Ferbose
Headphoneus Supremus
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- Jun 27, 2004
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PreSonus Central Station (CS) is a seemingly complex product packed with more features than most audiophiles are used to. But it is an elegant one-box solution that competes with many dedicated components. Its plain looks and modest asking price ($500) belies its reference-quality sound. By audiophile standards CS seems like a miracle product for its value/price ratio. CS is selling very well in the pro-audio market due to its features and sound, and hence the economics behind CS is totally different from audiophile products. From my personal experience and discussion with other CS users, I believe CS is the affordable ticket to hi-end sound that many fledging audiophiles seek. It is not going to be easy to explain what CS is and does, and how to get the most out of it, so bear with me.
Part I. Inside and Out
Front View
Rear View
Inside View (a separate rear circuit board is removed)
A closer look at the mechanical relays (yellow rectangles). 34 of these pricy relays ($200 for 100 pieces) are used to build a state-of-the-art passive preamp.
Part II. Main features
For audiophiles CS can provide a DAC, two independent headphone amplifiers, a passive and an active preamp, and a line-level input/output selector—it's the audio equivalent of Swiss army officer's knife. Before computers, the centerpiece of the studio is the mixer. With computer audio the mixer is no longer required but many of its I/O functions are still needed. CS is designed to replace the mixer in the computer audio setup. CS's many uses in a studio are illustrated in this picture:
To fully appreciate the many functions of CS, its manual includes this block diagram, which is complete and accurate AFAIK:
Part IV. DAC Quality
Simply put, CS's internal DAC (192 kHz/24 bit) can compete with stand-alone DACs in the $500 range. In all honesty, as receiving and D/A chips continue to improve, differences between DACs across different price ranges are quickly shrinking.
Looking inside, I see AKM chips for S/PDIF receiver (AK4117VF) and D/A converter (AK4394VF), and Motorola MC33079D for output stage. These chips are commonplace, but the proof of sound quality is always in the ear, not the parts list.
At home I compared CS to Benchmark DAC1 ($975 in 2004) and Sony DVP-NS900V ($800 in 2002). DAC1 sounds a bit more detailed and refined than CS, but the difference is so small that under instant A/B they could appear identical. The Sony is a first-generation SACD/DVD player known for its audio quality. But the difference between Sony and CS is less subtle. CS has better low-level details and less grain in the treble. To bring out the best sound from CS, I find power conditioning to be rather beneficial. CS uses an outboard PSU that looks like a jumbo wall-wart. Plugging CS into my Furman Power Factor Pro conditioner ($230), details are better resolved and treble becomes smoother. This is not to say CS has an apparent flaw in its power supply design, since my Sony player benefits similarly from power conditioning. In contrast, DAC1 seems to benefit minimally from conditioning if at all, but it is well known that DAC1 has a very robust power supply. In my system the Toslink sounds better than coaxial digital input, but YMMV.
A meet situation is less than ideal for judging a DAC, but it can still provide some perspectives. At a meet I set up an A/B of CS against Esoteric DV-50S's, while CS is plugged into my Furman conditioner. The person who brought DV-50S ($5000) did a blind test using my Cayin tube amp and K1000. He ended up picking CS as the better source after 10 min of listening. This is only for fun and proves nothing, but I was impressed by CS nonetheless. Also, DV-50S is a heck of a transport and probably made CS sound better than usual. In another setup, CS was not plugged into any conditioner in a four-way comparison against AQVOX ($800), Lavry DA10 ($1000) and Benchmark, and CS sounded almost as good except for a slight sibilance in the treble.
A fellow head-fier music_man took CS to his work place, a professional studio, and reported that CS outperformed certain DACs in the $1000 range. His studio has very clean AC coming out of a monstrous APC power system. Music_man's view is echoed in a pro-audio review in Mix magazine, in which CS is said to be as good, if not better than Apogee's Mini DAC ($900). Proper power conditioning can turn CS from a pretty good DAC into a hi-end unit holding its own against the big boys, and the same applies to its headphone amp. A decent conditioner like Furman Power Factor Pro ($230) is really a worthwhile investment for CS owners, in terms of sonic improvement and equipment protection. Furman is the leader in power treatment for sound professionals, and another trustworthy brand is APC, the power leader in the computer industry.
As such, CS can confidently compete with stand-alone DACs in the $500 range. I did find a cheaper DAC that sounds just as good, the fully modified Zhaolu D1.3 at around $300. But Zhaolu is shipped from Asian modders and offers practically no service or warranty. PreSonus is an American pro-audio company (CS is made in China) with real service and support. Moreover, CS can be bought at Guitar Centers for under $500 and this allows for home auditioning.
