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That 6BX7 twin triode is a sleeper. It's in my 300B amp as a CF driver.

[quote="tomp"][quote="SoundMods"]Walt,

(a well designed amplifier with high damping factor will not encourage ringing. A poorly designed amp with excessive negative feedback that has poor gain/bandwidth product can not only ring but can try to correct a problem after it is over. Very bad.)

And yet -- with the exception of Magnepans the trick renders unexpected benefits especially in the midrange.

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Walt

Can you clarify the benefits in the midrange? Thanks.

I will followup with more later today, but just to provide some discussion of the possible with a GM70 SE Class A2 design, attached is a loadline with a 10K transformer at 1050VDC on the plate for a GM70 driven into Class A2. The driver has to swing +/-150 V. Do not have grid current curves for a GM70, but expect it would probably need something like 20mA or so (maybe interpolate between 211 and 845 values in Class A2

David

Can you clarify the benefits in the midrange? Thanks.[/quote]

Along with the unexpected bass improvement (tighter with better detail) the midrange opens up like if a masking curtain has been lifted.

This gimmick has been recommended to others to give it a try and their experience duplicated mine.

I came to this realization when I had to protect the receiver used in my home theater system that warned against exceeding 6-ohms. Since my "ancient" Watkins dual-drive Infinities can reach down below 4-ohms impedance I added a 150-watt rated 3-ohm resistor to the mix. It's only video playback so I expected compromise. What I got for my trouble was much improved overall playback quality with tight bass with reach down to 26-Hz. (measured). The speakers by design could dig down in the weeds but not like that.

I have been using a passive equalizer with my Altecs to offset the speakers natural roll-off. Keeping in mind that it is based on a 10-ohm resistor in series. Hell -- it was worth a shot. The end result was that of unexpected pure genius on Altec's part that not only did the equalizer work as advertised A/B comparisons revealed much improved overall playback quality. The midrange opened up like magic as well as improved treble and overall clarity. WTF?! You heard the result yourself. That's with my Cary's.

But I have had this equalizer in service when I used a Threshold SS amp. I never took it out of service except to improve on parts quality.

I find it interesting that industry brags about high damping factor (low source impedance) and yet a manufacturer of high-end kit now incorporates that feature in their product. I am trying to recall who that was.

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Walt

Very interesting. I can understand the low pass filter changing the balance toward the bass but I I don't understand how the midrange was affected. Thanks for the info.

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Walt

FYI,

I Google searched information concerning this device, and appears to improve bass response with small speakers (8" woofers) by depressing the midrange/treble above 150Hz, i.e., a shelf network, with full bass effect at 60 Hz. This means you could turn up the overall system level to improve bass response without boosting mids/treble performance. It was intended for small, efficient loudspeakers, such as those built into consoles. It has an insertion loss of 6dB for 16 ohm speakers, and 10dB for 8 ohm speakers. Basically a passive implementation of a "Fletcher-Munson" curve, particularly useful for low level listening.

You can find the white paper at the following location:

https://manuals.plus/m/06a4837e3a826889 ... 6b6f2c29a5

Not sure if it provides any real advantage over an active equalizer, either analog or digital. Noting that the room response tends to dominate apparent bass.

David

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Walt

Thanks, David, for the explanation. It makes sense now.