anybody have or know of mods for marshall mark iii 2100?

[Nilo]

And btw. The NFB resistor is not R6. It's R17 on the poweramp board. You should however not tinker with this stuff if you do not know how to read a schematic and know the workings of a tube amp. You could end up turning your amp into a broken mess of shit... or worse, get yourself killed.

And as I said earlier, D1 has nothing to do with the clipping, it's BR1 and D2 in the preamp.

 

[ericsabbath]

I'd change all those plate resistors in the preamp to 220k, 100k//1n, 100k, in that order, bit more like most Jose-based hot rodded amps
And piggyback a 1uF cap on R6 (V2a cathode resistor) for that little extra push in the center mids and sustain
Apparently it already has a fixed depth in the negative feedback, but very subtle, so, in the power amp board I'd change R17 to 100k and C6 to 2.2n

if you really wanna change the marshall voicing into something more modern, you could swap C3 in the V1a cathode with a considerably greater value (let's say 10u up to 47u) and then swap C4 (first coupling cap) to a considerably lower value (1n should be fine)
this will deliver a more focused, modern and tighter sound and less british mids
more like a diezel or something
in the tonestack, I personally like raising the regular 33k resistor just a bit to a comfortable 39k, but you could try 47k or 56k for a mild midscoop
I'd also piggyback a 220p in parallel to C21

just remember the coupling caps and plate resistors must handle high voltages, so be sure you're getting components with proper rating

 

[donho]

And btw. The NFB resistor is not R6. It's R17 on the poweramp board. You should however not tinker with this stuff if you do not know how to read a schematic and know the workings of a tube amp. You could end up turning your amp into a broken mess of shit... or worse, get yourself killed.

And as I said earlier, D1 has nothing to do with the clipping, it's BR1 and D2 in the preamp.

you sure. it can be done in 2 ways.
no worries done lots of this. i can read. thanks anyways.
chilltone says differ. https://chilltone.wordpress.com/2013/10 ... odel-2100/

 

[donho]

I'd change all those plate resistors in the preamp to 220k, 100k//1n, 100k, in that order, bit more like most Jose-based hot rodded amps
And piggyback a 1uF cap on R6 (V2a cathode resistor) for that little extra push in the center mids and sustain
Apparently it already has a fixed depth in the negative feedback, but very subtle, so, in the power amp board I'd change R17 to 100k and C6 to 2.2n

if you really wanna change the marshall voicing into something more modern, you could swap C3 in the V1a cathode with a considerably greater value (let's say 10u up to 47u) and then swap C4 (first coupling cap) to a considerably lower value (1n should be fine)
this will deliver a more focused, modern and tighter sound and less british mids
more like a diezel or something
in the tonestack, I personally like raising the regular 33k resistor just a bit to a comfortable 39k, but you could try 47k or 56k for a mild midscoop
I'd also piggyback a 220p in parallel to C21

just remember the coupling caps and plate resistors must handle high voltages, so be sure you're getting components with proper rating

thanks
i think a bit more focused sound would be what i am looking for.
can i leave the plate resistors alone and just do the voicing mod and tonestack. R20 i think

 

[Nilo]

And btw. The NFB resistor is not R6. It's R17 on the poweramp board. You should however not tinker with this stuff if you do not know how to read a schematic and know the workings of a tube amp. You could end up turning your amp into a broken mess of shit... or worse, get yourself killed.

And as I said earlier, D1 has nothing to do with the clipping, it's BR1 and D2 in the preamp.

you sure. it can be done in 2 ways.
no worries done lots of this. i can read. thanks anyways.
chilltone says differ. https://chilltone.wordpress.com/2013/10 ... odel-2100/

Chilltone is wrong. I'm sure... EE and been doing this a long time. Remove BR1 and you'll take D2 out of the circuit as well. And no, it can not be done in two ways, removing D1 will not remove the diode clipping.

Of course you will have to revoice the amp a bit after Removing the clipping, but just look at a José schematic as someone said and you'll have a pretty good base to work with.

 

[donho]

And btw. The NFB resistor is not R6. It's R17 on the poweramp board. You should however not tinker with this stuff if you do not know how to read a schematic and know the workings of a tube amp. You could end up turning your amp into a broken mess of shit... or worse, get yourself killed.

And as I said earlier, D1 has nothing to do with the clipping, it's BR1 and D2 in the preamp.

you sure. it can be done in 2 ways.
no worries done lots of this. i can read. thanks anyways.
chilltone says differ. https://chilltone.wordpress.com/2013/10 ... odel-2100/

Chilltone is wrong. I'm sure... EE and been doing this a long time. Remove BR1 and you'll take D2 out of the circuit as well. And no, it can not be done in two ways, removing D1 will not remove the diode clipping.

Of course you will have to revoice the amp a bit after Removing the clipping, but just look at a José schematic as someone said and you'll have a pretty good base to work with.

sorry. i was talking about the neg fback. chilltone states 2 ways to do the nfb, but one way is easier. the easy way is to r6//1.8k. resistor
chilltone says this. doesnt mean he is rite though.

