Comparing first Gain Stage in MTS amps

[BesaMoogie]

Hi there, when comparing schematics of the RM50 with the RM100, I realised that there is an additional 3.3 Mohm resistor connected to ground after the 0.1uF cap in the RM50. This resistor is missing in the RM100 (labeled as "no part").

Any ideas what this resistor does? To my understanding, it does shunt some of the high end to the ground, before the signal is passed further to the module. Am I right? Or is this a grid leak resistor?

 

[glpg80]

Are there additional switchable features in the 100 that the 50 doesn’t have?

 

[FourT6and2]

I don't know what an RM50, etc. are. But if this is a typical tube gain stage, think about what would happen if this were simply a direct connection to ground. It would kill 100% of your signal, right? As you raise the resistance of this connection, it resists and prevents the signal from 100% going to ground. So the higher you make that resistance, the less signal gets dumped. It's a way to tailor the feel of the stage and how much gain you retain. But it also depends what the next stage looks like, as it can also interact with a gain control (which is usually found right after this point).

A capacitor to ground here would kill highs.

 

[glpg80]

I don't know what an RM50, etc. are. But if this is a typical tube gain stage, think about what would happen if this were simply a direct connection to ground. It would kill 100% of your signal, right? As you raise the resistance of this connection, it resists and prevents the signal from 100% going to ground. So the higher you make that resistance, the less signal gets dumped. It's a way to tailor the feel of the stage and how much gain you retain. But it also depends what the next stage looks like, as it can also interact with a gain control (which is usually found right after this point).

A capacitor to ground here would kill highs.

You’re not attenuating anything at 3M. That’s well above audible range. The point of my question is that those sizes are normally used to reference one side of a large capacitor to ground to prevent relay or switch popping. The resistor acts as a path for electrostatic discharge on the opposing plate that is building charge while the path is not in use/not seeing AC.

 

[FourT6and2]

You’re not attenuating anything at 3M. That’s well above audible range. The point of my question is that those sizes are normally used to reference one side of a large capacitor to ground to prevent relay or switch popping. The resistor acts as a path for electrostatic discharge on the opposing plate that is building charge while the path is not in use/not seeing AC.

You're right. I didn't look at the value.

 

[BesaMoogie]

Are there additional switchable features in the 100 that the 50 doesn’t have?

Yes, there is a 2nd Master Volume that bumps up loudness for solos in the RM50 (which has the 3M3 resistor). I am trying to figure out if this somehow connected with the resistor. But it`s kind of difficult with the labeling of the connectors all over the schematics.

 

[glpg80]

Yes, there is a 2nd Master Volume that bumps up loudness for solos in the RM50 (which has the 3M3 resistor). I am trying to figure out if this somehow connected with the resistor. But it`s kind of difficult with the labeling of the connectors all over the schematics.

Your answer is yes. Otherwise you’ll get electrostatic popping.

 

[BesaMoogie]

I don't know what an RM50, etc. are. But if this is a typical tube gain stage, think about what would happen if this were simply a direct connection to ground. It would kill 100% of your signal, right? As you raise the resistance of this connection, it resists and prevents the signal from 100% going to ground. So the higher you make that resistance, the less signal gets dumped. It's a way to tailor the feel of the stage and how much gain you retain. But it also depends what the next stage looks like, as it can also interact with a gain control (which is usually found right after this point).

A capacitor to ground here would kill highs.

That was my first idea as well. Either getting rid of some highs or part of the singal in general

 

[BesaMoogie]

Your answer is yes. Otherwise you’ll get electrostatic popping.

Thanks for the help!