Amplifier Damping Factor - Dynamic Testing

after seeing many comments on various Amplifiers 'sounding' different when driving the same Loads, I'm thinking of how to assess if this could be a result of differences in the Dynamic Damping Factors of different Amplifiers.

To explain, the normal method of measuring an Amplifier's output impedance is to compare 2 different resistive load load values and measure the difference in output voltage of the Amplifier to calculate it's value.
As such this then is a 'steady state' measurement as there is no effective inclusion of any effects which occur with real Dynamic loads.

I've able been over many years to observe effects on the test bench when finalizing Power Amplifier designs, of both capacitive and inductive elements connected in series or parallel with the test resistive loads which is a Dynamic effect.

So a question follows from this as to how best to measure or compare designs Dynamically in a way that can provide at least comparative, if not quantitative results for Dynamic Damping Factors.

Previously for comparative results; I've used squarewave test signals and by careful summing of the input and output signals from an amplifier to subtract the input signal from the output and thus leave any error residuals.

A good example of this is the overshoot when a capacitor is parallel connected with the resistive load and similar 'ringing' or 'early' protection action with a suitable inductor in series.
Relatively easy then to compare on a 'scope as circuit alterations are made.....

However to gain an insight between different Amplifiers, a 'standardised' test rig capable of repeatable results would be required - so what are Member's views/ideas on this as it will need to be simple to create so that as many as possible test houses etc could use it?

hope this makes some sense - it's getting late!
Mik   

Edited by audiomik - 03 August 2010 at 1:24am

The problem is buried in the traditional definition.

1. "Damping factor" defines how the amplifier output voltage drops due to the output impedance for various loads.

2. "Dynamic damping" means how the amplifier is able to handle reverse energy flow, when the speaker's voice coil turns to generator from motor operation and works against the amplifier output.

Since most of the amplifiers are specified with resistive loads there are not really standards for this type of dynamic testing out there...

However probably this is one of the most important behaviour which makes big differences between various amplifiers in listening tests.

True. There are amps and AMPS. Just like watts and real WATTS. There is no test for this. It is basically the bullsh-t one person con conjour into words. Like 3000W car amps!

kedwardsleisure wrote: In my business Damping Factor is how much beer the amp takes before it blows up

ditto.............

Muckerbarnes1 wrote: True. There are amps and AMPS. Just like watts and real WATTS. There is no test for this. It is basically the bullsh-t one person con conjour into words. Like 3000W car amps!   I do agree with Mik. A good standard test rig should be used.

Wasn't this discussed at length in the Amp Meet 2 thread (?) in terms of standardised power measurement methods into purely resistive loads?
Mik

you may be surprised to know that the vast majority of the Amplifier channels I built in the late '70's were for R&D use for driving between 40 and 500Hz into 3 phase motors. A 3 channel frame with a 1200VA power supply, providing up to 110V 3 phase output - and not transformer coupled!

Now back to the simulated 'real' load to measure/compare Amplifiers.... anything, such as 'fuzz', would appear as residuals after subtracting the input signal from the output so would thus become included in the measurements.

Measurement of the Amplifier output Current will provide an indication of the actual ability of an Amplifier to properly sink back EMF; so it might be as simple as using a single inductor of known values in series with a Resistor at a specific test frequency and drive voltage, to achieve repeatable results?
I think however that an 'equivalent' circuit will be a better option..... and is of course much quieter than a speaker in a box!
Mik

Edited by audiomik - 03 August 2010 at 8:15pm