Tubes delivery date is today for my Marshall JCM 800!

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Tubes delivery date is today for my Marshall JCM 800!

Post by ZeroPointEnergy »

For this order, I paid the extra $2 for "high gain" versions of my favorite preamp tubes, hoping to get the singing sustain back. But that's just part of the quest.

I also have two other items in mind. A (1) power attenuator, and (2) a Variac. I'd like to hear your thoughts on those.

As an inventor and wanting to test stuff, I've long wanted a variac, so if it also helps me also get better guitar sounds, then I'm all for it. I don't expect it to get so quiet I don't need a power attenuator, but every little bit helps.

They usually say, the less power attenuation, the less the attenuation degrades the sound. So I would probably end up doing both. Marshall forum has a DIY design for a reactive load. It uses resistors, but somehow partly emulates the physics of a speaker.

They say it can be made for around $100. Not sure yet which DIY project I will end up doing, but so far I'm leaning to the speaker emulated model, from the Marshall forum.
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Re: Tubes delivery date is today for my Marshall JCM 800!

Post by colossal »

The reactive component of the attenuator you are speaking of models the rising impedance of a speaker above 3kHz. This helps to preserve some of the treble response as the volume is reduced by the resistive portion. It does not reproduce the resonant frequency of the speaker as the speaker is still in series with the attenuator. The trick is impedance matching at all levels of attenuation which most attenuators don't. The Airbrake attenuator's impedance, for example, rises significantly as attenuation level increases, but it is purely resistive.
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Re: Tubes delivery date is today for my Marshall JCM 800!

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colossal wrote:
Fri 05/15/20 1:27 pm
The reactive component of the attenuator you are speaking of models the rising impedance of a speaker above 3kHz. This helps to preserve some of the treble response as the volume is reduced by the resistive portion. It does not reproduce the resonant frequency of the speaker as the speaker is still in series with the attenuator. The trick is impedance matching at all levels of attenuation which most attenuators don't. The Airbrake attenuator's impedance, for example, rises significantly as attenuation level increases, but it is purely resistive.
The designer said that to also put the bass frequencies in there, would be cost prohibitive. So there's just mid's and highs represented.

He also says, it doesn't really matter as much with bass, as it's resonance is developed at the speaker anyway.

His unit seems to sound pretty transparent, and he does lots of frequency curve charts for technical validation and comparison. And other Marshall users seem to like the results of using this partially modeled, reactive (from only resisters!) speaker attenuation design.

It seems like a poor man's version of a Weber MASS. A DIY alternative. Just build it properly, for safe economical use. But maybe that's my wishful side talking. I don't think the tone or frequency resonance needs to match perfectly. Is the frequency close enough to manually adjust for, and so if the answer is yes, then that is acceptable to me.

He talks about a slight high end roll off. Doesn't seem to mention that bass is not accurate. I think he presumes it's accurate.

And yet I agree, that the more transparency of the attenuated tone, the better. The more attenuation is applied, the more change is done to the tone. That is why I hope to eventually use both a variac and power attenuator.

I heard a JMP Master with a variac on it, and OMG, that was the best sound. My amp is modeled much after those JMP Masters, so before it's done, I plan to add a variac and reduce to 85-90 volts. As long as the power tubes are into overdrive saturation, and I'm getting singing overtones, then I don't care if the OT is not quite as good sounding/performing.

My hope is that the OT, being somewhat less optimal sounding, means a small change in sonic experience, that some if not many, might not even notice. Correct me if I'm mistaken, and I could be missing a few things, but I assume we mostly get lovely "sag" from a tube driven PI, and how it works with the output end of the amp.

If it's loosing a bit of sag for glorious power tube saturation, I want saturated power tube overdrive. ;) I figure the hit on the OT seems "brown sound" good enough. hehe

Johan Segeborn on youtube demo'd this, and OMG, the JMP on a variac, was SPLENDID! My virgin ears has heard the sonic goodness, and there's no turning back now. ;)

https://www.youtube.com/watch?v=OmlWxpqbdg4
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Re: Tubes delivery date is today for my Marshall JCM 800!

Post by ZeroPointEnergy »

The amp sounds better with higher gain mullards, but it's not yet where I want it to be. No singing overtone sustain yet. So I am planning on building a power attenuator, and might end up also buying a variac, to bring the volts down some.

The search for singing overdrive, is still on!
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Re: Tubes delivery date is today for my Marshall JCM 800!

