Santiago Alvarez (electronics engineer, JVM, YJM, AFD...)

santiall said:
I'd need to check but I think that schematics looks ok. I remember that back in the day, the most popular schematics had a value written by hand and it was wrong. Our service schematics and the original amp were different to that schematic online
Click to expand...
Thanks a lot Santiago!

The schem I linked above, is like the one in the old Marshall book "The first fifty years", which I own since 1996. So this schem should have been around in the late naughties as well.
I built my Jubilee clone according to this schematic (well actually the 2554 one, because the clone is only 50 W and without choke), and the amp sounds flat out fantastic. There is NONE of the scratchyness of the distortion many describe with the reissues, no matter where the master volume is set.
I also experienced the scratchyness while playing both the 2555x and the 2525H at Thomann.
Remember, when I asked about a possible difference in sound between 3mm and 5mm LEDs here a few months ago?
I am still wondering, if there is yet something different in the reissues that may cause that scratchyness. So when you made that remark while talking to Jason; I thought, well, maybe this is a hint... Although IF this is a 100n cap, I doubt it being the culprit.
Do you have the schematics of the reissues? If so, I am pretty sure, you're not allowed to share them, but in case, I'd highly appreciate if you might compare the old schem to the new one.
 
headcrash said:
Thanks a lot Santiago!

The schem I linked above, is like the one in the old Marshall book "The first fifty years", which I own since 1996. So this schem should have been around in the late naughties as well.
I built my Jubilee clone according to this schematic (well actually the 2554 one, because the clone is only 50 W and without choke), and the amp sounds flat out fantastic. There is NONE of the scratchyness of the distortion many describe with the reissues, no matter where the master volume is set.
I also experienced the scratchyness while playing both the 2555x and the 2525H at Thomann.
Remember, when I asked about a possible difference in sound between 3mm and 5mm LEDs here a few months ago?
I am still wondering, if there is yet something different in the reissues that may cause that scratchyness. So when you made that remark while talking to Jason; I thought, well, maybe this is a hint... Although IF this is a 100n cap, I doubt it being the culprit.
Do you have the schematics of the reissues? If so, I am pretty sure, you're not allowed to share them, but in case, I'd highly appreciate if you might compare the old schem to the new one.
Click to expand...
I don't have the schematics of the reissue and yeah, even if so, I couldn't disclose them but they were a 1:1 copy of the original schematics, verified against the sample in the museum. Back in the day, the schematics online were not exactly the same, that cap was different and connected by hand but I forgot which one, maybe the bass pot cap or the feedback, but I don't remember.
I'm still trying to see if I can put my hands in a reissue and test the LEDs, etc...
 
HEy Santiago, thanks! I sold my Jubilee Clone some months ago to a good friend, who absolutely fell in love with its sound. So I can't experiment with that one, but I as well keep searching for a cheap, used 20Watter in order to go deeper with that scratchyness. And its schematic :grin
 
santiall said:
Hi, you can try any of those, nothing is going to be damanged for testing those different tubes or removing two output tubes.
For V1 you could try an ECC832 as well, in the JVM the input valve is the second triode in the tube. It'll give you a different amount of gain for all the channels instead of only the high gain ones.
Removing two output tube will technically lower the outpot power to 50W but not sure how worth it is as the difference in volume is subtle.
Click to expand...
Be aware that the 832 will also effect other channels/modes.
It’s a sacrifice.
 
headcrash said:
HEy Santiago, thanks! I sold my Jubilee Clone some months ago to a good friend, who absolutely fell in love with its sound. So I can't experiment with that one, but I as well keep searching for a cheap, used 20Watter in order to go deeper with that scratchyness. And its schematic :grin
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as far as I remember the 20W Jubilee version is a copy paste of the 100W preamp schematic with the output level adjusted to suit the power amp.
 
TheTrueZoltan! said:
A JVM410H without the annoying hiss.
Click to expand...

There's trick for that.
You can bypass two noise generating stages that include the permanently wired FX Loop and Reverb, with a simple 1/4" jump cable, the signal path will be almost as pure as a JCM800.
You can pull out V9 to completely remove any extra noise form these stages.

