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Ultra-Quiet, Fully Discrete Phono Stage with No Op Amps
Audio Alchemy's PPA-1 phono preamplifier uses all-analog, discrete FET gain and EQ stages to transform the microscopic grooves in vinyl records into stunningly lifelike music. It includes all the features that serious vinyl enthusiasts demand, such as continuously variable input loading, MC/MM gain switching and XLR and RCA outputs. It can also be upgraded by adding the PS-5 power supply, which can simultaneously power the PPA-1 and one other Audio Alchemy component, such as the DDP-1 digital preamp.
Fully Discrete Circuit With No Op Amps
Any phono preamp has to incorporate the RIAA playback EQ curve to correctly handle the musical signal from the phono cartridge, and this basically consists of a bass boost and a treble cut. There are all sorts of ways to accomplish this, using various types and combinations of active and passive circuitry.
"The one that sounds the most musical to me is the combination of a discrete FET [field-effect transistor] input stage, a passive treble roll-off filter, and an active EQ circuit for the bass boost," says Peter Madnick, the founder and chief engineer of Audio Alchemy – and the cofounder of the original Audio Alchemy back in the late 1980s. "The basic circuit concept dates back to a phono preamp I designed for Dennesen Electronics in the 1980s. I’ve used it a few times since then, but the PPA-1 is the first chance I’ve had to implement it the way I’ve always wanted to: a fully discrete circuit with no op amps, a very quiet, well-regulated power supply, and versatile tuning options."
Magical Analog Musicality
As Audio Alchemy sees it, analog signals from vinyl records are already perfect when they leave the phono cartridge. All they need is to be handled with the utmost care in their path to the preamp. That's why Audio Alchemy use all-discrete, ultra-low-noise FET circuits for the PPA-1's RIAA EQ and gain stages, with no integrated circuits in the signal path.
With a phono preamp, especially running an MC cartridge, the gain has to be very high – in this case +67 dB – and, of course, the higher the gain the more you have to be careful about noise. "One of the main things we did to minimize noise was use multiple FETs in parallel in the input stage," says Peter. "When you run two transistors in parallel, you get a theoretical -3 dB reduction in noise. We use eight FETs per channel – four in parallel for positive, four in parallel for negative. This reduces the noise to virtually imperceptible levels."
Low Noise Power Supply
After lowering the noise levels in the preamp and EQ circuits, the power supply becomes key. The PPA-1 is very quiet, even with its stock power supply, which is just an AC transformer and not a switching-type power supply like you usually get with audio products. The incoming AC is rectified, and then it's run it through a large capacitor bank. Audio Alchemy uses a circuit called a capacitor multiplier, which increases the effective capacitance. "Coming out of the capacitor bank we have very smooth DC voltage, plus those capacitors store electricity and release it when the preamp needs extra power for highly dynamic musical passages," Peter notes.
The PPA-1 follows the capacitor bank with low-noise DC regulators, which in turn are followed by RLC [resistor-inductor-capacitor] filters that trap high-frequency noise.
According to Peter, "We also carefully researched the internal isolation for the different circuit elements. Everything that might interfere with something else is isolated from it, and we use star grounding to make sure all the various circuits have the same ground reference."
Still More Noise Control
After all of this attention to lowering the noise floor, Peter wanted to make sure that there was nothing inside the chassis that could produce its own noise. So there’s no display, no microcontroller, no computer interface, no wireless connection, no digital or RF or computer-based components of any kind. A nice side benefit of this is that the front panel is simple: just power, input selection, and mute buttons.
Transformations That Suit Any System
Serious vinyl enthusiasts need more than just the basic options, so the PPA-1 gives you what they need. Load impedance is independently, continuously adjustable for both inputs, so optimal performance can be achieved with any cartridge, and you're not locked into specific settings. Either input can be set for MC or MM gain, and balanced XLR outputs are provided in addition to single-ended RCA outputs.
"Of course, you can set the gain for MC or MM cartridges, and that’s for each input, so you can have two MC, one MC and one MM, or two MM," says Peter.
"What I’m most proud of is the way we set up the adjustable cartridge loading. Controls on the back let you select 47 kΩ loading for MM cartridges (and some people like that for MC, too), or adjustable loading from 1 ohm to 1000 ohms for MC cartridges." This gives the listener lots of flexibility to either use the cartridge manufacturer’s recommended loading or experiment to find a loading they like better.
It’s very easy to adjust the loading precisely, because the PPA-1 includes contact points on the back panel that let you measure the loading for the left and right inputs of channels 1 and 2. "All you need is a $10 digital multimeter to measure the load impedance," Peter notes. "Touch the meter probes to the contact points, and turn the knob on the back until you have the load setting you want."
Easy Upgrade Path with Optional PS-5 Power Supply
As great as the PPA-1 sounds, it can sound even better! Audio Alchemy provides an easy upgrade path via the optional PS-5 outboard power supply, which offers superior filtration, tighter voltage regulation, lower noise and greater energy storage. Adding the PS-5 makes the PPA-1 more dynamic, too.
"All the AC power is isolated in the PS-5, so the PPA-1 sees nothing but filtered DC," Peter explains. "It also provides a higher supply voltage: +/-20 volts DC. The stock power supply is 9 volts AC, which gives you a little more than +/-3 volts DC. The PS-5 also has a much bigger capacitor reservoir than what’s inside the PPA-1. So with the PS-5, you gain a lot in terms of dynamic capability."
“If you’re running a low output moving coil cartridge (or two or one MC and one MM) and you are looking for solid state in the under $2000 price range the Audio Alchemy PPA-1 is easy to recommend for its high build quality, attractive exterior, fully adjustable MC loading options, two input convenience and of course its accomplished sonics and background quiet.”
“Conclusion: The PPA-1 is a high performance, feature-rich, versatile, well-built in America, MM/MC phono preamp that is among a handful of the best under $2000 phono preamplifiers available today...”
- Michael Fremer, Analogplanet.com