Mk IV dropping treble?

[LesCarl]

Heya guys!

My first post in this VERY cool board Been frequently visiting here for the last year but i usually have my questions answered by just browsing the board.


Anyway, i have this problem where the treble of the amp just dies from time to time, the sound gets a bit closed i you know what i mean.. this happens some times almost (?) always when engaging the lead channel

I am not a genius when it comes to tube amps, i´ll be the first to admit that

I am also getting really tired of not getting that tight "ooomph" from my Mk IV, i used to have a triple Recto but ended up exchanging it for a koch powertone 2, and then to a Framus Cobra which i recently sold. Now i am thinking of getting a dual recto ONLY for having that "ooomph chuggah chuggah" you know :lol:

Anyway.. lots of text when i simultaneously introduce myself AND the problem of my Mk IV

Thx for any help guys 8)

(And btw, waving to CJG as i know you are a fellow Swede around here and you totally rule playing, anyone who ahsnt heard him play, find his myspace 8) )

 

[fpoon]

Post your settings/gear and we can try and help. If there is a drop in Treble or High Frequencies try raising the Treble to at least 7.5 or 8 or raise the Lead Presence and 6600 slider. The "ooomph" you are trying to get usually comes from the cabinet your are using. There was a huge change to my sound when I got my Recto Cab and the first thing I noticed was the increased bottom end. You can try pushing your presence to get the extra bottom end you are looking for. I strongly recommend you stay with the Mark IV and keep posting any questions you have about the amp. Once you get familiar with the amp you will be glad you didn't trade it for another amp because really all you need is the Mark IV.

 

[Bullen]

Sorry to hear about your troubles.

I was in the same situation a few years ago. I bought a used Mark IV head from Musikbörsen. Worked great when I tried it in the store, so I bought it. Got home, and just like yours it lost most of the treble and got very "woofy" (is that a word?) sounding. Turned it off and then on again and it sounded great for a few minutes and then it happened again.

To make a long story short, I returned it to the store after it had been checked out by at least 3 different techs at 5 different times. No one could find the problem. I even contacted Mesa and they thought it was tube related, but I had already changed all the tubes to new Mesa´s and then tried several different brands so I know it wasn´t the tubes that couded the problem. Perhaps it was the tube sockets or something, I don´t know.

A year or so later, there was a guy on this forum that lived in Umeå, I believe, that had the same problem. Turns out that he bought the same amp after me. He also got it checked by techs, but I don´t know if they ever found the problem.

So, just checking... is it a wide head, version A with one of the knobs (rhy 2 treble, I believe) replaced? If so, it´s the same "cursed" head that I had.

Hoppas någon kan hjälpa dig med problemet. Jag skulle vilja veta själv vad det kan vara för fel. Det var den bästa förstärkaren jag haft när den fungerade som den skulle (vilket inte hände så ofta eller särskilt länge). Jag blev jäkligt sur över att ingen kunde fixa den, men nu har jag beställt en ny Mark IVa, som borde komma vilken vecka som helst nu.

Ha det

Andreas

 

[LesCarl]

Ok.. What happens is the exact thing Bullen is describing.

It sounds normal at first and then it just looses the trebs, and becomes muddy (woofy). Turn it off, wait for a minute, turn it on, and it's back to normal again..


You know what Bullen, i can't see if a knob has been replaced since they are all the same.. but nothing is impossible.. kind of typical for "musikbörsen" to sell the same head to someone else after they had to take it back.


I am gonna try the LH-musik in Stockholm to see if they can figure it out.. if they cant.. i don't know what to do. I have had this amp for a year or so.

Anyway, my gear used with it is a Greco Les Paul, MIJ -82 with Seymore Duncan pickups (Jazz & PAF).

TC-Electronics G-Major in loop, tried both with and without this connected.

This in to a closed back 4x12 loaded with celestion v30s.. and since its actually changing during play i think we can rule out that its the rest of the equpiment cant we?

