It's not quite hifi but...

[icehockeyboy]

Start of night at a gig, amplifier behaves impeccably, later on, at the same volume level, the clip lights start coming on.

Any suggestions as to why that happens?

[DSJR]

Just a guess, but check bias/dc offset voltages, as these may drift over time and temperature - Gordin J King once tested a Quad 405mk1 when launched and found the power output dropped from a nominal 100W down to 32W at clipping as the case went from warm to too hot to touch

[cloth-ears]

I think you’ll find that that review by King was in error and in a later review he corrected his mistake. At the time he believed that the 405 would act as a standard Class A/B amplifier and as such was expecting the same results. The 405 is a Class C (no biasing and very low DC offset) amplifier with current dumping. It was designed to be almost indestructible and at the point of clipping current limiters kick in and reduce the output as a matter of design. Although under certain circumstances the 405 can get very hot indeed these temperatures are still well within the SOA (Safe Operating Area) of the individual components within.

Just saying, thats all

[Box13]

I think you are pushing it too hard, try a little less volume; say 10 instead of 11.

[Barry]

I think you are pushing it too hard, try a little less volume; say 10 instead of 11.

'Spinal Tap' have a lot to answer for !

[Box13]

'Spinal Tap' have a lot to answer for !

Barry you are the first person to understand my somewhat dry sense of humour.
Thank you for that.

[icehockeyboy]

Thanks for the opinions guys, but truth is I ain't pushing it at all.

I'm a scaredy cat when I see a red clip light and immediately back off the volume, so my question stands

[DSJR]

I think you’ll find that that review by King was in error and in a later review he corrected his mistake. At the time he believed that the 405 would act as a standard Class A/B amplifier and as such was expecting the same results. The 405 is a Class C (no biasing and very low DC offset) amplifier with current dumping. It was designed to be almost indestructible and at the point of clipping current limiters kick in and reduce the output as a matter of design. Although under certain circumstances the 405 can get very hot indeed these temperatures are still well within the SOA (Safe Operating Area) of the individual components within.

Just saying, thats all

Glad you did and thank you I always preferred the 405-2 after a few hours left on, but the poor thing didn't like high levels into ATC 20's and got very hot indeed - sweet sound though when it got there... The replacement AVI mono's ran barely warm after such thrashing.

Funny how time changes things, as I play barely above a very modest volume a lot of the time now and the gear I have currently retains clarity at such levels thank goodness.

Craig - I don't know the amp, but Anthony here (amongst others I'm sure), would be able to check it over and re-set it up as necessary.

[cloth-ears]

Glad you did and thank you I always preferred the 405-2 after a few hours left on, but the poor thing didn't like high levels into ATC 20's and got very hot indeed - sweet sound though when it got there... The replacement AVI mono's ran barely warm after such thrashing.

You are most welcome

[Macca]

Could be the speaker crossover is faulty. as it warms up it is drawing more power from the amp?

Obviously I'm guessing wildly here.