UHF 54 - Passive preamps

The Sima P-400
     Yes, the P-400 is from SimAudio, though the company has largely dropped the Sima name now. The unit is in a long, narrow cast alloy box, with just two controls, for input selection and volume. The styling makes it different from most other preamps, though Albert commented approvingly that it looked like a small Naim unit. There are four inputs. One of them is labelled "tape," but there is no tape output for recording.
     Inside are the same jacks, switch and Noble volume control used in many of SimAudio's much more expensive components. Everything about the unit spells confidence.
     We listened to the P-400 in our Omega system, comparing it to our Copland CTA-301 MkII preamplifier. The output cable is our own E2-W, a Wireworld Equinox fitted with top-of-the-line WBT locking connectors. As the model name suggests, it is two meters long, rather longer than we recommend. We use this longer cable for reasons of flexibility: short cables are impractical in a reference system into which we are constantly plugging new components.
     We began the session with Almighty God from the famous Antiphone Blues disc, not the original, but the superb HDCD-encoded version from First Impressions Music (FIM 010). With our efficient speakers (91 dB rated) and our high-gain SimAudio W-5 amplifier, we got very loud sound placing the volume control at two o'clock (five o'clock is of course the maximum). Would be it be true that, as some claim, this passive unit would lose bottom end and dynamics?
     Certainly it sounded different from our reference preamplifier, but not in the ways the critics suggest. Low organ notes in this unique sax and organ recording were both clean and solid. It was Arne Domnérus's sax that suffered slightly, losing a little (but only a little) of its legendary richness. Still, the sound was broad in its tonal range and arresting in its effect. "Not too shabby," commented Reine at the end of the piece.
     But this recording is known for its remarkable stereo image and its 3-D wraparound sound, and both were somewhat diminished by the P-400. Curiously, the image was shifted leftward, though technical tests failed to indicate why. The sound was slightly more distant, with less of an immersion effect. However we repeat that neither bottom end nor dynamics were affected.
     We then ran our favorite choral recording, Now the Green Blade Riseth (Proprius PRCD9093). The difficult choral voices were astonishingly clean and pure, a delight to listen to. Even in the difficult passages, when both the men and women are singing at once, there was no confusion. The important rhythm of the piece came through well. Never did the music have a grainy texture, as it does with some preamps, even expensive ones.
     Not that the P-400 quite matched our active preamp, whose purity of texture is even better. That extra purity allowed the guitar solo to emerge more clearly. Reine thought that the P-400 decreased the impact of the string bass, though Gerard had written in his notes that the string bass was solid and excellent.
     We ended the session with Saint-Saëns' Danse Macabre from the Minnesota Orchestra's magnificent Mephisto & Co. disc (Reference Recordings RR-82CD). Gorgeous! The dynamics captured by the HDCD process are awesome, and this session laid to rest any notion that a passive preamp can't transmit dynamics. The bottom end was impressive too. Even the passage when the tympany is struck very softly was perfect. Something was missing, though we had difficulty identifying the problem. The viola solo was smooth and even sensuous, but the violin section sounded different, not as refined, less realistic.
     As with the other discs, the stereo image was also a little narrower.
     At our listening level, the output impedance was 14 kilohms, rising to 16 kilohms at full level.
     Is this device as good as a top active preamplifier? No, but we quickly concluded that it can beat some quite expensive preamps -- all those, in fact, that don't do the job properly. At the price, needless to say, there aren't many alternatives.

The F. T. Audio "Little Wonder"
     Yes, we thought the same thing when we first saw the name (which, fortunately, is on a label on the bottom, not silkscreened on the front panel). But then we got a look at the way this passive control unit is made, and we gave it considerable respect.
     It doesn't have the impressive weight or solidity of the Sima, but it is well built, and the parts used are of good quality. The jacks seem to be the same ones SimAudio uses, and there are more of them (which may explain the premium price). Inside is a ceramic rotary switch and the same Alps volume control found in much more expensive active preamps. The Little Wonder has a tape loop -- tape in and out jacks, with a tape-source switch on the front -- something we had never seen on a passive preamplifier. It also has two outputs rather than one, handy if you want to biamplify or feed a subwoofer.
