Q I have a Denon AVR3600 which I use for both cinema and music. Do I require a separate amplifier for my music listening? If so, what would you recommend? For a subwoofer, would it be better to buy one that is active or passive? Having a look at your previous recommendations I feel maybe I should change my rear speakers to be the same as my fronts. I am still not sure of the benefit. My system consists of Denon AVR3600, Marantz CD53, Aaron ATS5 (front), Boston 575THX (rear), Aaron cc120 (center).

A The 3600 has 110 watts/channel for all five channels, and also has pre-out jacks for all the channels. It is a DD receiver, so I assume you are using that feature with a laserdisc player or DVD player. In any case, the power of this receiver is adequate for most listening in either cinema or music modes. If you like action movies and crank the system up, then it would probably be a good idea to get a three channel outboard power amplifier to drive the center and front left/right channels. This will free up the receiver's power supply to drive the rear left/right channels of the built-in amplifiers. Get something with 200 watts/channel for the center and front left/right. The Adcom GFA-5503 would be a good place to start your listening tests. Also look at the Carver A-753. Go with an active subwoofer. The built-in amplifiers for active subs have controls that are very handy, such as variable low pass and phase. The benefit of having rear speakers that are the same as the front is with digital surround where the sound is full spectrum in all the channels. That way, the tonality of the surround sound is the same all around the room. You will notice this benefit especially with such sound effects as jets, cars, and other moving objects that pass from front to back or back to front.

Q I noticed that the outputs from the rectifier diodes in my amplfier's power supply go to the capacitors, and the capacitors go to the amplifier section. Because the power supply capacitors are connected in parallel between the diodes and amplifier stages, rather than in series, doesn't this mean that the pulsing outputs of the rectifiers are connected to the amplifier stages?

A The power transformer is connected to a network of diodes, which creates bursts of DC voltages for both rails. The filter capacitors connect those voltage bursts to ground, and shunt that voltage until they're filled up. When the rail voltage reaches maximum, the rectifiers no longer apply any net voltage because, at maximum, it's equal to the rail voltage (voltage potential between them is zero), and at minimum, the nature of the diodes blocks any current and/or voltage potential the other way. So, the filter capacitance, by storing energy and maintaining voltage, drowns out the pulsing nature of rectified but not smoothed DC to make the pulses much smaller in amplitude, except that with the minor leakage of the caps, and the drain of the output stage, the upward slope is much sharper than the gradual drain, so it looks more like a sawtooth. The bigger the drain, the bigger the sawtooth amplitude, which is called "ripple". Also, even though a higher voltage in the capacitors at the same capacitance will have more energy storage, the ripple in the capacitors will be proportional to the current draw, and inversely proportional to that capacitance. Imagine a cylinder that you can fill with water. The voltage is height, the capacitance rating is the area of the circle at the top of the cylinder. If you take out x gallons of water, the voltage drop is directly proportional to the height, but inversely proportional to the area of the circle. A higher cylinder assures a higher maintainable rail voltage, but does nothing to reduce the ripple component.

It's partially, but not completely true that the rectifiers are connected to the amplifier stages. First, just because the filter capacitors are in parallel with the power supply output, doesn't mean that they're not in the signal path. Just like a parallel component in a crossover network, they still act as filters. Secondly, if the circuit is regulated (most are) before the power supply meets the output stages, it's controlled by an
active device, either a triode/tetrode/pentode, or a transistor. This device uses a component with a fixed voltage across it, like a few diodes
in series as a reference signal, and uses a negative feedback loop to maintain a constant DC output voltage, that compensates for the ripple.

There are limitations, of course. If the transformer's impedance causes a sag, or the rippled component is so large that the voltage at the
capacitors drops below the desired output voltage, regulation won't do much at all. That's why the rail voltage is often slightly higher than the
possible output voltage, to compensate for the sag and give the regulation more headroom to work. If the power supply is stiffly regulated, the
amplifier may clip substantially before the rail voltage is exceeded, because the regulated output is intentionally lower. This may seem a bit
self-defeating at first, except that it also lets the amplifier recover from clipping much more gracefully, since the capacitors are less depleted.

The alternative would be to let the amplifier output a lot of power for a short time, but completely exhaust its power reserves, adversely affecting
performance after that. Also, when current demands are high, the extra rail voltage isn't there anyway. It's being dropped by the impedance of
the transformer and/or the dips in the AC ripple. In that case, output isn't limited much at all, and ripple that can leak to the output stage is less than if they had attempted to maintain the full rail voltage at the power supply output.