@santiall what say you?

marshall-jvm410h.jpg


jumper.jpg
 
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the hiss mainly comes from the 1st and 2d triode stages, the contribution of the rest of the amp is negligible. As usual, the earlier the noise is introduced in the circuit the worst the final noise will be but then there is the trade off gain vs noise...
you will also notice that pretty much all the other modes are very quiet, actually with more gain and less noise than a 2203, which also indicates where the noise comes from. The noise is also reduced quite a lot when lowering the gain, another clue of where to look at.

If you bridge all that you will lose a few dB of signal level by V9B, V9A noise contribution is close to zero anyway.
 
Santiago, what is the purpose of C7+C8 and C24 in the JVM410 power amp?
Are C7+C8 the same as snubber caps on the plate resistors in some amps?
C24 is a peaking resistor in the feedback loop, so shelving down more highs?

C7 C8 C24.png
 
those are all there for stability reasons, probably set at 20kHz or higher.

C27 and C28 are effectively in parallel with R22 and R23, they are low pass filters. Calling them 'snubbers', and being pedantic, isn't really correct. A snubber would be a cap or whatever network used to suppress spikes, transients and the likes. For example the capacitors across the bridge rectifiers.

C24 is located across the feedback so it would let more highs pass through, lowering the overall high frequency response. It is the same as the typical cap across the feedback of an operational amplifier, for stability reason in many cases.
 
Im still waiting for the new components for the front panel, but i came up with a cunning plan if all else fails.

how about if remove all switching transistors and replace collector & emitter with individual relay contacts?
I'll build external Arduino board with Midi Input which controls the relays. Or course leds won't work and i need to know which relays must be on for corresponding channels, what do you think? 😃

IMG_0475.jpeg
 
Jonttu said:
Im still waiting for the new components for the front panel, but i came up with a cunning plan if all else fails.

how about if remove all switching transistors and replace collector & emitter with individual relay contacts?
I'll build external Arduino board with Midi Input which controls the relays. Or course leds won't work and i need to know which relays must be on for corresponding channels, what do you think? 😃

View attachment 16352
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I don't see much logic on that... the transistors aren't a problem at all and what you propose is to replace the transistors with relays that will need another transistor to be driven.
The 373 are latches, all the switching logic comes from the Atmega8 microcontroller.

Don't forget that there are 10s of thousands of amps like yours out there and they don't have any issues with the switching logic, I don't see the need to reengineer that but if you want to have some fun then why not
 
Hello Santiago..from a rainy winterized day in southern Florida,

Are their any plans or are the wheels in motion with a newer JVM model or something rad like that coming from Marshall?
Cheers for YEARS!
LEL.
 
Life Eats Life said:
Hello Santiago..from a rainy winterized day in southern Florida,

Are their any plans or are the wheels in motion with a newer JVM model or something rad like that coming from Marshall?
Cheers for YEARS!
LEL.
Click to expand...
Hi!, I don't work for them for some time already... who knows what their plans are :D
 
The reason for the fridges & stoves is everything will all be one feed, all the electronics/appliances will pair up in the chain of our existence.
 
@santiall I recall Bjon of In Flames going Marshall way back in the late 2000s (think he started using JVMs) and then recently saw a sit-down with Ola where he mentioned there was a prototype for the amp:



Would love to know more about how that amp differed from the main production line stuff :D
 
2dor said:
@santiall I recall Bjon of In Flames going Marshall way back in the late 2000s (think he started using JVMs) and then recently saw a sit-down with Ola where he mentioned there was a prototype for the amp:



Would love to know more about how that amp differed from the main production line stuff :D
Click to expand...

is it this one? Curious to know what it is. I want to say in Marshalls recording studio there’s something like this knocking around but maybe I misremembered…

1703881638420.jpeg
 
Looks like it was based on a certain Aldrich DLA prototype - that's interesting; I saw vids of a Cameron-Aldrich-modded 2203 on YT some time ago (amp sounded awesome)
 
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