Mark V tone issue

[FabParker]

Hello everybody,

A few months ago, I've bought a second hand mark v 90 w head and I after a while I have noticed that both the lead channels weren't able to make a saturated sound which it could be expected when you rise up the gain knobs so I decided to replace both power and preamp tubes and I went to a store to compare my ampl with another new mark V amp using the same speaker and cables and I noticed a really big difference between the two as mine wasn't able to make the same type of saturation sounding like it was a slightly distorsion making the same volumes and tones set up.Also the shop assistants did noticed the difference and the lack of saturation. I am in Bangkok Thailand and the amp has been inspected already by 3 technicians including some from the Thai dealer shops but they weren't able to solve the issue. I was wondering if somebody could give me some hints if this is a common problem for older amps, I think the amp is already 8 years old. It sounds like that raising the gain knob mostly increase volume instead of saturation and when we did the comparison with the other new amp, it was able to deliver a much more saturated sound once you were raising the gain in both channel delivering a much more powerful distorsion.Caps and knobs and also other elements have been inspected is there any possible reasons that can cause this problem?

 

[bandit2013]

No clue. The only thing that comes to mind is the triode/pentode switch on the back. If set to triode when using CH3 it does not sound as aggressive as it does in pentode setting.

Other things that may differentiate the one amp from the new one, were the same power tubes used? If so, do the bias colors match? Did the new amp have STR441 and what were the bias colors of those tubes compared to what you have in the older Mark V90?

The only other difference I know of is the transformer manufacturer changed after the pandemic. Doubt that matters. I can attest that the one I have made in 2012 did not compare to the other Mark V90 amps I tried after I got mine. The V90 I have is shrill, ice pick and unusable. There were ways to compensate for that, but it usually resulted in a dull sounding amp. For me it was a no-win situation and best to give up on it.

Hard to tell if there were any design changes to the Mark V90 over the years. Mesa does not make that public.

You could trade/sell the Mark V90 you have and buy a new one. That may be the best option for you than trying to figure out what may be different. I am not much of a fan for the Mark V90 in particular, at least the one I have. Wish I had sold it and may do just that.

 

[FabParker]

Thank you for the reply bandit2013,

The new amp had the STR441 as I checked, I am not sure about the bias color. Both amps had same power 6l6 and preamp 12ax7 Mesa original.
I also switched the triode/pentode function but not much changes. if I use both channel 2 and 3 and on both I try to crank the gain know after let say 4 and 5 it seems that instead of saturation it will loose the crunchiness and I will have to raise the master to unreasonable volumes. if I am on full power (90 w). Channel 3 it is a bit more powerful but still it will do the same thing if I will try to raise the gain.

 

[FabParker]

I can get a nice distortion, however, if I want to have something more powerful I need to use some pedals on both channels. If you also check some mark V videos on you tube even with channel 2 I should be able to get a powerful distortion with the right settings which unfortunately I can't. It is like having a Ferrari which you can only run half of the speed. I might keep it, using some pedals I still can get a good sound and the amp has no other issues it works perfectly but yes bit disappointing for sure!

 

[rarebitusa]

Curious have you tried playing it with the "Hard Bypass" switch on? That eliminates the FX loop and the master output circuit. With that it's just the chans straight out to the power section. Maybe start with that and the GEQ off and see if there's any change.

 

[FabParker]

Hi rarebitusa ,
I think I did that previously, that switch is on the back panel and it takes out the loop function, but unfortunately it didn't change much, and I did also switch off the GEQ but not many improvements.

 

[Eevil]

I can get a nice distortion, however, if I want to have something more powerful I need to use some pedals on both channels. If you also check some mark V videos on you tube even with channel 2 I should be able to get a powerful distortion with the right settings which unfortunately I can't. It is like having a Ferrari which you can only run half of the speed. I might keep it, using some pedals I still can get a good sound and the amp has no other issues it works perfectly but yes bit disappointing for sure!

Could you take some audio or video clip where the amp is played in every channel? And take pictures of the the every channel settings also. That’d give a bit more information what is going on.

 

[bandit2013]

First question: what preamp tubes did you put in the amp?

