Some more Sensor cord Drive: Sigma Drive

 

Sigma Drive by Kenwood

The Kenwood has also developed " Sigma Drive " which requires 4 wires for 1 channel.

Audio engineers has traditionally tended to regard the amplifier and speakers as separate entities in the hi-fi chain, linked only in the sense that the amplifier is supposed to drive the speaker. 

Recent research has shown, however, that the amplifier-speaker relationship is much tighter than is conventionally revealed by normal, static performance specifications. 

In fact, amplifier performance can be radically affected by the behavior of the speakers when high-energy transients in the music signal are being reproduced. Such dynamic considerations are the basis for the new Kenwood technology whose various facets are collectively called the Sigma Drive system.

Sigma Drive is a method of including speaker behavior within the scope of amplifier performance. It is not simply an improved speaker cord or a better performance specification, but a system that includes many interlocking elements. 

Now, Damping Factor is not just a vague nominal specification measured at the amplifier output, but a true indication of the amplifier's ability to control the speaker. 

The Kenwood amplifier Dynamic Damping Factor is actually measured at the speaker input terminals. 

The merits of the Sigma Drive system can be summarized as follows:

• Amplifier capability is optimized. 

• The speaker connecting cord is included in the amplifier negative feedback loop.

• Complete control of speaker counter-electro-motive force (back-emf) is achieved.

• The speaker is forced to reproduce music signals from the amplifier exactly.

• Constant-voltage drive is obtained.

Comparison

Other manufacturers have developed other types of circuits but almost exclusively, attention has been directed to amplifier output impedance and ways of reducing it. What are the characteristics of these other amplifiers?

1. RO Control (Yamaha B-4 & A-9, etc.) Fig. 20-1

Impedance between the amplifier and the speakeV is cancelled by sensing and feeding back the cur- rent through the speaker to the amplifier. This ultimately changes the impedance in the amplifier to a negative value.

Advantages:

— It obviates the need for a sensor cord. 

Disadvantages:

— The connection of the speaker cord requires a

small control which is practically impossible to supply. (No actual impedance can be detected).

— The added circuit incorporated in the NFB loop actually produces some impedance or even a further distortion.

2. Clean Drive (Aurex) Fig. 20-2

This is a stage of development beyond the RO Control which is intended to eliminate the need for the small control by making use of the speaker cord for this purpose.

Advantages:

— Any speaker cord can be used to cancel the impedance.

Disadvantages:

— As with the RO Control, the incorporation of an extra circuit in the NFB loop creates new distortion.

3. Remote Sensing NFB (Fidelix) Fig. 20-3

This is a BTL combination of two amplifiers, each of which is provided with an NFB circuit on the end of the speaker cord which is connected into the NFB loop.

Advantages:

— Unlike the other two designs, it is free from extraneous circuits and therefore from the distortion they might produce.

Disadvantages:

— The BTL connection produces serious distortion during Class B amplification which cannot be improved by using Class A amplification.

— The speaker has a floating ground and cannot be connected to the switch case or selector unit in the audio showroom.