Please help with my Mark IV

[fatbagg]

Hey errbody, having a 6 month issue...

My Mark IV is sounding bad...very bad. Let me start by saying I am an experienced Mark IV and Mesa user, it is not setting related. 15+ years with Mesa, including Mark IIc+ through the Jp2c. I have kept the mark IV through all of it. I took the amp to an authorized Mesa repair shop. Had it fixed, the guy said basically nothing was wrong. Got it back, still sounded terrible, fizzy, lifeless, no bass, harsh, distorting way to fast on the clean channel. So...I send it to Mesa. I just got it back, they said it had no problems but they replaced a few caps that were on the verge of going bad. Got it back, sounds the same. They said my tubes were fine, so I take their word for it. Amp still sounds very fizzy and harsh, no smooth fat lead tones that I’ve always had. I cannot figure it out.
What would a bad speaker do to this combo? I’ve already spent over $500 repairing this amp and it is the same. Any ideas? I’m on the verge of buying a different mark IV because this has been 6 months of frustration. I’m at the point of begging, please help.

 

[Rider1260]

Interesting if the amp USED to sound good or great then to me it seems like tubes, I know that they said the tubes were fine but its such and easy thing to check and a set of tubes is way cheaper than a new amp.
also try plugging into and extension cab to remove the speaker from the equation

 

[fatbagg]

I have an entire set up tubes coming, pre and power. I read the speaker (8ohm) with a meter and it’s reading fine, 9.2.

 

[Wyzard]

Sounds like it's heading towards a 11 or 12 ohm (?) you've got in there; not that that's necessarily a bad thing in a MkIV, just so long as the speaker's healthy

But a static reading on resistance should fall under the rated figure by a fair margin, and I'd expect an 8ohm speaker to read high 6s or low 7s if it was healthy. Checking with another speaker sounds like a good idea right now, given your concerns.

Incidentally, I use a Thiele under mine, and a lot of the time the combo speaker isn't used at all.

 

[fatbagg]

Does that reading indicate a potential speaker issue? Is there another way to test? I’ll try to find another speaker to try for the time being.

 

[Wyzard]

Go ahead and do it - what Rider1260 said above - get the speaker out of the equation, by subbing in another (preferably similar) speaker. First in another cab, then in the combo itself. What is the speaker - an EV? Did I miss this? What else do you use with the amp? More info about your signal chain might be helpful.

The speaker seems the likeliest candidate in this case, but who knows... you'll just have to go through the process of elimination, one thing at a time.

 

[fatbagg]

Guitar straight to amp. Loop has Strymon Big Sky and Flashback delay. The problems persists with loop disengaged and unplugged as well. Guitar is fine on other amps.
I DID use the Jp2c with it, and it sounded terrible. I didn’t suspect the speaker until I got the IV back.

 

[Wyzard]

I DID use the Jp2c with it, and it sounded terrible. I didn’t suspect the speaker until I got the IV back.

Sorry, having a hard time following you here - when you say you used "the JP2C with it", which "it" are you referring to, and how was it "used" instead of the MkIV's own amp? Maybe I'm just missing the obvious, in which case I apologise.

 

[fatbagg]

I used the Jp2c head into the speaker, my Mark IV head was already gone.

 

[fatbagg]

I’m unsure what it was supposed to sound like (Jp2c) but it surely didn’t sound anything like my iic+, it was very Vish.

 

[fatbagg]

I also noticed the lead channel sounds very different when I have the amp on lead channel with selector switch versus going into the foot switch lead.

 

[Wyzard]

Ah, I was confused when you wrote "What would a bad speaker do to this combo?", thinking it was a combo we were looking at fixing.

I think you have at least two, maybe three problems - a duff speaker, and a faulty relay on the lead channel switching. Maybe more...

I dug this old thread on Gearpage out: it's somewhat similar, and probably worth a read in any case:

https://www.thegearpage.net/board/index.php?threads/mesa-boogie-mark-iv-lead-channel-problem.907384/

How's the speaker substitution going?