Damping Factor >1000

[lumanauw]

MRFEEDBACK, I'm interested in your comments. Could you share with us the schematic you think as good one?

[mrfeedback]

You can start here-
http://users.ece.gatech.edu/~mleach/lowtim/ .
Pay close attention to power, layout and grounding.

Eric.

[Nexus]

Hello All,

I have a question about simulating the damping factor in spice.

Is the shortest route to do this put a sine wave current source in the output instead of the load, and place a 1k resitor on the input of the amplifier (no drive signal)?

Then choose 1A for the sine wave, and the measured voltage on the output is the output resistance?

Best regards:
Nexus.

[Steven]

I would say 'yes', Nexus.

Steven

[thoriated]

The issue I see with 'current drive' to speakers is that it's sonic effects may be effectively similar (not necessarily the same) as low damping factor. Plus, it may not give optimal results with speakers that were designed for use with low source impedance (high damping factor) amplifiers.

Another effect I think is of some importance wrt damping factor is that if the amp drives a multiway speaker with passive crossovers, a lower damping factor amp may allow more back emf from each driver to make it to the other (but so would higher impedance speaker cables unless biwired).

Probably damping factors over 200 at the speaker terminals become less important in the real world given practical speaker gauge wires and run lengths which will add series resistance, etc. to this.

I agree with one poster about the detrimental sonic effects of achieving high but nonconstant with frequency damping factors with large amounts of negative voltage feedback. However, my DC coupled OTL design achieves its high damping factor with only moderate negative voltage feedback (26db above 1hz) but uses positive current feedback to achieve damping factors over 500 to 10 khz (when trimmed out). One thing about positive current feedback is that when summed in the same loop as I do with the negative voltage feedback, it actually will reduce, if anything the total inverting feedback signal when it is boosting damping factor into any real world load.

[thoriated]

Erratum. I meant to post: "Probably damping factors over 200 at the Amplifier terminals... " above

[Ultima Thule]

Just noticed someone earlier asked how to find out the slew rate, I would like to suggest to use square wave at the input at a quite low frequency of 100 Hz for instance(, less risk to burn the amplifier).

Should be noticed that the input shunt capacitor forming a lowpass filter must first be removed before the test (at least one of the legg ;) since it doesnt have anything to do with the amplifier bandwith and decrease the slewrate at the input before the signal reach the first amplifier stage.

Connect an oscilloscope at the output and notice the speed of the rising or falling flanks.

Slewrate is often given in V/uS, a fair amplifier has at least 20V/uS I think.

I dont want to specify any type of standard how to check the slewrate but it could be good to check for both small signals let say 1 volt output and full swing.


When talking about the feedback and distortion the human ear is much more sensitive to TIMD than THD, even <0,1% THD for all frequencies and power levels is very good.