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

Safety standards are the same for everybody, probably bigger companies take them more seriously as first, you want your products safe to begin with. then the fines can be huge if you are not responsible. For a small company you probably risk bankrupcy if they catch you not complying, you can face legal punishment as well. It is more serious than some people think.

What I was meaning with that is that some older effects also had that ground lifting circuit. You'll end isolating your ground more and more as they are technicall in series althoug most likely the ground will be shorted through the rest of the wiring. Still the principle is easy, try to keep one continuous ground, then act if there are problems

I have some cables made with the screen cut on one side, work good for things like FX loops. A 10-100Ω resistor instead of open probably is a better idea but you know... shoemaker's son goes barefoot haha. You couls add the capactiro and diodes across the resistor, if they fit in the jack, and you will have the full circuit in your cable,.

Transformers are OK as well but yes, you need to drive them properly to avoid loses or create resonances. I haven't had issues with the usual short cable between an FX loop and a rack for example

cheers!
Thanks a lot! ;)

Regards!
 
Hi Santiago!

I have also question about jvm410 fx loop 🙃😆...

I'm trying to find ideal fx unit for jvm loop so I have MINIMAL tonal and dynamic loss.

Will use it probably only In "power amp" loop (no 4 cable method) for chorus, delay, reverb and master volume on expression pedal.

Thinking about g-system, hx effects, or something else If you have on mind?

Tnx!
 
Hi Santiago!

I have also question about jvm410 fx loop 🙃😆...

I'm trying to find ideal fx unit for jvm loop so I have MINIMAL tonal and dynamic loss.

Will use it probably only In "power amp" loop (no 4 cable method) for chorus, delay, reverb and master volume on expression pedal.

Thinking about g-system, hx effects, or something else If you have on mind?

Tnx!
Hi,
I've mostly used the TC G-Major and G-Force and the the Yamaha SPX-2000 as multieffect in the FX loop of my amps, not only with a JVM, but you will need a MIDI controller with them.
If you want something with footcontroller you'll be fine with those you mention. There are some other options but make sure that they can take line level signals, not just guitar/instrument levels or you may have trouble when using the power amp loop
 
Hi, Santiago! Congrats on designing the very underrated JVM. I feel it's the greatest Marshall ever because of the wide range of drive levels while always sounding like a Marshall. I love that it's very tight with intense harmonic content. I recently picked up the 1 watt JVM. Using a reactive load box and impulse responses for speaker sim has shown me that little amps can sound as good as the big ones! What can you share about that amp? How could its OD channel be modded to be like OD1 instead of OD2 from the big ones? Also, what can you tell us about the reverb on the JVM? What hardware units would you compare it to? Thanks in advance!

1 watt JVM demo
 
Hi Todd, thanks for the message and compliments. Not sure about the underrating of the JVM but I'd think it's not bad for something that is going to be 20 years old soon :). Nice playing and tone in your videos!

JVM1... actually that amp is based on the OD1 RED mode of the standard JVM. It is a very similar circuit but with a bit less gain than the 100W preamp. In a normal use case the 1W amp will be distorting more often that the 100W so I lowered the gain to balance the total gain. What I mean is that, usually, the 100W power amp would be used in its linear zone but the 1W power will be used distorted so it was too much pre+power amp distortion. On top of that,Tte 1W also has the low power mode to be more room friendly when used fully overdriven, also to encourage people to drive the power amp harder.

The reverb of the JVMs... it is whatever effects card Marshall had at the time. We did put some work on it to make it sound balanced in the amp but it wasn't exclusively developed for this amp nor based in any particular hardware. We alreay knew that just having a knob called "reverb" some people would complain and say reverb this and reverb that. Still happens today so yeah, it is one of those haha. At the end people who really like reverb will use their preferred one in the loop, the ones who don't like reverb will turn it to zero (and maybe come to a forum to complain abouthow a bad idea it is to have reverb in an amp hahaha).

Those were also the times when a combo had to have reverb but a head must NOT have reverb... The JVM had to be the same amp for head or combo to streamline development and production so it is in all the series. I see the reverb more like a nice-to-have commodity, like if you go with the amp to play somewhere and that particular room is really dry, or you just want to play guitar but without having to connect everything, so you have it in there but probably you wouldn't use it to record the amp.
 
Hi Todd, thanks for the message and compliments. Not sure about the underrating of the JVM but I'd think it's not bad for something that is going to be 20 years old soon :). Nice playing and tone in your videos!

JVM1... actually that amp is based on the OD1 RED mode of the standard JVM. It is a very similar circuit but with a bit less gain than the 100W preamp. In a normal use case the 1W amp will be distorting more often that the 100W so I lowered the gain to balance the total gain. What I mean is that, usually, the 100W power amp would be used in its linear zone but the 1W power will be used distorted so it was too much pre+power amp distortion. On top of that,Tte 1W also has the low power mode to be more room friendly when used fully overdriven, also to encourage people to drive the power amp harder.

