pair. Same level of output though when observing peak power, they are practically the same. However, I feel the Mark VII is louder but that is just based on perspective since the taper on the JP2C channel volume is different than that of the Mark VII. A 9:30am channel volume on the VII is about the same as the channel volume at noon on the JP. As I said before, I may need to change the preamp tubes, it has been in the back of my mind but never got there. Still curious why I had no adjustable gain on CH2 and CH3 when I installed the STR443. That was just weird. Tried them in the Mark VII and did not have that same effect. Always good to get some fresh cathode electron emissions going (new tubes). All tubes age, and the getter flash stops maintaining vacuum, so they begin to sound weaker. Cathodes will eventually run short fuel too. It can only spit off electrons for so long. The getter flash usually stops absorbing any outgassing first before the cathode runs dry. Not always true.

 

[bandit2013]

Makes sense. I didn't think of the differences in the tone stack originally, or how they work in one amp versus the other.

Are you saying those modes in those amps sounded better to you than the JP2C in-general or just with Ola's tone? I've never cared for that kind of sound and can't figure how that works in a band. Sounded especially harsh to me with leads. The same time, having the mids too high (more than noon or 1:00) seems to make the sound more dirty than I like... even with gain LOL!

With the JP2C, I run the mids past noon. There is a sweet spot for mahogany body gutiars. I normally run the gain about 11am, keep treble about noon or back it off if it gets bright, bass about 10am. Depends on how much low end I want but do not want it to flub out. I can dial in the same settings on the Mark VII and it is a good match. VII has a bit more presence in its tone than the JP2C. Not difficult to get them to match up though, not exactly identical but dang close to it.

When using CH3 on the JP, it is closer to the IV mode.

I am not much of a chug activist. I prefer more open sounds and the full grind. Classic rock to modern stuff, progressive metal? If the band does nothing but screaming (unless it is for satire) I lose interest.

I would suggest to download the manual and read over the content on the controls, there is more to learn from that and it really does work based on how they describe it. Midrange on the JP2C is quite influential with certain instruments as I found. The Mark VII seems not to have that characteristic. Not sure if the tone stacks are different, in some ways they may be. I do recall seeing in the schematics on the IIC or III where some parts are installed for simul-class models in the lead drive and tone stack areas, it may be present for the Class A/B and absent for the simul model. Each power section has a different characteristic to it. With that you can appreciate one or the other. So far, I have been impressed with this version of Simul-Class used in the Mark VII. The previous models tend to lack in some ways. Always ended up with tube sing "hearing the tube rattle at the same frequency you are playing and it can be loud if you are at bedroom levels" Mark IVB and the Mark V always seemed to rattle the tubes, not all the time but on clean it was a nuisance. Fresh power tubes did not always fix it as it would creep up eventually in a short time. Not sure what causes that to occur other than the plates and internals vibrating. Same tubes do not do that noise in a different amp, just in the Simul-Class amps. Really weird. So that has not been a factor with the Mark VII yet. At practice level or gig level it is of no concern, just when keeping this low in volume is where it can be noticed. May have well been the tubes and how they were constructed. Sure, my Mark IVb was a combo, and I converted the Mark V90 to a combo as well, it was when driving an external cab and not using the combo speaker is when it became apparent. The Mark V did the tube sing before I converted it to a combo. Thought the combo form would keep the thermals at bay as that amp would overheat often (had a bias issue). The Mark IVB did that with every tube, the Mark V was more or less with the Mesa branded tubes (mostly the STR440) but when I changed to the STR441 that noise never came back.

 

[ntotoro]

I'll have to check out more Mark VII videos. Most of the ones I see compare the MkII mode of the MkVII to the JP2C or are more Metal-oriented.

Makes sense to run the mids a hair higher on a mahogany guitar. Most of the Strat-scale mahogany guitar I've played tend to be brighter. My guitars are primarily swamp ash, alder or alder with maple tops.

Between the JP2C and the MkVII, which would you say had more girth with single-coils? Not to the point of making them sound like P90's or humbuckers, but some weight behind them and still let them be single-coils?