Headphone Amplifier Sound Quality
CS offers two independent headphone amplifiers that can play two different sources simultaneously. The OP-amp is Motorola MC33079D, and the distortion spec is not especially low (0.015% THD+N at 150 mW into 60 ohms). At the first glance, the amps seemed like an afterthought, and I had pretty low expectations because I was previously underwhelmed by PreSonus HP4. It turns out I am dead wrong.
At home I compared CS's headphone jack to Benchmark DAC1. Although DAC1's amp measures impressively, CS clearly betters it with smoother treble and warmer midrange. DAC1's amp is "lean and mean" while CS is "big and easy." To be fair, the amp module in DAC1 (priced at $150 as separate PCB) is decent for its price, at least still a league above the stock amp of a Zhaolu D1.3 which sounds muffled and loses details. CS is not as warm as my Cayin HA-1A single-ended tube amplifier ($750), but it is just as pleasant on the ears. Stereophile recently published a rave review on HA-1A but CS is just as good.
At a meet I compared CS with an RSA Hornet and found CS to sound bigger and Hornet ($300) a bit sweeter. Neither is better but just different. Strangely, CS and Grace m902 ($1500) instant A/B via a switch box sounded almost identical to me and another head-fier. I thought that was a fluke under the meet situation, until music_man posted a comparison of the two at his studio. He and his Grammy-winning engineer boss agreed that CS sounds better, and replaced m902 immediately. I must say I am surprised by CS "giant-killer" potentials.
In addition, Head-fier Uncle Erik posted that he detested K501's anemic bass until he used it on a CS. Another European head-fier told me in a private correspondence that CS is as good as his older Corda PreHead. Based on these opinions I think it is fair to say that CS is a reference-quality headphone amplifier (m902 is the current reference in studios). CS has its sonic character, which is smooth and relaxed by SS standards. It takes away the sibilance in K501's treble, and reduces the edge on SR225. The amp is very quiet but does not sound hyper-detailed. The background is black on portable cans like KSC-75 or PX-100. At the same it is immensely powerful, to the point that I regularly use K1000 (only 74 dB/mW) with CS for jazz. Considering that K1000 is 46 dB less sensitive than PX-100, the dynamic range of the amp seems boundless. The dynamic range, bass fullness and expansive soundstage together give the amp a "big" sound.
The headphone section on CS also improves with proper power conditioning, just like the DAC section. A more surprising finding is that "cue" pathway sounds better than "main" pathway through the headphone jack. According to the block diagram the "cue" pathway has one extra volume pot and two op-amps, but it actually sounds smoother.
Pre-amp Sound Quality
CS can be used both as a passive and an active preamp. The main selling point is CS is its passive preamp, a state-of-the-art design with utter transparency. The signal path consists of military-grade resistors and mechanical relays. Relays are controlled by programmable chips to determine the suitable combination of resistors for each volume setting. The proper name is digitally controlled analog switched resistor network. You can find similar designs in Theta Gen VIII DAC or Rega Cursa 3 preamps, but in those machines there are still transistors in the signal path (active). In CS it is completely passive. Although the volume is digitally controlled, PreSonus tries to make it feel analog. The main volume knob is not stepped and it only controls the programmable chip. The volume changes smoothly when the knob is turned and there is no digital readout. The relays (NEC EE2-12NUX, $200 for 100 pieces) look like yellow rectangles and 34 of them of used. CS is well worth its price just for these costly parts.
Theoretically the passive preamp has the cleanest sound, cleaner than any active preamp. In reality passive preamp is often compromised by impedance mismatch (low input impedance and high output impedance). To tackle the impedance problem multiple resistors in the signal path have to be variable/switchable. Passive preamps using only a single variable resistor (potentiometer or stepped attenuator) will always exhibit impedance mismatch. Some hi-end stepped attenuators have a separate resistor network (on a circuit board) at each step to swap multiple resistors in and out of the signal path. But these are bulky, expensive, and have limited steps and potential contact problems. The high-tech solution is to use a network of resistors and digitally controlled relays to do the switching. The relays in CS can withstand 10 million operations (that's 1000 times a day for 25 years), so it will outlast potentiometers or stepped attenuators. From my research I believe CS's circuitry is the best way to construct a passive preamp today, but it has not been adopted by any audiophile passive preamp.
