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

santiall said:
the curves may look like a pentode, although the input load is completely different to a tube grid input
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do designers ever use input eq in front of solid state clipping to mimic the tube input load tonal characteristic? I feel like the primary tonal difference of tube stage vs solid state distortion is a prominent pre gain mid scoop that's always missing from solid state breakup, like the impedance or input load of tubes creates a natural V curve at the input
 
0XI0 said:
do designers ever use input eq in front of solid state clipping to mimic the tube input load tonal characteristic? I feel like the primary tonal difference of tube stage vs solid state distortion is a prominent pre gain mid scoop that's always missing from solid state breakup, like the impedance or input load of tubes creates a natural V curve at the input
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I'd say that more than a pure EQ is some sort of distortion that depends on the frequency and the signal level which also affects the input impedance. The tube input is highly non-linear when the signals are relatively high but it is easy for a guitar to hit that point. I think a way to hear this is to use a buffer in front of a tube amp against connecting the guitar directly. In my opinion, the buffered guitar feels more immediate, perhaps a bit crisper too.

I'm not sure if anyone has done anything, people out there just claim "FET input" as if that would be same as a tube input but other than that I am not aware. I have done some experiments on my own but I don't have anything "polished enough" to go out there and claim that this circuit fully replicates a tube input...
 
santiall said:
Hi, if that noise is there with the master down I'd suspect of the phase splitter tube. It should be the closest to the power tubes/choke.
Do you have a spare to try?, otherwise take that one out and replace it with the next preamp tube in the amp.

Let's try that before suspecting of something else
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I'll try the swap and report back, thank you.
 
James Freeman said:
Try tapping each tube with a wooden stick.
Clean the tube sockets with a contact cleaner.
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Thank you James.

I've tapped them all already but none, but the EL34s, seems to produce more noise than the others. Looks like tapping on the valves is simply transmitting the vibration elsewhere.

I've also taken out and put back all the tubes and pins are very clean, like brand new.

The amp is only 2 years old and I keep it at home in my studio, I move it back and forth for rehearsals or gigs so basically has spent 99.9% of it's time in a warm and dry environment.
 
santiall said:
Hi,
those values pretty much convert the preamp into 1959/1987 values. To me still you will be missing the cathode follower, which is a big part of the plexi sound. You may try a MOSFET as "cathode follwer" between V1B and the tone control, there are a few examples over the internet if you search a bit :)
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Thank you for taking a look and your suggestions. Have a great weekend!
 
HotRats said:
@santiall I've swapped the tube but the noise while knoking is still there, still the same. :(
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try to be methodical when testing the amp. Those noises when hitting the amp are, most likely, a microphonic tube. The thing is that sometimes it can be hard to know which one is the culprit. Try this:
1- remove all the preamp tubes, tap the power tubes. Is it noise?
2- add the phase splitter (the one closer to the power tubes) and repeat. Is it noisy now?
3- add the next tube. Tap the amp with the master both full and zero. Is it noisy?
4- add the next and repeat
5- do the tone controls affect the tone of the noise?
6- does the gain control affect it

I am quite sure it would be relatively easy to diagnose in person but it is hard to do remotely.
Also,that the EL34 tubes are new doesn't mean they work. Precisely right now I was working in an amp here with two brand new EL34s and one doesn't even heat up... dead, zero, nada.... nice...
 
santiall said:
try to be methodical when testing the amp. Those noises when hitting the amp are, most likely, a microphonic tube. The thing is that sometimes it can be hard to know which one is the culprit. Try this:
1- remove all the preamp tubes, tap the power tubes. Is it noise?
2- add the phase splitter (the one closer to the power tubes) and repeat. Is it noisy now?
3- add the next tube. Tap the amp with the master both full and zero. Is it noisy?
4- add the next and repeat
5- do the tone controls affect the tone of the noise?
6- does the gain control affect it

I am quite sure it would be relatively easy to diagnose in person but it is hard to do remotely.
Also,that the EL34 tubes are new doesn't mean they work. Precisely right now I was working in an amp here with two brand new EL34s and one doesn't even heat up... dead, zero, nada.... nice...
Click to expand...

