Early Marshalls are single channel clean amps?

[ampmadscientist]

Some people are saying the earliest Marshalls such as the JTM45 and other Marshalls before the 70's are single channel clean amps (so they can't distorted) but they actually have two channels which are High Treble (Loudness 1) and Normal (Loudness 2). Is High Treble basically the overdrive or gain channel while the Normal is the clean channel?

Well yes it does have 2 preamps, not single channel.
Yes they are clean amps. Very clean.
Basically clean as a Fender amp.
And it remains clean until you drive the output tubes hard enough to distort.
Then the amp is extremely loud.

In this design:
when the power tubes start to distort, the preamp is still clean.
It's a clean preamp over-driving the power amp into distortion.
That is why these amps (and plexis) sound the way they do.

 

[ampmadscientist]

Well I say most of the components, not just the preamp, play parts in producing the "distortion".

Actually, it's the layout of the components more than anything.
And there: I just gave you the secret which very few people realize.

If you change the layout: the sound will also change, sometimes radically.
The layout influences the final sound much more than most people realize.

I can make an amp sound like a fender twin.....
I can make an amp sound like a screaming monster...
just be changing the layout of the parts.
Surprise.
(now you know what Dumble knows)

What the schematic shows:
There is waaaaay more going on, than what the schematic shows.
So, don't ever judge what an amp sounds like by the schematic.

 

[wonderingape]

You won't find frequency response charts for output valves. Depends on a million things but especially output transformers which are never linear.

The capacitors in the preamp do filter. In fact if you want to make a fender sound more marshal or vice versa that's where you would start. The output valves won't make the amp "brighter" or "darker" but when they go into harmonic distortion you will get different levels of each harmonic from different valves. The best way to understand the effect is to listen to a single ended class A like the old X84 circuits with self bias and mid point voltages so you can swap output valves without changing anything else. Use the classic as it has "vintage" ie lower preamp gain. Run it flat out into say an el34 then a 6l6 then kt66 and you will get different sounds. KT88 and 6550 probably won't distort very much because they can handle a lot bigger input before they are overdriven. Actually that's a point. Stick 6550s in a 60s marshall and it will clean right up. The preamp and splitter have not changed, so where did all that distortion go ? The 6550's aren't distorting because the amplitude of the signal out of the phase splitter is big enough to overload an EL34 but not enough to overload a more rugged valve like the KT88 and 6550.

So, if I understand you correctly, the only sound difference that each different power tubes produced is which one break-up/distorted first and characteristics such as mid-scooped or upper-mids boosted is 100% determined in the preamp circuits. No?

Actually I should check the data sheets because I'm assuming that from memory...

But then leave say an el34 in and swap out the output transformer for very different ones and you'll hear a difference there also.

Swap out caps in the preamp. Use a preamp with no tone controls, only volume, or 1 tone knob.

You will have heard a tweed fender champ running full tilt. That's output valve distortion. The preamp is low gain, relatively, very little clipping going into the 6V6.

Obviously class As distort a lot more than AB1, but it demonstrates the point. The trouble with AB1 is you have bigger volume to manage and a lot less distortion. So it's harder to see things, and they are more complicated so it's harder to isolate things.

Well, I have just found this audio on another forum . It sounds just like how those 60's-70's amps sounded like when they're cranked or maxed out.

 

[wonderingape]

Actually, it's the layout of the components more than anything.
And there: I just gave you the secret which very few people realize.

If you change the layout: the sound will also change, sometimes radically.
The layout influences the final sound much more than most people realize.

I can make an amp sound like a fender twin.....
I can make an amp sound like a screaming monster...
just be changing the layout of the parts.
Surprise.
(now you know what Dumble knows)

What the schematic shows:
There is waaaaay more going on, than what the schematic shows.
So, don't ever judge what an amp sounds like by the schematic.

Regardless of types of power tubes and preamp tubes?

 

[paul-e-mann]

Some people are saying the earliest Marshalls such as the JTM45 and other Marshalls before the 70's are single channel clean amps (so they can't distorted) but they actually have two channels which are High Treble (Loudness 1) and Normal (Loudness 2). Is High Treble basically the overdrive or gain channel while the Normal is the clean channel?

