Please help JVM410H questions....

Discussion in 'Marshall Amps' started by Mateo11, Feb 16, 2020.

  1. Jethro Rocker

    Jethro Rocker Well-Known Member Premium Member

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    Yup. Modded there at least. Id run away. Anyone that lists an amp as stock that has a dead loop, internal mods of unknown type and rusty corrosion is a big red flag.
     
  2. Mateo11

    Mateo11 New Member

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    Do you happen to know (or anyone for that matter) what that mod looks like it was for? I am curious what that type of mod would be addressing.

    I do agree with you on your statement but so far the guy I have been dealing with has been great to work with. We have been communicating and we are set to meet tomorrow to swap back the amp for the cash. I don't feel it was intentional but I am sometimes too trusting in people so who knows.

    He said the amp was recently (last month) gone over by a tech and given a clean bill of health. He said he contacted the tech who did the work and the tech said he didn't check the loop. Sounds fishy to me that a tech wouldn't check the functionality of the loop when going over an amp but I don't know.

    I am just hoping a stock JVM like the one I just bought off a guy over at TGP sounds as good as this one.

    I have owned plenty of Bogners, Friedmans, 3rd Power , Soldano etc etc and I was absolutely floored by the JVM. Jaw dropping good. I instantly bonded with it way more than any other amp Ive had.

    The first day I got it I told myself I would run through all the channels make sure everything works 15 minutes tops then had to run out for work errands. Two hours later i was still playing and I hadn't even made it past the crunch channel!
     
  3. ampeq

    ampeq Well-Known Member

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    Glad your returning it. Just in case, take good pics of the board everywhere so if there is a mod on it you like a tech can see what it is. There are a lot of std. mods for them and a good tech will know what to look for.
     
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  4. Mitchell Pearrow

    Mitchell Pearrow Well-Known Member

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    Welcome to the forum, sucks you’re having problems with your amp brother, but seems to me that you have a plan.
    Cheers Mitch
     
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  5. ido1957

    ido1957 Active Member

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    Most people don't leave the back cover off their amps. That raises a red flag. Footswitch supposedly comes with the amp so another red flag. Call me paranoid but that's my 2 cents. It sucks to buy something and have to return it. It's just annoying.

    Go to a music store and try out a different JVM to see if you like it.
     
  6. Jethro Rocker

    Jethro Rocker Well-Known Member Premium Member

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    I am unfamiliar with mods other than the neg feedback which the above one is not. They sound fantastic. IMO they need no other mods. Im betting you are just as happy with a real stock unit.
     
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  7. Mateo11

    Mateo11 New Member

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    I’m hoping you are right because if it sounds and feels that way stock I don’t think I would do any mods to it. I use my volum knob a lot and the amp responded extremely well to that.

    What does the negative feedback mod bring to the table?
     
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  8. Jethro Rocker

    Jethro Rocker Well-Known Member Premium Member

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    I looked up all the regular mods to this amp and none use R52. So I habe no idea what was done to it.
    The neg fdbk mod opens it up more for lack of a better word? Can have the openness of an 800 etc. I put a pot in mime so it is variable.
     
  9. spacerocker

    spacerocker Well-Known Member

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    Firstly apologies for missing these changes the first time I looked! - I had a quick look at the PCB for mods, but wasn't looking in this area! I don't think the changes are "mods" as such, rather some sort of repair?

    [​IMG]

    The first change is the replacement of R52. This should be a 2W 22K power resistor. This appears to have been replaced with two 10K (1W?) resistors in parallel, and connected in series with another (value cannot be seen from this angle). This could be another 10K, making 15K in total, or (hopefully!) 15K making a total of 20K, which is near-enough the stock value!

    R52 is wired off the stand-by switch and provides the HT supply "HT1" This appears to power the Phase-invertor valves, and maybe some other things too.....It is not clear to me why this resistor would need to be replaced?


    Secondly, the capacitor C12 has been replaced with a much larger capacitor. C12 provides the positive going signal to the power valves, whilst C14 provides the negative going signal. They should both be 47nF 630V caps. Again it is not clear why C12 has been changed, or whether it is still the same value? Possibly it is the same value in a larger package (1000V?)

    These apparent repairs are NOTHING at all to do with the effects loop, and should not cause any problems, assuming that the right values have been used? But it does raise the question of why a repair of this sort was necessary in the first place?


    I think Mateo11 said he was going to return the amp? I think (given the general condition, the non-working effects loop, and the strange repairs) - this is a very wise decision!
     