Ok thank you, I'll follow your steps.
 
santiall said:
try to be methodical when testing the amp. Those noises when hitting the amp are, most likely, a microphonic tube. The thing is that sometimes it can be hard to know which one is the culprit. Try this:
1- remove all the preamp tubes, tap the power tubes. Is it noise?
2- add the phase splitter (the one closer to the power tubes) and repeat. Is it noisy now?
3- add the next tube. Tap the amp with the master both full and zero. Is it noisy?
4- add the next and repeat
5- do the tone controls affect the tone of the noise?
6- does the gain control affect it

I am quite sure it would be relatively easy to diagnose in person but it is hard to do remotely.
Also,that the EL34 tubes are new doesn't mean they work. Precisely right now I was working in an amp here with two brand new EL34s and one doesn't even heat up... dead, zero, nada.... nice...
Click to expand...

Man you are right, I've run the tests and in the end it was the brand new el34s.

that's crazy. one or both (on day I'll test it) of a matched quartet never pulled out of their box. the other 2 are perfect.

Thank you so much for your help, I really, really appreciate that.
 
Hey Santiago, thanks for providing this opportunity to pick your brain!

So I just bought my third JVM 410h after a coup[e of years of not having one. It appears to be all stock, except I am having a slight issue.
It does not take boost pedals well on OD 1 or 2, particularly on the orange and red modes.
I know.. plenty of gain already, but I use boosts to tighten and sculpt a little. My SD-1 seems to work ok, but anything with more kick than that produces an ugly, raspy distortion, and it feels like the amp is caving in on itself. This occurs even with the amp gain down pretty low. With my previous JVMs I always boosted the OD channels and they didnt do this.

My question is, could this amp just be biased too hot? or could it be a bad preamp tube?


Also I have ordered an ECC328 to try in the V6 spot because I read that might help.
Any ideas on what I should look at if the new preamp tube doesnt fix it?
thanks!
 
battlecat said:
Hey Santiago, thanks for providing this opportunity to pick your brain!

So I just bought my third JVM 410h after a coup[e of years of not having one. It appears to be all stock, except I am having a slight issue.
It does not take boost pedals well on OD 1 or 2, particularly on the orange and red modes.
I know.. plenty of gain already, but I use boosts to tighten and sculpt a little. My SD-1 seems to work ok, but anything with more kick than that produces an ugly, raspy distortion, and it feels like the amp is caving in on itself. This occurs even with the amp gain down pretty low. With my previous JVMs I always boosted the OD channels and they didnt do this.

My question is, could this amp just be biased too hot? or could it be a bad preamp tube?


Also I have ordered an ECC328 to try in the V6 spot because I read that might help.
Any ideas on what I should look at if the new preamp tube doesnt fix it?
thanks!
Click to expand...
Hi, I've experienced similar issues lately with other amps too and many of them ended being the input tube but in the JVM sometimes a bad cathode follower also has similar effects. It sounds like 'soft' and 'anemic', weird in a way.
As far as I know they haven't changed the circuit so there is no reason why the old amps worked and the new don't apart from the type of tubes you have in there. Maybe you have JJs?, they have low noise and very low microphonics but they also tend to have extremelly low gain, and some just don't sound right at all... I know tubes aren't cheap but you should try some other ECC83 too

Santiago
 
santiall said:
Hi, I've experienced similar issues lately with other amps too and many of them ended being the input tube but in the JVM sometimes a bad cathode follower also has similar effects. It sounds like 'soft' and 'anemic', weird in a way.
As far as I know they haven't changed the circuit so there is no reason why the old amps worked and the new don't apart from the type of tubes you have in there. Maybe you have JJs?, they have low noise and very low microphonics but they also tend to have extremelly low gain, and some just don't sound right at all... I know tubes aren't cheap but you should try some other ECC83 too

Santiago
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Thanks, I will try some different tubes. I have a handfull of spare preamp tubes, and enough amps that ordering a few more to try isnt a bad idea anyway.
 
Szlast said:
Hi Santiago! I recently was making research about Doug Aldrich old rigs and one thing is that he has Marshall JMP 1978 modded by Suhr and I wonder if he turned it into SE100 and also found that he received from Marshall this DLA 100 prototype. Here someone was selling it on reverb:


Do you know this amp and say something what is special about it?

Thanks!
Pawel
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Hi, roughly it was a JVM OD1 green with a tubescreamer and the Kerry King noise gate. It was being designed by another engineer, Jonathan Langstaff and intended as a "metal amp". Not sure how many were made, just a handful but never saw the light. It was going to be marketed as a "metal amp"
 
santiall said:
Hi, roughly it was a JVM OD1 green with a tubescreamer and the Kerry King noise gate. It was being designed by another engineer, Jonathan Langstaff and intended as a "metal amp". Not sure how many were made, just a handful but never saw the light. It was going to be marketed as a "metal amp"
Click to expand...
Cool! Thanks for the information!
 
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