Does your amp get louder as the night goes on???

[Monsta-Tone]

My DC-5 (and the Heartbreaker I had before the DC) get much louder as the night goes on.
They also get more mushy!
Last night, by the end of a 4 hour practice with the band, my amp had no clarity at all. It just sounded like mud.

I am wondering if it is the design of the amps (with plate resistors for power tubes only being 1/2 watt and soldered onto the board) or power tubes.
Anybody else have this issue?

I've thought about increasing the resistors to 5 watt and raising them off the board.
I've also thought about installing a Mark IV fan that I have sitting around.

Power tubes in the DC are newer JJ's, with only about 40 hours of time on them.

The Heartbreaker did this, no matter what tubes I used (6V6, 6L6, and EL34's).

 

[thunda1216]

similar thing with my Heartbreaker. Not mushy, just gets louder after about two hours of use.

 

[MJ Slaughter]

I thought I've experienced this myself but concluded it may have been fewer people around at the end of the night. Second set I will turn up a little bit when it's packed. Never a problem with mushy though. Could it be that your ears are just fatigued? Sometimes alcohol can make an amp get louder too.

 

[screamingdaisy]

Not necessarily louder but my experience with Mesa is that they start off cold and harsh and get warmer and smoother as the amp heat up.

 

[Monsta-Tone]

I thought it was just me, but the bass player mentioned that the tone just disappeared after about 3-4 hours.
All note clarity was gone.
We don't play extremely loud. I start off with the amp at 11:00 and end up with the master at 9:00 after a few hours.
I also let the amp warm up (on Standby) for about an hour before practice.

I haven't used this amp in months, we haven't even practiced in months.
I remember it getting louder, but never noticed a loss in clarity before.

Can't be the transformers, they are Mercury and severely over sized.
Can't be the crowd, it was just band practice and nobody came.

Unfortunately I don't have any spare 6L6's (except an old tired set of Sovtek 5881's) to try out.
Might have to bite the bullet and order some =C= tubes soon!

I am going to change the resistors today and see if that helps for next week. I'll probably install a fan today as well.
Could be old, tired filter caps, but this is one of the last ones made.

 

[tonejam]

Take the word of someone who's been gigging for 43 years (and boy am I tired!!).

It's at least 90% psychological. You and the band start out fresh, your ears are fresh, you're keen to play. Everything sounds great.

Couple of hours later, fatigue, maybe a few drinks, and your hearing is affected. You make "minor" adjustments to your amp settings ("I'll just turn up a LITTLE...."). Also, you just PLAY harder.

I've used a lot of different amps over the years, and I always find the best tone I've had all night is in the first few sets.

 

[McBarry]

Tricky call.
Certainly for my Mark's they stay dead-on volume-wise all night, BUT if I get tone changes I suspect it's from within my head..
Over 4hrs show I usually have 2 or less beers and don't wear ear plugs.

I suggest U get a digital recorder. I love my Olympus LS-11 but our drummer loves his Zoom H2.. Set it up near the amp, and when U tweak ANYTHING, speak into it so next day you'll remember the changes when U listen back.

If U do hear objective proof of your suspicions, I reckon it's tech-time. Might need some protracted time on the operating table to elicit the fault.. and there's a zillion possibilities for the culprit(s)..
Good luck, keep us posted..
DB

 

[Jameson]

My DC-5 (and the Heartbreaker I had before the DC) get much louder as the night goes on.
They also get more mushy!

Louder at night? Check the voltage in your outlet - maybe it is lower than normal during the day and returns back to normal at night (when the total number of power-consuming devices becomes lower in the city)... Or maybe it's just a psychological factor (as mentioned above), or maybe your ears are just tired after a 4-hour practice

 

[Tuna141]

As others have said, I also think the mudiness you perceive is simply due to ear fatigue. I have tinitus and my ears get fatigued very quickly, despite my ear plugs. Two songs into each set everything starts to sound like mush.

 

[Monsta-Tone]

Thanks guys, but.........
The fatigue issue is probably not an issue. We don't play loud enough to even make my ears ring.
Our crappy 300 watt PA keeps us at small club volume, luckily.

The volume issue really exists. By the end of the night, if I don't turn down, you can't even hear the drums or the PA!

The mushiness is definitely present also. We record everything. The first few hours have great crunch and sustain. The last hour or so just sounds like sonic mud.


I was wondering if anybody else had experienced this particular issue.
Hate to spend hours trying to fix something......

 

[MJ Slaughter]

Sorry I can't help but I would like to know how or if you're able to resolve it.

 

[SonicProvocateur]

Mine is kinda the opposite. I have 5W resistors and it starts off cold and a little mushy and after warm up (when I push the amp to normal volume where it stays) it stays clear and sweet. Actually the gain comes off a little bit once it gets nice and really hot, but the volume never changes. Yours is bias modded right? If your bias is set ok and your caps aren't leaking maybe it's a bad ground on the tube sockets or the board. Maybe the control grid or cathode isn't grounded fully?

 

[topcat0399]

My guess also would be something electrical in nature, A component getting hot or something.

I too once thought this symptom was happening occasionally - thought I imagined it. After a total retube and overhaul by Mesa - I haven't notice anything like that any more.

keep us posted.

 

[McBarry]

Given U guys don't play loud, and your recordings back up what your intuition is telling you, it's time for a doctor visit.
I'd be guessing wildly to accurately point U in a direction without the amp in front of me, but who knows, BoogieBabies might have some good recommendations for you.

Let us know what it ends up being thugh - I'm intrigued now... DB

 

[dante]

YES, my amp does get louder.

