When Brüel & Kjaer entered the pro audio market, they set themselves some very exacting standards. Now, more than a decade 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 Hi-Voltage Microphone Amplifier and the hi-voltage microphones.

HMA4000 - not only a comprehensive PSU

The HMA4000 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 HMA4000 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 HMA4000 is not only a comprehensive power supply unit.The outputs of the HMA4000 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 HMA4000, 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 HMA4000, 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.

Difference between hi and convential powering methods for the Standard Microphones.

Self noise, dynamic range and headroom

The dynamic range of a DPA microphone is calculated in dB from the total A-weighted equivalent noise floor to the sound pressure level where 0.5% distortion occurs. Sound pressure levels beyond 0.5% distortion are specified as the microphone's headroom in dB up to the sound pressure level where clipping occurs - the clipping point being set by the microphone sensitivity and the supply voltage. For example, the hi-voltage microphone Type 4003 has an equivalent noise floor of 15dB(A), 0.5% THD occurs at 129dB SPL peak and clipping occurs at 154dB SPL. All specs are measured in a live acoustic field using a B&K Type 4221 High Pressure Calibrator. The dynamic range and the headroom of Type 4003 is then easily calculated to 114dB and 25dB respectively. The phantom-powered microphone equivalent to Type 4003 is the well-known Type 4006 and here the clipping occurs at 143dB SPL peak. The self noise and the sound pressure level where 0.5% THD occurs are the same as with the Type 4003. Dynamic range and headroom for the Type 4006 can therefore be calculated to 114dB (again) and 14dB respectively.

The hi-voltage solution

To ensure the lowest possible low-frequency distortion and the best possible low-frequency response in the hi-voltage system, DPA introduced a transformerless design in both the microphone preamplifiers and in the HMA4000 Microphone Amplifier. Phantom microphones like Type 4006 and Type 4007 have transformer outputs and it is interesting to compare their specs and features with those of their hi-voltage equivalents, Type 4003 and Type 4004. But first, we have to make it crystal clear that high quality output transformers also offer advantages that no other electronic components or circuits can offer.

Primarily, the galvanic separation in the audio transformer ensures that no false signals or voltage can damage the microphone electronics. Secondly, the high quality transformer has a higher common mode rejection than any other electric circuit. Last but not least, the transformer has a very good cable drive capability. Bearing these advantages in mind, we will not do the quality transformer any injustice if we compare the two powering concepts in the table. Compare the two microphone type in each microphone category and let the table speak for itself.

Conclusion

It is obvious that the two different powering concepts both have interesting advantages to offer and this is of course the reason why DPA offers both solutions. It is a fact that the hi-voltage system is the advanced concept without any compromises when it comes to audio transparency, clarity and faithfulness to the original sounds, regardless of sound pressure levels or tonal balance. Please let me conclude this section by listing up the features and advantages you can obtain by choosing the hi-voltage concept:

The hi-voltage concept offers:
- Enhanced SPL handling capability
- Audio leads separated from powering leads


The HMA4000 Hi-Voltage Microphone Amplifier offers:
- Two channels with up to 90dB channel separation
- Balanced Class A line driver output design
- Transformerless in and out
- Line level outputs
- Up to 300m cable drive capability
- Enhanced low-frequency handling capability
- 140dB dynamic range with attenuators in "0dB"
- Maximum input signal 160V peak