And, there's in between cases too, so that more capacitance and larger transformers always make the regulation easier. Rail voltage is good, but you notice that for a certain value transformer, it's rated in terms of VA. If you gear it for a higher rail voltage, you can draw less current before the transformer's own impedance becomes a serious factor, so it's really a balance of a bunch of factors, and the relative benefits of each will be a function of the loudspeaker impedance. Being able to "double" down to 1 Ohm doesn't do you much good if your speakers don't dip below 6. At the same time, being able to put out 1,000 watts into 8 Ohms isn't the issue if the loudspeakers average 4 and dip below 2. This probably accounts for a lot of loudspeaker/amplifier matching difficulties.

As to the nature of the ripple specification with power supplies, I should explain that ripple isn't 60 Hz hum. It may have a 60 Hz component if it's not bridge rectified, but with bridge rectification, the fundamental of the ripple would be 120 Hz, and then harmonics would arise off of that, as ripple is not a sine wave function, but more of a lopsided triangle wave. The spec sheet for an amplifier may state that it has no more than 1% ripple under normal operating conditions. As for 1% ripple being audible, it would manifest itself as noise which could coincide in level with current output, as there's virtually no ripple when current drain is minimal, barring class A designs, of course. Another thing to consider, is where the ripple is occurring, and specifically at what output level. If the ripple is before regulation, a 1% deviation would be quite good. If it were occurring at the actual output, that would mean that the noise floor occasionally raises to -20 dB, which is undeniably bad. Also, even without power supply regulation, all transistor amplifier gain/output stages have at least local feedback in order to operate linearly within their bandwidth (some that employ no global feedback state that they use no feedback), and that feedback will, to some extent, counter some of that ripple which could otherwise leak through, though the measure will only be a bandaid and doesn't provide any of the previously discussed benefits of regulation. If the question is, what does ripple sound like, I don't know, because it's going to be more of a problem in power supplies that are underbuilt and poorly designed, and those tend to have other effects which are hard to distinguish against. How can you tell whether mushy bass is an effect of distortion caused from soft clipping, sagging rail voltages, or signal dependent ripple generated noise in roughly the same band? You could probably test for the audibility by running continuous high level output across the lower part of the spectrum into a reactive load, drawing a large sum of current, and measuring noise floor spectrum, and a spectrum display of distortion vs. current and voltage output. But then you'd have one of those waterfall charts that nobody wants to look at.

If an amplifier has hum, it's most likely due to grounding, either between itself and associated equipment, or itself and the wall socket, or itself and itself (if the ground impedances between stages are substantially different within the amplifier itself, the designer should be bounced in the head).

Q I am looking for a preamplifier. I have a Bedinie Class A amp and a Parasound CD Player with a pair of PSB 600s, and Tara lab cables. I was looking at the Parasound 1500 class A preamp for $850.00. I read your article on the Audio Electronic AE-1 class A preamp for $600.00. What would you recommend for my system? I am worried about the tubes on the AE. Well they go out on me and would I have to change the tubes after so many hours of listing? What kind of responsibility do you have when owning a tube component?

A Since the time we reviewed the AE-1, it has gone up in price, but it is still very reasonable. Although I very much like the sound of a tube preamplifier with solid state power amplifiers, that does not mean everyone else will. Audio Electronic sells direct, so you should go and listen to the tube preamp-solid state power amp combination before you buy. Tubes in preamplifiers are very easy to maintain because they are not putting out the kind of current that power amplifier tubes do. Preamp tubes will last thousands of hours, and even when it is time to replace them, the expense is very low. The AE-1 only has a few tubes, and I have never had to replace them in mine. They do produce a lot of heat though, so it is important to keep the AE-1 well ventilated. I placed mine on top of a stereo cabinet, with wide open space above it.

Q I recently bought an old Threshold 400A power amp, and it creates a fairly big thump when I switch it on. Any suggestion as to how to take this out? I imagine this involves putting a cap across somewhere, but the switch already has a tantalum capacitor across its terminals.

A Most amplifiers eliminate turn-on thump by using solenoid switches that engage only after the amplifer has been on for a few seconds. Others just live with the thump rather than put any additonal contacts or capacitors in the signal path. If the thump really bothers you, I would suggest getting a speaker switch. Leave the switch open when you power up, then after 5 seconds or so, close the switch. One additional thing you should try is to turn on the preamplifier, then wait about 30 seconds before turning on the power amplifier. Some preamplifiers have a little DC offset that dissipates after a few seconds. If you turn the power amplifier on before it dissipates, the DC will cause a thump.