There is a possibility that you have a weak preamp tube. V1, V3 or V7 may be at fault. I would check those three first before looking into V2, V4, V5 and V6.

There is a possibility it could be something else and not tube related but in most cases, it is just a preamp tube that is causing the issue.

 

[FabParker]

Could you take some audio or video clip where the amp is played in every channel? And take pictures of the the every channel settings also. That’d give a bit more information what is going on.

Hello, I definitely will soon I am just moving to another place once all set up I'll do if it can be posted with a free account.

 

[FabParker]

First question: what preamp tubes did you put in the amp?

There is a possibility that you have a weak preamp tube. V1, V3 or V7 may be at fault. I would check those three first before looking into V2, V4, V5 and V6.

There is a possibility it could be something else and not tube related but in most cases, it is just a preamp tube that is causing the issue.

Hi bandit2013 I decided to change all the preamp tubes replacing them with original Mesa 12ax7 before I did the comparison with the other amp but not much changes.

 

[Eevil]

Hello, I definitely will soon I am just moving to another place once all set up I'll do if it can be posted with a free account.

Upload to youtube (and sharing with link only - if you want) and share link here. That’d work too

 

[FabParker]

Upload to youtube (and sharing with link only - if you want) and share link here. That’d work too

 

[bandit2013]

With the stock tubes, it set the bench for what is in the new amp. As for the tone, not sure what makes the new one different than the older one. Mesa has made some changes early on but after 2012, hard to say what other fixes or changes they made to the preamp, either component change or circuit mod. Too bad there is no posted list of changes made to the model over the years it was manufactured. Some of the DC blocking capacitors could be different. I wish I had the answers but I do not. Do they sound the same if you disable the GEQ on both? At least that way you can rule out any components in the GEQ circuit. Is it possible to dial one to sound like the other? I lack the full knowledge to say, yeah if you change cap X or remove it, it would sound like this.... Sure I have experimented removing caps, just the minor components and not something major like a dc blocking cap between gain stages.

 

[bandit2013]

Having a recording of the new V compared to the older V would help some come up with ideas. I am not sure if that would help me help you. (if that makes any sense).

 

[FabParker]

Thanks again, unfortunately I am not an expert I really beleived once the preamp tubes were replaced I could get a better response but it didnt much changed. As I ve talked again with the last technician after he did some basic tests he wasn t able to find any big issues I will soon post a video so that it might give you a better idea of what I m talking about thanks for your support!

 

[MarkV User]

The amp could be modded? Make sure the bias switch is in the correct position for the tubes you have installed. And the tube selection is critical for this amp. It isn’t enough to just put in a set of Mesa tubes in my experience. The amp also sounds very different depending on the speakers and cabinet… but the real gotcha is that in its default configuration every knob in your signal path has to be set just right or you won’t get the sound you want. The gain knob in particular may only sound good in one very precise position. Too high or too low and the amp will sound bad or at least not how you want. Make sure to fine tune it after you change any other knob.

To start with spend about 20 hours with the amp just experimenting with the front and back knobs and your guitar and try a lot of control combinations. With the effects loop bypassed you get one character. With the loop in and the volume turned down to various levels you get a different gain character. All the tone knobs and sliders are very sensitive and they all have a big effect. And in the default configuration if the amp the gain knobs need to be set exactly right.

But if the early gain stages clip too hard then you won’t get the kind of distortion you want. This amp only works well if the preamp tubes are individually selected to create the sounds you want. At least that is how it was for me.

Individual Mark V amps do seem to vary in their sonic character based on build variations. I only love my amp after changing the presence circuit, using lower gain preamp tubes (with a lot of swapping tubes to get things just right), and changing the combo speaker to the 300W Celestion BN12-300S bass speaker. Before those changes I hated it. Well, I have a lot of tonal range now that didn’t exist when I started out. I can get killer medium gain tones from all channels, have a large control range of good tones, and the instrument is absolutely unique.

