
barefoot
barefootsound.com
Wow!
I just did a quick search and found that Threshold has resurfaced as a pro amplifier manufacturer. They used to be a very hi-end/hi-fi company. For a mere $7000 here's something to drool over. http://www.threshold-audio.com/Stasis7.html
Cool Lesson in No Compromise Amplifier Design
Warning: The following is very geek/techy.
Threshold uses a completely brute force method of amplification. Bipolar transistors have an optimal collector current (Iopt ) where noise and distortion are minimum. They also have a current gain versus collector current curve. This means the gain versus input level is not flat over the working range of the transistor. What Threshold does is run a whole bunch of high current output transistors in parallel class-A with the idle current in each equal to Iopt . In the case of this amp it's 16 output transistors.
A 100W amp delivers a maximum current of 5A (Ispkr ) into an 8 Ohm speaker at full output. Each of the 16 transistors shares the current (Ishare ) equally.
Ishare = Ispkr /16 = 5A/16 = 0.3125A
If you make Ishare small compared to Iopt (about one 10th) then each transistor stays very close to its optimal current regardless of the current delivered to the speaker. The speaker drive current is only a small perturbation of the idle current. And since the output current of each transistor changes very little, the input current gain versus collector current curve is essentially flat over the small range it covers. This results in very linear gain from the lowest level signals to the highest.
Iopt ± Ishare = Iopt (approximately)
So each transistor idles at
Iopt = 10*Ishare = 3.125A
And the total idle current of each cannel of the amp is
Itotal = 16*Iopt = 50A
50 Amps! From 40V supplies this translates to 2000 Watts!
A 100W stereo amp built on this design principle would dissipate 4000W just sitting there!
I doubt Threshold has gone to such extremes in this pro amp design, but in the past they actually have built amps like I've described. The $7000 price tag of this new model is relatively cheap compared to their old stuff.
barefoot
I just did a quick search and found that Threshold has resurfaced as a pro amplifier manufacturer. They used to be a very hi-end/hi-fi company. For a mere $7000 here's something to drool over. http://www.threshold-audio.com/Stasis7.html
Cool Lesson in No Compromise Amplifier Design
Warning: The following is very geek/techy.
Threshold uses a completely brute force method of amplification. Bipolar transistors have an optimal collector current (Iopt ) where noise and distortion are minimum. They also have a current gain versus collector current curve. This means the gain versus input level is not flat over the working range of the transistor. What Threshold does is run a whole bunch of high current output transistors in parallel class-A with the idle current in each equal to Iopt . In the case of this amp it's 16 output transistors.
A 100W amp delivers a maximum current of 5A (Ispkr ) into an 8 Ohm speaker at full output. Each of the 16 transistors shares the current (Ishare ) equally.
Ishare = Ispkr /16 = 5A/16 = 0.3125A
If you make Ishare small compared to Iopt (about one 10th) then each transistor stays very close to its optimal current regardless of the current delivered to the speaker. The speaker drive current is only a small perturbation of the idle current. And since the output current of each transistor changes very little, the input current gain versus collector current curve is essentially flat over the small range it covers. This results in very linear gain from the lowest level signals to the highest.
Iopt ± Ishare = Iopt (approximately)
So each transistor idles at
Iopt = 10*Ishare = 3.125A
And the total idle current of each cannel of the amp is
Itotal = 16*Iopt = 50A
50 Amps! From 40V supplies this translates to 2000 Watts!
A 100W stereo amp built on this design principle would dissipate 4000W just sitting there!
I doubt Threshold has gone to such extremes in this pro amp design, but in the past they actually have built amps like I've described. The $7000 price tag of this new model is relatively cheap compared to their old stuff.
barefoot
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