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I tried this out with the resistors you linked to across the primaries of the Heyboers, and it's a nice improvement. Cleaner, better separation of instruments and voices, smoother transients, tighter bass. The effect on the Williamsons is to make it seem like those scant 20 watts go a little further without feeling the strain. Great tip, thanks Walt![/quote]

That's been my experience exactly on different amplifiers. What I can't understand is why the manufacturers haven't done this. What I did was just apply basic electronics -- inductors have storage (hysteresis) and can interact with other components. I figured why not "clamp" the coils? This idea started in the '70s when I couldn't get my speakers to do what I wanted. Certain mechanical resonances (colorations) wouldn't go away. When I took a hard look at the crossovers and investigated the series LC and parallel LC networks then looked at the resonances of those reactive "tuned" circuits -- my brain light-bulb lit up. The resonances caused by the resonant behavior of the crossover components was causing the issues. With low impedance crossovers I paralleled each inductor and capacitor with typically 400-ohm power resistors. Either carbon composition or non-inductive wire-wounds work beautifully. Later in time I have applied that scheme to audio transformers as noted in this thread as well as digital pulse transformers (aka. galvanic isolation). The values used depend on the impedance of the circuit as you do not wish to corrupt the original intent of the design -- only get it under control.

Getting back to speakers for a moment -- after a dinner with David Wilson (Wilson Audio) around 1986, he first poo-pooed the idea even after discussing it at length over desert. Two weeks later he called and told me he decided to play with the idea and using a scope and signal generator confirmed through A/B comparisons that the clamping resistors got rid of ringing that had him frustrated. YAY!

Anyone that has visited here for a listen has heard what damping resistors can do to enable much improved playback. Working knowledge of electronics theory and some thinking "outside the box" (aka. the industry at large) one can create some cool DIY innovations.

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Walt

Walt is right on the money about damping energy in any circuit that has energy storing components like capacitors and inductors. With passive speaker crossovers the large values of C and H can cause lots of energy to float around inside. That is another advantage of getting rid of passives and using actives directly connected from the amps to the drivers. There are also other advantages along with some disadvantages. No one method is perfect. The best results are obtained by optimizing whatever method is used.

I want to followup with Walt’s suggestion of the damping resistor across the primary. I have similar Williamson amps w/Heyboer outputs as Grover, and just installed the resistors. I think it really has made an improvement, cleaner, more relaxed. I have to do more listening (I admit I have been using my 211 SET amps for the past week or so, so relying on aural memory…a dangerous thing to rely on). BTW, I bought the resistors on Amazon, and were delivered in two days.

David

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Walt

There are a couple of places that I would not apply damping resistors. (1) across primary from B+ to triode-loaded plate for a single-ended amp; (2) across a fully-loaded secondary such as one that has an 8-ohm tap being used to drive a speaker, and does not include a higher-impedance tap such as a 16-ohm tap. It could include a 4-ohm tap, as long as it is not a separate isolated winding; and (3) UL screen taps. But yes to plate connections in class AB pentode amps where the plates can go into cutoff. For P-P triode amps using low-impedance tubes like the 300B or 2A3 I would not use them since these tubes only cut off when the amp clips, even when using low-idle-current biasing. Remember that damping resistors do use power that otherwise would drive the speaker.

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Walt