Saturday, May 10, 2014

Onkyo P-3000R Preamp Review - Part 2

In Part 1 of this review, I evaluated the single-ended (RCA) inputs. The performance was stellar and I praised the circuitry for doing what I recalled it did best: sonic accuracy, imaging stability, and front-to-back depth.  However, also included in this preamp are some pretty sophisticated digital components worthy of mention.

In comparing the quality of any two sources, switching back and forth between two sources – preferably within two seconds – is the best way to evaluate such differences. Very few golden-eared folks have adequate long-term sonic memory to recall all of the nuances and subtleties when taking more than two seconds or so to switch between sources but devising a good method that itself does not influence the test results has been an equal challenge.

Some people believe that a Y-splitter is one way to achieve quick results and such a method will allow you to quickly switch between two RCA interconnect cables.  For example, two RCA cables can be connected to two inputs on a preamp (e.g., CD and AUX) and the other ends to the same output on a CD player via the Y-connector.  But I suspect that such a test method introduces errors in the form of ground loops between both cables.  So if the introduction of a Y-splitter is of questionable value when evaluating two sources, how can one do so without such degradation?

Y-Splitter RCA Cable Test

The answer is pretty simple: think light.  The Onkyo P3000-R preamp has four RCA and two TOSLINK optical-digital inputs allowing you to perform simple source A/B switching without introducing ground loops into the test.  So for Part 2 of this preamp’s evaluation, I will use my reference 1-meter RCA interconnects and a 1-meter Better Cables TOSLINK cable both connected to the same source: my stock OPPO BDP-105.

With such a configuration, I am able to play the same track on the OPPO and instantly switch the preamp between the CD and AUX inputs. What this configuration allows me to do is instantly hear the difference between the DACs in the OPPO (ESS Sabre32 Reference) and the DACs in the Onkyo (Burr-Brown PCM1795 192/32). This should be interesting.

P-3000R Rear Panel Inputs

Upon first hearing, I could distinguish very little difference between the two sources, something I did not anticipate. I listened to MP3s all the way up to DSDs and although there WERE differences, they were so slight that I could not consistently identify them from one format to another. Even my wife said that the differences were so small that she would have a hard time deciding which sounded better, other than the TOSLINK cable giving a slightly deeper bass output. From the get go, I knew this was going to take the right source material and more time than originally anticipated.

As my wife heard, the deep bass was a tiny better with the TOSLINK cable than the RCA so I was at an impasse. However, I had planned to make another modification to the woofer's crossover network in my speakers and now seemed like a good time to do so. With a 4-ohm woofer, the insertion loss of a typical large value wire or foil inductor - even with 12AWG wire size - approached a DC resistance of 0.5 ohms. This means that 10% of the power to the woofer is dissipated by the inductor.

I have always wanted to try a high-power toroid coil since the DC resistance in these inductors is about 1/10th that of any other coil type and now seemed like a good time to give it a go. I also wanted to lower the crossover point from 850Hz to 500Hz , a much better upper-frequency limit for a 12" driver. With a  quick check to Parts Express, I found a 3.3mH toroid that with a bit of unwinding would work in my crossover network.

Now unwinding this type of inductor is not as simple as measuring it with an inexpensive RLC meter. Because of the low DCR, higher currents are required to accurately determine the value and so I drug out my oscilloscope, sine wave generator, and a known value capacitor and resistor. It took about 11 turns off of this inductor to get it to the value I needed as determined by the LC tank circuit it created (carefully measure the minimum "null" and read the frequency, then simple math tells you the value).

A Toroid Inductor

I rolled this toroid inductor into the woofer crossover network and immediately I noticed a much cleaner, tighter bass. Considering that the moving mass on these woofers is an incredibly low 40g, this was not expected. But the surprise came when watching Star Trek: Into Darkness.  WOW did that extend the extreme LF response and remove muddiness! So the weak link in my chain was the woofer inductor and now I have never been happier - as is my wife who loves bass, especially explosions and deep thuds.

Back to the TOSLINK/RCA (aka Burr-Brown/ESS Sabre32 Reference) dilemma. Now that the LF extension and clarity is better, I hoped to hear more differences and be able to easily discern them. The large organ recorded by 2-L on the  Kare Nordstoga improvisation proved to be the right choice.

All throughout this 24/96 piece (also available in SACD), wall-rattling bass can be heard that captures the true character of a very large brass pipe. Through the Burr-Brown/TOSLINK version, the bass was present but not full nor did it reveal the true timbre of the largest ranks. Sounding muted rather than forward, this configuration - although pleasant - just did not compare to the OPPO/RCA version. The OPPO extracted more information from the source and left you feeling more like "you were there" listening in a pew somewhere forward of the pipes in the balcony. More depth, more width, and more height all combined to giving a well deserved and decisive advantage to the OPPO/RCA version. While other parts of the frequency spectrum were also different, these differences were not as noticeable nor as obvious as the very deep bass and hall ambience.

As I have mentioned in the past, if you are searching for ways to improve your system, look at the size and shape of the sound stage and then choose what sounds more realistic. For now, I will stick with the OPPO/RCA combo for decoding.

Yours for higher fidelity,
Philip Rastocny

I do not use ads in this blog to help support my efforts. If you like what you are reading, please remember to reciprocate, My newest title is called Where, oh Where did the Star of Bethlehem Go? It’s an astronomer’s look at what this celestial object may have been, who the "Wise Men" were, and where they came from. Written in an investigative journalism style, it targets one star that has never been considered before and builds a solid case for its candidacy.

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