geoff1200gs Posted July 19, 2019 Share Posted July 19, 2019 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 Quote Link to comment Share on other sites More sharing options...
Chienmortbb Posted July 23, 2019 Share Posted July 23, 2019 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? Quote Link to comment Share on other sites More sharing options...
geoff1200gs Posted July 23, 2019 Author Share Posted July 23, 2019 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 Quote Link to comment Share on other sites More sharing options...
b7l4s Posted July 24, 2019 Share Posted July 24, 2019 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. Quote Link to comment Share on other sites More sharing options...
geoff1200gs Posted July 25, 2019 Author Share Posted July 25, 2019 Cheers thanks for reply Quote Link to comment Share on other sites More sharing options...
Sparky Mark Posted July 25, 2019 Share Posted July 25, 2019 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? 1 Quote Link to comment Share on other sites More sharing options...
VTypeV4 Posted July 25, 2019 Share Posted July 25, 2019 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.. 1 Quote Link to comment Share on other sites More sharing options...
Deedee Posted July 26, 2019 Share Posted July 26, 2019 (edited) 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 1 1 Quote Link to comment Share on other sites More sharing options...
geoff1200gs Posted July 26, 2019 Author Share Posted July 26, 2019 Thanks for the info appreciatedg Quote Link to comment Share on other sites More sharing options...
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