This is true but if you crank them up loud they will distort and overdrive.

 

[Buzzard]

I have build a replica of the Number One Amp at the Marshall museum for a member here on an old Marshall chassis with original old parts and transformers It was suprisingly gainy!!! I ended playing Drop D tuning!!! Haha!
Is that the offset model? I’ve seen kits but jud
I am making one replica for my self on a new chassis and it will be interesting if it also is as gainy as the first replica. I think there is a thread about it here on the forum.

plexi

I have build a replica of the Number One Amp at the Marshall museum for a member here on an old Marshall chassis with original old parts and transformers It was suprisingly gainy!!! I ended playing Drop D tuning!!! Haha!

I am making one replica for my self on a new chassis and it will be interesting if it also is as gainy as the first replica. I think there is a thread about it here on the forum.

plexi

Is that the offset model? I’ve seen kits but judging from johan segborn’s demos of originals they sound pretty clean and dull. Imo. Then again he makes just about everything sound the same. Like early kiss lol

 

[wonderingape]

From another forum, which is interesting.

"Take a the JTM45 for example
people will claim this is an example of power tube distortion
but it is not ....

because it has 4x more negative feedback than the bassman it is copied from
and a higher primary impedance on the output transformer
it has less power tube distortion than the bassman

it also has more gain in the pre amp 12ax7 v1 instead of 12ay7
so the creamy texture of the JTM45 is a result of more pre amp distortion
than the simmilar bassman

STOP right there !
because there is third major difference and source of "distortion"
the power supply on the 45 is inadequate compared to the bassman

the PT supplies less available current,
the first filter is 32uf vs 40uf on the bassman
the second is 16 on the 45 vs 20 on the bassman
and so on ...

In fact in both cases the power supply collapses about the same time as the power section and pre amp hit distortion
so with either amp you get a delicious mix of pre amp distortion, power amp distortion and browning out power supply ....

to put it another way
with pre amp gain alone it is difficult to get the power supply to brown out
when both sections are running well and you dip into the brown zone
everything is magic

other examples of very brown amps are tweed deluxe and tweed champs

well designed modern amps actually use sections of the pre amp running
at lower voltages to mix this sound back in with their pre amp distortion

Many reissue amps are simmilar to the old design but offer more PT current
and power supply filtering to "reduce noise and increase stability" these amps tend to sound sterile compared to their vintage cousins

most people blame the speakers, wooden box, or pcb style of manufacture instead of the improved power supply

ex look up a jtm45 reissue schematic and compare it to an original
likewise with the 5f6a bassman"

 

[guzzis3]

So, if I understand you correctly, the only sound difference that each different power tubes produced is which one break-up/distorted first and characteristics such as mid-scooped or upper-mids boosted is 100% determined in the preamp circuits. No?

Sort of. The BIG thing affecting the EQ of your amp is in the preamp, you could call this the coarse control, but everything matters. As ampmadscientist says above you can get signifigant changes just by moving stuff around. Use a different capacitor, same value but different construction. All sorts of stuff.

Well, I have just found this audio on another forum . It sounds just like how those 60's-70's amps sounded like when they're cranked or maxed out.

No it doesn't, it sounds pig awful. Listening to that was making me physically ill. Get in a room with a well set up 59 or 87 stack on full song. It is a joyous experience.

Regardless of types of power tubes and preamp tubes?

If you keep the components the same but change layout it will change the amp. Keep the layout the same but change valves it will change the sound. Change both and it will change the sound.

 

[wonderingape]

Sort of. The BIG thing affecting the EQ of your amp is in the preamp, you could call this the coarse control, but everything matters. As ampmadscientist says above you can get signifigant changes just by moving stuff around. Use a different capacitor, same value but different construction. All sorts of stuff.



No it doesn't, it sounds pig awful. Listening to that was making me physically ill. Get in a room with a well set up 59 or 87 stack on full song. It is a joyous experience.



