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Dying amplifier

SwamiRob

SwamiRob

Aug 23, 2007
2,151
33
Scarborough, N. Yorks, England
#1
My backup amp is gradually running out of clean power, beginning to give out the classic distortion at all volumes kinda effect but without being too bad for now.

So I was just wondering what exactly causes this effect? Obviously it happens when you demand more from an amp then it can deliver (although I never really push mine THAT much and it also has a limiter which tells me when to turn down a little and should be helping to even out those peaks anyway to some extent at least) but why the gradual decline in clean sound and power? What's deteriorating as opposed to flat out blowing that makes that god awful sound?
 
#3
Ah ok, I'll see later today whether that might be the case cos the bass player in my other bands gonna be using it with another cab, it doesn't seem to be very volume related however though.

Perhaps it's pre-amp related because it only seems to be when I play my bass hard that it does it. Only had this problem recently, and my bass is passive AND I haven't had a problem with other amps, tried it through the active input and no improvement either, so I could only guess that either the wiring or some component inbetween the jack and the gain stage is knackered perhaps if it's nothing to do with the poweramp or speakers.

Cheers for the help again though alex.
 
#7
Right, I ran the matching rig yesterday, and I was playing about with it a bit to see if I could figure it out. I could get a really clear sound with it when I set the gain at a pretty reasonble level even at pretty much the the peak of what the poweramp can take without the limiter kicking in. Conversely when I started to play hard (having turned the gain down) there was the same nasty muddy distortion kinda sound, tried turning my gain down to some stupidly low levels and it was still there so it seems like it might be a pre-amp issue. Another guy borrowed my entire rig yesterday too and he didn't sound too bad either when he wasn't playing too hard/low either.

The Jazz pickup on my ATK does sound a bit muddy when pushed for my liking, think I might end up getting a DiMarzio Super J or something instead when I can afford it, but certainly nothing to this extent, especially given that my balance is set about 2/3rds toward my humbucker which is one of the most open sounding pickups I've heard. My bass hasn't really been an issue since it got modded and had a few things fixed by a local guitar tech, and it's sounded great through other setups too, it's not a dying battery or anything either cos I've been running it passive for a good while now too.
 
#10
SwamiRob said:
My backup amp is gradually running out of clean power, beginning to give out the classic distortion at all volumes kinda effect but without being too bad for now.

So I was just wondering what exactly causes this effect? Obviously it happens when you demand more from an amp then it can deliver (although I never really push mine THAT much and it also has a limiter which tells me when to turn down a little and should be helping to even out those peaks anyway to some extent at least) but why the gradual decline in clean sound and power? What's deteriorating as opposed to flat out blowing that makes that god awful sound?
Click to expand...

If its a tube head, I'd suspect tired tubes in the final stage, if its solid state, probably a sign of transistors, again in the final stage about to go. It could also be a cap gradually straying from its specs.
 
#11
It's solid state, so at least it shouldn't be too expensive, cheers.

greenboy said:
Another thread only this far away (pinches thumb against finger) from receiving my "long distance amp tech diagnostics" hammer. With special emphasis, as always, on: "How long do you wish to be out of commission before doing what you should have done immediately?" ; }
Click to expand...

I was gonna take it in soon, but it's in my somewhat irritating and childish nature of needing to know absolutely everything about everything that I just wanted to know what the problem was likely to be. Not just for my amp really, but playing alot of gigs with punk bands you come across a recurring sound of amps that have been pushed to 11 on far too many occasions and was wondering what made them tail off like they do rather then die a quick dignified death :p
 
#15
BassmanPaul said:
After a long time as a bass player, one truth became obvious: if you look after your gear it will serve you well. If, on the other hand, you abuse it, it will fail you - usually at the most inconvenient time.

Take your amp in for some TLC, it needs it.

Paul
Click to expand...

Exactly right. And part of abusing an amp is pushing an amp or the speakers beyond what they're capable of doing. It seems your amp is capable of putting out 300 watts into the minimum recommended load. Don't know what cabinet you're using. But it does sound like you've been putting too much into your speakers and they're on the way out.
 
#16
Yeah I think on second thoughts after testing my Trace 15 yesterday that this is more of a speaker problem. Although there are a couple of scratchy pots that could do with cleaning, the preamp sounded as clean as ever and the poweramp never broke up in any way. Didn't get to push it cos I live in a terrace house and my walls are paper thin, plus the trace has a pretty thick low end too. Either way it seems like it's just the cab that's dying, which is a shame cos it was quite nice at lower levels, just obviously been lent out at too many punk gigs it would seem.

The amp itself is quite nice though, got quite a warm tone for a solid state head and got a nice midrange thing going on, just a pity it's not really loud enough for what I need. The sounds it was making with my other cab are kinda odd though, cos it seemed to very much depend on how hard I played as opposed to how loud I set my amp. Purely on ratings the speakers can take "240" watts and the amp can put out "300" as you say, but I don't think either - especially the cab which uses some horrifically cheap looking celestion drivers - are rated properly in all likelihood.
 
#17
SwamiRob said:
Yeah I think on second thoughts after testing my Trace 15 yesterday that this is more of a speaker problem. Although there are a couple of scratchy pots that could do with cleaning, the preamp sounded as clean as ever and the poweramp never broke up in any way. Didn't get to push it cos I live in a terrace house and my walls are paper thin, plus the trace has a pretty thick low end too. Either way it seems like it's just the cab that's dying, which is a shame cos it was quite nice at lower levels, just obviously been lent out at too many punk gigs it would seem.

The amp itself is quite nice though, got quite a warm tone for a solid state head and got a nice midrange thing going on, just a pity it's not really loud enough for what I need. The sounds it was making with my other cab are kinda odd though, cos it seemed to very much depend on how hard I played as opposed to how loud I set my amp. Purely on ratings the speakers can take "240" watts and the amp can put out "300" as you say, but I don't think either - especially the cab which uses some horrifically cheap looking celestion drivers - are rated properly in all likelihood.
Click to expand...

You're right about the speaker ratings. They never rate them using measurements that reflect real world bass playing. I always ignore the manufacturer's specs.

We don't see much Laney gear over here.
 
#18
SwamiRob said:
...it seemed to very much depend on how hard I played as opposed to how loud I set my amp.
Click to expand...

The volume control sets the required input the amp needs to provide full power; it doesn't limit the output.

For example, let's assume an amp with a volume control that goes from zero to 10, and that the volume control is completely linear.

With the control at 10, this example amp can produce full output with 0.3 volts of input signal. Set halfway---at 5---it now needs twice the input (0.6 volts) to produce full output.

So you set it at 5 and your normal playing produces 0.3 volts. The amp produces half output, since it now needs 0.6v for full output.

Now you start slamming the strings harder. Suddenly you're providing 0.6v of input level, and the amp puts out full power. Surprise...

Though you thought having the volume control "halfway" would help, that's not the case.

NOTE: Volume controls are almost always logarithmic: There's little change in the first third of the rotation, but the upper 2/3 really moves quickly. This only makes things more dangerous when you move from, say, 5 to 7 on the knob.
 
#19
I appreciate what your saying but I meant volume as in the output level actually coming out my speakers, if I turned down the volume (control) and played hard the tone sucked as much as, but with playing gentley with the volume up and the overall sound coming out the cab being louder too aswell, for some reason it managed to be clearer.
 

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