M Jarve
Audio Geek and NGE Freak
Sometimes this hobby brings about curious bedfellows. As I noted in another part of this forum, my numero-uno amp, the Yaqin MC-10L II recently had a tube give up its ghost, and, because I cannot at the moment afford a new matched quad of glass, and half of my gear is on loan to the Falkowski Collection, that left me with my rank 3 kit- the Audio Dynamics CA-2000E.
The CA-2000E is a mighty fine unit, and compares very much favorably with my old reference amp, the h/k PM660. However, either the years of apparent disuse or something else had left the input selector board with some bad solder joints, and the input would randomly change from one source to another on its own- very annoying that.
So, I dug really deep all the way to the 4th-rank pile of unloved HT receivers and pulled out a somewhat recent if forgotten acquisition, a Sony STR-GX900ES. This is the unit I've been listening to and using for the past week.
The STR-GX900ES is an early '90s Dolby Pro-Logic unit rated for 100-watts per channel to the three front channels (@8Ω) and 30 watts per channel for the rear. Like most high-end receivers of the era, it performs a plethora of additional tasks including acting as a parametric EQ, DSP, AV-switcher, and so on. Since the surround output is a bit on the weak side, the GX900 featured surround-channel preamp outputs. Rather unique is that through the use of a so-called Power Swap feature, you can route the surround channel signal through the main L&R power amps, and have the main L&R channel's signal output through the preamp output. Additional pre-outs include center and subwoofer outputs.
The build quality of the unit does not recall the glory days of Sony ES series components. No wood side trim, no composite G-chassis, or any other indications of high-end accouterments. The three conceits made to high-endness are the thicker than usual steel bottom, binding-posts for all the channels, and the aluminum front panel; thin, 1/8" aluminum, but aluminum none the less.
When I first connected up the GX900, I was really unimpressed with it, as it seemed to be missing nearly all the bass. Even the Bass Boost function and bumping up the bass on the parametric EQ had little effect except to exaggerate midbass. I then found out about the system-wide Low-Cut filter. It engages a 90Hz high-pass filter on all internal amps, presumably for using a Sat-Sub setup. It is activated in a convoluted fashion, but once deactivated, the sound became very well balanced.
Of course, I'm using the GX900 in 2-channel setup, and so my impressions that follow are based entirely on its performance in that regard. Also, when I used the Infinity QLS-3, the power amp was set to 4Ω mode and 8Ω mode for the IMFs (which is how the majority of my listening was done).
As I mentioned, the GX900 is rated for 100 watts per channel into 8Ω, and when the power amp impedance switch is in the 4Ω position it presumably outputs 100-WPC into 4Ω as well. These are FTC RMS ratings, but the owners manual also lists Dynamic Power output (IHF). Although the IHF ratings have been long ignored for the more accurate RMS ratings, they do provide a small amount of insight into the real-world performance of the unit. Dynamic power for the amplifier portion is 125-watts into 8Ω, 195-watts into 4Ω, and a whopping 255-watts into 2Ω. I do not believe that these ratings are unrealistic for the unit, as it does posses a very healthy power supply.
The power supply is divided into multiple sections, but of most interest are are three of them. Each of the three front main channels has its own secondary transformer winding, rectifier, and filter caps. In this case, their are three banks (pairs) of 63V/5600µF caps. The L&R channels each have 11,200µF of storage. Not too bad at all for a HT amp, where space is at a premium. Further, just by virtue of the design, the rear channel amps, although only 30 WPC, also have their own, shared power supply. Indeed, there are no less than 8 separate secondary windings on the power transformer, as each major circuit has its own power supply. The power transformer, as per the service manual, is a 410VA unit.
The voltage amps for each of the three main channels is an STK350 (one per channel). The outputs IC's for each of the three front channels are unusual dual-BPJ transistors (NE-N250 and NE-P250) that contain two NPN/PNP dies on each chip, each of which can be tested individually. This effectively gives the front amps 4 output transistors per channel, although only two devices are present for each channel. Bias and DC offset are unadjustable- the former is permanently set, while the latter appears to be controlled by NFB or servo, as the DC offset measured a nearly miraculous 0.01mV on my meter. The main heatsink is a bit underwhelming, no cast and machined aluminum, but it apparently does the job.
Unlike the CA-2000E, the inputs are not individually buffered, and all audio input is routed through the DPL decoder and DSP regardless of whether these functions are used, unless the Direct Pass option in engaged. Most of my listening was with in the Direct Pass mode. I will admit that, as long as the surround effects and EQ were unused, there was very little difference between the Direct Pass mode and the regular mode.