Did CS actually solve the impedance mismatch problem? According to PreSonus the output impedance of CS is the same as the upstream source but the input impedance of CS is 2-5 kohms. Active preamps generally have input impedance of 50-100 kohms. So the key is the ability of the source to drive a load of lower impedance. 2V output into a 2 kohm load requires only 1 mA of current, and the output stage of decent sources today should not distort at such levels. For instance, Benchmark DAC1 can even drive a 120 ohm load (i.e., a headphone) very well via XLR out. Of course it is also desirable to keep the cable length short and capacitance low, but most audiophiles are already doing that.
On paper, CS's passive volume control is state-of-the-art. But how does it sound? I have read half a dozen pro-audio reviews of CS and they all agree that it sounds like nothing is there. My personal experience is the same. I have connected different components to the passive preamp output of CS and never sensed any change to the sound. The engineer who designed Benchmark DAC1 insists that the front volume pot (bypassable) does not alter the sound, but many users and including myself feel otherwise. I actually bypass DAC1's volume pot and use CS's passive preamp to achieve total transparency.
I don't have another preamp at home to compare to CS. But music_man took a CS to his studio at work and posted that CS sounds better than a highly-regarded Manley tube preamp. Well, I guess the transparency of a passive preamp is hard to beat at any price.
CS uses cutting-edge circuitry to tackle the impedance problem which has plagued passive preamps for decades. It looks like PreSonus has succeeded and turned CS into a breakthrough product. A no-compromise preamp at $500 is unheard of, and PreSonus is only able to pull it off because of high sales volume. CS is aiming at the entire pro-audio market switching from mixers to computers. With the success of CS, I suspect that "switched resistor network" will soon become the new trend in volume control circuitry.
Input and Output
CS can act as a source selector (two digital, three analog), and as an output selector. The analog inputs and outputs are TRS jacks. One can use TS plugs for unbalanced and TRS plugs for balanced. CS automatically detects/converts between balanced and unbalanced signals. I personally use Mogami TRS-to-XLR and Pro-Co TS-to-RCA cable. CS might restrict the use of hi-end interconnects but I don't see why using hi-quality/low-price Mogami or Pro-Co cables would be a compromise in any way. The three passive outs (A/B/C) can be individually activated but A and B can't be simultaneously on.
Conclusion
PreSonus Central Station is highly versatile, and exhibits excellent sound quality in every application. It certainly can compete with standalone DACs or headphone amps in the $500 range. As a preamp it is state-of-the-art. CS is a great one-box solution for anyone trying to build a quality speaker and/or headphone system on a budget. No audiophile company could ever offer such a great value at such a low price, but fortunately CS is a pro-audio gear that sells a lot and therefore governed by very different economics. Its utilitarian looks might scare away some audiophiles but that's hardly a reason to not recommend this ground-breaking product to everyone.
Part I. Inside and Out
Front View
Rear View
Inside View (a separate rear circuit board is removed)
A closer look at the mechanical relays (yellow rectangles). 34 of these pricy relays ($200 for 100 pieces) are used to build a state-of-the-art passive preamp.
Part II. Main features
For audiophiles CS can provide a DAC, two independent headphone amplifiers, a passive and an active preamp, and a line-level input/output selector—it's the audio equivalent of Swiss army officer's knife. Before computers, the centerpiece of the studio is the mixer. With computer audio the mixer is no longer required but many of its I/O functions are still needed. CS is designed to replace the mixer in the computer audio setup. CS's many uses in a studio are illustrated in this picture:
To fully appreciate the many functions of CS, its manual includes this block diagram, which is complete and accurate AFAIK:
Part IV. DAC Quality
Simply put, CS's internal DAC (192 kHz/24 bit) can compete with stand-alone DACs in the $500 range. In all honesty, as receiving and D/A chips continue to improve, differences between DACs across different price ranges are quickly shrinking.
Looking inside, I see AKM chips for S/PDIF receiver (AK4117VF) and D/A converter (AK4394VF), and Motorola MC33079D for output stage. These chips are commonplace, but the proof of sound quality is always in the ear, not the parts list.
At home I compared CS to Benchmark DAC1 ($975 in 2004) and Sony DVP-NS900V ($800 in 2002). DAC1 sounds a bit more detailed and refined than CS, but the difference is so small that under instant A/B they could appear identical. The Sony is a first-generation SACD/DVD player known for its audio quality. But the difference between Sony and CS is less subtle. CS has better low-level details and less grain in the treble. To bring out the best sound from CS, I find power conditioning to be rather beneficial. CS uses an outboard PSU that looks like a jumbo wall-wart. Plugging CS into my Furman Power Factor Pro conditioner ($230), details are better resolved and treble becomes smoother. This is not to say CS has an apparent flaw in its power supply design, since my Sony player benefits similarly from power conditioning. In contrast, DAC1 seems to benefit minimally from conditioning if at all, but it is well known that DAC1 has a very robust power supply. In my system the Toslink sounds better than coaxial digital input, but YMMV.