I noticed it several times now - it's the entire amp, not just one channel. I typically use my clean channel and my Nova System for moderate gains. I only use the DC-5 gain for heavier stuff, so I honestly don't use it that much. When I do, it's short-lived (only a song or even a part of a song) but I have noticed my gain tone is fantastic at sound check. I will have to pay closer attention to how it sounds when the volume is back up to JET Engine levels.

The first time I noticed it, was immediately after a break, as we started the second set. I thought it just sounded louder because the drums hadn't kicked in yet...not the case, it was noticeably louder & I was using the clean channel. I don't know if that helps, but that's what I've been experiencing.

Monsta - Let me know if you figure anything out, this has been a head scratcher- I'm no techie (like yourself)

 

[MJ Slaughter]

All this talk has me thinking about taking a db meter and checking before and after each set for the next couple of gigs.

 

[sduck]

All other things being equal, there's no reason that most amps should make any discernable change in volume after about the first 10-20 minutes. Take out the first part of that sentence, and the second part goes all to whack however.

The biggest factor is going to be your ears, and sorry, but I don't trust them. Nothing personal, I'm a pro musician, and I don't trust my own ears either. You're going to need a professional grade db meter in a fixed position relative to the amp, and a fixed signal input to the amp (not just strumming your guitar - too variable). That's just to find out if there's actually a change in volume over the course of several hours. Don't trust your judgement about relative volume to the other musicians, etc - that's just too variable. I think if you actually did this kind of test, perhaps in the privacy of your home or garage, you'd be surprised at how little change there actually is.

Possible causes outside of your ears could be - change in AC line - quite often the amount of current available goes up in the evening as people use less for air conditioning or whatever. Depending on how you're running your amp this could have a large effect. Very small changes in the way one tube is working can be amplified many times by the other tubes if it's early in the gain stage. Another possibility is old and/or flaky tubes - often we end up liking and using ones that are perhaps marginal engineering-wise - perhaps that magic sounding preamp tube is kind of hyper sensitive to small current changes, especially if it's been running a bit hot for an hour or 4. Another possible culprit in this vein is the fixed bias - while it's a selling point, and most likely a good idea, many amp techs frown on this design because you can easily run tubes too hot or cold, which will exacerbate this sort of thing.

 

[Monsta-Tone]

Thanks sduck,

It wasn't my ears. When you (and the rest of the band) can no longer hear the PA or the drummer because the amp is overbearing, there is an obvious issue.

I called Mesa today.
I talked to a guy in Customer Service who said he had a DC-3 years ago that did this same thing. Turned out it was the LDR's.
I just couldn't believe it would be the LDR's since mine is a B version and has a much beefier power supply for channel switching than the A versions did.

I looked at the drawings and decided that there was no way an LDR (with the exception of the one for the graphic EQ) could cause this issue.
I called back and asked another guy.
The techs said they have never heard of this. I said, "I know, that's why I am calling."
They suggested that the power tubes were failing and causing the bias to drift. This is pretty much what I was thinking, so I checked it out when I got home this evening.

After checking the bias supply (just a tad high), in fact all voltages are almost perfect in the amp......almost.
The power supply for the LDR's and Relays is a tad high. It is supposed to be +15 vdc. It is actually around +16.5 or so. Not too far off, but you never know.
I looked closely at all of the components in the power supply. There are 2 270 ohm resistors that were burned. They still read 269 ohms, but I am willing to bet that they drift way out of spec when they are hot.
I didn't have any 270's, so I put some together and made some 280 ohm resistors. This brought the voltage down to +15.8 or so.

I'll try it out on Saturday and report back.
I'm wondering if the filter caps for the supply are drifting or if it is simply due to the fact that the resistors in question were only 1/4 watt.
If I still have the issue, I'll replace the entire power supply.
LDR's and 4N33's are all new, so there's not much else in the circuit.

 

[Rob Lockwood]

Regards the bias supply and voltages, the voltages may be spot on when the amp is running cool but I would think you would need to check again after it has got loud to be able to see if thet are drifting. It might not be practical/safe thing to do. If you have a bias probe you could play the amp with it installed and take occasional current readings.

I am not sure how a drifting bias supply itself would cause the amp to get louder. If I understand correctly the bias voltage just sets the dc current level and wouldn't affect the ac signal level on the grid at all, unless the bias with the amp running cool is so low that the signal is getting clipped which seems unlikely. An increasing plate voltage could probably do it though, although not sure what could cause that to happen. If so the idle current would go up as the amp got hotter/louder. I think that plate resistors could also affect power amp gain if they drift - again would affect the idle current too.

I suppose its possible that the problem is in the preamp either or the phase inverter either - I dont know whether 12AX7s gain can drift but the preamp could be the the cause - the master volume actually controls the output of the preamp, not the the power amp.

 

[Rob Lockwood]

Regards the bias supply and voltages, the voltages may be spot on when the amp is running cool but I would think you would need to check again after it has got loud to be able to see if thet are drifting. It might not be practical/safe thing to do. If you have a bias probe you could play the amp with it installed and take occasional current readings.

I am not sure how a drifting bias supply itself would cause the amp to get louder. If I understand correctly the bias voltage just sets the dc current level and wouldn't affect the ac signal level on the grid at all, unless the bias with the amp running cool is so low that the signal is getting clipped which seems unlikely. An increasing plate voltage could probably do it though, although not sure what could cause that to happen. If so the idle current would go up as the amp got hotter/louder. I think that plate resistors could also affect power amp gain if they drift - again would affect the idle current too.

I suppose its possible that the problem is in the preamp either or the phase inverter either - I dont know whether 12AX7s gain can drift but the preamp could be the the cause - the master volume actually controls the output of the preamp, not the the power amp.