Boulder's Jeff Nelson makes sense!

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mikeks

mikeks

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#1
From here:

When I inquired about negative feedback, I hit a brick wall—or a boulder. Here's what Jeff allowed: "A hallmark of Boulder designs is the proper use of feedback. Decades ago, feedback got a bad name because designers were asking the circuit to do something it couldn't do, and the amplifier's cry of 'I can't do it!' resulted in horrible distortions. Other designers who didn't know how to solve the problem simply tried to remove the feedback, which resulted in a compromised sound. The Boulder 500AE showed the audiophile community, perhaps for the first time, that proper use of feedback results in an improved sound. Using feedback, the gain of the output stage can be reduced and its bandwidth increased. The resulting design has lower distortion than any single-stage design."

As in all Boulder products, the amplification stages use nothing but bipolar transistors. Jeff: "Bipolars are inherently more reliable and aren't prone to static-related damage. More important, the circuit topologies required for FETs are awkward, with high levels of pre-distortion required to drive the outputs. I haven't yet seen one that I liked."

Low distortion is Rule #1 at Boulder. Jeff: "We must compare two similar phenomena—musical overtones and electronic harmonics. Overtones are the notes added to a fundamental that give it a recognizable character, making an oboe sound different from a violin, for example. And these overtones follow a certain numerical sequence. Harmonics are also notes, but electronically added to a fundamental frequency. These harmonics will follow the same numerical sequence as do the overtones. An amplifier adding these harmonics can, upon first listening, be deemed musically pleasing. For a fundamental note of C, the second harmonic is the C an octave above it; and the third harmonic is the G above that. These added 'notes' are on pitch for 90% of all music, so the deception is complete. That's how triodephiles get away with it!

"The sound of electronically added notes is like putting a sugar coating on everything you eat. You lose the different tastes. The individuality of recordings is coated over, and the maximum musical enjoyment is reduced. It's simply 'too many notes.' To our way of thinking, electronic harmonics are still distortion, and we work hard to design them out. We don't tweak for the best sound, but for the elimination of distortion, which we feel is the best sound."
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:nod:
 
#5
Until I conquer the all digital signal and amplification path, I’ve been including active crossovers inside my power amps which use the Nelson Pass discrete opamp with a matched JFET input pair. This has shifted my power amp designs to almost exclusively bipolar, even on the input stage where I have always used symmetrical JFET differential pairs. I have “heard” good results with a MOSFET in the VAS stage on test boards, but the 100% bipolar design measures better in distortion and slew rate. The new generation of ring emitter bipolar power transistors sound great and are very robust, which allows for non-intrusive protection circuits.

I hope some of the Krell Clone folks do a comparison between the original transistors and some big Sankens like the 2SC3264 + 2SA1295. There is a BIG difference.
 
#6
LineSource said:
Until I conquer the all digital signal and amplification path, I’ve been including active crossovers inside my power amps which use the Nelson Pass discrete opamp with a matched JFET input pair. This has shifted my power amp designs to almost exclusively bipolar, even on the input stage where I have always used symmetrical JFET differential pairs. I have “heard” good results with a MOSFET in the VAS stage on test boards, but the 100% bipolar design measures better in distortion and slew rate. The new generation of ring emitter bipolar power transistors sound great and are very robust, which allows for non-intrusive protection circuits.

I hope some of the Krell Clone folks do a comparison between the original transistors and some big Sankens like the 2SC3264 + 2SA1295. There is a BIG difference.
Click to expand...
Who can report more informations concerning the audible results between this different kind of power BjT's?
In the meantime Onsemi offers both kind of transistors - ones with 3-5MHz Ft and ones with more than ten times higher values - go to
http://www.diyaudio.com/forums/soli...istor-families-audio-power-output-stages.html
for getting a little overview.

BTW - schematic wanted about currently and legacy models from
http://www.boulderamp.com/800-Series.html
http://www.boulderamp.com/News.html
Who can upload some examples?
 
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