Q I have noticed that on certain passages of Dolby Digital movies, the dialogue sometimes will sound edgy or coarse. There are other equally loud passages that are very clear. I am using a Theta Casablanca with standard DACs and a McCormack DNA-HT1, three channel amp, going to my Aerial Acoustic 7s for L & R and Aerial CC3 for center. I am using a Pioneer Elite CLD-79 as a transport for laserdiscs and CDs. I have turned the gain up and down, and the edginess/coarseness is always there on the same passages. I have heard that it is in the Dolby Digital compression and if you have a system with very good resolution, you will be able to hear it. I even turned the processor off for the L & R so there would be full power to the center channel, and it is still there. I have read other reviews where they will mention the brittleness (if that's a word) or harshness associated with Dolby Digital and certain movies. Is this what I am experiencing? I don't believe it is the amp clipping. The one scene that sticks out in my mind is in the movie "Long Kiss Good Night' where Samuel L. Jackson screams out as she rips the bandage off his side. It is definitely very coarse or whatever you want to call it as he screams out no matter if the volume is loud or soft. I would appreciate feedback very much since this is sometimes bothersome especially when I am thinking I could be doing something to eliminate it such as better cables.

A There are a couple of possibilities. One is that the signal overloaded the original recording when he screamed. That would come through as harsh no matter how the sound was transferred to the disc. You might try switching over to Pro Logic, which is recorded in the digital tracks of the laserdisc rather than one of the analog channels where the DD sits. If the harshness is still there, then it is in the master. Explosions and other sound effects are done with Foley, which means the sounds are added later. This is much more controllable than the actual recording that has to be done with someone's voice when they yell on camera. Another possibility is the DD compression, but I would suspect this only if there were a lot of audio action occurring at the same time in the other channels. It is difficult to say exactly what is going on without hearing it in your system, but it is not power amplifier clipping, although it could be clipping in the preamplifier caused by too much signal from the DD decoder. Power amplifier clipping sounds more like a crackle and snap rather than courseness.

Q I recently purchased a Sony 550 used laserdisc player. It has a digital optical hookup on the back. I also have a Sony ESP-800 Surround Sound Processor, and a Sony 515 "Digital Ready Receiver." If I use an optial cable into the SP-800 and play a laser encoded with AC-3, will I be getting AC-3 sound? I called Sony three times and twice they said yes, and once no. So I am confused about this. I think the ESP-800 has a built in demodulator for AC-3 laserdisc sound.

Also, I want to know what the difference is between using a powered subwoofer, and one that just hooks directly into the receiver and passes through the other speakers. I recently acquired one and hooked it up, thinking it would not do much to improve the bass, and boy was I surpised. There was a noticeable difference. Now I am wondering if I should (or need) a separate powered subwoofer to hook up to the separate subwoofer outlet on the receiver. I use everything mostly for home theater.

My last question is about Yamaha receivers. I see that they have a special surround process called DSP Cinema. One of their advertisements shows the hookup of two additional special effects speakers in the front, and two additional surround speakers. Is that a hookup that you can use with any of their DSP receivers, or only the top end of the line, and is it desirable? Also, the only two Yamaha receivers I could afford have the DSP but only have either 20 or 35 watts to the surround channels. Most of the receivers today seem to give all the channels the same as the front. Is this wattage enough for todays DD and DTS sound?

A The digital outputs on laserdisc players deliver the digital bitstream from the digital audio tracks on the laserdisc. AC-3 (DD) is contained in one of the analog channels, so the DD info does not come out through the optical or coaxial digital jack on the back of the laserdisc player. In order to get the AC-3, you need an AC-3 RF output on the laserdisc player. Even if your receiver has the AC-3 RF input, you still must have the RF output on the laserdisc player.

Whether the subwoofer is self powered or not, you can use speaker level inputs to the subwoofer which will then pass speaker level high pass outputs back to your front left/right main speakers. All that is necessary for this is a crossover network in the subwoofer, which most have. To get the best results from the subwoofer output on the back of receivers, you should have a powered subwoofer that has a crossover bypass switch. This keeps the subwoofer from using two crossovers in sequence.

