aboulang@BBN.COM (Albert Boulanger) (09/04/90)
This is posted for a friend. Querys, etc. should go to his snail mail
address below:
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Kevin R.Kennedy
d/b/a Kennedy Audio Laboratories
273 Barker Ave. #5
Lowell, Ma. 01850
7/90
This the third in what I hope will become a regular series of
newsletters. Andrea and I were discussing the difference between the
various dealers we visited at the Stereophile show in N.Y.C and elsewhere,
many people have undoubtedly had similar experiences - if the audio press
is any indication. Some audio professionals have an enthusiasm which is
almost contagious, while others hardly even understand the notion of
courtesy... We noted that the designers and principals of many outfits
were courteous, enthusiastic and knowledgeable while many sales people
both at the show and elsewhere were surly, impatient and uninformative.
We both particularly liked talking to the people from Vandersteen,
Velodyne, Audio Concepts, Swan Speakers, Paul Heath Audio, etc.
I have heard that some dealers in the Chicago area (as well as others)
do not even bother to allow their equipment to warm up prior to a demo. I
have frequently observed that most audio equipment sounds better after an
extended warm up period, so before you do any critical listening you may
want to find out whether or not the equipment has had a few hours to warm
up.
Audio Concepts has a very interesting product line comprising both
high quality speaker kits as well as the Premier series of high
performance loudspeakers. Anyone on a budget with aspirations to own high
quality speakers will want to check them out. You can reach them at :
(608)784-4570, and they are located in Lacrosse, WI. I have no connection
whatsoever with them, but I have been impressed by the performance of
their speakers.
I recently acquired a Phase Linear DRS-900 stereo basic power
amplifier, I was initially unimpressed by the mediocre parts quality and
the seemingly excessive design complexity. After warm up however, I was
surprised to discover that it surpassed my Citation II in a number of
areas. It is surprisingly dynamic without the compression effect that is
pretty common in some solid state amplifiers, it images fairly well and
has a wide sound stage. Depth is not particularly good, but can be
improved by modification. It is not nearly as bright as a fairly stock
Citation, but seems slightly more detailed after extensive listening tests.
It seems subjectively cleaner without the subliminal "grundge" the stock
Citation II exhibits at anything beyond very low signal levels. (By stock
I mean an amplifier that still utilizes the original design, but has been
treated to upgraded parts, improved power supplies and minor mods that
don't change the basic topology.) I recently determined that some simple
modifications to the driver circuitry of the Citation greatly improved its
performance so that my previous objections to its weaknesses have been
mitigated. Contact me for further details. (I have several other friends who
own Citations who claim to hear something similar..) I am told that the
DRS-900 is a very good match for most ribbon and planar type speakers such
as the Magnepan, (which is why I bought it, as a pair of Magneplanars are
probably in my future) and although fairly rare should turn up from time to
time in Audio-Mart. A fair price range seems to be around $300.00 to
$400.00. I recently decided to modify the amplifier for improved
performance, hopefully....
The modifications in the following paragraph should only be performed
by those familiar with high power high voltage amplifiers. Dangerously
high voltages are present in this amplifier even when off!!! CAREFULLY
discharge ALL caps in the power supply before attempting any mods....
If you cannot figure how to do this then do not even attempt to do these
modifications... Your soldering skills need to be of the highest order as
the traces on these boards are quite fragile... DISCLAIMER: I cannot be
held responsible for the use/misuse of the information provided!!
