Slewmaster - CFA vs. VFA "Rumble"

yes the are thimios I was checking cost, and this one is 5mm LS 7W and $0.64 cents part number 2-1623789-1 also 2-1623788-5 5W $0.57 cents 🙂
 

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What's with all these exotic packages ?

Wirewound or metal film 15 and 20mm LS 3-5W - available everywhere.
The standard wirewounds have a few hundred picohenries inductance.
They won't affect operation until a few Mhz.

Metal films are a bit better , but still have both inductance + C ,
less powerful.

Bifilar and Ayrton-perry military wirewounds are the best - both 15 and
20mm one go for 1.50 - 2.71 EACH !!
Lot's of choices in the standard axial resistors. Spend up to $27.10 on
just the Re (Vishay MRA series). Vishay - MRA - Wirewound Resistors, Non-Magnetic, Non-Inductive, Axial Lead .

"Fanatics" , for sure !

OS
 
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Latest Krell Amps appear to be CFA, and use a tracking "iBias circuit" to maintain ClassA operation. Rear cooling fans are present to support smaller, HT rack mount format. The pending patents appear to still be unpublished. I suspect that transistor array chips are used for tight tolerance multi-output current mirrors.
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Circuitry Highlights
The new iBias circuitry is built on a foundation of core Krell circuit technologies. All signal gain is realized in the current domain using proprietary multiple-output current mirrors with extraordinary open loop linearity. Each amplifier channel uses all discrete components. There are no generic integrated circuits or op amps used anywhere. Gain is distributed among several stages, allowing each to have a large linear operating area.

Audio signal voltages are converted to current at the amplifier input, and the audio signal remains in the current domain throughout the entire amplifier.

Current mirrors in the final gain stages use a new output power device that operates at a 73% higher voltage, delivers almost 10% more current, and offers 120 watts of additional power handling capability as compared to other devices.

With this combination, the iBias amplifiers may now deliver substantially more power while using a smaller footprint. Normally used in demanding, high-bandwidth video circuits, these transistors allow the design of gain stages with superb accuracy and very low distortion. The signal path is fully complementary and fully balanced from input to output. Independent complementary pre driver and driver stages for the positive and negative output transistors make the output stages extremely fast and linear. This unique circuit is impervious to low-impedance or reactive loads; it simply drives any loudspeaker with absolute confidence, achieving the very best possible sonic results.

Most amplifiers use coupling capacitors in the signal path to block DC and prevent damaging offset voltages from reaching your speakers. Krell amplifiers are fully direct-coupled, with no capacitors in the audio signal path. This design gives the Krell amplifiers lower internal impedance, which allows firmer, more precise control of your speakers. It also provides flatter, more extended low-frequency response, because coupling capacitors not only block DC but also affect the lowest bass frequencies. Krell employs expensive, non intrusive DC servos that remove DC without impacting the musical signal. Thus, the iBias Class A amplifiers deliver the full breadth of the music with detail, impact, and space intact.

Network connectivity brings convenience, monitoring, and reporting to end users from any smartphone, tablet, or laptop. Amplifier configuration options include display brightness and timeout. For energy conservation, the amplifiers can be programmed to power off at a preset time of inactivity. Individual channels can be muted and firmware updates can be initiated from the web server. Excessive current, output DC, fan speeds, short circuit, and overheating are all monitored in real time. Messages are displayed on the front panel and reported on the web server interface. Additionally. end users can be sent an email notifying them of any operational anomalies.