Q&A # 32 - October 7, 1997
Staff
Q I would like to limit the signal going to my front speakers to frequencies greater than 60 (or maybe 70) Hz. Is there a simple, inexpensive way to do this?
A To do this at the speaker level would take a huge capacitor.
On the other hand, you can put a capacitor in the line level of each channel between the preamp and the
power amp if you have the preamp separate from the
power amp, or have pre-outs and pre-ins on your receiver (the kind with the little metal U-hooks that connect the front left/right pre-outs with the power amp pre-ins). If so, the
formula is C = 0.159/R x Frequency, where C is in Farads, R is the
input resistance of the power amplifier in Ohms, and Frequency is the
crossover frequency in Hz. So, if the input resistance of your power
amplifier is 50,000 Ohms, and you want a crossover frequency (high
pass) of 60 Hz, it would be C = 0.159/50,000 x 60. This = 0.000000053 Farads, or 0.053 µF. Another useful formula for double checking your calculations is Crossover frequency = 1 divided by (2 pi times the input resistance times the capacitance value). Use a metallized tubular polypropylene capacitor (one in each channel), which can be ordered from any of the several companies advertising in the electronic build-it-yourself magazines found at bookstores. There are several websites that you can look at too, including http://www.capacitors.com/multicap/multicapcatalog/s-ppmfx.html. The capacitors would be put into the hot portion of the signal path, not the ground. There will be some phase shift, but you are after a particular result, and there is always a price when you alter the signal path. Experiment by building a little metal box (for shielding purposes) with RCA jacks on either side, and the capacitors wired into the hot signal path inside the box. Then, you can change the value of the capacitors without a big hassle, until you get the effect you want. Using the single capacitor will result in a "first order" crossover, which means the slope will be very shallow. So there will still be some less-than 60 Hz info in the signal, at the rate of 6 dB/octave dropoff below 60 Hz. Therefore, you may end up using a capacitor based on a somewhat higher crossover frequency, say 80 Hz - 90 Hz.
Q My present set-up is as follow:
1.Adcom GFA 5500
2.Golden Tube Audio SEP-1
3.Acurus ACD 11
4.Chario Academy 1
5.Audioquest Midnight Speaker Cable
At the moment, my Adcom seems to have some heat sink problem. The left
side heat sink appears to be 5 degrees Celcius hotter than the right.
Also at high volumes, you can hear electrical hum on the right speaker.
The present sound is very dynamic and powerful on new age and jazz
music. However when it comes to vocals, it sounds quite harsh and lacks
transparency and soundstage. Many people say its because my Charios are difficult to drive (81 dB sensitivity!) What would you recommend me to
change/upgrade? I was thinking of changing the Adcom to either the Aragon
8008 or the Plinius A100? Your valuable suggestion is greatly
appreciated. Thank you!
A The Adcom 5500 is a good amp, but 81 dB/w/m sensitivity speakers are a stress. I would suggest getting your Adcom GFA-5500 repaired, and then getting another one so that you can bi-amp the speakers (this assumes you have bi-wiring/bi-amping capability on the Charios). Otherwise, you might indeed move on to something like the Aragon 8008. They have two models, the 8008ST and the 8008BB. Both are rated at 200 w rms/ch into 8 Ohms and 400 w rms/ch into 4 Ohms, but the BB has a complete separate power supply for each channel, while the two channels of the ST share a power transformer. If your speakers are bi-ampable, borrow another GFA-5500 first to try that option, but if you choose the Aragon route, make sure you can take the Aragon back if it does not give you what you want. I suspect part of your sound staging problem may be the speakers, and simply changing the amplifier would not necessarily alleviate that. Bi-amping, particularly if you could use an active line-level crossover between the preamp and power amps, bypassing the crossover in the speakers, could significantly change the sound stage, as well as improve the performance of the amplifiers since they would not be dissipating heat in the speaker crossover components. Let us know what you decide to do, and how it works out for you.
Q After reading your primer and Q&A, I decided to check out some Class A amplifiers. GEEEEEEEZ! Why are they so expensive?
