Available with participating US Dealer and vpidirect.com
When Harry Weisfeld reviewed the Genesis Phono, he was mesmerized. He said that it is “so enjoyable, so easy to listen to, and so revealing I feel almost compelled to turn it on…. If you have the money, this is a must-have combination and I cannot imagine getting more information out of the grooves. World class phono and fully recommended with no negatives I can find.” (Except the price!)
So, we called our good friend, Gary Koh, the Chief Designer at Genesis and asked him if he could design one for VPI….. at a quarter of the price!
The Design
The moving-coil phono stage arguably has one of the toughest jobs of any of the electronic components of a hifi-system. It has to take a tiny, delicate signal from the phono cartridge and amplify the voltage by at least 1,000 times (typically 60dB of gain @1kHz) for a low-output moving coil cartridbe.
What’s worse is that because of RIAA equalization, it needs to amplify the bass frequencies even more. The same phono stage needs a gain factor of over 10,000x @20Hz (80dB of gain). At 20kHz, gain is just 100x or 40dB – a difference of 40dB between 20Hz to 20kHz. Hence, huge headroom is needed.
Despite amplifying the cartridge signal by over 60dB, the phonostage also has to be low-noise across a broad spectrum. Otherwise, any noise will be amplified together with the music. You can’t filter this noise either, as the filter is unable to distinguish between music and the noise and only throw out noise.
Due to the delicate nature of the signal from the phono cartridge, it has to be handled with kid gloves. Hence, it is also extremely important to do no harm to the signal.
The Avenger Phono incorporates only a single high-gain/variable gain amplification stage and is completely isolated using a battery power supply. It implements the RIAA de-emphasis required as part of the variable gain architecture.
An absolute minimum of components is used. But because there are so few components, each part has to have quality beyond reproach. Every component used on left and right is tightly hand-toleranced far beyond manufacturing tolerance and broad-frequency spectrum matched.
1) Voltage-gain phonostage, not current mode.
Despite not needing loading, the Avenger Phono is a voltage phono, not a current-mode phonostage. We chose this because the phono cartridge is a tiny electrical generator, if current is drawn from a generator, it will have to work harder. Cartridge compliance will change depending on the current drawn affecting the sound of the cartridge. Also, cartridges that cannot generate any current (like the Grado’s) cannot be used with current-mode phonostages. Being voltage-based, the impedance of the cartridge also does not make too much of a difference. A broad range of cartridges from even as low as 1 ohm can be accommodated.
2) Why does it not need loading?
The need to load comes from a resonant spike in the circuit between the inductance of the cartridge and the capacitance of the tonearm cable. This spike is usually above 120kHz, and about 30dB in magnitude. With the characteristics of RIAA de-emphasis in a moving coil phonostage, about 60dB gain is required at 1kHz, 80dB gain is required at 20Hz, and only 40dB gain is required at 20kHz. We take the RIAA curve beyond 20kHz: to 20dB gain at 40kHz, and 0dB gain at 80kHz. Hence, where the resonant spike comes in, the gain is close to zero. Since the resonant spike is 30dB, this spike is 30dB below the music signal at the output, and hence does not affect the phonostage, and doesn’t overload the preamp.
This requires that the phonostage be very wide-bandwidth, and very high gain. Then, the gain is shaped by the RIAA de-emphasis curve so that it performs correctly. In order to deliver dynamics, the gain needs to be at least 100dB (20dB more than gain at 20Hz).
3) Why does sound so transparent?
It does not require loading. The load is a resistor across the input of the phonostage. Hence, the cartridge needs to drive a current across this load resistor and thereby do work. The phonostage reads the voltage across this resistor, hence changes in this resistor will affect the sound of the cartridge. The lower the value of this resistor, the higher the current needed, and the harder the cartridge needs to work. Hence, the higher the loading (lower resistance) the more dull the sound is. Without loading, the resonant inductance/capacitance tank circuit spike overloads the input, and you get harshness. Loading is always a balance between 2 evils.
Check Our Hi-Fi Chicken's Review on Our Avenger Phono!
