Cable "burning": Real or VooDoo ???

Stevenj, I cannot tell if your post is in jest, or you are sincere. If you are suggesting that lowering and raising the damping factor with a switch is a joke, I can assure you that it is not.

Controlling an amplifiers damping factor is not novel. The Wolcott Presence amplifiers have had this feature for two years. The user has easy access to a toggle switch for both high and low position, and a rotary knob that adjusts within each range. Adjustment of these controls provides performance changes that are not only easy to hear, but at the discretion of the listener.

The man who invented this product is an engineer who values specifications, but is also aware that the reproduction of music is an art as well. If it is of any interest to you, the switch changes the positive control feedback voltage internally, without affecting the load to the output transformer.

albert, i have a suspicion that stevemj's post *was*, in fact, in jest. ironic, that, as you show, it's actually what smart designers *do*. seems to me they know something *isn't* "technically perfect", as stevemj purports, if it in fact cannot accurately portray *the real event* of live music.

regards, doug s.

doug - I wasn't jesting. I was just musing. I'm not up to date on amplifier designs. So, it is interesting to hear that some of what I mentioned has been tried. There was an amplifier some time ago called "Ampzilla". It sounded different. The trick that amp's designer had used was to set the damping factor to one. Typically, this will increase the low end. With the advent of cheap powerful processors there maybe a lot of interesting possibilities. The processor looking at the music and dynamically fiddling with the an amplifiers characteristics. I'm gonna think about this a little.

Steve, funny you should bring up Jim Bongeorno's GAS Ampzilla. The reason that amp developed such a cult following in 1976/77, was because of just that reason (not because of the apes in the ads). It was highly listenable and had some very judicious tradeoffs that juggled between transient detail and a rounded loose and whompy bottom. Sounds like that Damping factor of 1 to me. Trying very hard for the tube sound again. Terrible amp for running electrostats even though it did handle low impedance loads very well. Why was that the case? dont know.
One thing I can say though, is that the ingrediants for good amp sound have remained the same for years.
1) Little use of negative feedback
2) Stiff Power Supply that can supply the current required to make the amp a TRUE voltage source regardless of load. The importance of the Supply can't be stressed enough. Its a fact that no amp can is gonna be better than the stuff travelling down the supply rails. I am not an EE, just what I have observed over time that has proved consistently true.......Frank

frap - I enjoyed hearing your take on the Ampzilla. I'm not a EE either but I have had the luxury of working with several. Here are a few things I've learned that relate to power supplies, voltage sources and damping factors. You may already be familiar with this.

It is a high damping factor that makes an amp a true voltage source. Damping factor is the measurement of change in output voltage as load impedance varies. In the case of the Ampzilla as the speaker impedance climbed from say 8 ohms to possibly 30 ohms at resonance (closed box), the output voltage of the amp increased. You got to have more bass without feeling guilty about using the tone controls :-) Naturally there is a price to be paid, two actually. One, the speaker impedance doesn't always change in a favorable way. This is probably why the electrostats sounded bad. The amp is changing the frequency response based upon speaker impedance. No one will argue that even tiny changes in frequency response are not easily detected. Second, when a dynamic driver overshoots or rings (as they all do) they generate a correction signal that acts like a shock absorber to dampen the overshoot. If an amp has a low damping factor much of this signal is lost. This may be the whoopyness you refer to. If you want to fool around and see what your amp would sound like with a lower damping factor, hook you speakers up with 24 or 27 gauge wire. Even that may not get the DF as low as the Ampzilla.

As I understand it, in SS amps stiff power supplies are a benefit to the designer but not to the listener. Suppose you want to get all the power you can from your output transistors. In that case you design a rock solid (expensive) power supply that parks the power supply voltage near the maximum voltage the output transistors can handle. As transistors got better it became possible to have a higher voltage spongy (less expensive) power supply. It would sag and deliver the rated power of the amp and under music conditions operate at higer voltages and deliver greater power to the speakers than a stiff supply of the same RMS rating. I'm not sure but it may be that this technique doesn't work so well with tubes. I think the tubes are biased to operate at a particular voltage and to have the power supply bouncing around one or two hundred volts could screw up the amps performance.