A Class A amplifiers are costly for several reasons. One is that a manufacturer does not mass-produce Class A products. They are made in small numbers. Secondly, Class A amplifiers use top-of-the-line premium parts, including the capacitors, resistors, inductors, etc. You have to multiply the manufacturer's cost times 3 or 4 to get to the consumer's cost, and that adds up fast. Third, Class A amplifiers require huge power supplies, and the power supply is the most expensive part of an amplifier. Even at idle (no music playing), Class A amplifiers dissipate a lot of power in heat. If the amplifier is 100 w rms/ch pure Class A, it dissipates 300 w - 400 w/ch in heat at idle, because current is always flowing whether there is a music signal going through or not. So, for there to be such a high continuous drain on the power supply, it has to be very big.
Q I have an old A/V system and I'm considering to upgrade my system (I
intend to use my system as a 50/50 music/movie entertainment). The
following are my plans:
1. Processor/preamplifier:
a. Parasound's P/DD-1500 + P/SP-1500 (I think these are the newest
Parasound proc/preamps)
b. B&K Components' AVP-3090
2. Amplifier:
a. Parasound's HCA-1205A
b. Adcom's GFA-7000
c. Rotel's RB-985
I have a few questions regarding this matter:
1. Which components pair (processor/preamp + amplifier) will give me the
best home/music entertainment?
2. I've heard about Klipsch horn-loaded speakers (I'm talking about
their middle class speaker - the KSF series). What are the advantages or
disadvantages of speakers designed like this? What's the diferrence between
Klipsch's horn and JBL's horn? Are these speakers being superior compare to
speakers that employ convetional drivers?
A I've heard so many positive remarks about B&K lately, you should definitely check the 3090 out. Since there is now at least one company that can install decoders in receivers and processors that are not there to begin with, it is no longer really important to make sure the processing you want is either built-in, or available as an option (including simply a set of 5.1 input jacks). However, the B&K 3090 has both DD and DTS already on board, which for me, would be a definite plus. An advantage for the Adcom and Rotel power amplifiers you mentioned is their use of DB-25 input connectors which saves you having to deal with multiple cables running all over the place, but the Parasound P/SP-1500 has the DB-25 connector only for an outboard AC-3 decoder input, rather than outputs to power amplifiers, and the B&K does not have any DB-25 connectors. The HC-1205A has 120 w/ch, the GFA-7000 has 130 w/ch, and the Rotel RB-985 has 100 w/ch, all amps rated into 8 Ohms. Soundwise, the Parasound HC1205A, Adcom GFA-7000, and Rotel RB-985 will be very similar.
There are several advantages of horn-loaded speakers, such as Klipsch, one of which is that they are more sensitive than regular cone speakers, making them ideal for low powered amplifiers. Their downside is typically (for high efficiency speakers) a frequency response that is not flat. So, they are not superior to regular speakers, just different. They have a specific function (high sensitivity). When movie theaters first had sound, they used horn speakers so sensitive that it took only about 5 watts of amplification to drive them to sufficient volume for the whole theater! For every 3 dB increase in sensitivity, you need only half the amplifier power to drive the speakers to the same volume. So, if you were comparing speakers with a sensitivity of 86 dB/w/m with 100 watts of power driving them to "X" loudness, it would only take 50 watts of power to drive different speakers to that same loudness using speakers with a sensitivity of 89 dB/w/m, and 25 watts for speakers with 92 dB/w/m sensitivity. Again though, the more sensitive the speakers, the more likely the response will be bumpy.
Q I am currently upgrading my stereo system, and I am thinking about gettting a Marantz special edition CD changer I currently have an Audio Alchemy DDE.2.0 D/A converter and 2.0 anti jitter interface. Is there any reason I should
upgrade my D/A converter, or would that money be better spent some where else
since I am going to use the Marantz for a transport only? The converter in
the player does not matter. I just want a good transport and power supply. Also
do you know if the Special Edition of this player is worth the extra $100? What are the improvements over the basic version? Have D/A converters
changed enough to justify getting rid of my old one for a new one?
A Keep your AA DAC and anti-jitter device. They are very good products for the money. The special edition players have a copper chassis and upgraded parts, including the DAC. So, I would suggest getting the regular version of the player and using your AA components with it.