The parametric EQ is, in my opinion, of limited use for my purposes. Although it gives a plethora of options, it controls frequencies only between 125Hz and 8kHz (±10dB of gain or cut), and the slope of only the midrange pass band can be adjusted. The Low Boost circuit is equally limited, providing +7dB @ 70Hz, and does not, apparently, act as a loudness compensation by providing volume dependent gain or boost of the high-end. Essentially just gives the music a bit more boom. Again, all this proved to be of little consequence for my actual listening given that I did not make use of these functions, aside from experimentation.
Now that I've gone through all the ways I did not use the GX900, let me get into how I did use it. Throughout all my listening, the sources used were the ADC CD-2000E CD player, T-2000E tuner, and Philips GA312 turntable with AT11E cart. I should explain one thing right off the bat- Why use an external tuner when a receiver, almost as part of its very definition includes a tuner. Well, its not because the tuner in the GX900 is bad, or does not work, but rather because it accepts only 75Ω coax input, I use 300Ω twinlead and I cannot, for the life of me, find my adapter!
On to listening...
The GX900 performed much better, musically, than I had anticipated. It does not seem to lack for power, though the high-end does become a bit harsh when driven to very loud levels. I would put the overall tonal quality as either neutral or just a bit cool of neutral with the Infinity QLS-3 and very neutral with the IMF TLS-50. No one, I imagine, would accuse this amp of being overly warm, lush, or laid-back sounding. The high-end is a little harder and more etched than I'm used to, but it's not fatiguing or distracting.
Low-level details are very well delineated, but the "big-picture" sound is somewhat artificial. Imaging is okay- neither great nor bad, with proper proportion and L&R placement, extending even beyond the speakers, but lacking in depth, regardless of source. In this regard it is very similar in performance to the ADC CA-2000E.
The phono section is setup only for MM carts and provides reasonably good performance. It's quieter than my Herron Audio VTPH, with slightly more gain, but it has something of an "empty" quality to it that I cannot quite put my finger on. I would not rate it as highly as the phono stage in my ADC CA-2000E, which provides nearly the same sound quality as the Herron Audio unit. Still, I found myself using the in-built phono stage instead of the Herron unit purely out of convenience, not to mention that I thought that the Herron and its awesome imaging capability was somewhat wasted with the Sony.
Overall musical performance was very good, and I found myself less distracted by the shortcomings than simply listening to the music. There are only two other HT receivers that really compete in terms of musical capability- the Pioneer VSX-9300 (which had a warmer sound) and a Mitsubishi unit I owned at one time, but the model number escapes me at the moment. Certainly the GX-900 is a much better performing and sounding unit than I had been willing to give it credit for. The quad power supplies, quality power amp, and sonic performance are all very strong points in its favor.
The CA-2000E is a mighty fine unit, and compares very much favorably with my old reference amp, the h/k PM660. However, either the years of apparent disuse or something else had left the input selector board with some bad solder joints, and the input would randomly change from one source to another on its own- very annoying that.
So, I dug really deep all the way to the 4th-rank pile of unloved HT receivers and pulled out a somewhat recent if forgotten acquisition, a Sony STR-GX900ES. This is the unit I've been listening to and using for the past week.
The STR-GX900ES is an early '90s Dolby Pro-Logic unit rated for 100-watts per channel to the three front channels (@8Ω) and 30 watts per channel for the rear. Like most high-end receivers of the era, it performs a plethora of additional tasks including acting as a parametric EQ, DSP, AV-switcher, and so on. Since the surround output is a bit on the weak side, the GX900 featured surround-channel preamp outputs. Rather unique is that through the use of a so-called Power Swap feature, you can route the surround channel signal through the main L&R power amps, and have the main L&R channel's signal output through the preamp output. Additional pre-outs include center and subwoofer outputs.
The build quality of the unit does not recall the glory days of Sony ES series components. No wood side trim, no composite G-chassis, or any other indications of high-end accouterments. The three conceits made to high-endness are the thicker than usual steel bottom, binding-posts for all the channels, and the aluminum front panel; thin, 1/8" aluminum, but aluminum none the less.
When I first connected up the GX900, I was really unimpressed with it, as it seemed to be missing nearly all the bass. Even the Bass Boost function and bumping up the bass on the parametric EQ had little effect except to exaggerate midbass. I then found out about the system-wide Low-Cut filter. It engages a 90Hz high-pass filter on all internal amps, presumably for using a Sat-Sub setup. It is activated in a convoluted fashion, but once deactivated, the sound became very well balanced.
Of course, I'm using the GX900 in 2-channel setup, and so my impressions that follow are based entirely on its performance in that regard. Also, when I used the Infinity QLS-3, the power amp was set to 4Ω mode and 8Ω mode for the IMFs (which is how the majority of my listening was done).