DSP is Digital Signal Processing. It refers primarily to the "sound fields" that all receivers have these days, such as "Stadium", "Jazz Club", and others. DSP takes the original signal and modifies it so that it sounds like it were in a stadium, jazz club, etc. This type of DSP is used for enhancing two channel stereo rather than enhancing surround sound modes. The top Yamaha receivers have seven channels, which include the original 5 or 5.1, plus two front effects channels. These extra two channels would be considered as DSP. Cinema DSP, as they call it, is DSP applied to surround sound modes such as Pro Logic, DD, and DTS. Other manufacturers call this type of DSP by different names. "Pro Logic Enhanced" is another name used for DSP applied to a surround sound mode. DSP is everywhere, but the front effects channels are only on a few designs. For DD and DTS, 25 watts to the rear will not be nearly sufficient. Particularly if you like action movies, 100 watts or more per channel are required. The receivers with 70 - 80 watts/ch all the way around will work OK if you keep the volume at modest levels.

Q I just wanted to know your opinion about the new Panasonic portable DVD player, DVD-L10. Before I shell out 1400 dollars of my money, I'd like to know if I'm getting what I'm paying for. Being able to watch a movie on DVD while stuck in traffic or on a plane trip is very appealing to me. Plus I can also hook this up to my theater system at home or my friend's home for that matter. Do you think portable players by other brands coming out in the future will cost significantly less, meaning at half the cost? Is it better to wait? If it's only going to be a couple hundred less, without siginificant improvements, then I really wouldn't mind buying the DVD-L10 now.

A The DVD-L10 looks like a very cool product, and I kind of like the idea of being able to watch my favorite movies on a long jet trip myself. However, it is at a premium price for a specific use, and I would not recommend watching movies when you are in the driver's seat of any vehicle. Even car phones are causing accidents, let alone television. You will also probably get better results at home with a full sized player. Like all new technology, the L10 is high priced, and subsequent models from other companies will drop the cost, but I doubt it would be a reduction by half. More likely, they would settle down in the $999 range.

Q My current system is the following: Harman Kardon AVR 85 Receiver, Sony DVP-S715 DVD Player, Infinity Ref 61i main speakers, Ref 100i center, Ref 21i rear, and PSB Century 2i sub. And a turntable, Thorens TD147, pick-up Ortofon X5 MC, with Rotel's RIAA, RQ970. Not High End, but my wallet said stop!

1. The receiver does not have a phono input, so I connected the RIAA to the tape 2 input. It works, but is there any better way to do it? Will it
be better using the CD input?

2. I have noticed there is a big difference in cables. I'm using cables from Monster: the M850i for the DVD, and the M550i on the RIAA. When I got my DVD player, I used the 550 the first day, connected to my old CD player, and then went with the 850 (connected to the RIAA). That made a huge difference. I could hardly believe my ears. More body to the music. I liked the sound much better. Of course my LPs deserve a new 850 from the RIAA, but what about the cables from the turntable? For now I have Interlink 300 (advice from the dealer). Will I get value for the money changing to 850? (I have to solder them inside the turntable.) There is too little "punch" in the music, too "thin" in the lower bass. (Taken care of by the sub.) Suggestions?

3. For speaker cables, my dealer advised me to buy cables for biwiring, although my speakers don't have that ability. I simply stripped and
connected the thin and thick blue cable, and ditto with the red. Will it make any difference with "ordinary" cables (two leaders)?

4. And the sub. I'm quite new in this hi-fi arena, and wondering if I shall use it with music or not. My main speakers reach down to 35 Hz, and the sub to 25 Hz. I have tried several positions for low pass, and am now using it at 60 Hz. I don't play very loud (neighbors everywhere), and the sub is doing a decent job in hi-fi. In fact I have problems saying it is boomy and not clean. (Too cheap to not be?) Of course I feel the music
much more, but the definition in the bass is there, in my opinion. I bought the sub for movies, but am using it for music too, sometimes, when
playing LPs. Any suggestions for the settings?

A The use of either the tape 2 input or the CD input should work fine, since the output of the RIAA is line level and equalized. For interconnect cables, low capacitance appears to be the best. Get some that are very well shielded, since the output from the cartridge is very low, and subject to hum and noise. Biwiring has not made any significant differences in my experience, but I used high performance cable to test this. It may make an improvement when using zip cord (the 30 cents a foot stuff in bulk). This could occur even when your speakers are not biwirable, simply because you are increasing the total amount of copper that is carrying the signal. Since you don't play your system loud, your subwoofer could very well be clean and without boominess. Definitely continue to use it with music. The lowest key on a piano has a fundamental frequency of 28 Hz. Since your main speakers go pretty low, you might get better results by changing the low pass frequency to 50 Hz.

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