Fractal Audio AMP models: 1959SLP (Marshall SLP1959 Vintage Re-issue)

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* EDIT: Up-to-date information is available in Yek's Guide to the Fractal Audio Amplifier Models *
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1959SLP: based on Marshall 1959SLP (Super Lead)

The world’s greatest rock amp is a Marshall “Plexi”. These came to the market in the mid ‘60s, when Marshall and Fender started to make loud amps. These amps are referred to as “Plexi” amps because of the gold Plexiglass front panel, later replaced with gold aluminum. Plexis with 4x12 cabinets gave rise to the "Marshall stack". The Plexi was built for almost 20 years, and was then replaced by the JCM 800. Even today amp builders still design amps based on the Plexi, such as the Bogner Helios. And its looks are being copied for all kinds of guitar amps.

So why has the Plexi become such a popular amp? According to Legendary Tones:

“Many things. First and most important perhaps is the sense of dynamics and rich harmonics. No large-production amp created before or since the early Marshall plexi series has been able to capture the feel of the player through varying degrees of dynamics and coloration from the (mostly) EL34-based tube circuits of these Marshalls. Call it a lucky accident with the folks at Marshall, but they were able to create amplifiers that really responded well to the guitars that played through them. A wide palette of distortion color that is rich and full and just powerful and timeless in tone is what these amps deliver. It takes some time to really get used to playing a basic amp such as a Marshall plexi. No multi channels or reverb or effects and no master volume controls. Turn up the amp and play – play hard and the amp rewards you with fullness of tone and smooth distortion. Back off your playing and the amp will respond, and move into lighter shades of overdrive. Roll down your guitar volume a touch and you’ve got a warmed up clean sound. There just isn’t anything like the ability to feel a set of power and preamp tubes overdriving together musically.”​

A Plexi is raw, unrefined, honest and touch sensitive. Hit a chord on a Plexi and feel that explosion of sound in your face and body...

Numerous guitar heroes played some kind of Plexi: Pete Townsend, Jimi Hendrix, Jimmy Page, Angus Young, Yngwie Malmsteen, Jeff Beck and of course Eddie Van Halen.

The Plexi came in various incarnations. Some of these are modeled by Fractal Audio, so we’ll discuss these later. Many (but not all) Plexis have a JMP logo.

The ‘60s Marshall Super Lead was one of the original 100 watts Plexi amps, a very desirable amp (no. 9 on Vintage Guitar's list of valuable amps) . The 1959SLP is a re-issue of the Super Lead, made in the ‘90s, as part of the Vintage Re-issue series. The number “1959” does not refer to the build year, it’s a model number. Marshall:

“The 100 Watt Super Lead head of the late ’60s (’68 – ’69) with the famed Plexiglas front panel, is re-issued here in all its glory. The 1959SLP ‘Plexi’ head is the amp that defines classic rock tone. To ensure absolute tonal authenticity, we took a ‘Plexi’ head from said era, and using it as a template, our R&D experts developed a replica so exact, that sonically we couldn’t tell them apart. The 1959SLP truly is the sound of rock."​

Not only do we have the model of the SLP re-issue in our Fractal Audio, we also have a model of the original: the Plexi 100W. Cliff: "The old one (Plexi 100w model) has a 2.7K cathode resistor on the first stage, the new one (1959SLP) has an 820 ohm."

Like the original Plexi, the SLP comes with four EL34 tubes and blasts 100 watts through (preferably) a 4x12 cabinet.

It provides two channels: Normal and Treble, and two inputs per channel. Both channels are modeled by Fractal Audio.

The Normal channel is (duh) less bright and has loads of bass. Cliff:

"Don't be afraid to turn the bass all the way down or the treble all the way up. Just like with the actual amp. For example, on the normal channel of a Plexi most people turn the bass way down. Otherwise it's too flubby."​

The Treble channel can be very (duh) bright, even painfully bright. A popular “amp mod” of the real Plexi was clipping the bright cap. In Fractal Audio’s amp model that’s easy: you turn off Bright. Or you can adjust the Bright Cap value on the Advanced page. Note: turning off Bright will result in noticeable loss of amp gain. Cliff:

“One of the first mods people make to real 'Plexi' Marshalls is to "clip the bright cap". The bright cap varied over the years, supposedly depending on what was lying around in the shop. The model defaults to the bright cap in the circuit. If you turn off Bright you're effectively clipping the bright cap. The bright cap in Marshalls can be very bright and harsh. However, if you crank the Master you might find the extra brightness helps compensate for the power amp getting darker.”​

Apart from the Volume controls, the amp has Bass, Middle, Treble and Presence controls. Cliff: "My settings for a "typical" Plexi tone are Bass: 2, Mid: 8, Treble 7.5. Adjust Presence to taste."