    Last edited: Feb 17, 2020
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  10. MonstersOfTheMidway

    MonstersOfTheMidway Well-Known Member

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    @Mateo11 :
    Hello.
    I think you're getting some good information from many members regarding the condition of the your first 410H (it sounds like you're returning the first 410H and buying another).

    If it's accurate that the differences in components reflects a repair than a modification, it would stand to reason that your second/incoming 410H should sound & feel like the first.

    What you can be sure of is the tubes: write down the brand and type of all power tubes and preamp tubes of your first 410H so that if your second/incoming sounds a little different, you can purchase the same tubes for your second/incoming 410H that were in your first 410H. Additionally, check the bias of the first 410H, and if it's a safe & reasonable setting, you can apply that bias setting to your second/incoming 410H.

    I think you'll like your second/incoming 410H very much. First time I played a 410H at a store, I instantly fell in love: the sound paired with the awesome versatility made it an easy decision. 410H covers so many different music genres very well and has proven a very reliable amp for me since 2008.

    Good luck with your second/incoming 410H. Let us know how it turns out.
     
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  11. lespaul6

    lespaul6 Member

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    What an excellent evaluation and illustration....bravo
     
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  12. Mateo11

    Mateo11 New Member

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    Yes thank you so much for the detailed response, illustrations and explanation. Very well put together and helpful.

    I just now got back from returning the amp to the seller. I have a bone stock 2017 in really good condition orderedthat shipped out today...I’m guessing I should get it by Friday since it only has to travel from St. Louis to Nashville.

    I believe you are correct in your assessment that it’s not necessarily mods that were done but repairs. To be on the safe side though since the amp I returned sounded oh so very good I took a bunch of extra pics of the insides just in case the one I’m getting sounds different I’ll have something to show a tech.

    I will be amazed if that’s how a stock JVM sounds and feels. I couldn’t see myself changing anything if that’s how it is stock. I run it maybe differently than some though with all the preamp volumes dimed and use my vol pot on the guitar a bunch with Master around two and it sounds the best that way to my ears. Well it would definitely sound better with Master at 4 but I do have neighbors ha.

    I have had Friedman amps, Bogners, 3rd Power, Soldano even some older Marshall JCM’s etc etc lots of great amps but the JVM for me personally leaves them all in the dust. Versatility is off the charts.

    The first day I had it I told myself I would run through all the channels 15 minutes tops to make sure the amp works properly before running some work errands. Two and half hours later I was still playing and hadn’t even made it past the crunch channel! The JVM and I seriously bonded that day and I hate that it took me this long to give one a shot. Would of saved me a ton of money and time if I would of started with one first but oh well glad I did finally get one.

    I would like to say thanks again to you and everyone else here on this forum who has been extremely helpful and responsive in sorting me out on this amp. Much appreciated!

    Keeping my fingers crossed this incoming JVM is going to have that same mojo!
     
  13. Mateo11

    Mateo11 New Member

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    So the tubes that were in the one I returned were Mullards El34’s & JJ preamp tubes ECC83’s . The incoming one has all JJ’s EL34’s and ECC83’s.

    Any experience in the difference between these two power tube brands? Thanks!
     
  14. spacerocker

    spacerocker Well-Known Member

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    Interesting regarding the power valves! They may affect the tone slightly, but as the JVM power amp is intended to run quite clean, I don't think the different valves will affect the tone much. I am still on the stock Svetlana/"Winged C" power valves myself, so I can't comment on how JJs would sound in comparison...

    The ECC83 pre-amps are a type, not a brand, and are just the UK designation for 12AX7 (i.e they are the same type of valve) - Do they have "Marshall" written on them and part numbers in red or yellow? In my amp, the pre-amp valves are mostly the chinese "Shuguang" brand - which sound excellent (bright and clear) with one JJ. JJ's sound too dark for me (although others like them). The JJ may have been a replacement by Marshall when they were helping me investigate another problem!

    Don't get too hung up on Channel Volumes Vs Master Volumes. On a standard JVM (i.e. NOT the Joe Satriani version) it makes NO DIFFERENCE whether Channel Vols are high and Masters low, or vice versa!

    You can use all the options of the JVM however you like - but I like to set individual channel volumes depending on what I am playing, and 99% of the time leave the guitar volume up full (which is quite different to how I played for the previous 20 years before I got the JVM - when I used a single channel 2203!) My channel usage is as follows:

    Clean = Clean Green
    Normal Ryhthm Guitar = Crunch Channel Red Mode (also sometimes green or orange)
    "High Gain" Rhythm Guitar = OD1 Orange
    Lead Guitar = OD2 Orange

    This way I can pre-set a different volume for each style of playing.
     
