Amp suddenly sound bright / muddy

Travisthedog

Gigging the supersonic last week I found myself really struggling with washy brightness that I just couldn't dial out.

I was in a venue we've played a million times and using my board which is set up as it always is.

I just couldn't get it sounding like its normal thumping self.

Valves ?
Pedal fault?

Richardj

Does it sound odd back at home in it's usual place?  At the venue did you have it sitting on anything different to how you normally set it up?

Sounds a bit too simple but I have found that what either of my amps is sitting on radically alters the tone.  Otherwise I might have a look at the preamp valves, sorry.

ICBM

Valve(s) probably.

How loud were you playing? Was there any loss of volume or more distortion than you would normally expect at that volume?

If you weren't playing all that loud so you might not really notice a major loss of power, have a look at the power valves and check both are glowing normally - both the orange filament glow and if possible the faint blue glow (easiest to spot as you switch from standby to fully on, if it's not very obvious).

Travisthedog

Volume? Hmmm

I was thinking "flippin 'Eck" I've got this up higher than normal. I'll go check what the volumes on as I haven't touched it since last gig.

As for placement it's nearly always on a quick lock stand which leads me to another possible source of the problem - at the show before this last one, I put it on the stand and it the stand just collapsed and the amp went crashing backwards to the floor

Ouch

Travisthedog

Been to the garage - the amp is on 3.5 which for me is loud

ICBM

Travisthedog said:

Volume? Hmmm

I was thinking "flippin 'Eck" I've got this up higher than normal. I'll go check what the volumes on as I haven't touched it since last gig.

As for placement it's nearly always on a quick lock stand which leads me to another possible source of the problem - at the show before this last one, I put it on the stand and it the stand just collapsed and the amp went crashing backwards to the floor

Ouch

That's one of the reasons why I don't like amp stands…

That could have done anything from damaged a valve to cracking a circuit joint.

Travisthedog said:

Been to the garage - the amp is on 3.5 which for me is loud

At low volume (below about a quarter of maximum output power, which may not correspond to a quarter on the volume knob), you barely notice the loss of one power valve because the amp is working in the 'pseudo-Class A' range where both are conducting the full waveform - you might notice a loss of bottom end or a harsher top-end since the impedance matching will be off, but probably not much. It will also be slightly quieter so you might need to turn the volume up a bit more to get it loud enough.

At higher levels than that where the remaining valve is cut off for part of the cycle, you'll hear the asymetric waveform and it will sound oddly distorted and weak.

Definitely check that both power valves are glowing properly - they're the most fragile part of the amp and the most likely to have been damaged.

Travisthedog

Thanks mate - cracking advice as ever

bertie

Ive had these symptoms,  and it indeed was a failing power valve

Travisthedog

@icbm

The power valves "look" ok. Both lit, both flash blue when going from standby to on.

However when switching off again there's a hell if a crack and the amp does seem very noisy on standby

ICBM

Sounds like it needs a trip to a tech .

Unlikely to be valves at this point.

Travisthedog

Arse

ICBM

Have a look at the phase inverter valve as well - outside chance, but if one half of it has stopped working it will do the same thing. It's unlikely physical damage would do that though, since if it's cracked it would stop both halves working.