(2) make it louder: the NFB on the 2100’s, both MkIII and the SL-X is a lot more than other Marshalls: 27K/4.7K from the 4 ohm tap, compared to the dual reverbs and most other Marshalls which have 100K/4.7K from the 4 ohm tap. The 2100 ratio is 0.148 while the standard Marshall ratio is 0.045–almost 3x more NFB! That does contribute to the tight and almost hi-fi sound of the 2100’s stock, but at the cost of making them the quietest 100W amp you’ll find.

There are two ways to reduce the NFB–increase the series resistance or decrease the shunt resistance. Initially, I increased the series resistance, but that took removing the back panel components to access the underside of the power amp board and is a PITA. It then dawned on me that a paralleling resistor across the shunt will get you to the same spot. Parallel a 1.8K or 2.2K across the shunt resistor R6 to get a net resistance of about 1.3K or 1.5K there and you then get 27K/1.3K-1.5K and a voltage division of 0.045-0.053.

NOTE: THERE ARE TWO R6’S ON THE MKIII SCHEMATICS AND AMPs! There is one in the preamp below V1b’s cathode, which is adjacent to a 0.22uF cap on the preamp board, which is NOT the one you are looking for. The on eyou are looking for is the resistor at the bottom of the phase inverter. It is on the poweramp board in between the rear panel direct out jack and the impedance switch:

 

[Nilo]

Yes and no.

You will be able to affect the nfb with both resistors, but the 4.7k is in parallell with the pot and will alter the sweep of the pot for one. The fact that the actual NFB resistor is bypassed with a cap too boost the low end will also be affected. Just looking at the total series resistance won't cut it here.

I would recommend you to not be lazy here. If you wan't great results you can get it, but you have to work for it

You could also change your nfb by changing the tap on your output secondary. A 47k 4ohm combo would be almost equal to 100k 16ohm.

But I recommend that you try 100k 8ohm, and do it right, pop the pcb out and replace R17.
You could also try 100k 4ohm and removing the bypass cap.
I generally don't like bypassing the nfb-resistor though. I much prefer other ways to add tight bottom end.

 

[Nilo]

I would also say that the main reason for the amp being quiet is the diode clipping. Remove the rectifier bridge and you should have a lot of signal to drive the poweramp. Think about it for a second, why does it work? Because when your guitar signal (amplifier by two triodes already) exceeds the threshold voltage of the diode, your signal is dumped to ground. This makes it impossible for the signal to be any greater than the threshold voltage of the diode (or in this case diodes since they are multiple in series). If you remove this limiter you have no restrictions on how strong your signal can be as long as your tubes can put up with it.

If you look at the zeners on the input these work almost the same way. Although your signal most likely will not exceed the threshold voltage of 5.1v zener + 0.7v forward voltage drop of the opposite diode, this just giving you a limiting/compression effect. It does however screw with your dynamics and basically unables you to boost your front end for more gain, som I would remove them as well. If you use single coils and no boost you might want to keep them though.

 

[donho]

thanks nilo.
with the sens knob low the zd are basically inoperable. no?

if a guy removes br1. do i have to replace it with something else or just omit it

 

[Nilo]

No, the Zeners are always in line. Lowering the input to the amp (turning down your guitar volume) is the only thing that could make them inoperable. I see now though that they are 9.1v but it's just a bit more headroom. The same theories apply... Remove them, it's just a wierd thing to have there. I would remove the zeners and put R2 (1M) in their place, jumper R1 and replace C2 with a 39k resistor. There you have a classic plexi input.

Just omit BR1 and you will break the connection for D2 as well. You might want to put a gridstopper somewhere as well if you experience blocking distortion. And maybe play with the cathode values of V1B to get a nice mid push and keep things sounding nice and tight.

You can calculate the break off frequency by 1/2*pi*R*C

So the classical 2.7k//0.68uF is 1/(6.28*2700*0.68*10^-6)= approx. 87Hz.

 

[Nilo]

Here's a clip of a mod I did not too long ago. Just to show you I know how to get the most out of these boxes

https://youtu.be/D0ID76BoZwI

 

[donho]

Here's a clip of a mod I did not too long ago. Just to show you I know how to get the most out of these boxes

https://youtu.be/D0ID76BoZwI

sounds great bro.
thanks for your help.

i am really not looking for a plexi type tone on my 2100, but just to thickn it up a bit.
i am using active pups so snipping zd1 might be a good start. i was gonna snip the + side and see what it does. if i dont like i can reverse it.
this does not affect the sens knob does it?
also r20 seems like the one that would do the most to the tone.

 

[Nilo]

Just because it has a plexi input doesn't mean it'll sound like a plexi. The Suhr amps all have the same input, the fenders and a lot more. I was just trying to say it's the most classic input stage.

To thicken up the tone follow my directions so far and get back to me with what you want to change and i'll point you in the right direction.

You cant just snip the zeners and expect a great result, that's not a fair comparison. You have to change other components to compensate for the alterations in the circuit.

The sens knob is basically just a second gain knob as in the José style amps.