THERMALLOY HEATSINKS
THE FOLLOWING IS a note for your readers regarding the Thermalloy heatsinks I used in my Pass amps ("Showcase," TAA 2/96, p. 44). I was fortunate enough to find a returned item at Thermalloy. This was heatsink #15217, available at half-price at Thermalloy's warehouse. The sinks are pre-cut to 6 1/2" in height and are priced at $12.72 each. Thermalloy may not even be aware of these items.
Call Thermalloy at (214) 243-4321 and ask for Jim Richardson at the warehouse. Quote part #15217-ux6.5.
Make him look for them. Good luck.
David Hurd; Placerville, CA
AUDITION OF DANBURY PREAMP
I AUDITIONED MIKE DANBURY'S preamp--featured in "A Phono Preamp" (AA&E 3/96)--by driving a modified Hafler DH-220 amplifier through Neglex cable, feeding parallel-wire (ten per polarity) speaker cables. These drive three-way speakers, designed by Dr. Victor Staggs, consisting of a port-loaded Philips 10" woofer, a 2" fabric-dome midrange, and a 1" fabric tweeter. The comparison preamp is a modified DH-110, using a buffered op amp for phono (OPA-627 and LT-1010) and a hot-rodded line driver, feeding Teflon coax interconnects. Both preamp and power amp are servoed, among numerous other changes.
High-quality records offered the best sonics. Mike's playback system is a highly modified Radio Shack automatic turntable and Audio Technica AT-440 cartridge, carefully integrated with the preamp.
Some of the records I played in this comparison were Vivaldi's The Four Seasons (Drottningholm Baroque Ensemble), BIS LP-275; Wagner's Die Walkiire: Ride of the Valkyries (Leinsdorf), Sheffield Lab 7; Orienta-The Marco Polo Adventures (Gerald Fried), RCA Victor LSP-1919; Mozart: The Music for Solo Organ (E. Power Biggs), Columbia MS 6856; and Doctor Zhivago Original Sound Track Album (Maurice Jarre), MGM S1E-6ST.
Several things about Mike's preamp attract immediate attention. First is the musical detail and accuracy over the entire audio range-even the bass is tonally detailed. There is a sensation of quickness, ease, and openness. The frequency extremes give the feeling of no limits, and transient response is in the same class as live music, probably limited only by the power amp. This "slam" gives visceral impact to music, as bass is felt as well as heard. CDs (modified Magnavox CDB-472) exhibit the same comparative sonic improvements as records.
Imaging is excellent-wide and continuous. The organ played by E. Power Biggs is the reconstructed "Mozart" in the Great Church of St. Bavo, Haarlem, Holland, which has a 5s reverberation time. This causes decaying echoes to return from each arm of the church while the organ continues to play, allowing you to appreciate the structure's size. The locations of the ranks are clearly discernible.
Even though my preamp has benefitted greatly from the many improvements it has received, Mike's offers audible improvements in slam, detail, accuracy, and musicality. His choice of topology, power supply, and assembly detail have resulted in definitive high end sound.
Darcy E. Staggs; Orange, CA
I2S REACTION
I READ WITH great interest Kalman Rubinson's previous article "Get on the Bus," in TAA 3/95 and the present article in Stereophile. 1 have a question for him. Do all of the Philips CD players use the SAA2500 MPEG? I have tried Philips' technical support, without success. Also, do you have the pin-outs for the SAA2500 SCK, WS, and SD? I plan to modify a Philips CD player and use Analog Devices' AD1859 stereo DAC. I really don't like the analog output section Analog Devices suggests on the AD1859 data sheet, and will design my own.
In case anyone wants the datasheet for the AD1859, the FAX number is 1 800-446-6212. I am looking forward to Rubinson's next article.
Bill Perry; Sandpoint, ID
Kalman Rubinson responds:
I am surprised that Mr. Perry is asking about the Philips SAA2500, which, as he states, is an MPEG decoder. Its primary purpose is the decoding of compressed dig ital data. Since it is not, per se, a compact disc decoder, it is unlikely that it is used in any audio player/transport. I think Mr. Perry is confusing it with the Sony CXD2500 disc-decoder chip found in many players, including my erstwhile Pioneer/Elite PD-65. Nonetheless, the SAA2500 does have I°S output. The rele vant pins are 29(SCK), J0(WS), and 26(SD). This information can be found in the Philips Audio/Video Databook or downloaded from its website.
From the rest of Mr. Perry's letter, I infer that he plans to rebuild his Philips player by replacing the original filter, DAC, and analog stages. This is a worth while effort, although I probably would not have chosen the particular chip that he has.
The AD1859 is one of a new generation of highly integrated devices that include the oversampling filter, dual DACs, and I/V conversion in a single package. It can accommodate I°S as well as Sony/BB formats. Consequently, it would be relatively easy to build into an existing CD player.
Alternative devices are available from Crystal, Philips, and Burr-Brown.
Finally, while I am happy to address general issues here in the pages of Audio Electronics, the huge range of specific applications makes it impossible for me to provide individual assistance. Please heed the warnings in the articles; these modifications are not for those unfamiliar with the workings of digital audio electronics.
Good luck.
IT TOOK ME several readings of Kalman Rubinson's article, "Get on the Bus" (TAA 3/95) in order to realize what a translucent and important piece of writing this is in our times.
