Mark IIB Tonestack

[MK IIB]

Hi Guys.
I'm wondering if the tone stack on my IIb is behaving as it should?
I have to have the treble up full to have just a moderate/normal amount of treble.
It's a non EQ model.
Also I don't like using the presence control as it's a bit too harsh sounding for me but if I have it at 0 it sounds like there is a blanket over the amp so I have to have it on(around 2-3) but it makes the lead channel sound really bright.
The clean channel does sound nice but I'm having to turn treble up full to get any kind of definition/clarity and I feel there should be a bit more top end?
Typically does the tone stack on a 2B have a good sweep or is the amp voiced a certain way with the controls not affecting the tone so much?
I'm curious to know if my tone controls are working/responding properly on the frequencies that they should and how I can determine this?
All tone controls do respond but don't have a lot of tonal sweep.
There doesn't seem to be a lot of range on the controls and from what I've read etc these amps can be "difficult to dial in" with a very minor turn of a knob affecting/changing the tone.Well this isn't the case here at all.
I have an SOB where I can have my treble around 5-6 and have plenty top end but with the 2B I have to have it up around 10.
The tone controls on the SOB are way more effective.
I would have thought with the treble up full it would be really trebly/bright but it isn't at all.If I have the treble at around 7 it sounds dull.
Speaker is the MS-12 by the way.
Hard to diagnose via the internet I know but apart from tubes what could cause these problems (if infact there is a problem)

 

[Boogiebabies]

Please check that the treble caps are 250pf for the first cap and 750pf for pull shift mode. A good IIB should have plenty of spank.

 

[MK IIB]

Hi BB.
Are you able to tell from this pic what the value of the caps are?
If not I'll take the chassis out and take some new photos.
That's a good way to describe it.The amp is definitely lacking some "spank"
There's something not quite right with the sound/feel of this amp.It's been recapped with Mesa BMI caps too.The cathode bypass caps were not replaced though.Do these need to be replaced too and could they cause said problem?
Thank you.

 

[BlackBoxy]

just change those oxydised ceramics caps with something like polysterene caps

and the spank will get back

 

[MK IIB]

Are these caps you're saying to change original/stock or have they been changed at some point?
Here's a couple of clearer pics!

 

[lovetoboogie]

Hi...

The tone stack caps look fine...those ceramics are not oxidized. That is silicon that Boogie puts on when they are built to help quell any microphonics that are inherant with ceramic disc capcitors...

With that said...make sure you are checking the tone stack with the "Pull Boost" feature off. On a IIB I believe it is on the Master Volume control. make sure that is pushed in. Standard Mark Series tone setting to get a nice clarity on the top end. Bass:2, Mid:5, Treble 6-8...

If the tone controls, particularly the treble seem unresponsive, you should start checking the pots, and the way the seat properly on the control panel. I have come across this before. Even though Boogie really cranks those potentiometers down on the panel, if they don't have a good clean contact with the ground you can lose some tone control. There is no ground bus on the pots so they ground through the chassis....

Have you tried a different guitar? Are you plugged in direct to the amp without going through any pedals?

 

[MK IIB]

Hi...

The tone stack caps look fine...those ceramics are not oxidized. That is silicon that Boogie puts on when they are built to help quell any microphonics that are inherant with ceramic disc capcitors...

With that said...make sure you are checking the tone stack with the "Pull Boost" feature off. On a IIB I believe it is on the Master Volume control. make sure that is pushed in. Standard Mark Series tone setting to get a nice clarity on the top end. Bass:2, Mid:5, Treble 6-8...

If the tone controls, particularly the treble seem unresponsive, you should start checking the pots, and the way the seat properly on the control panel. I have come across this before. Even though Boogie really cranks those potentiometers down on the panel, if they don't have a good clean contact with the ground you can lose some tone control. There is no ground bus on the pots so they ground through the chassis....

Have you tried a different guitar? Are you plugged in direct to the amp without going through any pedals?

Hi thanks for your reply.
I was wondering what was meant by oxidized?
Yeah the "Gain Boost" is off.
I'm using both my strat and Les Paul straight in to the amp.I can get more clarity by having the presence on around 3-4 but still the treble has to be at least at 8-9-10.If it's at 6-7 it's dull and also really affects the amount of gain on the lead channel.
I've got my bass at 2 and mids at 4.
Is it normal for the amp to sound dull with presence at 0 and treble at 9-10?Ie does the presence control have to be on?It's just the lead channel sounds smoother to me with it off but it just won't work on the clean channel?
I'm having to have volume 1 around 6-7 with the pull bright on to have a reasonable amount of sparkle?

 

[stokes]

I would check for a bad ground contact as lovetoboogie pointed out.I would actually take off the nut,pull the pot off and check the lockwasher and contact point on the chassis and pot for corrosion.Do the same on the mid and bass control as well.Also get some contact cleaner spray and clean the pots.Those caps are fine,unless they are the wrong value,as Ed suggested,leave them be.I dont know what he's talking about "oxidized".Those caps rarely fail,unless they get burned,not possible in that part of the circuit,no appreciable current.I suggest you listen to Ed (boogiebabies) if he replies again,he knows these amps better than everybody,even Mesa.If the ground check doesnt fix it,post back and wait for Ed,maybe drop him a pm.
You should set the pressence a little higher,setting it at 0 will make it dull.

 

[MK IIB]

Thanks a lot for the advice guys.Much appreciated.

 

[BlackBoxy]

as the new pics show, it seems they aren't rust at all!

next step, get a look at treble pot, and solders!

good luck

 

[stokes]

Ceramic doesnt rust

 

[BlackBoxy]

Ceramic doesnt rust

leads does , and sometime brain haha :lol:

 

[stokes]

Ceramic doesnt rust

leads does , and sometime brain haha :lol:

You would know,froggy

 

[Henz]

Old post. But with my C+, the mid and bass hardly noticable. Only thing treble pot does in my amp is just increases signal.