Q&A # 245 - August 8, 2001

Staff

Q I have a question about hybrid amps (tube pre/SS out). Are they really a viable technology or just another marketing gimmick? How do they compare to a regular tube amp or a solid state amp in terms of sound staging, imaging, frequency response, bass response etc? Could you suggest a good hybrid amp for two-channel music? Also is it better to couple it to a tube preamp or a solid state preamp?

A What you are referring to is a power amplifier that has a tube input stage and transistor output stage. Whatever distortion and other characteristics the input stage has, will be amplified at the output stage, and that is why this unique kind of amplifier was created. The tube, perhaps a 12AX7A, or other classic triode tube, is used as the input stage and run in pure Class A. This results in mostly even-ordered harmonics, which is characteristic of triodes. Secondly, because the plate voltage of tubes is usually way above the voltage that goes to the next stage, or the speakers, tubes are actually much more linear than transistors. So, less negative feedback is required, and often it is none. This even-order harmonic-rich signal is then fed to the output stage (usually a driver in between), and the output stage delivers the current based on the waveform template that the input stage generated. This gives you the rich sound of tubes, but the power of transistors. So, no they are not a gimmick. They really are a neat item. We reviewed one recently (Smart Home Theatre 2X150VT), and it appears to be excellent, especially for the price. You can pay $20,000 for such hybrid amplifiers.

Q Hey guys, just wondering if you could tell me where the better DACs live, in the Toshiba 9100 or the Yamaha RX-V1000? It seems that when I use the Yamaha's DACs, music seems louder, but a bit harsher. Using the analogue outputs on the 9100, the music is softer, but sounds much more mellow. I'm talking about using the 9100 purely as a CD player in these comparison tests. I obviously use the Yamaha for doing all of my DTS and DD decoding.

A It is more than just the DAC chips. The associated circuitry makes a difference too, such as the ability to drive various impedances at the next input down the line. I do not like harshness, so I would use the analog connections that employ the 9100 DACs.

Q Are you planning to update your renown DVD Player shootout to include the Denon DVM-4800 DVD player? I'm most concerned as to why they have gone with the Genesis chipset rather than staying with the Silicon Image de-interlacing chipset used in the DVM 2800. Have they resolved the chroma up-sampling errors you reported in the DVM 2800? Inquiring minds want to know! I'm planning on buying one of these beasts within the next 6 months.

A Fortunately, all the manufacturers know about the chroma bug Don Munsil and Stacey Spears discovered, and I suspect it will be fixed within a year or so. It will be expensive because things have to be completely redone, but in that time frame, if we find players that still are not fixed, it would be best to consider other players where it has been fixed. And the sooner, the better.

Q Is it possible that you could tell us when the results of the DVD shootout II will be available? I just purchased a plasma monitor and have no progressive scan player and need to buy one ASAP. I am afraid of buying the wrong one. I am not even sure which ones have the chroma bug problem. Maybe you could just recommend what to do.

A We are well underway with getting the data ready for publication and will list which players have the problem and which ones don't. However, the chroma bug is not the only thing to consider, and there are lots of nice players out there that happen to have the bug, but otherwise are excellent. The fact that no one seemed to notice it in the first place, until Don Munsil and Stacey Spears first reported on the chroma upsampling error, indicates that it is not that obvious anyway. It is just a problem that we want to see corrected. I have a Toshiba SD-6200 DVD player, and it has the chroma bug, but I still enjoy it very much because the overall picture is really good. I don't pay attention to the chroma bug when I watch movies. What we are trying to do is get manufacturers to fix all the little things that detract from the wonderful picture that DVD is capable of. After the chroma bug, I am sure we will find something else to complain about.

Q I have Sony STR-V333ES receiver and Audiosource Amp3 connected to Klipsch SB-3 monitors. I find the Sony to be an excellent home theater receiver, but the musicality left something to be desired. As a remedy, I bought an Amp3 connected to the receiver pre-outs. This make a big difference, making the bass fuller, the piano and violins less shrill and hard, and gave depth to the stage. Now, I'm wondering about the receiver's preamp stage. I bet I can do even better with a dedicated preamp. But, I still like the flexibility of being able to use some of the many sound effects the receiver gives me, and I like using the sub in the line-out circuit. The receiver has an Analog Direct feature which is a total bypass, but it doesn't use the sub, and I don't want to use the speaker ins to wire it. Given all this, is there any way to connect up a preamp, which would be able to use the sound processing features of the receiver, yet bypass the receiver's pre-out?

A With multiple preamplifier arrangements like this, even using a bypass circuit, you still have to contend with the extra set of cables and RCA jacks that are in the path because you are going through the receiver. In other words, it works, but it is a bandaid at best. A dedicated preamplifier would probably improve the sound over the receiver's preamplifier, but only if it is a good preamplifier. The way I would do this is to have the CD/DVD player go directly to the dedicated preamplifier, and its outputs go to two channels of the power amplifier. Then, using the rec-out jacks of the preamplifier, wire it so that you can switch over to having its outputs go to the receiver for home theater use, and the pre-outs for the front left/right being fed back to the dedicated preamplifier for front left/right control. The pre-outs for the center and rear would go to a different power amplifier (three channels). It sounds complicated, but the idea is to keep the signal path as short and uninterrupted as possible for two-channel listening with the dedicated preamplifier. The other alternative is to just get a top notch surround sound preamp/processor such as Meridian or Theta, and use it as a two-channel preamp when not listening to surround sound.

Q I recently purchased a Rotel RCD-961 CD player. On Rotel's website, the product description says it's a 24 bit player. However, the owner's manual describes the unit as having an 18 bit equivalent DAC. I wrote to Rotel technical support about the issue, and they said that while the 961 is 24 bit capable: "Rotel designers have determined to utilize it at 18 bit resolution for best results in the RCD 961 design." I'm completely confused. If the player is being underutilized at 18 bits, then why design it as a 24 bit in the first place?

A This is not as uncommon as you might assume. By having 24 bits capable, but limiting it to 18 bit, some problems with trying to deal with faulty 20 - 24 bit info is eliminated. Right now, true 24 bit music is pushing the real world capabilities of music recording and reproduction. The truncated bits are in the regions of very quiet detail, and most amplifiers are noisy to the extent that this region is not even relevant.

Q I recently I bought a 36" Sony Wega TV. A friend of mine told me to leave it on for a week to break in the TV. Does this make sense or is it not necessary at all?

A Every electronic component changes over time, including TVs. However, TVs use lots of electricity and are usually set far too high in brightness and contrast. I would suggest, therefore, that you just calibrate it right away for that excessive brightness and contrast, enjoy watching TV, and then, as it changes, readjust the controls.

Q I noticed in the PS Audio P1200 review that when Multiwave was used, the measured AC shot up quite a bit. This can happen if you are not using a "True RMS" meter to measure AC. I work on theatrical and motion picture AC dimming systems and a true RMS meter is must to measure dimmed outputs.

A We are aware of that problem, but when Jason Serinus used Multiwave with the high voltage readings, his tubes started burning out. So, to deal with this issue, we recommend just using the very flexible controls to adjust the voltage readout on the P1200 panel to be about 112 Volts or so, which produces a volt meter reading of no more than 120 Volts.

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