7 years ago I got an order from the Hong Kong based Audios Physics who specialised in headphones and headphone amps. They ordered my headphone amp the Ear 90. A few months later we started to discuss a new headphone amp, a more expensive flagship level unit. The name of the new amp was Ear 909. It was based on the same amp board as the balanced version of Ear 90. The PSU section was from Pre 906. Later, I designed a new amplifier unit for the Ear 909. I had designed the Pre 906 in the 1990s. It is still in production with exactly the same outside and internal architecture as when it was new 22 years ago, but all sections are upgraded or totally new. 

The PSU system was totally redesigned in 2009. Pre 906 was long before its time, with an inbuilt DAC with three digital inputs as option. I realised early that standard voltage regulators not can be used into an audio amplifier. In all my units I use a voltage reference followed by an impedance converter. I also use active filters to suppress interference from the rectifiers system and the mains. One other thing that is extremely important is the physical design of the boards and the system. Today when 4 layer PCBs are used, this is not as important as when 2 layer boards are used, but an electronic engineer must understand how to solve the physical design. The power supply section in the Ear 909, is exactly the same as used in the Pre 906, it is a very lavish system with big Elyt caps, shielded rectifiers, active filters, a very stable voltage reference and, in the end, a voltage regulator based on three operational amplifiers. 

This PSU board is completed with an additional voltage regulator for each channel. These regulators are located on the same 4 layer board as the amp itself. This means that the losses in the connection between the voltage regulator and the amp is as small as possible. The mission in my units is to get a good technical spec, but also a neutral sound. This is the reason why I only use high performance op amps and other semiconductors and why I prefer to build my own voltage regulation system. A non coloured sound is more important than the technical quality, but I always want to have both before they have a relation to each other. Take a look on different level controls. Almost all pots, mechanical or electronic, has some kind of coloration. Some plastic pots have a very good sound quality, viewed from the technical side, but from the musical point they are coloured. Therefore I use the Alps RK27, also called Alps Blue, in my budget units and a level control based on an Elma switch with discrete resistors in my best units. Today IC based level controls are usual. I have tested so many of them that I can say that they don’t work. The only level control that can sound really good is the digital, that is placed before the DAC or some kind of mechanical, a switch with fixed resistors. The Alps pot is not at all perfect from the technical point, but it is musical, it has a low grade of coloration that is unique. Therefore it is a very good choice into amps that not are allowed to cost to much. The Elma (I use the Elma in a version that is mounted by the Danish Dact Audio) has both: Technical quality and neutrality. This is the ideal choice on a unit that prioritises sound before cost. Care must also be taken on all other components in order to not add any colourations. Especially with film caps this is a real issue. There are a lot of good caps that cannot be used because of their addition of coloration to the sound. 

I started my firm approx 25 years ago. At this time I mainly worked with CD player modifications. The parts that were exchanged was the op amps and voltage regulators in the analog sections and some more. No matter of brand or cost, it was the same things in almost all CD players. Later I also replaced the clock oscillator. The PCB boards that I added into the players was my own design, but for a short time I mounted a clock that I bought from the outside. When my own products started to sell more and more, I stopped with the modifications. It is a hard work to create good modifications. I will absolutely not call myself an audiophile. I am an engineer who spends a lot of effort to design audio units with a high grade of industry quality. I want to be as close to the customer as possible before this result in a good value for the buyers.

The output voltage from Ear 909 is approx 8V RMS. This results in a power of 0.65 W if the headphones has an impedance of 100 ohms. If the headphone impedance is 20 ohms the power will be 3 watts, but this will result in permanent ear damage. The maximum output current is approx 1A. The PSU can deliver that, but the output transistors in the final voltage regulator cannot deliver that power static. The transistors themselves can handle more than 1A, but if this current shall be constant, cooling is needed. The same is with the output transistors. They are oversized if only the power is regarded, but as a system they are what is needed. The gain switch increases the signal with approx 3 and 6 db. The purpose with the gain switch is to use the stepped level control more effective. The gain switch can be used to dampen the signal resulting into more usable steps on the level control. 

The price in the EU is 19 500 sek including shipping. The warranty is 5 years. To be honest, if there is some problem with a unit, this will show up during the first time, but if there is some default with an old unit, I want to know that. So the 5 year warranty is a safety both for me and the owner. 

Maybe it would be interesting to know something about the production of the Ear 909: We produce the parts of our units in the industry in Sweden, mainly located into our area. Gotenburg is an old industrial town that is a good region are for production. But the PCB boards are produced into China, as all boards in the world these days. The assembly of the components and machine soldering of the boards are done in our facilities. We also handle the production of the wood panels, screen printing and some more in house. All assembly is done in our facilities. I do all final mounting and testing myself. Normally we do not have units in stock, but we have always all parts that are needed for final assembly. Ready mounted and tested boards, ready enclosures, etc. 

The Ear 909 is DC coupled. The output is protected from DC by a DC sensing circuit. If there is DC from the source, the level control will “click”. When the DC on the output is over approx 1 VDC the output will be disconnected. I would recommend the user to use a balanced cable. When the 6.3 mm output is used the ground for both channels are mixed into the connector and then connected to the main power supply. This is the only way to handle the 6.3 mm connector ground. When the LR outputs are used, the signal reference is the refpoint for the amp and the cold leads are not mixed. This result into better sound. A XLR cable can also be pair twinned as it should be.

 

-Mattias Stridbeck

http://www.harmonydesign.se/eng/

Josh Coleby
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