mikec@wheaties.ai.mit.edu (Mike E. Ciholas) (05/03/90)
(SID is a sound digitizer for any Mac. Download info-mac/sound/program/sid.hqx on sumex to see what its about). UPDATE: I've gotten about 70 responses. Getting close... If you want to make sure it goes, better respond and tell me so. DESIGN: How close is close enough? Due to the very limited availability of 1.558Mhz resonators, I have been searching exhaustively for a replacement circuit. Criteria are: cheap, avaiable parts, and close frequency. But how close is close enough? Here are the following choices: 1. 800KHz resonator with a divide by 2 followed by an 18 state conversion. - conversion frequency is 0.145% low - virtually no parts changes (just the resonator) - parts: $1.00 2. 1.000MHz crystal with a divide by 3 followed by a 15 state conversion. - conversion frequency is 0.145% low - more stable than resonator - minor parts changes - parts: $4.00 3. 6.144MHz crystal with a divide by 23 followed by a 12 state conversion. - conversion frequency is 0.028% high - two extra chips - longer assembly - parts: $6.00 4. 22.1184MHz crystal with a divide by 71 followed by a 14 state conversion. - conversion frequency is 0.012% low - two extra chips - longer assembly - more power - parts: $9.00 Some additional data: Resonators vary in tolerance from 0.05% to 0.5%. I don't know how stable they are. Somewhere I got the idea that the 1.558MHz resonator from muRata Erie was 0.5% tolerance, which means any of the above circuits are better. Even if it is 0.05%, 3 and 4 are better initial tolerance. The difference in frequency between 'C' and 'C#' (sharp) is about 5.5%. If I went with the first circuit, could you hear the 1/38th interval? I may be possible to "pull" the resonator frequency slightly. I'll see if I can find a way to do this without an adjustment (it is usually done with some sort of trimmer capacitor). My personnal favorite is #1. People who have already bought parts can still use it, the freq difference is minimal, and it is cheap. Mike Ciholas email: mikec@ai.mit.edu snail: 289 Highland Ave, #108/Somerville, MA 02144 phone: (617) 623-3563 air: N1909C, 1954 Cessna 170B
dplatt@coherent.com (Dave Platt) (05/04/90)
In article <8223@rice-chex.ai.mit.edu> mikec@rice-chex.ai.mit.edu (Mike E. Ciholas) writes: > Due to the very limited availability of 1.558Mhz resonators, I have been > searching exhaustively for a replacement circuit. Criteria are: cheap, > avaiable parts, and close frequency. But how close is close enough? How about the 1.558 MHz quartz-crystal substitution that the SID Trio suggested in their followup note? Drop out the resonator, drop in the crystal, and change the value of the two resonator capacitors. They even provided a source or two for the crystal. The parts cost was at the high end of the range you specify, when the crystals are bought in 1-sies... the price might come down significantly if you bought a few dozen at once. The biggest advantage, I think, is that it doesn't require any changes to the circuit topology. -- Dave Platt VOICE: (415) 493-8805 UUCP: ...!{ames,apple,uunet}!coherent!dplatt DOMAIN: dplatt@coherent.com INTERNET: coherent!dplatt@ames.arpa, ...@uunet.uu.net USNAIL: Coherent Thought Inc. 3350 West Bayshore #205 Palo Alto CA 94303
mikec@wheaties.ai.mit.edu (Mike E. Ciholas) (05/04/90)
In article <55692@coherent.coherent.com> dplatt@coherent.com (Dave Platt) writes: >In article <8223@rice-chex.ai.mit.edu> mikec@rice-chex.ai.mit.edu (Mike E. Ciholas) writes: >> Due to the very limited availability of 1.558Mhz resonators, I have been >> searching exhaustively for a replacement circuit. Criteria are: cheap, >> avaiable parts, and close frequency. But how close is close enough? >How about the 1.558 MHz quartz-crystal substitution that the SID Trio >suggested in their followup note? Drop out the resonator, drop in the >crystal, and change the value of the two resonator capacitors. They >even provided a source or two for the crystal. > >The parts cost was at the high end of the range you specify, when the >crystals are bought in 1-sies... the price might come down significantly >if you bought a few dozen at once. The biggest advantage, I think, is >that it doesn't require any changes to the circuit topology. Well, that is an option. I can get 1.557818 MHz crystals made for $7 in 100 unit quantities (large case style). When you need that much quartz, it costs money. A faster crystal costs only about $2 to be made. I dunno, $7 seems like such a high percentage of the cost for just a timer. I am still hoping that people find the 800Khz resonator solution acceptable. One fellow said he is using 3Mhz and dividing it down by 2. This is off by about 4% so the 800Khz being off by 0.145% doesn;t sound so bad. Mike Ciholas mikec@ai.mit.edu
dplatt@coherent.com (Dave Platt) (05/05/90)
In article <8223@rice-chex.ai.mit.edu> mikec@rice-chex.ai.mit.edu (Mike E. Ciholas) writes: > The difference in frequency between 'C' and 'C#' (sharp) is about 5.5%. If > I went with the first circuit, could you hear the 1/38th interval? I certainly couldn't, I would think. > I may be possible to "pull" the resonator frequency slightly. I'll see if I > can find a way to do this without an adjustment (it is usually done with > some sort of trimmer capacitor). Maybe the board could have a provision for a trim-cap, which people could include or omit at their own choice? > My personnal favorite is #1. People who have already bought parts can still > use it, the freq difference is minimal, and it is cheap. I like approach #1 for another reason... it has a low fundamental frequency. This may make it easier to keep the SID from radiating EMI which would interfere with radio/TV reception. Using a higher-frequency resonator or crystal (e.g. approach 4 or 3) would raise the relative level of the higher-frequency overtones, and might make it harder to shield the SID to meet the FCC Class B emission limits. -- Dave Platt VOICE: (415) 493-8805 UUCP: ...!{ames,apple,uunet}!coherent!dplatt DOMAIN: dplatt@coherent.com INTERNET: coherent!dplatt@ames.arpa, ...@uunet.uu.net USNAIL: Coherent Thought Inc. 3350 West Bayshore #205 Palo Alto CA 94303