Does the LPB have negative feedback?

[Caferacernoc]

Just a quick beginner question. It seems obvious that a single transitor boost is class A and probably "single ended". But I can't tell, does a LPB type circuit have a negative feedback loop? If not, I gather that this type of circuit really brings out the difference in various transistor's sounds.
Thanks.

LPB link:  http://www.muzique.com/schem/lpb1.gif

[Sir H C]

Yes.  The 360 ohm resistor of the emitter is a form of negative feedback. 

[Caferacernoc]

The 360ohm resistor going to ground? How does it "loop" to give the feedback?
Thanks for the info.

[brett]

Hi
like you, I've been puzzled why the emitter resistor is considered the feedback resistor in a "common emitter" amplifier (and the base resistor and collector resistors are the feedback resistors in common base and common collector amplifiers, respectively.

In the common emitter amplifier the resistor affects the gain, so something is happening.  But what?  This is an explanation from a good source: 

Perhaps the simplest way to add negative feedback to a common-emitter amplifier is to add some resistance between the emitter terminal and ground, so that the input voltage becomes divided between the base-emitter PN junction and the voltage drop across the new resistance

The mental image that I have is that the input signal not only has to bridge the base-emitter junction (0.7 V) and its associated resistance, it has to "push" against some external resistance, too.  The bigger the resistor, the more effort (voltage) is expended in the resistor and the less is available in the transistor (for amplification).

You're right, there's no feedback loop - it's more like closing off the end of a free-flowing hose - pressure feeds back through the hose itself. This analogy is pretty bad, but I hope you get the concept.

There are 3 main benefits of using emitter resistors that I can think of just now: (i) the gain can be fixed to particular values, (ii) they increase the input resistance, and (iii) the gain is much less affected by temperature (the forward voltage drop of NP and PN junctions is quite temperature dependent, which can make gain drift around if there's no emitter resistor, as seen in Fuzzfaces).

The quote above is from http://www.allaboutcircuits.com/vol_6/chpt_5/12.html
cheers

[Sir H C]

The emitter can be an output (common collector configuration) or an input (common base).  So therefore that signal out causes changes to the bias conditions that make it act as an input.