The reverb of the JVMs... it is whatever effects card Marshall had at the time. We did put some work on it to make it sound balanced in the amp but it wasn't exclusively developed for this amp nor based in any particular hardware. We alreay knew that just having a knob called "reverb" some people would complain and say reverb this and reverb that. Still happens today so yeah, it is one of those haha. At the end people who really like reverb will use their preferred one in the loop, the ones who don't like reverb will turn it to zero (and maybe come to a forum to complain abouthow a bad idea it is to have reverb in an amp hahaha).

Those were also the times when a combo had to have reverb but a head must NOT have reverb... The JVM had to be the same amp for head or combo to streamline development and production so it is in all the series. I see the reverb more like a nice-to-have commodity, like if you go with the amp to play somewhere and that particular room is really dry, or you just want to play guitar but without having to connect everything, so you have it in there but probably you wouldn't use it to record the amp.
Thanks so much for the reply and info! On the reverb...I'm an at-home studio enthusiast. I always use reverb, but I really don't like tweaking them or obsessing about which one sounds best. I guess I was just wanting you to tell me that the reverb on the JVM is exactly like a top-of-the-line Lexicon plate reverb or something similar. I really like the idea of a great reverb, already dialed-in, with just one simple knob for more or less.
 
Thanks so much for the reply and info! On the reverb...I'm an at-home studio enthusiast. I always use reverb, but I really don't like tweaking them or obsessing about which one sounds best. I guess I was just wanting you to tell me that the reverb on the JVM is exactly like a top-of-the-line Lexicon plate reverb or something similar. I really like the idea of a great reverb, already dialed-in, with just one simple knob for more or less.
yeah, I could tell you that but I guess I'd be lying. I don't think the JVM reverb is bad but I wouldn't put it at the level of the best studio reverbs.
 
Hi Pawel, the 'low power big tube' power amps from Marshall were designed by me around 10-12 years ago. Initially intended for the Origin 20 , used in the mini-jubilee first and then everywhere else, also based on my experiments from then AFD and YJM amps, with the variable output power system.

The reason for using octal power tubes was flexibility as you can use pretty much anything in there, 6L6, EL34, 5881, KTxx, 6CA7, even 6V6 as the voltages are low enough to be safe for that. So many people asked me that how come that a "25W" tube can only deliver 15W haha. On top of that, we were having trouble with the EL84, and it wasn't much cheaper than the octal tubes... Bear in mind though that the octal tubes need more heater current than the EL84 so the power transformer has to be rated accordingly.

Sound-wise all can sound good and bad, depends on the circuit but, if it is me, I'd again choose an octal tube over the EL84

cheers
Santiago
So can you swap octal tubes with no ill effects? I think EL34s pull more current than a 6V6 or 6L6 so I assume the PT would be ok?

Also, what is the effect on output power? These are cathode biased and the tubes are run with relatively low plate voltages so I wouldn’t think the output would be affected that much, maybe the tone would. Any reason not to do this? Thanks.
 
So can you swap octal tubes with no ill effects? I think EL34s pull more current than a 6V6 or 6L6 so I assume the PT would be ok?

Also, what is the effect on output power? These are cathode biased and the tubes are run with relatively low plate voltages so I wouldn’t think the output would be affected that much, maybe the tone would. Any reason not to do this? Thanks.
Hi, yes, you can swap octal tubes without any problems or install EL84s with an adaptor. The power transformers were calculated for KT88/6550 although I'm not sure if they physically fit in the cabinet. In any case you can try other tubes without concerns.
These low power "big bottle" tube amps were designed for the Origin series but the mini jubilee was launched before those. I chose cathode biasing for simplicity as the amps wouldn't need to be adjusted in the factory, just. plug the tubes and play. The output power will be around 16W "clean", it may vary with different tubes but not too much.
 
Hi Santiago

Glad to have You here and glad to have JVM410H as one of my amps. Great one, lately serviced by Waldek Glomb who You may remember from Marshall years :).

Ever since I got the JVM, I've been wondering what was the reason that in two-channel amplifiers the overdrive channel was based on the more modern OD2 and not on the classic sounding OD1?

Best Regards
Andrzej
 
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Hi Santiago Glad to have You here and glad to have JVM410H as one of my amps. Great one, lately serviced by Waldek Glomb who You may remember from Marshall years :). Ever since I got the JVM, I've been wondering what was the reason that in two-channel amplifiers the overdrive channel was based on the more modern OD2 and not on the classic sounding OD1? Best Regards Andrzej
Hi Andrzej, thanks for the message. I don't remember how the final decision for implementing OD2 in the jvm2 series was made.
There were few arguments, one was that OD2 was more modern sounding, and perhaps preferred back then. We also knew that OD1 orange was the favorite mode of the 4 channel series, so the question was whether to keep it exclusive to those amps or to try to increase jvm2 sales by implementing it there as well...

All in all, OD2 option won and made it to production but there was not a clear winner or strong argument towards any of the options.
 
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