     Though you'd think there can't be much to a passive preamp's circuit, F. T. Audio has something else up its sleeve. Whatever it is can be found inside a sealed module at the output. What's in it? Well, let's see. When we connected the unit to our Omega system, we got a surprise. Because it has no gain, you'd expect to be running the volume at perhaps two o'clock. Not with this one. We turned the volume to ten o'clock and there was plenty of volume, just as on an active preamplifier! What was going on?
     No, it's not magic, but it's clever. Our guess is that an electrical network in the sealed module modifies the potentiometer's resistance curve so that high volume comes early on in the rotation. Sure enough, volume rises slowly beyond ten o'clock, and the total available volume is about what it is with the Sima. But it's a neat trick all the same.
     The output impedance at full level is 100 kilohms, too high for all but a tube amplifier, but at normal level we measured a much more reasonable 16 kilohms.
     Would there be any other differences with the Sima unit? The answer is yes, despite the apparent similarity in the two products.
     The Little Wonder reproduced Almighty God very well, with a little more fullness and a broader stereo image than the Sima. Once again the organ notes were clean, and the saxophone was clear, with beautiful articulation. We could hear the acoustics of the church where this famous recording was made. The image was clear and stable.
     The bottom end? Those who claim passive preamps have a thin bottom end have been listening to the wrong ones. Indeed, we have heard plenty of active preamps whose handling of the lowest notes is way, way inferior.
     We smiled when we heard the bottom end on our choral recording, which was as good as we've heard from any preamp. Highs were altered, however, with some gloss on female voices. Gerard complained of a sheen on the female singers, though he said the effect wasn't truly unpleasant. Instrumental and vocal textures were excellent, but the Little Wonder didn't handle the final crescendo with the same ease as the P-400.
     On the Danse Macabre, the impact of full orchestra was superb, and the bottom end rich. The violin section was smoother than it had been with the P-400, though it still didn't have the refinement and the startlingly lifelike tone it had with our Copland preamp. Other instrumental timbres were rich and clear. We admired the plentiful detail and the dynamics. The melodic line emerged clearly from that mass of sound, prompting Reine to say that the sound served the composer well. The stereo image was excellent, though the recording's great depth was somewhat reduced.
     But, as in the previous recording, the high end was a little more prominent, and this time there was a touch of graininess on loud passages. We're not sure where that graininess comes from, but it underlines the fact that, in audio design, small details count. And despite their similarities, these two passive preamplifiers sound significantly different.
     But it is difficult to state that one of them is simply superior to the other. The sound of one may appeal to you more, of course. The Little Wonder's tape loop may be important if you have a tape deck. And of course the P-400 is simply cheaper.
     But the conclusion can only be this. Whichever you choose, either of these units is a better choice than a second-rate active preamp. And those are more common than is usually supposed.

Model: F.T. Audio Little Wonder
Price (in Canada): $695
Dimensions (cm): 21 x 7.6 x 21.5
Warranty: Not stated
Most liked: Very good performance, fine stereo image
Least liked: A bit of a sheen in the top frequencies
Verdict: Nice product, but lose the name

     If I were using an integrated amp and looking for an upgrade, I would certainly consider a good power amp coupled to either one of these two passive preamps. As a matter of fact, I could then afford a much better power amplifier if I went this route and, after listening to these units, I’m convinced that anyone could develop an equally long and lasting friendship with either of them.
     With the Sima the stage receded slightly and voices were wonderful. With the FT Audio I was closer to the performance and I could locate the instruments with more accuracy but when voices rose to a crescendo I wanted to move back a few rows.
     Both units had good solid bass and instruments timbres were quite good. Musical textures were amazingly reproduced as a whole and it was soothing to hear the near silkiness of strings without effort. I find that rare, even among preamps costing two or three times the price of these passive control units.
     Don’t skimp on the cable, though. You want your passive preamp to be as transparent as possible and not get in the way of the music. If you get a poor cable to link it to your (now great) power amp, you’d be like this car driver who keeps cleaning his glasses while trying to save on windshield washer fluid.
—Albert Simon

     Why am I even surprised that these two devices, which appear to be similarly made, don’t actually sound the same? After all, I know from experience that two pieces of wire that look perfectly identical may not sound alike either.
     In fact, there’s an important lesson in this test for preamplifier designers, and the lesson is this: your circuit design is not the only factor that will determine the sound of your product. Even the tiniest details make a difference, and if you don’t pay attention to them then the rest of your work may have been for nothing.
