A Good Power Supply is Essential for Great Sound
The Heart of a Quality Tube Mic Preamp is a Good Quality Power Supply.
The old adage “You get what you pay for” is as true as it’s ever been.This includes microphone preamps. The vacuum tubes used in high quality tube preamps require a hefty power supply to give the tubes the high voltages they need for optimal performance. In the Edwards LE-10 series preamps, we use high quality tubes, top of the line audio and power transformers, and many other high end components, to come up with a World Class preamp.
At the heart of any quality tube gear is a good quality power supply. When designing the LE-10 series preamps we looked for a power supply that sits on the floor with one cord going to a wall outlet and the other going into the preamp. This type of supply is called a “brick”. Another type of power supply has a transformer that plugs directly into the wall with a cord leading to the device it is powering. This type of supply is known as a “wall wart”.
Since many studios use expensive Power Conditioners, we have chosen to use the brick form of supply, which takes up the space of only one outlet on a power conditioner. Having an external supply in the form of a “brick”, gives us protection from electrical surges before they even get into the preamp. In addition, the brick that we use is UL Approved (Underwriters Lab) which satisfies an important manufacturing requirement. This brick has an output of 24 Volts AC. That voltage is way too low to operate our tubes in their best operating ranges. Not only that, but the 24 volts is AC voltage and the tubes require DC voltage.
When designing our power supply, we consulted the RCA Tube Manual, the “go to” book for tube design. We discovered that the 12AX7, our main tube, operates best with plate voltages between 250 and 300 Volts DC. The plate voltage is the highest voltage in the circuit. If plate voltages are too low or too high, everything about the sound of the preamp suffers. But how do you get 250 or more volts DC out of a 24 Volt AC brick?
Since we are using an AC Voltage brick, we are able to use a transformer to step up the 24 volts AC to a higher value of 120 Volts AC. From there, we use a common circuit which raises the voltage and at the same time changes it from 120 Volts AC to 240 Volts DC. This circuit is called a “Voltage Doubler”. But, as they say on the infomercials, “There’s more”. The voltage doubler gives us a voltage that is more than double. The preamp components then draw current, creating a resistive load which drops the voltages to where they should be for optimal performance.
You may ask “How does all of this apply to a mortal like myself?” The answer is simple. If you are thinking about acquiring a microphone preamp, check the specifications very carefully. However, even specifications can be deceiving. The best thing to do is to hear one. In our case you can easily find our demos of music recorded through an Edwards LE-10 Microphone Preamp.
Many tube preamps do not use adequate power supplies. The result is poor frequency response, high distortion, low headroom and other issues. On the other hand, a well designed preamp with a very strong power supply will give you lots of gain, good frequency response, low distortion, plenty of headroom and a great sound.
The Edwards Audio Research Microphone Preamps have been described by reviewers and customers alike as “World Class”. It takes a lot of good engineering to come up with this kind of a product.
At Edwards Audio Research, we are always excited about our products, and would love to share more info with you. Simply click on the Contact Tab for info on how to reach us. And don’t forget to check out our Demos!