Post by colossal »

ZeroPointEnergy wrote:
Sat 05/16/20 7:25 am
The designer said that to also put the bass frequencies in there, would be cost prohibitive. So there's just mid's and highs represented. He also says, it doesn't really matter as much with bass, as it's resonance is developed at the speaker anyway.
The speaker is still in series with the attenuator, so you are getting the reactive properties from the speaker. If you want to go with a reactive silent load, then yes, the low frequency response would be important so that the amp is reacting to the load and you would be getting the normal "feel". Yes, the added components will add an increased cost (you need more inductors and some large value film capacitors).
His unit seems to sound pretty transparent, and he does lots of frequency curve charts for technical validation and comparison. And other Marshall users seem to like the results of using this partially modeled, reactive (from only resisters!) speaker attenuation design.

It seems like a poor man's version of a Weber MASS. A DIY alternative. Just build it properly, for safe economical use. But maybe that's my wishful side talking. I don't think the tone or frequency resonance needs to match perfectly. Is the frequency close enough to manually adjust for, and so if the answer is yes, then that is acceptable to me.
The impedance match is an important component in the transparency.
I heard a JMP Master with a variac on it, and OMG, that was the best sound. My amp is modeled much after those JMP Masters, so before it's done, I plan to add a variac and reduce to 85-90 volts. As long as the power tubes are into overdrive saturation, and I'm getting singing overtones, then I don't care if the OT is not quite as good sounding/performing.
This is the foundation of the Van Halen tone, as revealed by Dave Friedman some years back...variac'd Superlead down to 85VAC and bias cranked up.
Correct me if I'm mistaken, and I could be missing a few things, but I assume we mostly get lovely "sag" from a tube driven PI, and how it works with the output end of the amp.
I think you are referring to the warm biased Plexi PI. If the preamp is pushing the PI hard and into a non-sinusoidal waveform, then you are getting the PI overdrive sound and the square wave harmonics pushing the power section. This is very much part of the Trainwreck Express formula as well; power amp distortion first.
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Re: Tubes delivery date is today for my Marshall JCM 800!

Post by Bieworm »

ZeroPointEnergy wrote:
Sat 05/16/20 7:25 am
colossal wrote:
Fri 05/15/20 1:27 pm
The reactive component of the attenuator you are speaking of models the rising impedance of a speaker above 3kHz. This helps to preserve some of the treble response as the volume is reduced by the resistive portion. It does not reproduce the resonant frequency of the speaker as the speaker is still in series with the attenuator. The trick is impedance matching at all levels of attenuation which most attenuators don't. The Airbrake attenuator's impedance, for example, rises significantly as attenuation level increases, but it is purely resistive.
The designer said that to also put the bass frequencies in there, would be cost prohibitive. So there's just mid's and highs represented.

He also says, it doesn't really matter as much with bass, as it's resonance is developed at the speaker anyway.

His unit seems to sound pretty transparent, and he does lots of frequency curve charts for technical validation and comparison. And other Marshall users seem to like the results of using this partially modeled, reactive (from only resisters!) speaker attenuation design.

It seems like a poor man's version of a Weber MASS. A DIY alternative. Just build it properly, for safe economical use. But maybe that's my wishful side talking. I don't think the tone or frequency resonance needs to match perfectly. Is the frequency close enough to manually adjust for, and so if the answer is yes, then that is acceptable to me.

He talks about a slight high end roll off. Doesn't seem to mention that bass is not accurate. I think he presumes it's accurate.

And yet I agree, that the more transparency of the attenuated tone, the better. The more attenuation is applied, the more change is done to the tone. That is why I hope to eventually use both a variac and power attenuator.

I heard a JMP Master with a variac on it, and OMG, that was the best sound. My amp is modeled much after those JMP Masters, so before it's done, I plan to add a variac and reduce to 85-90 volts. As long as the power tubes are into overdrive saturation, and I'm getting singing overtones, then I don't care if the OT is not quite as good sounding/performing.

My hope is that the OT, being somewhat less optimal sounding, means a small change in sonic experience, that some if not many, might not even notice. Correct me if I'm mistaken, and I could be missing a few things, but I assume we mostly get lovely "sag" from a tube driven PI, and how it works with the output end of the amp.

If it's loosing a bit of sag for glorious power tube saturation, I want saturated power tube overdrive. ;) I figure the hit on the OT seems "brown sound" good enough. hehe

Johan Segeborn on youtube demo'd this, and OMG, the JMP on a variac, was SPLENDID! My virgin ears has heard the sonic goodness, and there's no turning back now. ;)

https://www.youtube.com/watch?v=OmlWxpqbdg4
I watched the video. IMHO the attenuator really wrecked the tone . The variac was awesome. The Standard MV too ...
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Re: Tubes delivery date is today for my Marshall JCM 800!

