Tube amp gets louder!?

chrisjac2

Hey!
I currently have a laney cub 10, which I bought because I was tired of lugging my big amp to and from rehearsal but am so pleased with it after replacement tubes and speakers its now my no1 amp. My issue is I have noticed it gets louder as the night goes on. I watch back some videos of our last gig and it appears to get about 15% louder by the end of the gig!

Is this just a tube thing? Never noticed it on the 30 watt peavey delta blues but it was never driven as hard as the laney.

Anyone have any tips on the best way to manage this?

RandallFlagg

I think they put a volume control on a lot of amps nowadays, it's a little off the wall but you could try using that and turning it down.

chrisjac2

RandallFlagg said:

I think they put a volume control on a lot of amps nowadays, it's a little off the wall but you could try using that and turning it down.

Yeah but the problem is the levels are fine at sound check then as the level goes up on stage its not that noticeable to me over the drums and vocal monitor but it throws the levels out at front of house. 

Winny_Pooh

Unusual, is the speaker brand new or anything like that? 

ecc83

Have you marked YOUR levels on guitar and amp? You get deafer as the night progresses and that causes "SPL creep"!

Dave.

ICBM

This is a real effect with a lot of valve amps. I’m not certain what the mechanism is other than that it’s heat-related.

It’s definitely physical and not just perception because you can hear it as an outside observer - or soundman. The guitar amp gets noticeably louder relative to the rest of the mix even though no settings have been changed.

bbill335

I've had it go both ways - amps get a bit louder and clearer by set 2, and other amps get mushier and less clear after a bit. The only correlation I can pin down between valve types and the results is that 6L6s - clearer, EL84 - mushier. If I'd had a bigger pool of examples over the years I might have better observations but that's what I've got!

octatonic

chrisjac2 said:

Hey!
I currently have a laney cub 10, which I bought because I was tired of lugging my big amp to and from rehearsal but am so pleased with it after replacement tubes and speakers its now my no1 amp. My issue is I have noticed it gets louder as the night goes on. I watch back some videos of our last gig and it appears to get about 15% louder by the end of the gig!

Is this just a tube thing? Never noticed it on the 30 watt peavey delta blues but it was never driven as hard as the laney.

Anyone have any tips on the best way to manage this?

Main thing is not let the rest of the band in on this being a thing.

chrisjac2

Winny_Pooh said:

Unusual, is the speaker brand new or anything like that? 

Yeah i guess that doesn't help. Had about 15hrs on it

chrisjac2

octatonic said:

Main thing is not let the rest of the band in on this being a thing.

  ill do my best

RiftAmps

ICBM said:

This is a real effect with a lot of valve amps. I’m not certain what the mechanism is other than that it’s heat-related.

It’s definitely physical and not just perception because you can hear it as an outside observer - or soundman. The guitar amp gets noticeably louder relative to the rest of the mix even though no settings have been changed.

It's a stumper, that's for sure.

The only 'common' fault condition with a progressive volume increase as a symptom is simple bias drift, but I can't imagine that all of these amplifiers suffer the same problem and of course, that does not apply to all OP stage architectures.

I'll have a think...

pintspiller

octatonic said:

Main thing is not let the rest of the band in on this being a thing.

As a gig goes on everything sounds like mush to me. Voices and guitars through PA, live drums and me on bass through Sound City. In an attempt to cure it, I usually just turn up. LOL

gringopig

.

p90fool

Your drummer is getting tired and hitting more lightly?

Joking aside, I noticed the same thing with one of my 50w Superleads. In fact it was a good test because I used to run a pair of them, both on 8, and the slightly quieter one overtook the other one in volume as the gig wore on.  

chrisjac2

Just had a chat with a local amp guy, Dave Smart in oxford. Has done great work on my guitars. He reckons it may be a bias issue but I will update you when he has had a chance to have a proper gander.

richardhomer

You could always join a band with the drummer in the other thread, who won’t play quietly....

ecc83

I no longer have access to the necessary equipment or space but this is something I would liked to have investigated.

If anyone else want to have a go the first step would be to obtain a decent Sound Level Meter. You want A and C scales and data logging to a PC would be very useful. I recently saw one such on 'Zon for around 40 quid. After that a monitor of the mains voltage is vital.

"Bias wander" is the only possible idea I can come up with. The problem is IME valves tend to improve in their grid current with age and heat and so bias current drops! The OPT, PT and voice coils will show an increase in resistance with time and that WASTES power!  I suppose it is possible that the increase in OPT and VC resistances become a better "match" to the anodes but I think that is stretching things a bit..and ALL amps are so "miss matched" when cold?

N.B. Match in " " because of course we don't!

Dave.

ICBM

I'm not sure it's actually that the power output increases - to me it sounds more like the *gain* increases (in the power section, rather than preamp), which does produce a volume increase if the amp is below full power. It could also be a narrowing of the frequency response, which increases both perceived volume (more mids) and possibly the actual volume since less power is being wasted on frequencies that can't be reproduced properly.

I'm fairly sure it isn't a speaker effect or anything to do with the mains voltage, since only valve guitar amps seem to do it, not the rest of the equipment which is on stage at the same time, and not solid-state guitar amps either - which they would if it was the speaker.

Legba

Valve amps especially, warm up/get hot... this can affect some components and alter the characteristics of the amp including the volume level.  Favorite is a failing resistor and or capacitor.  An amp tech would need to check voltages, soak test then check them again for any substantial change.

Modulus_Amps

Its a small box, heat rises and there is no air vent on the top side, I suspect the heating up is causing the power drift, run a small computer fan in the cab to see if it helps...