     As for me, if I were trying to build a really good system on a budget, I would consider these two products most seriously. Buy a great power amplifier, add either of these inexpensive boxes, and link them with a good cable, and you’re well launched on the road to great music at home. You may pick up a conventional active preamp later, but it’s going to take a good one to beat this.
     Which one to pick? I do like the Sima’s top end better, but then again I wish it projected as strong a stereo image as the Little Wonder does. The difference is not huge, frankly, and I like them both.
—Gerard Rejskind

     If it’s musicality and lyricism that matter to you when you listen to music on your system, these two passive preamplifiers are excellent. They produce a warm, clear, detailed sound. They are strong on rhythm, and either energetic or gentle as the music demands. Voices are pleasant, and even choral sopranos have a smoothness that is reassuring. I liked the stability of the image. In the orchestral piece, whose theme calls up a strange atmosphere and disconcerting dances, the natural reverberation takes us to the world of the story. It is easy to imagine the scenes the composer draws. The tuttis are energetic. As for the organ, whose stops are varied and forceful, they suffer no confusion.
     I consider that these two preamps are a sure value at attractive prices.
—Reine Lessard



			Two Passive Preamps A preamplifier that doesn't amplify may be cheap, but is it good? The answers turn out to be yes and yes. (Reprinted from issue 54 of UHF Magazine. To purchase the issue, click here.)
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			You'd think it would be easy to design a high quality preamplifier, because it doesn't really need to do much amplifying. It takes a signal of one to two volts and puts out a signal of two to four volts. Some 6 dB of amplification should be more than enough, shouldn't it? Yet that 6 dB of gain isn't easy to come by, not if you want to maintain the musical values of the signal (and many preamps have more gain than anyone could use). Cheap preamps sound bright and hard and awful, and good ones have large price tags. Enter the passive preamp. What if you could do without that 6 dB of gain, just by turning up the volume a bit louder? Wouldn't no circuit be better than a poor circuit? Some people claim otherwise. They maintain that a passive preamp ("passive" because it has no "active" amplifying circuit) has weak dynamics and weaker bass. Our experience contradicts that. We decided to compare two passive preamps to the reference preamp in our Omega system. One is made in Canada, the other in Hong Kong. Both are far cheaper than virtually any active preamplifier Before we go on, we should add that passive preamps won't work in all systems. If your loudspeakers are too inefficient (less than 87 dB or so), then turning the volume control all the way up may not give you all the loudness you want. A few rare amplifiers with low input impedances (below 20,000 ohms) won't match the high impedance of a passive preamp without distortion. Finally, that same high impedance tends to magnify the flaws in the cable linking the passive to the power amp. That cable must be both short and excellent. Of course, if instead of a passive you bought an active super preamp, you wouldn't want to hook it up with a piece of string either. The Sima P-400 Yes, the P-400 is from SimAudio, though the company has largely dropped the Sima name now. The unit is in a long, narrow cast alloy box, with just two controls, for input selection and volume. The styling makes it different from most other preamps, though Albert commented approvingly that it looked like a small Naim unit. There are four inputs. One of them is labelled "tape," but there is no tape output for recording. Inside are the same jacks, switch and Noble volume control used in many of SimAudio's much more expensive components. Everything about the unit spells confidence. We listened to the P-400 in our Omega system, comparing it to our Copland CTA-301 MkII preamplifier. The output cable is our own E2-W, a Wireworld Equinox fitted with top-of-the-line WBT locking connectors. As the model name suggests, it is two meters long, rather longer than we recommend. We use this longer cable for reasons of flexibility: short cables are impractical in a reference system into which we are constantly plugging new components. We began the session with Almighty God from the famous Antiphone Blues disc, not the original, but the superb HDCD-encoded version from First Impressions Music (FIM 010). With our efficient speakers (91 dB rated) and our high-gain SimAudio W-5 amplifier, we got very loud sound placing the volume control at two o'clock (five o'clock is of course the maximum). Would be it be true that, as some claim, this passive unit would lose bottom end and dynamics? Certainly it sounded different from our reference preamplifier, but not in the ways the critics suggest. Low organ notes in this unique sax and organ recording were both clean and solid. It was Arne Domnérus's sax that suffered slightly, losing a little (but only a little) of its