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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
lostbears's avatar
lostbears
538 posts
 

You really don't want to wait until you can hear an audible difference. The bias can also drift upward beyond tube tolerances and if left unchecked, lead to a tube failure. It is best to check the tube bias often and make any adjustment that is necessary. If you start to hear an audible difference you are not checking the bias often enough. Think of a tube amp as a fine sports car. You want to keep the engine finely tuned and running well. You don't want to wait until it starts running ragged before you consider having it serviced.
rrog
1,958 posts
 
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.
robsker
132 posts
 
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.
stanwal's avatar
stanwal
3,147 posts
 
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.
samhar
1,048 posts
 
+1 Stan
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