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

Nerd said:
Cheers Santiago, take all the time you need. It's essentially one digital unit set to instrument level acting as a host to some other gadgets.

Thank you
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Hi, just had a quick look at the H90 and I don't think you should have any issues with it as looks pretty flexible. I don't have one (not I have a JVM with me either) to test but I'd try two options:
1- use the Power amp insert loop, set the H90 as LINE level. This series-only loop is just a passive insert in the signal before the power amp. The level here is on the hot side, I have used without problems with devices that tolerate line levels but you'll see the vu-meters quite high
2- Use the series/parallel switchable loop in LINE level (H90 again set to line), then set the MIX on the back to 100%.

I am assuming that you will have the JVM loop ON all the time, is this correct? If this is the case you shouldn't have any issues at all with the parallel loop (if you set the mix to 100%)
 
Jonttu said:
Could be? I will replace the tube once i put the amp back together.

I removed every IC, transistor and relay from the frontboards and now im waiting for new components to arrive.



View attachment 15655
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Helllo there! It's been awhile... allmost year when I replaced all the relays, transistors and IC's... Everything worked fine for a couple of minutes and then amp channel "jammed" again :D

It has new mainboard (so new Atmel and everything) and new components in the channel changing ciruit but no.. problem is still there!

So i got new JVM410h and i forgot the whole thing... maybe if i ever feel motivated i will build external controller board for this... we will see :)

Cheers!
 

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Hello Santiago!

I recently watched your interview with Jason from Headfirst and also checked out your designs especially AFD100 and YJM100. I'm super impressed by your work and brilliant soultions. I'm now trying to implement some power scaling in my DIY 50W head (which on begining was supposed to be just 800 and now its 800, Plexi, Friedman BE Deluxe in one with all possible switches :p) and have some related to that questions.

1. What is better in your opinion Power scaling or using Reactive Attenuator/Load?

2. Inspired by your Power Scaling and measurements to get relation between Screen Voltage, bias and response I made some with my amp and notice that response has quiet big impact on volume and distortion. For amps like Plexi, 800 adjusting this 100k resistor is fine but what when we have depth control on lower power and lower response value increasing depth control which is 1m ohm pot with 4n7 cap parallel will increase distortion and volume more then low frequencies?

3. In YJM100 like regular Plexi part of distortion is done in power amp so in this amp (YJM100) reverb and effects in effect loop are not getting distorted?

4. You said in interview that in YJM100 you also adjusting in power scaling input level. Can you share why? Btw. lifting cathodes of power amp with mosfets and replacing if faulty is brilliant!

5. Did you try any sag emulator circuits, do you know any to recommend? I implemented something like here (it's in polish) in my amp with adding resistors around pot to limit range and effect is subtle.

6. What is your opinion about Post Phase Inverter Master? What type is best? I implemented in my amp the one from newest Suhr SL67 MKII or Friedman Plex works not so bad but anyway in lower position amp gets fizzy and thin.

Regards from Poland!
 
Szlast said:
Hello Santiago!

I recently watched your interview with Jason from Headfirst and also checked out your designs especially AFD100 and YJM100. I'm super impressed by your work and brilliant soultions. I'm now trying to implement some power scaling in my DIY 50W head (which on begining was supposed to be just 800 and now its 800, Plexi, Friedman BE Deluxe in one with all possible switches :p) and have some related to that questions.

1. What is better in your opinion Power scaling or using Reactive Attenuator/Load?

2. Inspired by your Power Scaling and measurements to get relation between Screen Voltage, bias and response I made some with my amp and notice that response has quiet big impact on volume and distortion. For amps like Plexi, 800 adjusting this 100k resistor is fine but what when we have depth control on lower power and lower response value increasing depth control which is 1m ohm pot with 4n7 cap parallel will increase distortion and volume more then low frequencies?

3. In YJM100 like regular Plexi part of distortion is done in power amp so in this amp (YJM100) reverb and effects in effect loop are not getting distorted?

4. You said in interview that in YJM100 you also adjusting in power scaling input level. Can you share why? Btw. lifting cathodes of power amp with mosfets and replacing if faulty is brilliant!

5. Did you try any sag emulator circuits, do you know any to recommend? I implemented something like here (it's in polish) in my amp with adding resistors around pot to limit range and effect is subtle.

6. What is your opinion about Post Phase Inverter Master? What type is best? I implemented in my amp the one from newest Suhr SL67 MKII or Friedman Plex works not so bad but anyway in lower position amp gets fizzy and thin.

Regards from Poland!
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Hi Szlast, thanks for the message, let me try to address everything
1. I've used both, for simplicity a reactive load but I wouldn't say it is "better". Both are two attempts to solving the problem of playing loud without being loud :D.