Post by ZeroPointEnergy »

Awesome! Thanks for the quick response guys! Before I respond to your posts though, here's something he specifically said about the bass side of the attenuator. He seems to think it's not a problem, or that his attenuation of bass frequencies tends to be more or less transparent.

"This is the current design since January 2019, now well tested by many builders. It captures the rise in treble impedance and lets the amp see this and respond dynamically to it. The bass resonance is developed at the speaker as in the resistive design, but is not seen at the amp. It continues to work well."
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Re: Tubes delivery date is today for my Marshall JCM 800!

Post by ZeroPointEnergy »

Bieworm wrote:
Sat 05/16/20 11:23 am
ZeroPointEnergy wrote:
Sat 05/16/20 7:25 am
colossal wrote:
Fri 05/15/20 1:27 pm
Johan Segeborn on youtube demo'd this, and OMG, the JMP on a variac, was SPLENDID! My virgin ears has heard the sonic goodness, and there's no turning back now. ;)

https://www.youtube.com/watch?v=OmlWxpqbdg4
I watched the video. IMHO the attenuator really wrecked the tone . The variac was awesome. The Standard MV too ...
Yeah, I've heard nearly a dozen youtube videos on Weber's MASS unit's, and this one is especially harsh in the upper highs. I assume he somehow accidentally had the high part of the signal represented too much.

Because on the unit, he has "several" ways of compensating for the treble frequencies, but he did not seem to compensate, and it's noticeable.

The top end is a bit harsh and brittle. However it may be a trend that some MASS units sound a bit treble heavy. So this may be a slight error to his setup, and partly due to the nature of Weber's MASS units, IDK.

Good call tho, I totally agree. That Weber attenuator sample, is by far, the most noticeable and problematic. Hehe, I would hope most of that treble overkill, could be filtered out.

The question arises, could a variac, lowering my JCM 800 from 120 V, say to around 82V, be enough, to effectively raise the MV, from 3 to 5, and still experience the same volume from the speakers? How about 3 to 4.5?

Because another guy on the Marshall forum said, when he used the variac on a Marshall Master JMP, it not only sounded better, but it also got quite a bit quieter too. I'm waiting on his response to my question about how much volume reduction might be realized by using a variac.

My amp's power section really starts opening up and producing singing overtones, early for an older amp, like after say 4.2 on the MV. Below 3 it looses warmth and drive, and the lush overtones are dulled or gone, the whole amp is less lively.

So what do you think? Would a variac, allow me to experience about enough drop in volume, that I could functionally go from 3 to 4.5 on the MV, on my 50 watt all tube path, '82 JCM 800 Marshall amp?

MY amp design, is a lot like the JMP Master Super Leads. That's what that guy said could take even lower Voltages. I don't want to go into extremes. Just enough to get singing sustain, from the power tubes. Hi-ya
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Re: Tubes delivery date is today for my Marshall JCM 800!

Post by colossal »

ZeroPointEnergy wrote:
Sat 05/16/20 1:03 pm
The question arises, could a variac, lowering my JCM 800 from 120 V, say to around 82V, be enough, to effectively raise the MV, from 3 to 5, and still experience the same volume from the speakers? How about 3 to 4.5?

Because another guy on the Marshall forum said, when he used the variac on a Marshall Master JMP, it not only sounded better, but it also got quite a bit quieter too. I'm waiting on his response to my question about how much volume reduction might be realized by using a variac.
You will lose volume using a variac because the heater filament supply is part of the power transformer and therefore, you are also lowering the heater voltage as you dial down the mains voltage. This results in lower emission from the heaters.
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Re: Tubes delivery date is today for my Marshall JCM 800!

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colossal wrote:
Sat 05/16/20 2:32 pm
You will lose volume using a variac because the heater filament supply is part of the power transformer and therefore, you are also lowering the heater voltage as you dial down the mains voltage. This results in lower emission from the heaters.
This is a very good point. Running the heater voltage too low will also reduce the life of the tubes.
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Re: Tubes delivery date is today for my Marshall JCM 800!

Post by ZeroPointEnergy »

I also heard the power tubes break up quicker under lower voltage, and that's the critical factor I'm looking for, plus the amp gets quieter.

I can collect hotter glowing tubes as some seem colder and hotter based on how much they glow, since it's heaters are a concern. But you have not talked me out of a variac. Nice try tho. hehe

I bet I can get to 4.5 on the MV from 3. That's all I need to transform my amp into lively singing sustain. We all heard that video comparison, the variac was the best in sonic goodness. Sweet organic goodness.