legendary richness. Still, the sound was broad in its tonal range and arresting in its effect. "Not too shabby," commented Reine at the end of the piece. But this recording is known for its remarkable stereo image and its 3-D wraparound sound, and both were somewhat diminished by the P-400. Curiously, the image was shifted leftward, though technical tests failed to indicate why. The sound was slightly more distant, with less of an immersion effect. However we repeat that neither bottom end nor dynamics were affected. We then ran our favorite choral recording, Now the Green Blade Riseth (Proprius PRCD9093). The difficult choral voices were astonishingly clean and pure, a delight to listen to. Even in the difficult passages, when both the men and women are singing at once, there was no confusion. The important rhythm of the piece came through well. Never did the music have a grainy texture, as it does with some preamps, even expensive ones. Not that the P-400 quite matched our active preamp, whose purity of texture is even better. That extra purity allowed the guitar solo to emerge more clearly. Reine thought that the P-400 decreased the impact of the string bass, though Gerard had written in his notes that the string bass was solid and excellent. We ended the session with Saint-Saëns' Danse Macabre from the Minnesota Orchestra's magnificent Mephisto & Co. disc (Reference Recordings RR-82CD). Gorgeous! The dynamics captured by the HDCD process are awesome, and this session laid to rest any notion that a passive preamp can't transmit dynamics. The bottom end was impressive too. Even the passage when the tympany is struck very softly was perfect. Something was missing, though we had difficulty identifying the problem. The viola solo was smooth and even sensuous, but the violin section sounded different, not as refined, less realistic. As with the other discs, the stereo image was also a little narrower. At our listening level, the output impedance was 14 kilohms, rising to 16 kilohms at full level. Is this device as good as a top active preamplifier? No, but we quickly concluded that it can beat some quite expensive preamps -- all those, in fact, that don't do the job properly. At the price, needless to say, there aren't many alternatives. Model: Sima P-400 Price (in Canada): $495 Dimensions (cm): 13 x 7.4 x 24 Warranty: 5 years, transferable Most liked: Smooth, broad bandwidth, solid construction Least liked: Limited stereo image Verdict: A great way to free up money for a terrific amp or source The F. T. Audio "Little Wonder" Yes, we thought the same thing when we first saw the name (which, fortunately, is on a label on the bottom, not silkscreened on the front panel). But then we got a look at the way this passive control unit is made, and we gave it considerable respect. It doesn't have the impressive weight or solidity of the Sima, but it is well built, and the parts used are of good quality. The jacks seem to be the same ones SimAudio uses, and there are more of them (which may explain the premium price). Inside is a ceramic rotary switch and the same Alps volume control found in much more expensive active preamps. The Little Wonder has a tape loop -- tape in and out jacks, with a tape-source switch on the front -- something we had never seen on a passive preamplifier. It also has two outputs rather than one, handy if you want to biamplify or feed a subwoofer. Though you'd think there can't be much to a passive preamp's circuit, F. T. Audio has something else up its sleeve. Whatever it is can be found inside a sealed module at the output. What's in it? Well, let's see. When we connected the unit to our Omega system, we got a surprise. Because it has no gain, you'd expect to be running the volume at perhaps two o'clock. Not with this one. We turned the volume to ten o'clock and there was plenty of volume, just as on an active preamplifier! What was going on? No, it's not magic, but it's clever. Our guess is that an electrical network in the sealed module modifies the potentiometer's resistance curve so that high volume comes early on in the rotation. Sure enough, volume rises slowly beyond ten o'clock, and the total available volume is about what it is with the Sima. But it's a neat trick all the same. The output impedance at full level is 100 kilohms, too high for all but a tube amplifier, but at normal level we measured a much more reasonable 16 kilohms. Would there be any other differences with the Sima unit? The answer is yes, despite the apparent similarity in the two products. The Little Wonder reproduced Almighty God very well, with a little more fullness and a broader stereo image than the Sima. Once again the organ notes were clean, and the saxophone was clear, with beautiful articulation. We could hear the acoustics of the church where this famous recording was made. The image was clear and stable. The bottom end? Those who claim passive preamps have a thin bottom end have been listening to the wrong ones. Indeed, we have heard plenty of active preamps whose handling of the lowest notes is way, way inferior. We smiled when we heard the bottom end on our choral recording, which was as good as we've