If you keep the components the same but change layout it will change the amp. Keep the layout the same but change valves it will change the sound. Change both and it will change the sound.

Usually when we compare a cranked single-ended class A power amp with EL34 or EL84 with others such as 6L6, 6V6, KT66, etc. the one with the EL (EL34/EL84) power tubes will distort earlier, but I heard if the EL34 or EL84 and say, 6L6, are cranked to the maximum the EL power tubes still sound mellow because they have more 2nd harmonics distortion while the 6L6 will sounds much harsher because they have more 3rd harmonics distortion. No?

 

[guzzis3]

Depends. What voltages are you running on the valve ? exactly how gainy is your preamp ? What output transformer ?

Also I spoke about 6L6 and EL34 specifically because they are close on power output. A 6V6 and 6BQ5/EL84 are much lower output valves so if you have everything the same and switch an EL34 for a 6V6 I'd bet the 6V6 will distort earlier, but I've not tried it.

So what you typed is a generalisation, probably true most of the time, but not always. Another generalisation is that running the output valve at it's maximum voltages will give you more "headroom" and possibly "crisper" distortion while lower voltages give less volume and in my experience "muddier" distortion. But again this is generalising.

 

[scozz]

MEDIA]. It sounds just like how those 60's-70's amps sounded like when they're cranked or maxed out.

Really?!?! I don’t think so bud!

It doesn’t sound like ANY 60s or 70s Marshall I’ve ever heard, and I’ve been playing and listening since 1966!

Do you really think that sounds like a 60s or 70s Marshall cranked??

 

[scozz]

All the early Marshall amplifiers were actually single channel amps with a bright side and a Darkside and they were all on the cleaner side of things

Not when they were dimed!

 

[pleximaster]

Is that the offset model? I’ve seen kits but judging from johan segborn’s demos of originals they sound pretty clean and dull. Imo. Then again he makes just about everything sound the same. Like early kiss lol

Both are Dudley Cravens take of cloning the 59 Fender Bassman. However these Elstone transformer found in the Number one amp differ from the ones mostly found in offsets (Radiospares, even two examples off offsets are known with Elstone transformers too)

These Elstone MT seems to not deliver as much power as the RS under full load and pressure adding sag and brownier sound and the OT gets saturated much more easily. Actually not considered good hifi transformers... but sounds cool in a guitar amp. These transformers were 50´s surplus sold out at the local electric shop near where the Three Amigos responsible for making these initial amps Dudley Craven, Ken Bran and Ken Underwood. They used the parts they found and parts influence sound so amps differ from example to example much more than they do today when parts and production is more standardized.

plexi

 

[wonderingape]

Really?!?! I don’t think so bud!

It doesn’t sound like ANY 60s or 70s Marshall I’ve ever heard, and I’ve been playing and listening since 1966!

Do you really think that sounds like a 60s or 70s Marshall cranked??

How about this? Around 3:10? This JTM50 according to Johan himself has EL34 in the output section instead of KT66.

 

[wonderingape]

Depends. What voltages are you running on the valve ? exactly how gainy is your preamp ? What output transformer ?

Also I spoke about 6L6 and EL34 specifically because they are close on power output. A 6V6 and 6BQ5/EL84 are much lower output valves so if you have everything the same and switch an EL34 for a 6V6 I'd bet the 6V6 will distort earlier, but I've not tried it.

So what you typed is a generalisation, probably true most of the time, but not always. Another generalisation is that running the output valve at it's maximum voltages will give you more "headroom" and possibly "crisper" distortion while lower voltages give less volume and in my experience "muddier" distortion. But again this is generalising.

6L6 and EL34 are close on power output, so the distortion sound from both of these power tubes at their maximum voltages will sound exactly the same with similar harmonics level?

You previously said, "You have to remember that the distortion levels in 60's Marshalls were pretty low even at full tilt. If you remove the neg feedback you get a bit more. Class A has massively more, about 3 times the THD of a class AB1."

By the way, below is a 10w class A amp equipped with EL34. The volume is at max according to the description, but still doesn't sound as distorted as the distortion sounds from the 80's and onwards.