2. Yes, and the response isn't linear or proportional. That's why I ended using a microncontroller to map the different variables rather than trying to compromise all the voltage/parameter settings. The feedback is always a problem when lowering th epowe amp voltages because the power amp gain will be lower so the feedback won't work at all. THe feedback relies, by definion, on the gain without feedback. The more the gain the "better" the control will be. This is why for example operational amplifiers aim to have as much gain as they can.
Unfortunately (or not) the gain of a power amp ir rather low already in nominal/full voltage settings so there is not much you can do if you really want to be able to adjust the resonance with the feedback.
If it is me, I'd implement a resonance control before the power amp, at the end, if you are distortion the power amp, the feedback resonance control won't be doingmuch either. Don't forget that many amps with a resonance control are amps that create the distortion in the preamp.

3. The YJM100 adjusts the signal level before the FX loop, then the signal is recovered to be able to drive the amplifier properly in all conditions. Since the signal sent and returned from the loop depends on the output power setting you will avoid, mostly, the prblems you are referring to. Also, I think the reverb level is adjusted with the power control as well but I am not 100% sure. As the reverb is after the FX loop it could well be that the lower levels already made the reverb work right.

4. When you are at very low power settings, saw 1W or less, blasting the power amp input with a huge audio signal sounds bad. You start getting more of a fuzz than a nice distortion so my solution for that was to adjust the input level. Both the AFD100 and the YJM have a controlled input level for this reason.

5. I haven't experimented much with that. Your circuit is one of the circuits to try, you may also lower the screen voltages instead of playing with the input capacitance. I am not sure if you will have a lot of 100Hz modulating the power supply in a nasty way with your solution.

6. It seems to work like you say, only at a limited range. Then starts sounding fizzy and harsh which makes me question if it is actually useful. You put there a circuit to reduce the output power but when you really reduce the power to a level that actually you can listen to in a room, it sounds fizzy... I haven't experimented much with that but perhaps "assisting" the PPIMV with a pre-MV control will help to balance everything better. Also I'd check if reducing the feedback like in the AFD and YJM helps.
 
Thanks for your answers!

1. In the interview you mentioned that first version of Origin amps had power scaling and from some range as I assume resistive load like L-pad? I noticed that (if correctly) that resistive load is ok for 10-15W amps but for higher power they start to add muddiness to the tone.

2. Thanks for explanation! Plexi don't need depth control but for 800 it's nice to have feature. On the other hand normally nobody is cranking 800 like plexi :)

3. What I meant in this question is that in cranked Plexi overall beautiful distortion comes from preamp, PI and power tubes. FX loop and reverb are between preamp and PI so e.g signal through delay in FX loop and reverb will be distorted in PI and by power tubes, so it I guess should sound like putting delay in front of 800. I'm I right? I see that on the market there is not so many Plexi like amps with Fx loop like Suhr Sl67 or Friedman Plex.

4. So by input level you mean that you adjust automatically post preamp/master volume before PI?

5. To be honest didn't notice any issues with this sag mod only that that is very subtle, I guess I won't do it again :)

6. I tested today adjusting feedback in this PPIMV but it didn't help unfortunately. Will do some test to combine PPIMV with power scaling to improve sound for very low voltages.

7. Wanted to ask if there is some news about your amp that you are working on? :)

Thank you!
 
Szlast said:
Thanks for your answers!

1. In the interview you mentioned that first version of Origin amps had power scaling and from some range as I assume resistive load like L-pad? I noticed that (if correctly) that resistive load is ok for 10-15W amps but for higher power they start to add muddiness to the tone.

2. Thanks for explanation! Plexi don't need depth control but for 800 it's nice to have feature. On the other hand normally nobody is cranking 800 like plexi :)

3. What I meant in this question is that in cranked Plexi overall beautiful distortion comes from preamp, PI and power tubes. FX loop and reverb are between preamp and PI so e.g signal through delay in FX loop and reverb will be distorted in PI and by power tubes, so it I guess should sound like putting delay in front of 800. I'm I right? I see that on the market there is not so many Plexi like amps with Fx loop like Suhr Sl67 or Friedman Plex.

4. So by input level you mean that you adjust automatically post preamp/master volume before PI?

5. To be honest didn't notice any issues with this sag mod only that that is very subtle, I guess I won't do it again :)

6. I tested today adjusting feedback in this PPIMV but it didn't help unfortunately. Will do some test to combine PPIMV with power scaling to improve sound for very low voltages.

