Bias on solid state?


My amp has just been serviced - an MF NuVista M3 integrated - and among other things the tech said that he biased the amp. I've heard of biasing tube amps, but this is a solid state amp section with tubes only in the pre. I have heard references to bias on SS A/AB amps, of which this is one.

Can anyone explain what all this means? I'm clueless on it.
grimace
Bias is a DC Voltage that is placed on the "input element" of the amplifying device. (For Tubes, this is the Grid, for Transistors, it is the Base)

This allows the tube/transistors to amplify an AC signal without destroying the waveform. Basically, without bias, the tube/transistor becomes a diode, and rectifies the signal - you don't want to do that.

Let's say the AC signal is a line-level input of maximum 2V AC. This means that 2V of electricity flowing in both directions. Bias turns the AC into Varying DC, so the tube won't badly distort the signal.

Bottom line: Bias sets the tube/transistor up so it can amplify a signal without chopping it up badly.

On Tubes, there needs to be a way to adjust the bias, as a new set may need slightly different bias for even the same model tubes. Transistor bias is usually fixed.
also, the Nuvistor is actually a tube, not a transistor.
Right, but to the best of my knowledge, the Nevistors are only in the pre section of the integrated, not the output power amp section.

Should the adjustment have any practical effect on sound?
right you are Grimace . . . I neglected to engage my brain before that post.

As for your question - there may be more authoritative responders, but it does affect sound, and also determines class of operation. For example, by B&K M200s are biased to deliver 10 watts in Class A. The bias can be set to deliver more or less class A power.
Well, I not sure what helped what BUT the pots were cleaned out, the power caps were replaced, and the amp was biased and the results are not subtle. The amp is MUCH quieter and the highs are noticibly smother and more detailed. I have not idea how much of this has to do with the bias, but it sounds terrific. In the end, I guess thats all that matters.
07-15-10: Grimace
Right, but to the best of my knowledge, the Nevistors are only in the pre section of the integrated, not the output power amp section.

Should the adjustment have any practical effect on sound?

you usually do not bias the preamp tubes (I cannot think of one tube preamp that gives the end-user the option of tweaking the tube bias. Someone do correct me if I am wrong). It is the power tubes in a tube power amplifier that have their bias adjusted by the end user. The reason that this is done is because bias on a (power) vacuum tube or a solid-state device is the key to the amplifier's sonics. No bias, no sonics & plenty of distortion.
Bias is key & each amp has it's sweet spot based on the designer's intentions. The MF Nuvista is no different.
Good to read that your amp sounds really nice after maintenance.
If your tech can teach you & if you are willing to learn, you should find out exactly how your amp is biased & which test-point you should measure (with a voltmeter) to ascertain the bias. Bias of an amplifier can drift over several months hence it might be a good idea to simply do a bias check every 6 months & ensure that the bias is where you'd like it to be or where the manuf suggests it be.