PowerDAC-SX and Speakers

The PowerDAC-SX can drive most speakers, it is not necessary to choose sensitive speakers.

It is basically a high power multibit DAC that drives the speaker directly using just a large number of power MOSFET switches and a power resistor array.

Because of this fundamentally different (almost all digital) setup we get some new properties that are not possible to obtain using conventional (digital) amplifiers:

– Quasi constant power steering is more compatible with electromagnetic drivers. Cone movement is determined by the number of turns on the voice coil and the current running through the voice coil.

– No local nor global feedback loops that could get disrupted (distortion) by the ac voltage generated by the driver.

As the voice coil resonates within a strong magnetic field it will generate an AC voltage similar to a dynamo or generator. Most conventional amplifiers get disrupted (feedback loop out of control) by this unwanted AC voltage injection into the amplifier output stage. One side effect is excessive cone movement during bass reproduction. Needless to say that this also creates distortion across the complete audio spectrum, the louder the speaker plays, the more AC it generates the more the sound colours or distorts. This is no longer the case with the PowerDAC-SX so this alone offers exceptional clarity regardless of how loud the speaker plays.

As an experiment we bought affordable Teufel Optima 40 speakers (approx. EUR 400 / set). These functioned fine with the PowerDAC-SX, but as expected from the price there is still room for improvement. Most conventional speakers have a number of flaws that are ignored for whatever reason:

– Chokes are usually located close together in order to have a cheap and compact crossover. This causes unwanted magnetic coupling (crosstalk) that degrades clarity. This can be fixed by placing the chokes as far apart as possible and apply 90 degree angles to direct the magnetic field (center of the choke and outward) away from nearby chokes. reduced magnetic coupling = increased clarity.

– The crossover filter is usually located directly behind a driver and it’s strong magnetic field for easy access.

This can lead to wrong inductance values and or saturated cores. The solution is placing the crossover as far away from drivers as possible, for example on the (wooden) bottom of the speaker. More difficult to access but much cleaner music reproduction.

– In order to ensure that drivers operate within their specified range and protect the drivers against overload, steep, high order crossovers are often used. In most cases the crossovers are second order (2 filter parts) and up. These filters cause significant phase distortion and a lack of coherence.

The PowerDAC-SX has limited output power (up to 16W rms) so it is unlikely to overload a driver. Now it is possible to apply lowest order filters (first order, one filter component) and obtain excellent phase coherency and minimal phase distortion.

High quality filter components can be used as only few components are needed. So we applied all of the above to standard Teufel Optima 40 speakers and this resulted in really stunning music reproduction with the PowerDAC-SX, as if listening to a speaker costing ten times as much. This combination offers a highly realistic music reproduction as if one is attending a live performance. Bass is superb and while there is loud, deep and clean bass, the woofer membranes barely move. This means the woofer cone couples well with the surrounding air (load) and nothing gets out of control (no feedback loops). All this for roughly EUR 500 and some tweaking.

So the speaker choice should no longer be an excuse for not choosing the PowerDAC-SX.

Optima 40 crossover tweak for PowerDAC-SX:

Tweeter (8 Ohms) : 4.7uF in series with tweeter

Midrange (8 Ohms): 270uH air core choke in series with 100uF bipolar in series with the midrange driver.

Bass (parallel, 4 Ohms): 2.7mH air core choke in series with the paralleled woofers.

All drivers in phase, driver minus to PowerDAC-SX minus.