Another clip of maxed out class A amp, afaik Brunetti Mercury is using EL34. The distortion even at its max is a low gain distortion in today's standards.

 

[guzzis3]

6L6 and EL34 are close on power output, so the distortion sound from both of these power tubes at their maximum voltages will sound exactly the same with similar harmonics level?

You previously said, "You have to remember that the distortion levels in 60's Marshalls were pretty low even at full tilt. If you remove the neg feedback you get a bit more. Class A has massively more, about 3 times the THD of a class AB1."

By the way, below is a 10w class A amp equipped with EL34. The volume is at max according to the description, but still doesn't sound as distorted as the distortion sounds from the 80's and onwards.



Another clip of maxed out class A amp, afaik Brunetti Mercury is using EL34. The distortion even at its max is a low gain distortion in today's standards.

The jtm 50 sounded about right but he makes everything sound like that.

Swapping a 6L6 to an EL34 will dramatically change the sound of the amp. If oyu can't build you may be able to buy an amp off ebay that allows plug and play output valve swapping. If you can find one I cannoy recommend strongly enough get an EL34, a 6L6 and a KT66 and compare them. If the amp accommodates it get a 6V6 and a KT88 and try those also. you might be amazed.

Those 2 links you posted to class A amps were awful. If I built an amp that sounded that bad I'd burn it, but it could be something else. Speakers ? Microphones ? Players ? Dunno.

However the bigger point is this:

A 60's amp with a clean preamp AB1 will deliver maybe 3% THD. A class A built properly will deliver about 8% THD. A high gain amp with the extra 12AX7 in the chain adds a whole bunch of distortion before it gets to the output stage, so it might be giving 8% THD then the output is giving another 3%. Numbers are examples, you can make them anything you want depending on the circuit.

I tend to leave out the negative feedback. It gives more distortion, a little more power and it changes the "sound" of the amp. But remember I build amps to amuse myself. Cleverer people than me can make good clones of classic amps and then change them to YOUR desires. And do all sorts of other clever stuff. I've done enough to know what I like and I build accordingly.

I'm a mechanical engineer who has played with electronics all my life. I am NOT an electrical engineer. I know enough to know how little I know, but I do know a thing or two...

 

[guzzis3]

Here he is comparing output valves but as I said he makes everything sound the same.



I'll see if I can find a better comparison.

You might get a bit more here:

 

[wonderingape]

However the bigger point is this:

A 60's amp with a clean preamp AB1 will deliver maybe 3% THD. A class A built properly will deliver about 8% THD. A high gain amp with the extra 12AX7 in the chain adds a whole bunch of distortion before it gets to the output stage, so it might be giving 8% THD then the output is giving another 3%. Numbers are examples, you can make them anything you want depending on the circuit.

I see, noted the bold statement. So power tubes alone with no preamp tubes and anything else can't produced high gain distortion sounds like in the 80's and onwards. Isn't it?

 

[wonderingape]

Here he is comparing output valves but as I said he makes everything sound the same.



I'll see if I can find a better comparison.

You might get a bit more here:

I've already watched both videos, but what accounted for the differences in sound especially in the second video when played the hard rock riffs? Power tubes only or what? Some said the EL34 and EL84 have more upper-mids but aren't such qualities actually come from the preamp circuit? I can see the preamp tube on the circuit just besides the power tube in the second video.

 

[guzzis3]

Correct. If you have say a 1959 on full song with no pedals etc it will have less distortion than an 80's hi gain amp with the extra preamp tube all on full song, everything "dimed" as they say.

I think Eddy Van Halen used a hi gain amp on say "you really got me" their cover of the Kinks song. You can't make a stock 60's marshall sound like that without pedals or something similar. You can get a higher gain type sound by using a booster pedal, so the signal into the amp is already boosted but clean. That will distort the signal in the preamp, but it probably won't sound exactly like an amp with an extra 12AX7. Then there are all sorts of distortion pedals, some use valves! But just amp and guitar, no.