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PCB PRODUCTION The big problem with PCB art is getting it into Gerber format so the PC house photo plotter can read the data. There's no need for expensive PCB software. Here's the method I use: The art for the board is put together in CAD. I use GEN CAD (one of the best programs ever written) or Visual Cad 3. Autocad works as well, but it's cumber some. You do need to produce items such as pads as components. Once the art is done, you need to export it to DXF format. Not a problem except the line (trace) width information becomes lost. The big trick involves a wonderful conversion utility program (specifically to convert DXF files into Gerber data) called GERBCON. You can download it from the net. This takes the DXF in and produces all the data needed for Gerber. A Drill file is produced from the inner diameter of the pads in question. Line widths are assigned according to color. So just make all your 0.040 traces red, and during the conversion this color is translated to .040 width lines, and so on. GERBCON allows multiple layers, silk layer, and solder mask, if you like, and, as I mentioned, produces the drill tape layer as well. I can't say enough about how great this little program is. My copy is backed up several different places. It's also wise to get an older version of CAMTASTIC 99, which allows you to view Gerber data. On the older versions this function remained "free" after the 45-day evaluation. CAMTASTIC allows you to see whether your conversion was performed as expected, and, since it thinks exactly like a photo plotter, you can catch little things you may have missed in CAD. The beauty of the previous is that, aside from the CAD program needed, the other two programs are essentially free! Have you checked the price of even the cheap Gerber converters lately? Be sides, any decent CAD program allows far greater flexibility than most PCB pro grams. I'll admit this process requires a little learning, but I think it's well worth the effort. Now, of course, the easiest way is to use the EXPRESS PCB software, which is free, but you must use their service and you have no Gerber data for use by any other PCB house. Marc S. Wauters NO REASON TO CHANGE In April of this year I purchased two SM 70 amps from Monarchy Audio. Gary Galo's review of the amps ("Product Review," AE 5/00, p. 28) is dead on in terms of sound quality, but not in terms of the problems he had. My amps don't hum (and any hum at all really annoys me), they don't blow the fuses, and they don't have much of a turn-on thump- more of an innocuous click. Mr. Poon [Monarchy Audio president] promptly answered my pre-purchase questions by e-mail, and the customer service rep taking my order was courteous and efficient. The amps were delivered promptly and well-packaged; the manuals were clear and to the point, and the build quality was just as I like it: simple, clean, and solid. This must be the most pleasant purchasing experience I have had in a long time. I am using unbalanced inputs, so I can't speak to Mr. Galo's comments on the improvements from this option. However, even with single-ended inputs, I hear the same detail and articulation that he mentions. It's a cliché, but these amps are really forgettable in the sense I can quickly forget about the equipment and drop into the music as soon as I start listening. My system, which has been evolving for over 20 years, contains two components that I hear no reason to change: my SM-70 amps and my Magnum-Dyn lab Etude tuner. But there's still the CD player, speakers, and preamp ... plenty of fun left! Doug Burkett Eaton, Ohio DIGITAL PROCESSOR I am interested in buying an HHB CDR 800, but I am puzzled by the terminology used in your evaluation of this ma chine ("Product Review," AE 2/00, p. 32). The review states, "All analog and digital outputs on the CDR-800 remain unbalanced. This may appear odd at first, but most pro audio users are likely to use the CDR-800 with an external digital processor for playback, making balanced 'analog outputs unnecessary." Please tell me what an "external digital processor" is. I will be using this CDR with a Sony STR-DA30ES receiver or an ADCOM GFA-5300 amplifier and ADCOM GTP-450 tuner/preamplifier. I will appreciate any help you can give me. Dick Pettit Gary G. responds: An "external digital processor" is an outboard digital-to-analog (D/A) converter, which usually offers performance superior to the internal D/A converters found in both professional and consumer equipment. If an external D/A converter is used with the CDR-800, the S/PDIF digital output on the CDR-800 is connected-via a 75-ohm cable-to the S/PDIF digital input on the external processor. The processor's analog outputs are then connected to the line inputs on a receiver or preamplifier. If you wish to use the CDR-800 as a stand alone unit, its RCA analog inputs and outputs should match the equipment you mention with out problems. By the time you read this, the CDR-800 may no longer be available. In that case, I recommend the replacement CDR-850, which is also compatible with CD-R/W discs. UPDATE Dr. Thagard's reply to my letter regarding the use of bridge rectifiers as voltage doublers (AE 5/00 Letters, "A Network of Ideas”) reminds me that I, too, first came upon this basic idea in the on-line magazine, Tube CAD Journal. Those interested in further reading in this area may wish to visit tubecad.com and look up the article " Extracting Extra Power Supply Voltages" (pp. 13-15) in the January 2000 issue. If editor John Broskie reads this, perhaps he will write in to shed light on the deeper origins of this idea, if any. The idea of using two such voltage doublers to produce a bipolar supply is my own humble addition. In that regard, please note that Dr. Thagard's suggestion to check the connection of the lower (negative) bridge rectifier refers to an earlier "buggy" version of the schematic, and not to the corrected version published with the letter. -Joe Berry HELPWANTED I'm trying to locate a schematic for a Fisher FM90 tuner. Have you ever published one or know where I can get one? Bob Noriega 480 Richfield Dr. #3 San Jose, CA 95129 I'm looking for cat preamp schematics and would appreciate any help in locating some. Velissarios Georgiadis Kallikleous 4-6 Athens 10442 Greece Readers with information about these topics are encouraged to respond directly to the letter writers at the addresses provided. -Eds.
Also see: A Filter For Treble Distortion In Recordings
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