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  15. MonstersOfTheMidway

    MonstersOfTheMidway Well-Known Member

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    Hello.
    It would be interesting to know if the Mullard EL34 in your first 410H were current production (abbeviated as "cp") Mullard, or if they were "new old stock" (abbreviated as "NOS") Mullard. My hunch is that they were probably current production Mullard EL34, which means you can find current production Mullard EL34 from just about any tube dealer/vendor whether online or brick and mortar (also, cp Mullard EL34 will not be as expensive as NOS Mullard EL34).

    As said previously by others, the tone aspect of power tubes in JVM amps will not be as significant as with vintage Marshalls, for comparison, due to design aspects. Instead, appreciable differences might be noticed in low end projection, beak-up, noise/microphonics, "feel"/reponse, etc.

    If your second/incoming 410H does indeed have JJ EL34, I would recommend trying those for a few days to see how you like them. In my experience, current production JJ power tubes have a good reputation in a number of key points I mentioned previously in the paragraph above.

    If your second/incoming 410H has JJ ECC83 preamp tubes, you might want to keep these for a few days as well since your first 410H used these preamp tubes so that the tone characteristics might be similar, which is something I think you enjoyed. Preamp tubes in JVM amps will have a greater impact on tone than power tubes because the JVM amps gets a lot their tone from the preamp section. For example, the preamp section in channel one features a "pre-gain" tone stack, which greatly impacts the tone of the amp. Additionally, different channels/modes will use different halves of the first two preamp tubes due to the internal design of the amp. So, selecting preamp tubes that get you close to the tone you want is something to consider.

    I do like JJ tubes in my JVM410H. I currently use quad of JJ E34L that I absolutely love (I'll probably stick with JJ E34L from now on in the 410H). I also own several JJ ECC83-S preamp tubes, which are among the quietest and most reliable preamp tubes I own. I currently use them in the gain stages (a position where tone is critical), but I also used them in the reverb/fx mix section, cathode follower section, and phase inverter section.

    I've used other brands and types in the 410H (such as 12AX7 type as well as Electro-Harmonix brands) for a variety of reasons. If you feel you'd like to try something else, consider that an option but make sure you research the tubes for compatibility with your 410H before you make a purchase.

    Good luck with your second/incoming 410H amp. After a few days trying it out, let us know what you think.
     
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  16. Mateo11

    Mateo11 New Member

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    Interesting! I assumed diming the channel volumes would push the preamp tubes harder.

    I listened to the ToneTalk podcast with Santiago and I think I remember him saying he liked the cheap Chinese preamp tubes in the JVM the best.

    (The ECC83 tubes that were in the one I returned were all JJ's except for one that had Marshall on it in white lettering)
     
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  17. Mateo11

    Mateo11 New Member

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    Thanks! Here is a pic of one of the Mullard's that was in the JVM I returned.

    UPS sent me an email a few minutes ago saying my amp should be delivered today! Thats amazing since the seller shipped it yesterday at noon!

    [​IMG]
     
  18. spacerocker

    spacerocker Well-Known Member

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    Yes - that is a logical assumption to make! But in fact the Channel Volumes are at the END of the pre-amp chain, and the Masters are at the beginning of the Power amp section, so they are kind of doing the same thing! The only thing between them is the effects loop, which generally will not be adding any gain (especialy when set to "bypass"). The only difference is on the JS model (as Santiago corrected me!) - where the is a capacitor on the Master volume which (if I remember correctly) makes the amp brighter at low volumes, but less bright at higher settings. But the standard JVM does not have this!

    Yes the Shuguang valves usually have white (or gold) lettering, whilst the JJ's have red! Shuguangs seem to be brighter, whilst JJ's are darker, but higher gain! I find a mix of the two gives the best results - I have 1 JJ and the rest Shuguang!
     
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  19. Jethro Rocker

    Jethro Rocker Well-Known Member Premium Member

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    That Mullard is a reissue as its made in Russia. You can get them pretty much anywhere, nothing overly unique or rare about them.
     
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  20. Matt_Krush

    Matt_Krush Well-Known Member

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    JJ EL34s were Ok in the JVM.

    But Tung Sol EL34's or JJ KT77s are better.
    Sound bigger/fuller than the JJEL34s.
     
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