heard from any preamp. Highs were altered, however, with some gloss on female voices. Gerard complained of a sheen on the female singers, though he said the effect wasn't truly unpleasant. Instrumental and vocal textures were excellent, but the Little Wonder didn't handle the final crescendo with the same ease as the P-400. On the Danse Macabre, the impact of full orchestra was superb, and the bottom end rich. The violin section was smoother than it had been with the P-400, though it still didn't have the refinement and the startlingly lifelike tone it had with our Copland preamp. Other instrumental timbres were rich and clear. We admired the plentiful detail and the dynamics. The melodic line emerged clearly from that mass of sound, prompting Reine to say that the sound served the composer well. The stereo image was excellent, though the recording's great depth was somewhat reduced. But, as in the previous recording, the high end was a little more prominent, and this time there was a touch of graininess on loud passages. We're not sure where that graininess comes from, but it underlines the fact that, in audio design, small details count. And despite their similarities, these two passive preamplifiers sound significantly different. But it is difficult to state that one of them is simply superior to the other. The sound of one may appeal to you more, of course. The Little Wonder's tape loop may be important if you have a tape deck. And of course the P-400 is simply cheaper. But the conclusion can only be this. Whichever you choose, either of these units is a better choice than a second-rate active preamp. And those are more common than is usually supposed. Model: F.T. Audio Little Wonder Price (in Canada): $695 Dimensions (cm): 21 x 7.6 x 21.5 Warranty: Not stated Most liked: Very good performance, fine stereo image Least liked: A bit of a sheen in the top frequencies Verdict: Nice product, but lose the name CROSSTALK If I were using an integrated amp and looking for an upgrade, I would certainly consider a good power amp coupled to either one of these two passive preamps. As a matter of fact, I could then afford a much better power amplifier if I went this route and, after listening to these units, I’m convinced that anyone could develop an equally long and lasting friendship with either of them. With the Sima the stage receded slightly and voices were wonderful. With the FT Audio I was closer to the performance and I could locate the instruments with more accuracy but when voices rose to a crescendo I wanted to move back a few rows. Both units had good solid bass and instruments timbres were quite good. Musical textures were amazingly reproduced as a whole and it was soothing to hear the near silkiness of strings without effort. I find that rare, even among preamps costing two or three times the price of these passive control units. Don’t skimp on the cable, though. You want your passive preamp to be as transparent as possible and not get in the way of the music. If you get a poor cable to link it to your (now great) power amp, you’d be like this car driver who keeps cleaning his glasses while trying to save on windshield washer fluid. —Albert Simon Why am I even surprised that these two devices, which appear to be similarly made, don’t actually sound the same? After all, I know from experience that two pieces of wire that look perfectly identical may not sound alike either. In fact, there’s an important lesson in this test for preamplifier designers, and the lesson is this: your circuit design is not the only factor that will determine the sound of your product. Even the tiniest details make a difference, and if you don’t pay attention to them then the rest of your work may have been for nothing. As for me, if I were trying to build a really good system on a budget, I would consider these two products most seriously. Buy a great power amplifier, add either of these inexpensive boxes, and link them with a good cable, and you’re well launched on the road to great music at home. You may pick up a conventional active preamp later, but it’s going to take a good one to beat this. Which one to pick? I do like the Sima’s top end better, but then again I wish it projected as strong a stereo image as the Little Wonder does. The difference is not huge, frankly, and I like them both. —Gerard Rejskind If it’s musicality and lyricism that matter to you when you listen to music on your system, these two passive preamplifiers are excellent. They produce a warm, clear, detailed sound. They are strong on rhythm, and either energetic or gentle as the music demands. Voices are pleasant, and even choral sopranos have a smoothness that is reassuring. I liked the stability of the image. In the orchestral piece, whose theme calls up a strange atmosphere and disconcerting dances, the natural reverberation takes us to the world of the story. It is easy to imagine the scenes the composer draws. The tuttis are energetic. As for the organ, whose stops are varied and forceful, they suffer no confusion. I consider that these two preamps are a sure value at attractive prices. —Reine Lessard [TABLE OF CONTENTS] [READING ROOM] [HOME PAGE]