Q I just finished reading the reviews of the Bryston 3B-ST and of the NHT 2.5i floorstanding speakers and I was wondering if I could
ask a few questions. I am just starting out in the process of trying to
pick out a stereo, and from the various reviews that I have read, both of
these components always receive stellar evaluations. In the article written
by J.E. Johnson Jr, he states "Careful matching of the components is
necessary in order to obtain a pleasing sound" and that you shouldn't go
into one store, buy one component, then into another to buy another without
listening to the combination of them together. That makes perfect sense, but
so far I haven't heard these two components together and so here is my
question, "Have any of you put these two together and if so how was the
result?" I did hear the Bryston 3B-ST and the 4B-ST power a pair of Mirage
OM-6 speakers and a pair of Thiel speakers, both sounded but good, but I
don't have the $4000 to shell out for either of those pairs of speakers. So
far I have only read about those two components. I haven't even looked at
pre-amps or CD players yet so if anyone has some good suggestions that would
complement the Bryston amp and the speakers I would appreciate the advice.
A Jim Moretti was reviewing the NHTs while I was reviewing the Bryston amps, and we didn't get the two components together. However, I would recommend using the Audio Electronics AE-1 tube preamp with the Bryston power amps. They are a very nice match. The NHTs should do alright, but the best speakers for the Brystons are those with a slightly laid back high end. The CD player choice should not be a problem with this preamp and power amp combination. If you want a carousel type, Sony's ES series is nice, and Adcom makes a good one too.
Q I have owned a Toshiba TW40F80 since early May. Unfortunately, my
nearest ISF technician is a good hour-and-a-half away, and his meter
runs
from the moment he leaves his driveway until he returns there. Thus
I've
got three hours travel time in addition to the calibration cost, so
I've
passed on having it calibrated since it would cost over $300.00.
Your reviews do us readers a BIG favor when you give us your
objective (as well as subjective) opinions about the merits of any
piece
of audio/video equipment. However, you could go one step further and
advise us just what settings you have the various viewing parameters. And,
since the Toshiba TW40F80 must be reset for differing sources, in
instances like that could you describe the settings for a particular
source?
I bought the Toshiba TW40F80 primarily for DVD and am awaiting the
Meridian player (mainly for the audio quirks which I feel Meridian
will
be in the forefront of addressing) becoming available. Also, I've
asked
MSB to put me on the list for adding component video outputs to my
Sony
DSS receiver so I can utilize this with the TV. However, in the
interim
I've tried to calibrate it as best I can with Video Essentials. If
you'd let me know what settings you have yours at, I'd be most
appreciative. Thanks.
A I would like to give you my values that I have for color, tint, etc.,
set up. Unfortunately I have adjusted the sub internal controls, so all my
standard values are all at their defaults 50. Let me explain what I mean.
First thing you should do is go to theater mode. This will turn
down Scan Velocity Modulation and also move contrast from 100 to 50 and set
color temp to low. Instead of adjusting the values here, I went into the
service mode (how to do this is in the service manual, though going into
and messing with these controls should be done by a trained tech.) and
adjusted the sub-color, sub-tint, etc., controls. These are what the levels
will be at in the default position. I did this in case the TV was unplugged
or I had guests who decided to mess with my values. They could easily be brought
back to normal by hitting the reset button.
Now I do remember a few things. Out of the box, the contrast
was at 100, when using VE I brought the contrast down to around 14.
That was the biggest change. Color and tint were pretty close to begin
with. There is no sub control for sharpness, so I have sharpness based
on my LD player and set at 24. When using the component connection,
sharpness is bypassed (this is a good thing).
The defaults are based on my LD player. I watch cable and DSS
with the TV adjusted to those settings. When I watch DVD, I must move color from
50 to 55 and move tint from 0 to -2. This is based on my DVD player. The
thing with DVD is that each player's outputs are different. Even taking two
Sonys will require two different settings! The Sony's black level is right
on, so I do not have to adjust contrast or brightness. With the Toshiba,
you have to make adjustments to brightness. The Meridian should be dead on. They, and Faroudja, are taking large measures to insure that their outputs are
exact to broadcast standards.
By using VE, you are 2/3 of the way there. The grayscale is
important but $$$ can be a good reason not to mess with it. If you
decide to spend the money for the ISF work, you should find out who's
sets he has done and see how they like the results. Just because someone has
been certified does not mean they can do the best work. This goes for
anything, like THX, a doctor, a lawyer, etc, not just the ISF.
The Toshiba only has one set of component video inputs. Once you get
your DSS modified, you will need a component video switcher. Perhaps
MSB will come out with one, like Entec, in the near future.
� Copyright 1997
Secrets of Home Theater & High Fidelity
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