Frequency response vs. output power

[Nelson Pass]

Originally posted by gl
I don't recall having heard of an XA100.5 previously. What is the difference between it and the the XA100?

The XA100.5 is an updated product, with more output current.
Compare to its predecessor it has a wider, more lush midrange,
and better clarity and detail.

[gl]

Thank you. I will look forward to it's release.

Graeme

[GRollins]

Originally posted by Babowana



the rolloff is hapenning depending purely on the RC network

Unfortunately, this is one of those 'ain't no free lunch" things. Yes, the RC network (I'm assuming that you're referring to the feedback loop) rolls off the frequency response, but even in a circuit with no feedback at all, the frequency response will decrease at higher gain levels.
Plays havoc on my intentions to build wide bandwidth circuits.

Grey

[azira]

Originally posted by MikeW
How much does the frequency response change for one watt output to full rated output power on a Pass labs amp? All the reviews I read are for small signal frequency response. Is there a difference. Does anyone have some data?

Mike,
There is a concept in amplifiers called "Gain-Bandwidth product". Basically an amplifier typically has a constant value for the closed loop gain * bandwidth of the amplifier. In other words, for a given amplifier, your bandwidth changes porportionally to the gain you set (typically through NFB). In a normal amplifier, your gain will be fixed regardless of the input signal (and therefore the output signal).

So, the bandwidth, which is essentially your frequency response, should not change regardless of output power because the output power was adjusted simply by injecting a stronger input.

NPs response should validate this statement.

Typically NFB is used to adjust the closed loop gain (and therefore expand the bandwidth). Although emitter/source degeneration is typically not considered feedback, it does affect this as well. This is why, as a previous poster said, many opamps have open loop bandwidths of only 100Hz but when feedback is applied (ie, the closed loop gain is reduced), the bandwidth is extended.

Now, if you instead adjusted the output power by adjusting the through the feedback/degeneration or Rc/Rd's then you woudl be adjusting the bandwidth as well.

--
Danny

[Babowana]

Originally posted by GRollins


Unfortunately, this is one of those 'ain't no free lunch" things. Yes, the RC network (I'm assuming that you're referring to the feedback loop) rolls off the frequency response, but even in a circuit with no feedback at all, the frequency response will decrease at higher gain levels.
Plays havoc on my intentions to build wide bandwidth circuits.

Grey

I was referring to the original question.

I still believe that the different output power levels change neither R nor C values, which are forming internal RC networks and their critical frequency points.