A meet situation is less than ideal for judging a DAC, but it can still provide some perspectives. At a meet I set up an A/B of CS against Esoteric DV-50S's, while CS is plugged into my Furman conditioner. The person who brought DV-50S ($5000) did a blind test using my Cayin tube amp and K1000. He ended up picking CS as the better source after 10 min of listening. This is only for fun and proves nothing, but I was impressed by CS nonetheless. Also, DV-50S is a heck of a transport and probably made CS sound better than usual. In another setup, CS was not plugged into any conditioner in a four-way comparison against AQVOX ($800), Lavry DA10 ($1000) and Benchmark, and CS sounded almost as good except for a slight sibilance in the treble.
A fellow head-fier music_man took CS to his work place, a professional studio, and reported that CS outperformed certain DACs in the $1000 range. His studio has very clean AC coming out of a monstrous APC power system. Music_man's view is echoed in a pro-audio review in Mix magazine, in which CS is said to be as good, if not better than Apogee's Mini DAC ($900). Proper power conditioning can turn CS from a pretty good DAC into a hi-end unit holding its own against the big boys, and the same applies to its headphone amp. A decent conditioner like Furman Power Factor Pro ($230) is really a worthwhile investment for CS owners, in terms of sonic improvement and equipment protection. Furman is the leader in power treatment for sound professionals, and another trustworthy brand is APC, the power leader in the computer industry.
As such, CS can confidently compete with stand-alone DACs in the $500 range. I did find a cheaper DAC that sounds just as good, the fully modified Zhaolu D1.3 at around $300. But Zhaolu is shipped from Asian modders and offers practically no service or warranty. PreSonus is an American pro-audio company (CS is made in China) with real service and support. Moreover, CS can be bought at Guitar Centers for under $500 and this allows for home auditioning.
Headphone Amplifier Sound Quality
CS offers two independent headphone amplifiers that can play two different sources simultaneously. The OP-amp is Motorola MC33079D, and the distortion spec is not especially low (0.015% THD+N at 150 mW into 60 ohms). At the first glance, the amps seemed like an afterthought, and I had pretty low expectations because I was previously underwhelmed by PreSonus HP4. It turns out I am dead wrong.
At home I compared CS's headphone jack to Benchmark DAC1. Although DAC1's amp measures impressively, CS clearly betters it with smoother treble and warmer midrange. DAC1's amp is "lean and mean" while CS is "big and easy." To be fair, the amp module in DAC1 (priced at $150 as separate PCB) is decent for its price, at least still a league above the stock amp of a Zhaolu D1.3 which sounds muffled and loses details. CS is not as warm as my Cayin HA-1A single-ended tube amplifier ($750), but it is just as pleasant on the ears. Stereophile recently published a rave review on HA-1A but CS is just as good.
At a meet I compared CS with an RSA Hornet and found CS to sound bigger and Hornet ($300) a bit sweeter. Neither is better but just different. Strangely, CS and Grace m902 ($1500) instant A/B via a switch box sounded almost identical to me and another head-fier. I thought that was a fluke under the meet situation, until music_man posted a comparison of the two at his studio. He and his Grammy-winning engineer boss agreed that CS sounds better, and replaced m902 immediately. I must say I am surprised by CS "giant-killer" potentials.
In addition, Head-fier Uncle Erik posted that he detested K501's anemic bass until he used it on a CS. Another European head-fier told me in a private correspondence that CS is as good as his older Corda PreHead. Based on these opinions I think it is fair to say that CS is a reference-quality headphone amplifier (m902 is the current reference in studios). CS has its sonic character, which is smooth and relaxed by SS standards. It takes away the sibilance in K501's treble, and reduces the edge on SR225. The amp is very quiet but does not sound hyper-detailed. The background is black on portable cans like KSC-75 or PX-100. At the same it is immensely powerful, to the point that I regularly use K1000 (only 74 dB/mW) with CS for jazz. Considering that K1000 is 46 dB less sensitive than PX-100, the dynamic range of the amp seems boundless. The dynamic range, bass fullness and expansive soundstage together give the amp a "big" sound.
The headphone section on CS also improves with proper power conditioning, just like the DAC section. A more surprising finding is that "cue" pathway sounds better than "main" pathway through the headphone jack. According to the block diagram the "cue" pathway has one extra volume pot and two op-amps, but it actually sounds smoother.
