Marshall tone stack in a Real McTube

[ranchak]

I just added a Marshall tone stack in my Real McTube. The problem I'm having is I don't have much control, the bass/mid/treble do not do much for the circuit. I used this circuit:

http://www.diyguitarist.com/PDF_Files/MarshallToneStack.pdf

Any suggestions?

[zachomega]

Not sure how accurate that is when compared to a plexi style tone stack, but here are my observations from my friend's plexis (two different friend - two plexis). 

The tone controls don't do much on those amps either.  The controls you use are the midrange and presence.  The presence functions as your high end and the mid as your low end.  The bass and treble controls are just there for looks...or if you play bass, they seem to work really well. 

Strangely, I find these control all of the sudden work infinitely better with a master volume marshall. 

Anyway, that could be part of the problem.

-Zach Omega

[Paul Marossy]

The McTube isn't really something that would pair up very well with the Marshall tone stack, IMO. In practice, it works better on something like the Smash Drive or the Blackfire.

[ranchak]

I'm using the Real McTube with a Marshall. I really didn't need the tone controls, but I thought they would look "cool". I got the idea from someone who modded one of these. I'm just trying to salvage what I have. I'm going to build a new McTube with a tube compressor and I probably will not have tone controls unless I can get better results. I might try the Fender/Marshall/Vox setup like this:

http://amps.zugster.net/articles/tone-stacks#Baxandall

[Izzy]

Try changing the freq in tonestack according to your need, so that those tone stack will "response" to your circuit.

[RedHouse]

It really needs to be driven by a cathode-follower stage to have maximum effect (another tube), just slapping one in on a Real McTube won't get it done right.

Have a look at a real Marshall schematic (1959SLP/1987/2203/2204 etc) and see where the tone stack is located, it's right after a cathode follower which drives the tone stack from a low impedance.

[Ben N]

Besides the cathode follower, I would think that you are feeding the stack a different set of frequencies with the McTube than a Marshall would.  At a minimum, if you are going for that sound you might want to match the cathode bypass caps on the McTube to the Marshall values.

OTOH, if you are feeding a Marshall with this, maybe a different tye of tone control would be more useful than duplicatinng the stack on the amp.  Maybe an AMZ-modified BMP tone stack, or something like the active control on the ROG Thor.
hth
Ben

[Paul Marossy]

Besides the cathode follower, I would think that you are feeding the tack a different set of frequencies with the McTube than a Marshall wouild.

+1. Therefore, it doesn't have the intended end result.

[PaulC]

In the JTM45 and early plexi amps you'll have those values.  The Bass 100 watters also had them.  In the later plexi and metal face amps the 56k resistor is a 33k, and the cap going to the treble pot is a 500p (I've seen 470p and 560pf in "stock" amps).

The resistor is known as a "slope" resistor.  The reason the tone stack is fed from a low imp source is because the value of the slope resistor can load down the driving stage.  Also with the 33k you get some loading on the CF buffer causing it to distort when driven hard.

The lower the value of the slope resistor the less the tone controls will work, but you'll also have a stronger overall signal.  The higher values (100k in black face fenders) and the tone stack will have a lot of play.

You can down load duncan's tone stack calc to see what happens when you play around with the values.

Later, PaulC
Heritage amps/Tim & timmy pedals