Eddie Van Halen had all these controls maxed out. And to emulate his variac: set the parameter “AC Voltage (Variac)” on the model’s Advanced page to 75 or so.

Some people complain that a Plexi can sound fizzy. Cliff:

"It's the way a Plexi is supposed to sound. That's due to the cathode follower. That raspiness helps it cut through in a mix. I own three of them and they are that fizzy."​

Some players of a real Plexi use patch cables to “jumper” the inputs (2nd input of channel 1 goes into 1st input of channel 2). This enables them to have the benefits of both channels at once. This is modeled in the “Jumpered” model of the 1959SLP in the Axe-Fx II and AX8. That’s why this specific model has two Drive controls. Set them at the same position, or keep Normal Drive lower than Treble Drive.

Like an original Plexi, the 1959SLP doesn’t have a Master Volume, so keep the Master control in the model dimed. Without a Master Volume control, Plexi amps rely on power amp distortion. To achieve a nice overdriven rock tone, you need to turn up the 100 watts Plexi a lot. This makes it a very loud amp in real life.

If you like to experiment, turn up Supply Sag in the model for more compression. Note that high Sag settings may cause "ghosts notes". Exactly like on the real amp at high volume: check the interview with J.D. Simo below. If you don't want ghosts notes, switch Supply Type to "DC".

Another tweak is to turn on Boost on the Advanced page, to slam the model's input stage for more gain.

You can’t discuss Marshall amps and leave out speakers, in particular: greenbacks. Early Marshall amps were used with 4x12” cabinets with Celestion G12M speakers. Greenbacks have a sweet midrange and good bass reproduction. The rear of those speakers was green, and the nickname “greenbacks” was born. They are the reason that 4x12 cabinets were designed: the G12M was only 20 of 25 watts, so you needed four of them to prevent blowing them up.

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Another popular speaker in those days (and it still is): the G12H. A 30 watts Celestion speaker that compresses less than a greenback and has a flatter response. It’s the “Jimi Hendrix” speaker.

You check this page for the stock "greenbacks" cabs, suitable for the Marshall models. Personal favorites among the stock cabs are: 54 and 55 (Cab Pack 20), 58 and 59 (Cab Pack 8), 103 (Cab Pack 2), 131 and 132 (Cab Pack 14, I think…).

Click to open the 1959SLP's handbook.

A selection of YouTube videos:









 
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Yek, you've really outdone yourself with this latest edition! I especially like your video selections. Thanks for doing this.
 
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When I retire in many years, I plan on spending all day every day playing my LP Special into a jumpered Plexi............

Rock on!
 
I'm sorry, I just cant help myself. I know I should just be appreciative of the efforts that yek has taken, and I'm am totally appreciative of the many contributions he has provided and just keep my mouth shut, but that guy from premier guitar is totally full of crap. Go ahead, let the exorcism begin.
 
I'm sorry, I just cant help myself. I know I should just be appreciative of the efforts that yek has taken, and I'm am totally appreciative of the many contributions he has provided and just keep my mouth shut, but that guy from premier guitar is totally full of crap. Go ahead, let the exorcism begin.

:)

The interviewer or the guitar player ?
 
Yek, with all due respect, while there is some useful info there, the player indulges in almost every thing ever "hyped" about tube amps. In all fairness I only got through 12 or 13 minutes. I guess it would be fair to list a few of the things I talking about? Well, let me tell you that there were huge differences in voltages in those amps and it had nothing to do with the wall voltage. Preamp tubes - I once found a nos 12au7 that sounded better than a 12ay7 in the 1st position on a '59 bassman. Point being; while that first position tube matters, and you may have found a particular tube that you like, there where tremendous variations in tubes built way even back when. Consider the machining mechanisms used back then. Almost every component you can think of was potentially less precise than those manufactured today. Mil spec doesn't carry any real weight. I worked on a missile system in which the missile electronics where pretty much all tube. Half the time the missile misfired. Guitar amp tubes are almost always ran outside of any normal parameters. To suggest that a particular 12ax7 consistantly sounds different and arguably better than any other just doesn't fit my experience of tube amp tweakage for the past 35 years. I do believe if you really want that amp flat you bring the treb and bass down and mid full up. All tone controls full up is not flat. Anyway, doesn't really matter and I shouldn't have said anything. Your efforts are greatly appreciated.
 