Being an avid reader of TAA and an occasional browser through the glossy mags on hi-fi, high end, and high crap (which would like me to take a fancy to a power line for $4,000 or a piece of furniture to rest my preamp on "worth" $1,500), I thoroughly enjoyed being told about the basics of the business. Although Mr. Rubinson perhaps did not really want to show up Messrs. Levinson, Krell, Burmester, et al, let's face it, they all want to make a lot of money.
The fact is that at present the price per high-end low-power box (i.e., pre amp, CD player, or tuner) is around $20,000. What better idea than to sell those who just want a high performance CD player two boxes, thus doubling the amount of money the customer can be persuaded to spend. It is a wonderful coincidence that this offers a third party the opportunity to promote a third box containing what other engineers have come up with to clear up the mess the inventors of the first two boxes left behind. All for the simple reason that a whole host of information has to be squeezed through a two-wire cable.
Thanks to Mr. Rubinson, we row know that reverting to one of seven already existing bus standards could have saved a lot of trouble. Surely it would have been easier to implement a few buffers to make the 12S-bus (or any other, for that matter) operate from box to box rather than devise an encoder and decoder, plus the two optional optical transducers as well as the obligatory anti-jitter devices that now are a lamentable standard. The fact that this wasn't done, and a different, costly, and bug-ridden approach was chosen borders on engineering with malice aforethought.
Klaus Noll Cologne, Germany Part 2 of the Rubinson series is slated for AE 1/97 -Eds.
DESIGNS ON CANVAS
IN HIS AUDIO AMATEUR 1/96 article on DIY PC boards, Mark Florian mentions using Canvas for layout design. I wonder if he has a set of Canvas templates (IC pads, etc.) that he could make available to other Canvas users who would like to do our own PC board layouts. Hopefully you can forward this message to him.
Thanks for your time.
Sherm Clow
Mark Florian responds:
I do not have a complete set of templates for all components. I've found that trace widths and circle sizes are not that critical.
That is, they do not need to be a standard size when doing your own layout design.
If, however, you work with integrated circuits a lot, then you need to copy a standard pattern for an 8-pin DIP and then lay it out in Canvas under magnification.
For a 16-pin DIP, you can duplicate the 8 pin pattern and "add it" to itself, keeping the center-to-center spacing (0.1") correct.
24-Pin DIPs are 0.6" wide when measured center-to-center between the two rows.
Individual pins are on 0.1" centers.
While looking around in a drafting sup ply store, I found an old Chartpak catalog (1988) entitled, "Printed Circuit Aids" which included dimensions of various components. You might still be able to find one of these, but I believe Chartpak has since discontinued these products because designs are rarely laid out by hand any more. I would suggest you measure the spacings on a silk-screened board for components you are interested in and store them in a macro.
SUGGESTION BOX
I SINCERELY APPRECIATE Audio Electronics and applaud your intention of adding two issues a year. The more projects the better, and the modest price increase is more than fair.
I would like to make two suggestions concerning the projects in AE.
First, I would encourage you to suggest to the authors of the articles to explain in simple terms the concepts and rationale regarding their projects.
This suggestion comes from my own rather basic understanding of electronics in general and my frustration in trying to understand some of the articles that have appeared.
As a biochemist, I know the difficulty of explaining to someone outside my field the type of research I do with out resorting to jargon. However, with a little thought and patience, it can be done, and the people to whom I've explained my research in this way are grateful. I have also learned that erring on the side of explaining things too - ' simply is far better than talking over someone’s head.
My second suggestion stems from my interest in home theater. I would very much like to see an article on surround-sound processors/preamps.
Although I know one cannot purchase Dolby Pro-logic chips in bulk, single units can be had from various sources.
In addition, perhaps the goal of achieving multichannel surround sound can be reached by using discrete components.
Of course, I realize you may have had no article submissions on this subject. Perhaps you could invite such an article in your editorial section. You might also suggest that readers send in suggestions for projects they would most like to see appear in AE and invite articles on the most popular of these suggestions.
Timothy A. Fritz
Irvine, CA
AMENDING THE AMP
AUTHOR DICK CRAWFORD reports that some readers with good eyes have noticed that Q1 and Q2 are not listed
FIGURE 1: 10W Class A corrected schematic.
... on the parts list for his article "10W Class A" (AA&E 3/96). Q1 is a 2N3904 and Q2 is a 2N3906. These are listed in the Mouser and Digi Key catalogs. Other catalogs may list them as PN3904 and PN3906.
Other readers noticed a more serious error in the PC board layout and circuit drawing.
FIGURE 2. Solder side 100%.
FIGURE 3. PCB layout.With 72 holes.
Exchange IC1B for IC1A so that the signal from C1 connects to the positive input of IC1A (pin 3), with the feedback from R2, R3 tied to pin 2.
This puts IC1B in the amplifier loop with pin 6 tied to R5, R6 and pin 5 tied to ground through a new resistor R12, 178Q. Refer to the corrected schematic (Fig. 1) and PC board layouts (Figs. 2 and 3).
TONE-ARM INSTRUCTIONS
I RECENTLY EXHUMED my old phonograph from storage to put back into service, only to discover that the phonograph arm needs to be realigned, but the original alignment instructions-after 17 years-are nowhere to be found.
The arm is a Grace G-707 Quad Master stereo tone arm (MKII). Might there be someone out there who could advise me where I could obtain a set of alignment instructions?
A.J. Steen
25115 Kirby St. #71
Hemet, CA 92545
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Also see:
Audio Aids: Capacitorless CD Output; Taming CD Stridency