7. Wanted to ask if there is some news about your amp that you are working on? :)

Thank you!
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1. Yes, it was a bit different to what they finally released. Origin's preamp was designed around power amp distortion, it is a bit dull if you hear to it alone but came to life with the power tubes distorting. The attenuator was resistive, actually it is not bad that the amp gets darker when attnuated as it helps to clean the fizz too

2. Yes but the 800 still needs the power amp compression to sound right, otherwise it can be way too trebly and the power amp will clip those harsh spikes in the waveform

3. You can make a reverb or delay work with power amp distortion but you have to make sure that its level is low enough so it remains in the linear part of the power amp. It is still not the same as having the reverb after the amp but not the mess of distorting the echos all over the place

4. Yes, the PI / power amp input. It is an "automatic master volume" and it is in the same place as the master is.

5. You noticed that the sag effect can't be noticed = no need to put it then :D

6. It is tricky, you may be able to make it work by playing with everything, including the power amp input level. You may also experiment by changing the cathode resistor of the PI. Some "power scaling" is done by increasing that component value

7. Work in progress, some of the designs are quite advanced and some companies have been interested on selling them but still not ready. It is always the same problem, always too busy with other people's projects :)
 
santiall said:
1. Yes, it was a bit different to what they finally released. Origin's preamp was designed around power amp distortion, it is a bit dull if you hear to it alone but came to life with the power tubes distorting. The attenuator was resistive, actually it is not bad that the amp gets darker when attnuated as it helps to clean the fizz too

2. Yes but the 800 still needs the power amp compression to sound right, otherwise it can be way too trebly and the power amp will clip those harsh spikes in the waveform

3. You can make a reverb or delay work with power amp distortion but you have to make sure that its level is low enough so it remains in the linear part of the power amp. It is still not the same as having the reverb after the amp but not the mess of distorting the echos all over the place

4. Yes, the PI / power amp input. It is an "automatic master volume" and it is in the same place as the master is.

5. You noticed that the sag effect can't be noticed = no need to put it then :D

6. It is tricky, you may be able to make it work by playing with everything, including the power amp input level. You may also experiment by changing the cathode resistor of the PI. Some "power scaling" is done by increasing that component value

7. Work in progress, some of the designs are quite advanced and some companies have been interested on selling them but still not ready. It is always the same problem, always too busy with other people's projects :)
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@santiall Thank you for you answers and help! No more question from my side for now ;)
 
Any thoughts on the new preamp pedals?

Do you feel like the classic Marshall circuits (and indeed your JVM) are something that can be approximated in a small solid state box? Is that something you’d ever considered yourself?
 
Hmmm, interesting question... I may actually know a thing or two about the jvm pedal. Perhaps it's somehow related to a circuit that I had prototyped years ago and brought with me when I rejoined Marshall while all these pedals were under development..

My opinion about any of these (any brand), that claim to sound like an amp is that pretty much they are a distortion pedal that you somehow shape to "sound like" but I don't think they are any sort of real amp models. At the end you depend on what amp you are using and how you set it up. Mind you, back in the day, pedals like the boss DS-1 and SD-1 were already described as pedals that replicate your "cranked full stack" in a box...

Doing myself that?, well, not really, not claiming specific amp models but I do understand why they are doing it. Every brand has their - insert brand name here - pedal, Marshall can of course do it too. I also can imagine that they want to present some new products in various market segments.

That "jvm" pedal started just as a high gain pedal experiment back in the day, I'm curious what they have changed in 3 years. I have improved it since then and I use it with clean amps from time to time, hopefully it can see the light sooner rather than later ;)
 
santiall said:
Hmmm, interesting question... I may actually know a thing or two about the jvm pedal. Perhaps it's somehow related to a circuit that I had prototyped years ago and brought with me when I rejoined Marshall while all these pedals were under development..

My opinion about any of these (any brand), that claim to sound like an amp is that pretty much they are a distortion pedal that you somehow shape to "sound like" but I don't think they are any sort of real amp models. At the end you depend on what amp you are using and how you set it up. Mind you, back in the day, pedals like the boss DS-1 and SD-1 were already described as pedals that replicate your "cranked full stack" in a box...

Doing myself that?, well, not really, not claiming specific amp models but I do understand why they are doing it. Every brand has their - insert brand name here - pedal, Marshall can of course do it too. I also can imagine that they want to present some new products in various market segments.

That "jvm" pedal started just as a high gain pedal experiment back in the day, I'm curious what they have changed in 3 years. I have improved it since then and I use it with clean amps from time to time, hopefully it can see the light sooner rather than later ;)
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Is your JVM pedal fet based @santiall? That was my guess for these new pedals.
 
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