The same thing happens if i connect it to my Isolationbox with a single v30 in it.

Nice to see more swedes here Andreas btw And thx for the help!!

 

[fpoon]

No idea man, I thought maby you had the amp dialed in wrong but it's probably something else.

 

[Platypus]

This sounds like a thread for BB or RR

 

[LesCarl]

This sounds like a thread for BB or RR

BB? RR? :roll:

 

[Platypus]

This sounds like a thread for BB or RR

BB? RR? :roll:

Boogiebabies or Restless Rocks.. two forum members here.

They'll be able to help you I imagine

 

[Boogiebabies]

Um, well, hmm it could be LDR1 failing. Has the treble pot been changed?

 

[LesCarl]

Um, well, hmm it could be LDR1 failing. Has the treble pot been changed?

I don't know but i don't think so.. I have only owned this amp for a year, and I donät know the history behind it really.. So I don't know..

 

[Restless Rocks]

Let's see; could use a couple more specifics: does it stay the same in all three channels once the problem occurs or is it just on the lead channel. does it occur when there are no (zero) effects plugged into the FX loop? First I would try a good contact cleaner in the Output Volume pot and Check the FX loop jacks. Also clean all your pull switches and presence pots. While you're at it go ahead and clean ALL the pots and pull switches. Then report back if any of them have been replaced with non originals. Like BB says it could also be an LDR. That's why I'm curious if it happens on only one channel or all three. Let us know more specifics and of course you've tried different guitars, cords etc. to be sure it is an amp problem.

 

[Boogiebabies]

If LDR 4 and 5 are bleeding, both tone stacks may be engaging at the same time thus doubling the capacitance between 500pf to 2000 pf depending if the pull fat functions are engaged. When in the lead channel, try lowering your R1 settings and see if it has any effect on the tone, also see what it sounds like with all of your R1 setting at 0. If all the capcitance in your tone stack doubles, I would imagine that amp would be a flubby, woofy mess.

Just a thought.

 

[LesCarl]

Let's see; could use a couple more specifics: does it stay the same in all three channels once the problem occurs or is it just on the lead channel. does it occur when there are no (zero) effects plugged into the FX loop? First I would try a good contact cleaner in the Output Volume pot and Check the FX loop jacks. Also clean all your pull switches and presence pots. While you're at it go ahead and clean ALL the pots and pull switches. Then report back if any of them have been replaced with non originals. Like BB says it could also be an LDR. That's why I'm curious if it happens on only one channel or all three. Let us know more specifics and of course you've tried different guitars, cords etc. to be sure it is an amp problem.

Nah.. i have just noticed it in the lead ch.. Cleaning pots? I am afraid to even touch this amp..

 

[Restless Rocks]

Okay, first try BB's suggestion about rotating the R1 controls while in the lead mode to see if you hear anything happen. If not: when the problem kicks in try rotating the gain, drive and master pots of the lead channel. You might just hear some crackling noises and the problem could suddenly clear up: this would indicate a dirty or bad pot. If none of the above has any effect try: when the problem occurs, rotate the channel selector switch on the back of the amp and see if it clears up the problem, if so this would indicate a glitch in your switching matrix or posibly the rotary selector switch itself. And finnally if none of the above produce any results you may have to find a qualified tech to check for a much more complicated problem. If cleaning the control pots and switches is not your cup of tea then you have few other options.

 

[Antoine]

If LDR 4 and 5 are bleeding, both tone stacks may be engaging at the same time thus doubling the capacitance between 500pf to 2000 pf depending if the pull fat functions are engaged. When in the lead channel, try lowering your R1 settings and see if it has any effect on the tone, also see what it sounds like with all of your R1 setting at 0. If all the capcitance in your tone stack doubles, I would imagine that amp would be a flubby, woofy mess.

Just a thought.

Boogiebabies, i'm speechless :shock: ... i think i'm gonna call you The Doctor :wink: