NP100 Upgrade Details



    
NP100 Details

To begin the upgrade, the MOSFETs are removed from the heatsinks and replaced with Motorola metal TO-3 bipolar output transistors, noted for their unsurpassed ruggedness and reliability. The amplifier's original circuit board is removed and a new motherboard is installed. The new motherboard uses two 6SN7 (low, or "normal" sensitivity version) or 6SL7 ("high" sensitivity version) octal-based tubes, which are reliable, easily found in many different brands, years, and sound qualities, and which offer consistently excellent performance in terms of musical involvement. All supplies for the tubes are regulated. The signal path is clean and direct (see the chart below for the reason why).

The new NP output stage is unique in that it is much easier to drive than other bipolar transistor output stages. It requires no feedback to linearize it. This allows the driving tube stage to be simpler, cleaner, and since it has no feedback it sounds livelier and more transparent. Reducing the number of coupling capacitors from three to one provides deeper, more accurate bass.

Hybrid Power Amp Topologies

The SA-12 and SA-100 needed a three-stage tube circuit to drive the MOSFET's, but the NP100 output stage needs only a single stage. Where two tubes and three coupling capacitors per channel were previously required, the new design needs only one tube and one capacitor per channel. Where the SA-12 and SA-100 used about 20dB of negative feedback to control the tube stage, the new design needs none. The result is more liquid, open and lively sound.

MOSFET Output Stage Traditional Bipolar Output Stage NP Output Stage

Distortion Low - no feedback required. High - requires negative feedback. Very low - no feedback required.

Ease of Driving Requires high drive current at high frequencies. Nonlinear: Requires high drive current at high current output. Very easy to drive, very linear.

Tube Stage Complex: 3 stages needed to drive MOSFETs Difficult to interface with tube stage Simple, one-stage design.

NFB Needed for Tube Stage Required Required Not needed

Finally, the internal power supply and speaker wiring is re-done using Sound Connection's Continuous Cast Copper (CCC) wire.

The finished product is biased and full-power tested to assure performance.

Click here to see the specs of the modified amplifier.

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The SA-12 and SA-100 needed a three-stage tube circuit to drive the MOSFET's, but the NP100 output stage needs only a single stage. Where two tubes and three coupling capacitors per channel were previously required, the new design needs only one tube and one capacitor per channel. Where the SA-12 and SA-100 used about 20dB of negative feedback to control the tube stage, the new design needs none. The result is more liquid, open and lively sound.
	MOSFET Output Stage	Traditional Bipolar Output Stage	NP Output Stage
Distortion	Low - no feedback required.	High - requires negative feedback.	Very low - no feedback required.
Ease of Driving	Requires high drive current at high frequencies.	Nonlinear: Requires high drive current at high current output.	Very easy to drive, very linear.
Tube Stage	Complex: 3 stages needed to drive MOSFETs	Difficult to interface with tube stage	Simple, one-stage design.
NFB Needed for Tube Stage	Required	Required	Not needed

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