I have performed these minor modifications to my DRS-900 in the light
of increased listening experience. I have replaced many of the cheap
carbon film resistors with metal films of comparable ratings and value, I
forced the LF351 op-amp in the input circuitry into class A operation by
installing a 10K ohm metal film resistor between pins #6 and #4. In
addition there are several cheap mylar and ceramic caps that should be
replaced with Wonder Caps, Wima's, CDE's or whatever... Spade lug
connections are used extensively in this amplifier and should be replaced
with hard wired (soldered) connections. I also upgraded the speaker wiring
with good quality OFC silver plated teflon wire and beefed up the power
supply and output etches on the various boards as the copper is rather
thin... If you are lucky enough to own a dremel tool or high speed drill I
would also recommend the addition of two 10uF 25 WV bypass caps on each
driver board for the LF-351's , observing polarity, connect one to the red
leaded power (+) and one to the black leaded power (-) connection on the
five pin connector at the bottom of the board. Ground can be picked up from
the green wire at the top of the board. Additional bypass caps should be
installed across the various power supply caps, about 0.22uF is fine.
Finally it would be a very good idea to delete the five pin connector
mentioned above and solder the respective wires directly to their etches.
I also replaced the input wiring with twisted teflon pairs for a large
improvement. If you are inclined to make the effort, soldering wonder wire
on most of the smaller traces will probably also net a small improvement.
(I haven't tried this yet, though.)
Sonically, the DRS-900 is greatly improved by the changes, it is
cleaner, quicker and more detailed. Dynamics are slightly improved. Sound
stage depth which was almost non-existent before, is now considerably
better... I have found that leaving the amplifier on all the time improves
its sonics considerably over a cold start.
I recently developed a new driver design for the Dyna ST-70 power
amplifier as well as a series of modifications that work almost as well in
a stock ST-70 as they do in one with the new driver circuitry. Contact me
for further details and literature on some easily performed mods for the
ST-70 and Citation II.
A small caveat about using tube power amplifiers with solid state pre
-amplifiers. If the pre-amp. generates a subsonic pulse or generates a d.c
offset on its output when switching sources, or is otherwise defective in
this respect, it is possible for the transient so generated to swamp the
output stage bias which can result in anything from a really nasty thump
to catastrophic destruction of the output tubes. I have seen this in
several Dyna amps. as well as others. Some NAD 130 pre-amps can cause this
problem.
I don't have any idea how many of you out there keep as weird hours as
I do, but perhaps some of you have observed that your stereo systems seem
to sound better very late at night? In my area there is a lot of computer
and moderately heavy industry, we also have trolley cars - I suspect that
there is a lot of line borne noise during the daylight hours and into the
early evening, in addition I have observed that there is a problem with
voltage regulation in our area. Our line voltage hovers near 130 volts
most of the time, but has been observed to sag as low as 110 volts, and in
this situation it is imperative to use constant voltage or adjustable
isolation transformers, auto-transformers or variacs to protect the
equipment - what I wouldn't give to be able to afford a Tice Power Block..
(Some of you may have heard similar from Enid Lumley or Peter Belt ?!!)
I have been buying quite a few LP's and CD's lately, but I must say it
was quite a shock to walk into the Boston branch of Tower Records very
recently, and to see how few records were present even in the Classical
section which used to be predominantly LP. I would estimate that less than
10% of the overall stock in any section was LP, but less than a year ago
Tower had a large selection of LP's in every section. Last year over
4.5 million turntables were sold in the U.S. alone, and yet you can't even
find a decent selection of LP's in most stores.... If you like vinyl you
had better buy anything you can find at this time as virtually nothing will
be available new on vinyl within another year, excluding a few specialty
labels. Further, the few audiophile record companies still producing some
records are faced with the imminent closing of the last few decent record
pressing plants. TELDEC is already gone. (Yah, you've probably heard this
all before - I am just reiterating....)
For those of you looking for a really good, inexpensive moving coil
cartridge, the Sumiko Blue Point might be the answer to your prayers. It
has been compared favorably with some very expensive cartridges... It is
available for less than $100.00 from several sources including Audio
Adviser. (usual disclaimer) I have heard it on several tables by Linn,
Ariston, etc., and it was good on all of them....
Next time I'll be sharing some mods on the Dyna FM-3 Stereomatic tuner
as well as some further observations on tube quality.
Kevin