Your tonal goals are different from mine but I think you can either put a lot of work into getting this amp just right or switch it out for something that meets your needs better. There is a learning curve, and you should ideally sit down with the amp and figure out how it works and then figure out for yourself how to get the sound you want. Experimentation, reading, playing and listening will get you there. But the Mark V is an expensive and complicated platform for that learning. You can also get your amp tech friends to educate you and help build a great amp maybe.

Good luck!

 

[FabParker]

Thank you for your reply MarkV user, I will post soon a video link with a sample for both channel 2 and 3 I am just waiting to relocate at the moment and I got all my stuff packet but I surely will once I'll set up everything in my new place. I am not a real expert on electronic and amps functionality, but this was probably the first time I came across this issue after owing different guitar amps for a long time. I have spent reasonable time by moving knobs change settings and trying all the options that the amp is able to provide, bypassing the fx loop and switching cathode and pentode functions. By watching different videos on you tube I was able to have a roughly idea of how channel 2 and 3 are able to provide a type of saturated distorsion by rising the gain at about level 5 and 6 and you already can hear a tone that is close to Kirk Hammett modern kind of heavy sounds with a high gain crunch set up especially on channel 3. At the moment I am able to get a tone that is close to Santana with that type of gain settings on both channels and if I try to raise the knob I will get a raise in the volume rather than saturation even if I keep the master volume at a low levels. I replaced all tubes pre amp, power and rectifier and used Mesa as usually recommended but not much difference after. As I 've mentioned before the comparison that I did with the new Mesa Mark V in a shop by using same guitar, cables, speaker and settings (I am not sure about tubes but I presume in a new amp they might have put original 6l6 and Mesa preamp) was also noticed by the shop assistants; Channel 2 and 3 of my amp was definitely much weaker in terms of saturation compared with the new using the same settings in the front and the back of the amp tested at 90 w. It should definitely relates to a problem with the preamp section and hopefully a patient technician might be able to find out but it might be not easy because there are lot of parts involved, voltage on the plates, resistors, caps may be? I will keep you informed on the matter once I will be able to find a good tech may be specialized on Mesa but here in Asia it won't be an easy task!

 

[MarkV User]

Good luck! It sounds like you already understood the problem pretty well. For my amp the “Mesa recommended” approach didn’t work at all. I had to select tubes carefully for each stage. But that is not the only good approach. One of the YouTube guys pointed out that this amp is harder to dial in than other tube amps. Some of those YouTube videos are of amps that have been “set up” by a good amp tech, maybe at Mesa for marketing purposes, and they sound amazing—completely different from how my amp has ever sounded.

But your amp sounds like it may have a problem as you suspect. And of course it can’t be the bias switch as I was saying because you are not getting the preamp gain you should.

One thing to understand… do you not get enough gain even with the gain knob cranked, or do you go from not enough gain to too much, with no sweet spot in between? The second case is a common problem for this amp that you can fix by choosing tubes that clip in later gain stages slightly before earlier ones. Or kind of all stages at once. It sounds like you have the first case…

Hey, here is an idea. The amp would have less gain like your describing if the power rail voltages in the preamp were too high. You have a different mains transformer possibly. Is your amp set up for 50Hz 115V and you are running at 60Hz? Or by chance did the amp come from Japan where the wall power is 100V 60Hz? Either of those could conceivably cause the preamp to run at a higher voltage.

 

[bandit2013]

I would at least check the gain pot for CH3 to confirm that the solder tabs are not touching each other. Would be a good thing to check the wires for bad solder joints on the pot leads and on the PCB. The CH3 channel volume control could also be shorted. Simple things first before digging into the components. This issue is probably contained in the lead drive circuit associated with V5A and V4B. It can also be associated to the V6A circuit too. A leaky dc blocking cap will effectively shut down the next gain stage. That can be found with a voltage test on the control grid of the next stage or on a component lead on that side of the cap. Same for the V6A circuit as that is the final gain stage for CH3. If CH1 and CH2 are ok, that rules out V3A circuit. There should be some level of achievable gain or drive from CH3 even if it is out of spec. It could a number of things but should be easy to find with a voltage test to check for plate voltages, bad DC blocking caps. or associated defects in wiring or the pots are broken, shorted, etc. Just some assumptions.