As I mentioned, the GX900 is rated for 100 watts per channel into 8Ω, and when the power amp impedance switch is in the 4Ω position it presumably outputs 100-WPC into 4Ω as well. These are FTC RMS ratings, but the owners manual also lists Dynamic Power output (IHF). Although the IHF ratings have been long ignored for the more accurate RMS ratings, they do provide a small amount of insight into the real-world performance of the unit. Dynamic power for the amplifier portion is 125-watts into 8Ω, 195-watts into 4Ω, and a whopping 255-watts into 2Ω. I do not believe that these ratings are unrealistic for the unit, as it does posses a very healthy power supply.
The power supply is divided into multiple sections, but of most interest are are three of them. Each of the three front main channels has its own secondary transformer winding, rectifier, and filter caps. In this case, their are three banks (pairs) of 63V/5600µF caps. The L&R channels each have 11,200µF of storage. Not too bad at all for a HT amp, where space is at a premium. Further, just by virtue of the design, the rear channel amps, although only 30 WPC, also have their own, shared power supply. Indeed, there are no less than 8 separate secondary windings on the power transformer, as each major circuit has its own power supply. The power transformer, as per the service manual, is a 410VA unit.
The voltage amps for each of the three main channels is an STK350 (one per channel). The outputs IC's for each of the three front channels are unusual dual-BPJ transistors (NE-N250 and NE-P250) that contain two NPN/PNP dies on each chip, each of which can be tested individually. This effectively gives the front amps 4 output transistors per channel, although only two devices are present for each channel. Bias and DC offset are unadjustable- the former is permanently set, while the latter appears to be controlled by NFB or servo, as the DC offset measured a nearly miraculous 0.01mV on my meter. The main heatsink is a bit underwhelming, no cast and machined aluminum, but it apparently does the job.
Unlike the CA-2000E, the inputs are not individually buffered, and all audio input is routed through the DPL decoder and DSP regardless of whether these functions are used, unless the Direct Pass option in engaged. Most of my listening was with in the Direct Pass mode. I will admit that, as long as the surround effects and EQ were unused, there was very little difference between the Direct Pass mode and the regular mode.
The parametric EQ is, in my opinion, of limited use for my purposes. Although it gives a plethora of options, it controls frequencies only between 125Hz and 8kHz (±10dB of gain or cut), and the slope of only the midrange pass band can be adjusted. The Low Boost circuit is equally limited, providing +7dB @ 70Hz, and does not, apparently, act as a loudness compensation by providing volume dependent gain or boost of the high-end. Essentially just gives the music a bit more boom. Again, all this proved to be of little consequence for my actual listening given that I did not make use of these functions, aside from experimentation.
Now that I've gone through all the ways I did not use the GX900, let me get into how I did use it. Throughout all my listening, the sources used were the ADC CD-2000E CD player, T-2000E tuner, and Philips GA312 turntable with AT11E cart. I should explain one thing right off the bat- Why use an external tuner when a receiver, almost as part of its very definition includes a tuner. Well, its not because the tuner in the GX900 is bad, or does not work, but rather because it accepts only 75Ω coax input, I use 300Ω twinlead and I cannot, for the life of me, find my adapter!
On to listening...
The GX900 performed much better, musically, than I had anticipated. It does not seem to lack for power, though the high-end does become a bit harsh when driven to very loud levels. I would put the overall tonal quality as either neutral or just a bit cool of neutral with the Infinity QLS-3 and very neutral with the IMF TLS-50. No one, I imagine, would accuse this amp of being overly warm, lush, or laid-back sounding. The high-end is a little harder and more etched than I'm used to, but it's not fatiguing or distracting.
Low-level details are very well delineated, but the "big-picture" sound is somewhat artificial. Imaging is okay- neither great nor bad, with proper proportion and L&R placement, extending even beyond the speakers, but lacking in depth, regardless of source. In this regard it is very similar in performance to the ADC CA-2000E.
The phono section is setup only for MM carts and provides reasonably good performance. It's quieter than my Herron Audio VTPH, with slightly more gain, but it has something of an "empty" quality to it that I cannot quite put my finger on. I would not rate it as highly as the phono stage in my ADC CA-2000E, which provides nearly the same sound quality as the Herron Audio unit. Still, I found myself using the in-built phono stage instead of the Herron unit purely out of convenience, not to mention that I thought that the Herron and its awesome imaging capability was somewhat wasted with the Sony.
Overall musical performance was very good, and I found myself less distracted by the shortcomings than simply listening to the music. There are only two other HT receivers that really compete in terms of musical capability- the Pioneer VSX-9300 (which had a warmer sound) and a Mitsubishi unit I owned at one time, but the model number escapes me at the moment. Certainly the GX-900 is a much better performing and sounding unit than I had been willing to give it credit for. The quad power supplies, quality power amp, and sonic performance are all very strong points in its favor.
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