Indeed, the new stock cabs #54 and #55 are some of my personal favs as well. I've updated quite a few presets to use these since quantum dropped. Another great post.
 
That's just Simo. He's obsessive and "a little crazy". I enjoyed watching it, mainly because I went through that phase (the Axe FX cured me of all that mess).

On of my absolute favorite amps is the Maven Peal Ganesha, which is based on the Super Lead. Spectacularly great amp. External bias. Can take a wide range of power tubes. The Sag Circuit was just brilliant, and the Wattage Control made it extremely useable at home and live (yes, Fletcher Munson still applies!). I had cases of tubes. They're all gone now (thank you, Cliff!). But, it was tons of fun to experiment (and frustrating, and expensive). I also owned a Zeeta Gold (high-end parts), and some of the Emery Sound amps. The experiments I did with those amps, have helped shape my experience with the Axe FX, and makes me so glad that Cliff doesn't stop or settle.

Yek, with all due respect, while there is some useful info there, the player indulges in almost every thing ever "hyped" about tube amps. In all fairness I only got through 12 or 13 minutes. I guess it would be fair to list a few of the things I talking about? Well, let me tell you that there were huge differences in voltages in those amps and it had nothing to do with the wall voltage. Preamp tubes - I once found a nos 12au7 that sounded better than a 12ay7 in the 1st position on a '59 bassman. Point being; while that first position tube matters, and you may have found a particular tube that you like, there where tremendous variations in tubes built way even back when. Consider the machining mechanisms used back then. Almost every component you can think of was potentially less precise than those manufactured today. Mil spec doesn't carry any real weight. I worked on a missile system in which the missile electronics where pretty much all tube. Half the time the missile misfired. Guitar amp tubes are almost always ran outside of any normal parameters. To suggest that a particular 12ax7 consistantly sounds different and arguably better than any other just doesn't fit my experience of tube amp tweakage for the past 35 years. I do believe if you really want that amp flat you bring the treb and bass down and mid full up. All tone controls full up is not flat. Anyway, doesn't really matter and I shouldn't have said anything. Your efforts are greatly appreciated.
 
Off topic warning, as this is based on a Tweed, but here's some Maven Peal action. I worked with some folks on this. Tried to help get schematics, but there were no clear ones to be had.

 
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Thanks, Yek, another great post.

I love Johan Segeborn's YouTube channel. He's a great source of information for Marshall amps and cabs in particular, and I admit to 'borrowing' the odd lick from him too....:)
 
Thanks Yek, for me especially the J.D. Simo video I watched every second of it and found it extrem interesting. But thats probably because I like Simo's playing alot and I'm probably a weird guy too. So its all good - I enjoyed it very much - I think it was 42 minutes which actually did not want to spend, but it happend. ;)
 
The Plexi and the JCM 800 are the tones I hear in my head (when the voices quiet down...) more than anything else, this is RIGHT in my wheelhouse.

The thing about the Plexi, for me, is that it's pegged as 'one sound', when it can be a damned versatile box when you tinker.
 
Tried the 1959 and 1987 amp models this week. But the normal channels on both model sound very dull. Like there is a blanket over the sound. Very little highs and not an open sound. This turned me off at first but maybe it needs heavy tweaking? Is that dull sound also the case with real amps?

What are some of the settings you guys use to make it sound good?
 
don't use the normal channels. use the bright or jumpered channels. or just turn the bright switch on
 
Yes sure. Just was wandering if the normal channel with 'flat' settings of the real amp also sounds so dull? Never tried one but I can't imagine.
 
The normal channels on both model sound very dull. Like there is a blanket over the sound. Very little highs and not an open sound. This turned me off at first but maybe it needs heavy tweaking?

Whack the treble and mids up, run the bass lower. You might like running the drive lower and hitting the front end a little harder instead.
 
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