Mesa Express 5:25 question.

handsomerik

I'm really keen to get hold of one of these after trying one at the east anglian meet. Can someone tell me, are they quiet amps when just idleing? (just switched on but with the guitar volume rolled off) I play in church and if it has any hum that would continue after playing in the quiet environment that would be a deal breaker for me. Would the standby switch mute any of that normal transformer hum that amps seem to have (in varying degrees). I've never owned an amp with a standby switch!

Anyone selling one of these amps? I have funds waiting if so.

monquixote

Amps are usually silent on standby. 

ecc83

monquixote said:

Amps are usually silent on standby. 

Well, there is no such thing as an absolutely silent 50Hz mains transformer! The very nature of the periodic magnetization must cause some vibration. This is kept to virtually inaudible levels in high quality, "hi fi" equipment but few guitar amp traffs are in that class!

Nonetheless you can reasonably expect a guitar amp to be "silent" beyond a metre say, even in a very quiet church. Certainly the amp should be silent in standby but peversely, SOME transformers hum worse when under a lighter load!

Then you DO get the odd "buzzer"! These can often be fixed by tightening the bolts whilst hot. Some smaller amps use a "clamp" construction traff and often these can be fixed by a good squeeze in a big mother of a vice. 

Sometimes however you have a floating "lam" inside and all you can do is replace the component.

Dave.

stickyfiddle

Ive found mine extremely quiet at home, but it did buzz a bit when used with my pedalboard in a venue with LED parcans. The combination of a ground loop and RF from the lighting did it- ok in a pub but would've been annoying in church!!

jaygtr

Err can't help with the hum question, but I too was really impressed with the Mesa at the same meet.
And despite all the knobs it was pretty simple to set up.

It's on my list now too.

guitargeek62

Mine's got a fair bit of background noise, but the wiring in tis place is crap and all the amps I've had here have had it. Zilch on standby. Great amps though, you won't regret it (unless you can afford the Plus model, which i can only assume is better?).

JayGee

Mine's as quiet as what's plugged into it. Generally between sets I muted the guitar by switching on the tuner and assuming I didn't have a drive turned up to a silly level it would be pretty well silent.

It can actually be a bit of a liability around the house when you switch it on, bring up the volume on a guitar and *then* realise that you've left it set to gig volume :-)

jpfamps

There are two mechanisms that hum can be produced from a mains transformer.

1) Mechanical noise due to magnetostriction. Any loose laminates will make this effect worse. 

2) Stray magnetic flux from the mains transfomer inducing hum directly into the output transformer.

This second mechanism is a function of how much flux is escaping the mains transformer and the efficiency of coupling to the output transformer.

To reduce flux leakage from the mains transformer you need to run it more conservatively, ie you need a larger (and hence more expensive) transformer. As Dave points out you can get less hum after the standby switch is thrown as the current drawn by the HT pulls the mains transformer away from saturation and thus you get less stray flux to couple to the output transformer.

Coupling between the PT and OT is reduced by increasing the distance between the OT and PT, by optimizing their orientation for low hum, and by using a non-ferrous chassis (steel can conduct stray flux).