Please explain amplifier output impedance

Duke, No I don't and I don't have the means to measure it.

Some years ago when it was reviewed in 'phile JA commented that its output impedence 'rose' to 3.5 ohms in the bass region. I noticed this particularily because I had some electrostats which had a impedence droop to 3.5 ohms in the bass region. In use I 'think' they complimented each other as I had a very flat in room response (except for a 32hz room node induced rise of 6db) with the combo and no other major frequency abberations.

Facinating stuff.... :-)

Tvad,

If you accept solid state amplifier technology and you do not desire to tweak the sound and wish for a tight controlled bass and wish to simplify it to a damping factor then I would say 80 is adequate and perhaps an ideal number.... i.e. for an 8 ohm load the amp should have an output impedance of of around 0.1 ohms. There is very little to be gained with even lower impedance and probably not audible anyway unless the speaker impedance drops very low.

BTW: This discussion applies to equipment input impedance too.....ideally you want a high input impedance (nominally around 10K Ohm) on all equipment prior to your speakers or headphones. This reduces the effect of interconnects and coupling of equipment in your system to almost negligible levels.

Damping factor has less effect on a speaker than most might imagine. Keep in mind that any waveform will cause an amplifier to produce power (and incidently, it is *power* that drives all speakers- voltage cannot be produced in the absence of current and current cannot be produced in the absence of voltage...). That power will cause a voice coil (or other motive mechanism) to obtain a particular location with respect to rest. As the power level changes, the VC will follow it- in effect power driven to excursion and back again. Damping factor only plays a minor role.

What is really happening is that we are able to hear what negative feedback does to sound. Too much (more "damping") and the sound dries up, too little and with *some* speakers you loose flat frequency response.

In general tube amps have less feedback and many have none. This is not because it is not somehow available (this is the 21st century after all and we *do* have the technology). The problem is that feedack is a failed concept and many designers recognize that.

IOW having a 'constant voltage' output characteristic is a thought model and does not have a basis in the real world where our ears exist. As humans we are often looking for ways to place things in neat cubbyholes but Life itself does not care what we think- it exists in spite of our thought. Feedback and constant voltage are examples of cubbyholes that are thus not actually real.