Pre-amp Sound Quality
CS can be used both as a passive and an active preamp. The main selling point is CS is its passive preamp, a state-of-the-art design with utter transparency. The signal path consists of military-grade resistors and mechanical relays. Relays are controlled by programmable chips to determine the suitable combination of resistors for each volume setting. The proper name is digitally controlled analog switched resistor network. You can find similar designs in Theta Gen VIII DAC or Rega Cursa 3 preamps, but in those machines there are still transistors in the signal path (active). In CS it is completely passive. Although the volume is digitally controlled, PreSonus tries to make it feel analog. The main volume knob is not stepped and it only controls the programmable chip. The volume changes smoothly when the knob is turned and there is no digital readout. The relays (NEC EE2-12NUX, $200 for 100 pieces) look like yellow rectangles and 34 of them of used. CS is well worth its price just for these costly parts.
Theoretically the passive preamp has the cleanest sound, cleaner than any active preamp. In reality passive preamp is often compromised by impedance mismatch (low input impedance and high output impedance). To tackle the impedance problem multiple resistors in the signal path have to be variable/switchable. Passive preamps using only a single variable resistor (potentiometer or stepped attenuator) will always exhibit impedance mismatch. Some hi-end stepped attenuators have a separate resistor network (on a circuit board) at each step to swap multiple resistors in and out of the signal path. But these are bulky, expensive, and have limited steps and potential contact problems. The high-tech solution is to use a network of resistors and digitally controlled relays to do the switching. The relays in CS can withstand 10 million operations (that's 1000 times a day for 25 years), so it will outlast potentiometers or stepped attenuators. From my research I believe CS's circuitry is the best way to construct a passive preamp today, but it has not been adopted by any audiophile passive preamp.
Did CS actually solve the impedance mismatch problem? According to PreSonus the output impedance of CS is the same as the upstream source but the input impedance of CS is 2-5 kohms. Active preamps generally have input impedance of 50-100 kohms. So the key is the ability of the source to drive a load of lower impedance. 2V output into a 2 kohm load requires only 1 mA of current, and the output stage of decent sources today should not distort at such levels. For instance, Benchmark DAC1 can even drive a 120 ohm load (i.e., a headphone) very well via XLR out. Of course it is also desirable to keep the cable length short and capacitance low, but most audiophiles are already doing that.
On paper, CS's passive volume control is state-of-the-art. But how does it sound? I have read half a dozen pro-audio reviews of CS and they all agree that it sounds like nothing is there. My personal experience is the same. I have connected different components to the passive preamp output of CS and never sensed any change to the sound. The engineer who designed Benchmark DAC1 insists that the front volume pot (bypassable) does not alter the sound, but many users and including myself feel otherwise. I actually bypass DAC1's volume pot and use CS's passive preamp to achieve total transparency.
I don't have another preamp at home to compare to CS. But music_man took a CS to his studio at work and posted that CS sounds better than a highly-regarded Manley tube preamp. Well, I guess the transparency of a passive preamp is hard to beat at any price.
CS uses cutting-edge circuitry to tackle the impedance problem which has plagued passive preamps for decades. It looks like PreSonus has succeeded and turned CS into a breakthrough product. A no-compromise preamp at $500 is unheard of, and PreSonus is only able to pull it off because of high sales volume. CS is aiming at the entire pro-audio market switching from mixers to computers. With the success of CS, I suspect that "switched resistor network" will soon become the new trend in volume control circuitry.
Input and Output
CS can act as a source selector (two digital, three analog), and as an output selector. The analog inputs and outputs are TRS jacks. One can use TS plugs for unbalanced and TRS plugs for balanced. CS automatically detects/converts between balanced and unbalanced signals. I personally use Mogami TRS-to-XLR and Pro-Co TS-to-RCA cable. CS might restrict the use of hi-end interconnects but I don't see why using hi-quality/low-price Mogami or Pro-Co cables would be a compromise in any way. The three passive outs (A/B/C) can be individually activated but A and B can't be simultaneously on.
Conclusion
PreSonus Central Station is highly versatile, and exhibits excellent sound quality in every application. It certainly can compete with standalone DACs or headphone amps in the $500 range. As a preamp it is state-of-the-art. CS is a great one-box solution for anyone trying to build a quality speaker and/or headphone system on a budget. No audiophile company could ever offer such a great value at such a low price, but fortunately CS is a pro-audio gear that sells a lot and therefore governed by very different economics. Its utilitarian looks might scare away some audiophiles but that's hardly a reason to not recommend this ground-breaking product to everyone.
