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.
 
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