What Do You Hear When Your Amp Needs Biasing?


Hi, Everybody,

I was listening to my rig the other day and noticed that some (but not all) closely miked recordings of female singers (Diana Krall on some of the cuts on "When I Look in Your Eyes" comes to mind) sounded a bit edgy or harsh. I checked the bias on my Manley Mahi amplifiers and found that some of the values on the multimeter, which should have been at 250, were as low as 240. I made the bias adjustments and, lo and behold, the vocal tracks sounded better. So I'm wondering what, in general, is a tipoff that a to be of a fire needs to be biased?

Thanks!
rebbi
I find it hard to believe you could hear the difference between a setting of 240 and 250. Actually with a slightly lower bias setting the vocals could sound a little smoother unless it was only one tube here and there that was low. In that case you could have one or more low biased tubes in a push pull pair that is low which would cause a rise in distortion which would explain hearing edgy or harsh close miked female vocals.
On my Ayon Spirit II I audibly hear certain piano transients as having a ringing to them. Also, harshness in clarinet, some vibes transients, and some sibilance in female voices. What rectifies this situation is biasing to ensure that all 4 tubes are at the ideal setting, and moreover, that they are set identical to one another. When the adjustment is done, these distortions/harshness issues go (almost completely) away --- being reduced drastically.
Your amp need bias if it is sounding too neutral and uncolored. I recommend playing Rush's show to increase the bias on the right channel but since Keith is off the air I don't know what to use on the left channel.
More often than not I'll think I hear something off, check the bias and it's still dead on. There was one time however that a certain piano concerto I'm very familiar with sounded a bit zingy, so checked the bias and one of the power tubes was way off.

Most of the time though I think it's pretty hard to hear the small wanderings that are common.