Distortion on bass of valve power amp

[Parrot of Doom]

I haven't used the amps for a few months, and today noticed an odd bit of distortion on the heartbeat intro of Dark Side of the Moon. Is this indicative that the amp for that channel might want biassing again? Its probably 2 years since I set them up. The bass seems weak on that side through the album.

The power amps are Velleman monoblocs, about 35W each IIRC.

http://www.velleman.be/fr/en/product/view/?id=3391...

[Talkwrench]

Could be biasing, yes.
An offset on the input of the output transformer will cause early saturation of the core and thus softer, distorted bass.

[Parrot of Doom]

It went away once they'd warmed up, so I'm putting it down to a bit of drift. I'll see how it goes, thanks for the response.

[Driller]

Parrot of Doom said:

I haven't used the amps for a few months, and today noticed an odd bit of distortion on the heartbeat intro of Dark Side of the Moon. Is this indicative that the amp for that channel might want biassing again? Its probably 2 years since I set them up. The bass seems weak on that side through the album.

The power amps are Velleman monoblocs, about 35W each IIRC.

http://www.velleman.be/fr/en/product/view/?id=3391...

Microphonics?

[Parrot of Doom]

Not really loud enough for that.