Hi-voltage vs. Conventional Powering Methods

When Brüel & Kjaer entered the pro audio market, they set themselves some very exacting standards. Now, more than two decades after the introduction of digital audio technology, analog electronics is still superior with regards to both audio bandwidth and dynamic range. Still we see the digital domain moving closer and closer to the two transducer ends of the audio chain, from being a flexible storage media with direct access and interesting editing possibilities. The peculiar thing is that, now more than ever, we are discussing the dynamic qualities of both digital and analog equipment, probably because the sound engineer is being reminded daily of the limited dynamics of the digital equipment.

The dynamic problems in both the digital and the analog domain originate from the power supply. There is a tendency in the digital domain to stick to low supply voltages below 5V and try to expand the dynamic range by decreasing the self noise of the electronic components, whereas the analog domain has no limits on supply voltages and can easily obtain dynamic ranges of more than 120dB.

The DPA Quality Standards
With the Series 4000 Microphones, we have taken up the Danish traditions for quality craftsmanship in all details of the product. Our objectives are to manufacture condenser microphones with sonic qualities according to the highest studio demands, i.e. outstanding SPL-handling capability, dynamic range and linear frequency response, but at the same time develop rugged designs that ensure the product's reliability even under hostile conditions.

An alternative to phantom power
To be able to follow the objectives regarding the dynamic qualities of the microphones, it is extremely important to consider supply voltages for both the preamplifier and for polarization of the cartridge. As DPA has developed a technology using of prepolarized microphone capsules with a high polarization voltage, the microphones are not dependent on the phantom power for polarization and it is possible to obtain a large distance between the diaphragm and the back-plate to handle the high sound pressure levels. It took several years to develop a prepolarization concept that was so stable that it could live up to the extreme demands of both the Bruel & Kjaer and DPA standards. But the result was worth waiting for.

However, in a lot of situations, the 48V phantom was also too limiting to be used for supply voltage in the preamplifier design. Purists are expecting clarity, transparency, very low distortion, and above all, an extremely wide dynamic range. It was therefore decided that the Series 4000 Microphones should offer two different lines: a cost-efficient 48V phantom range for the many pro audio users, and a hi-voltage (130V) range for the purists' applications. This led to the HMA4000 (and later updated to HMA5000) Hi-Voltage Microphone Amplifier and the hi-voltage microphones.

HMA5000 - not only a comprehensive PSU
The HMA5000 is a dual-channel microphone amplifier with a built-in power supply for both 130V preamplifiers, 200V cartridge polarization and even 6V heaters. The amplifier and power supply circuits are built into a rugged and compact box and will endure extreme conditions like temperature, humidity, vibrations and shocks. The HMA5000 is designed to be placed close to the microphones, and optional high quality microphone cables of 5m are available to offer a short distance for the delicate microphone level signals.

But the HMA5000 is not only a comprehensive power supply unit. The outputs of the HMA5000 are driven by effective transformerless class A line drivers with a cable drive capability of up to 300m. As there is balanced line level out of the HMA5000, the signals stand a better chance against the electromagnetic noise that the cables might pick up on the way to tape or hard-disk. Using the HMA5000, you eliminate all the possible disadvantages in the console microphone amplifier like noise, distortion and limited dynamic range. You use the line level input on the console and go to tape pre-EQ.

Why then the 130V for the microphone preamplifiers? If you increase the supply voltage (the peak-peak voltage) of the preamplifier to about 3 times the voltage of the phantom power, you will increase the dynamic range of the preamplifier with 10dB when using a class A preamplifier design. In a class A design the distortion only starts to occur when the clipping point is reached, which therefore gives the designer a huge dynamic range to work with. It will then be up to the design of the microphone capsule to set the total dynamic qualities of the microphone. By offering two different preamplifier designs, a standard cost effective 48V phantom and a state of the art 130V system, we give the customer a choice.