new guy intro and question

[bsfc9]

Hi all, I've been playing guitar since about 1985 and have owned all kinds of gear at one time or another. I've owned several various tube amps and been successful tinkering with their innards.
I now have a Marshall Master Lead Combo Model 5010 dated circa. 1986. It's just like one I used to own in 1989. Lately I have been into reacquiring retro(old) gear I used to have.

This amp was supposed to be the solid state equivalant of a JCM 800. Well, to my ears...maybe.

I want to change some tone stack values around, and my question is if this is supposed to sound like a JCM 800 why is the tone stack so different?

Has anyone around here messed with one of these?

Thanks so much...Mike

[joecool85]

Welcome to the board, Mike.  I haven't played around with either of those amps, but there are many here with enormous amounts of experience.  Good luck!

[teemuk]

- "JCM800" is name for series of amps, not for a single amp. With that in mind, what are The "JCM800" values? Which out of the vast number of different JCM800's is the reference?

- Have you actually calculated the responses of the tone stacks? Just because component values or even overall design are different might not mean the response is. After all same RC filter can be built with various R values if C values are scaled accordingly, and vice versa.

[J M Fahey]

Agree and add: we are in the dark until you post both tone controls to compare.
Even so, as Teemu said, maybe one of them *is* basically the other one, but scaled , say, 10x (capacitors 10X larger, resistors 10X smaller) which ends up sounding about the same.
When people speak "JCM800" without further clarification, they usually refer to the "Master Volume JCM800", the one which has a "low gain" input, straight into a passive network+Volume pot, plus a "high gain" one, which passes through a 12AX7 triode for a fixed around 50X gain boost.
It's too much gain, so the beast is tamed by making the 2nd triode cathode resistor an unbypassed 10K one.
The most popular version is "2203" but there are, as Teemu noted, many other ones sharing the basic structure.
The sound is excellent.
Fire and thunder.
I don't think that any of the old SS Marshalls comes even close to it, no matter what they claim.

[bsfc9]

All right, thanks guys, I'll research and post some more specific details. Again thanks for the welcome and no flames!

Mike

[bsfc9]

Hi again, let's see if I can get this right. The 5010 Master Lead Combo was the transistor equivalent of the JCM 800 model 4010 50w 1x12 combo.

I will try to link schematics of each below for evaluation.

[J M Fahey]

Thanks for posting those very useful links.
Let's qualify

The 5010 Master Lead Combo was the transistor equivalent of the JCM 800 model 4010 50w 1x12 combo.

Only in the Marketing Department's mind.
That 4010 you post is even today an agressive balls-to-the-wall amplifier, almost the same as the 2203 I mentioned and many other "brothers".
It can hold its own decently against any modern amp, only lacking refinements as channel switching, loops, etc. but still world class in the tone department.
Soldanos, Mesas, and most others are in a general way refinements or tweaks of this venerable amp.
The 5010, on the other side, is an excellent SS amplifier, capable of some reasonable distortion (much better, in my personal opinion, than buzzy Valvestates), but *much* milder in character than the tubed one.
Besides the Tone controls, which are similar but not the same (different turnover points), the most important difference lies in the clipping method.
The simplest is the SS one: it just overdrives the last Op Amp, Ic1b, which provides typical Op Amp squarewave, with absolutely flat tops and perfect, stable, (boring) 50% duty cycle, meaning almost pure (boring) odd order harmonics.
It doesn't even overdrive it *that* much.
It goes through that tone control, and drives a conventional SS power amp, which is also a giant Op Amp, won't repeat the sound description.
I'm not insulting it at all, the sound is quite decent, better than most, and can take any distortion pedal you choose very well.
It's an evolution of the famous 5001 (or was it 5005?) 12W SS amp.
ZZTop used one of them as a preamp (stripped it and mounted it in a rack cabinet).
I have successfully made thousands of very similar 100W heads , so I know it's a winning combination.

Now the Tube one, it stacks distortion over distortion, all interesting.
The main distorter: V2A.
It has high gain and is slammed by the guitar signal amplified by V1a and V1b, pre distorted by V1b which is very poorly biased (it should really have a 1K5 cathode resistor) , and post distorted by cathode follower V2b, which also behaves unsymmetrically if overdriven.
As you see, you have 3 (count'em) cascaded distorters, not forgetting that it will later drive a tube power amp which will add its own "interesting" distortion.
As an intermediate design, JCM900 and many Valvestates use a half-way solution: they have an SS (Op Amp based) preamp, but overdrive a 12AX7 connected as V2(a and b), driving the "JCM800" tone controls.