ah 280-300 Smx

[geoff1200gs]

Hi just bought a AH280/300 Smx  amp but when compared to my GP7 130s and a previous AH400smx  that I sold 6 months ago DUH! 

The 280/300 has a slight hum when turned on with no volume as the other two were completely quiet . its not noticeable when playing as its very low noise,

had the top off to have a look and was told it had been serviced and is like new , no loose earths looks mint , do some have this? also when powering on it takes about 6 seconds to hear the hum as though its taking time to power up , Never noticed this on my others, Might be nothing , Any one interested in the GP7 the top one in picture,  I bought the amp GP7,4x10, 1x15 rig after I bought the Smx and to be perfectly honest it's a great sound and maybe might not have bothered with the Smx , it's  just not as versatile as the Smx more to fiddle with and more you do 

[Chienmortbb]

The delay will be due to the Dorset’s not being connected for a few seconds while the power supply settles down.

I am not familiar with the model but can you take some hi res pictures of the inside and paste them on here?

 

[geoff1200gs]

Sorry not got pics of internal was as clean as a bell inside and was told it had been serviced and s new valve fitted , some glue gun areas lead me to believe it had been looked at , cheers geoff

[b7l4s]

I've got a 250SMX and there is a constant low level hum when it's turned on - not enough to be a problem, but it's there... I am planning to get it serviced later this year and I'll mention it to the tech, but as long as it's doesn't get worse I won't bother spending a lot of money chasing it down if it isn't obvious what causes it. The amp is totally reliable otherwise.

[geoff1200gs]

Cheers thanks for reply 

[Sparky Mark]

As the design becomes more complex (dual band compression, valve pre, more presets, effects level,  etc) perhaps it is more susceptible to mains hum or other interference?

[VTypeV4]

I've never had a Trace hum although I tried a series 6 (GP12) once with a dodgy transformer that was physically humming - not through the speaker but the transformer itself. Not sure if that's the issue you have here but it might be worth checking - run the head with no speaker to confirm.. And yes, it's an SS power stage so it's fine with no load attached..

[Deedee]

I experienced this with one of mine once. Constant low-level hum, didn’t get any louder with volume and so obviously didn’t cause an issue at gigs/rehearsals. Still it used to get on my nerves.

I took it to a tech and it turned out to be the position of the transformer which is obviously secured with a bolt to the bottom of the casing. It must have turned slightly during its long life. After a bit of trial and error he rotated it slightly then tightened it back up and hey presto, the hum was gone.

Edited July 26, 2019 by Deedee

[geoff1200gs]

Thanks for the info appreciatedg