The 'Marshall' Sound

[Jaicen]

Just a quick question really.
I've been trying to decide what exactly it is that gives Marshalls their characteristic sound. Is it the pre-amp, or the push-pull output stage, or is it a combination of both??
What I really want to know is if I run a Marshall pre-amp into a SE EL84 output stage, will it sound a bit like a marshall, or will it be completely different, that sort of thing.

[Ray Ivers]

Jaicen,

IME any one-channel amp with a single Marshall 1959-style tone stack directly before the phase inverter will generally sound very much like a Marshall to me.

Ray

[rocket]

I think it's also the speaker that's important.

You might also use diode clipping to get some symmetric clipping as in a PP amp and you might even try to put antiparallel diode in series with the El84's grid stopper resistor to simulate some crossover distortion.

But I would make all the diode stuff switchable.

[spiffpeters]

I belive it is the tone stack that is largely responsible for the Marshall sound. Not the only variable, but I'd say it is the main one.

[Chadwick]

'marshal sound'

I think the caps they use are key to the tone. The tone stack is a fender bassman rip off many times. Or straight out of tube manual example circuits back when they were pushing glass.

You could definatly classify tones per output tubes and class a, ab . I think another classification is the number of gain stages in the preamp. 3 stages is magical to me but two stages has infinate tone variations as well.

those LCR filter caps are pretty cool too. I'm huge believer that the power supply gets the least amount of attention but has everything to do with the tone..

Those old Marshall transformers were buff and did a thing that also makes them unique..

So many aspects of famous amps can be dialed in with the right circuit. I'm still so amazed at the 'vintage' thing. If you really look up how many crappy amps fender and marshall put out to get those few gems it takes away the calendar appeal of 'vintage'.

So its everything and it takes years to appreciate the contribution of each component. Of course.

[R.G.]

I think the caps they use are key to the tone...

those LCR filter caps are pretty cool too. I'm huge believer that the power supply gets the least amount of attention but has everything to do with the tone..

How does that work? What makes the tone different if the power supply is different?

[Chadwick]

filter caps and tone

The filter caps provide the steady, clean, responsive DC voltage for the plates of the tubes, and the the plates is where we get our voltage fluctuation caused by the grids, so the characteristics of the filter cap on that stage makes a big difference.

In general the more uF on a stage the quicker/more completely resuplies the voltage drop on the plate and resuplies a larger voltage drop in higher gain circuits. I percieve this as tighter bottom end and quicker response when playing. This happens from 8uF to 40uF and beyond that range I don't really catch a big difference but its possible.

A customer brought me a ten year old amp of mine and to my surprise I freaked out on the filtering putting 400uf on the first two stages of gain... The amp sounded awsome but I've long ago settled into more average values because there is usually some other aspect that is being missed when you find your self tweeking one value to hell and back.

[Tom Phillips]

"Fender Circuits in Old Tube Manuals"

The tone stack is a fender bassman rip off many times. Or straight out of tube manual example circuits back when they were pushing glass….

I have heard many times the statement that Leo got his original circuits out of the old RCA tube manual. However, I have never seen old Fender style circuits in the old tube manuals. Has anyone seen the proof? It seems to me that it’s just old lore that keeps being repeated.
Comments invited.
Tom

[Ray Ivers]

Tom,

+1.

Ray

[bob p]

as I recall the lore, Leo licensed the circuits from Western Electric, and it was Dr.Z that got his tricks from the RCA tube manual.

[Tom Phillips]

Ah yes Bob...I stand reminded about the Western Electric reference. I have old RCA and Sylvania tube manuals but no WE. It will be interesting to see if anyone comes up with the "proof". The circuits are all so similar anyway. I wonder exactly what was licensed. For now I remain skeptical that the original bassman circuit was lifter out of a tube manual or application notes.

I have seen the section in the RCA manual that they put under the heading of "Corrective" filters. Dr. Z was very gracious in disclosing that reference rather than claiming that he invented it as some of the self appointed gurus have done for other circuits.

Regards,
Tom

[Chadwick]

RCA, Fender, Marshall

Since Leo didn't invent the tube and reverse engineer it to find out how it works, RCA released all the information needed to run tubes. Just like current op amps, transistors and such, the data sheet shows schematics and all relevant data to design a product.

So long as a pre-fender AM radio had a tone knob, there’s the birth of the tone stack. I'll bet a tube radio jockey could show us schemes of tube tone stacks before Leo put one out. Can't prove it in court today though.

Here is one RCA tube manual. Lets try and track down the one that has the 12at7 or equivalent. http://www.nmr.mgh.harvard.edu/~reese/RC10/

Its is certain the Marshall borrowed Fenders Bassman scheme, no doubt. How much Leo took from the manual? I'm sure they laid the circuit out enough that leo just had to plug in some values.

Leo is the man though, he definitely birthed the amps that we still play and copy and argue about.. Praise the Leo.

[bob p]

yes Tom, it was the conjunctive filter citation that i was referring to. that's a common trick from old HiFi amps. you did a good job of guessing what i was thinking!

regarding the WE licensing stuff, i seem to think i remember seeing a WE licensing reference on an old tweed tube chart, but i'd have to double-check on that to be sure.

fwiw, i'm not one to agree that we owe everthing to RCA because RCA invented tubes and told us how to use them. the magic that happens when guitars get played through tubes isn't something that was planned. the combination of intermodulation distortion, soft limiting and the artifacts that go with it were discovered serendipitously, not by reading an RCA tube manual.

back to the tone stack issue, i don't think that the marshall sound comes from the tone stack. it comes from a class A triode driving a cathode follower, and driving THAT circuit into the tonestack. IMHO THAT is the essense of the famous "Marshall" sound.

[Tom Phillips]

... i seem to think i remember seeing a WE licensing reference on an old tweed tube chart, but i'd have to double-check on that to be sure.

I'm wondering if this could be one of those cases where one feature of the circuit is licensed, the "used under license from..." statement is put on the product and people assume that the whole circuit was used under license.
Tom

[bob p]

could be. i have absolutely no idea WHAT was being licensed, and like everyone else i didn't bother to ask. i just seem to remember seeing something like that. this is, of course, exactly how the "lore" gets started...