Ta Ta!!! I have a variac to shop for. Singing sustain, SHALL BE MINE ONCE AGAIN!!! 8) :roll:
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Re: Tubes delivery date is today for my Marshall JCM 800!

Post by zaphod_phil »

So please tell us how your amp sounds with its new 12AX7s :)
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Re: Tubes delivery date is today for my Marshall JCM 800!

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ZeroPointEnergy wrote:
Sat 05/16/20 1:03 pm
Bieworm wrote:
Sat 05/16/20 11:23 am
ZeroPointEnergy wrote:
Sat 05/16/20 7:25 am

I watched the video. IMHO the attenuator really wrecked the tone . The variac was awesome. The Standard MV too ...
Yeah, I've heard nearly a dozen youtube videos on Weber's MASS unit's, and this one is especially harsh in the upper highs. I assume he somehow accidentally had the high part of the signal represented too much.

Because on the unit, he has "several" ways of compensating for the treble frequencies, but he did not seem to compensate, and it's noticeable.

The top end is a bit harsh and brittle. However it may be a trend that some MASS units sound a bit treble heavy. So this may be a slight error to his setup, and partly due to the nature of Weber's MASS units, IDK.

Good call tho, I totally agree. That Weber attenuator sample, is by far, the most noticeable and problematic. Hehe, I would hope most of that treble overkill, could be filtered out.

The question arises, could a variac, lowering my JCM 800 from 120 V, say to around 82V, be enough, to effectively raise the MV, from 3 to 5, and still experience the same volume from the speakers? How about 3 to 4.5?

Because another guy on the Marshall forum said, when he used the variac on a Marshall Master JMP, it not only sounded better, but it also got quite a bit quieter too. I'm waiting on his response to my question about how much volume reduction might be realized by using a variac.

My amp's power section really starts opening up and producing singing overtones, early for an older amp, like after say 4.2 on the MV. Below 3 it looses warmth and drive, and the lush overtones are dulled or gone, the whole amp is less lively.

So what do you think? Would a variac, allow me to experience about enough drop in volume, that I could functionally go from 3 to 4.5 on the MV, on my 50 watt all tube path, '82 JCM 800 Marshall amp?

MY amp design, is a lot like the JMP Master Super Leads. That's what that guy said could take even lower Voltages. I don't want to go into extremes. Just enough to get singing sustain, from the power tubes. Hi-ya
I'd go try the VVR mod first. It's only a couple of grams instead of pounds from a variac. But hey, I'm lazy by nature 😉🙃
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Re: Tubes delivery date is today for my Marshall JCM 800!

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ZeroPointEnergy wrote:
Sat 05/16/20 3:30 pm
I can collect hotter glowing tubes as some seem colder and hotter based on how much they glow, since it's heaters are a concern. But you have not talked me out of a variac. Nice try tho. hehe
lol, not trying to talk you out of it at all. I have an awesome variac. ;) But you should be aware of the effects. For example, you don't want to destroy expensive NOS tubes in there.
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Re: Tubes delivery date is today for my Marshall JCM 800!

Post by ZeroPointEnergy »

zaphod_phil wrote:
Sat 05/16/20 3:36 pm
So please tell us how your amp sounds with its new 12AX7s :)
It helps, but,, I guess my power section is not really cooking yet. It's closer, and I really like the Mullards in all three spots, with a close second given to Genalex, with great feel and sensitivity. Like a brighter Mullard, really.

The Tung-Sols have the gain structure down really nice, but I don't like the tonal nature. Not enough blooming notes, and not warm enough.

The Mullard MU12AX7, was surprisingly slightly higher gain specs than the other version, the CV4004, because the CV4004 specified it's slightly higher gain, but the other one, did not mention higher gain, so I probably need to order some more of these to really tell which is the higher gain version.

I find the Mallards are the richest, the warmest but full bodied, and sounding with the most blooming notes, very nice. I still lack something, as my amp does not yet have singing sustain.

I also replaced the power tubes recently, when I got my amp working, so I don't know if they need biasing or not. I am guessing my previous power tubes, saturated and broke up a bit earlier, and that's why I feel like I should have more singing sustain.

I get more increased pick sensitivity and great pinched harmonics, from the mullards and Gelalex. So I mostly miss the soaring overtones and singing sustain. Very controllable, not harsh. I'm probably missing that from the power section, because of the new Mullard EL34 tubes.

I figure I either need a Variac, or a decent power attenuator, or probably both! If only money was not a problem. @@ Puff puff pass.
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