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发表于 2006-8-27 11:35
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日立FT-5500 MK II
日立FT-5500 MK II欧版机器在英国曾获HI-FI评比大奖，它内带一个信号强度表可以显示实际信号强度（10 to 80 dB），在调整天线时非常适用，下面是FMTUNERINFO对它的评价：
Hitachi FT-5500 MKII (1984, $350, photo, schematic, Hi-Fi News review, Hi-Fi Answers review, New Hi-Fi Sound review) search eBay
Somewhat scarce in the U.S., our panelist Ray's favorite is a solidly built, low-profile, black digital tuner with some unusual and nice features. In the mid-1980s, the FT-5500 MKII was highly regarded by the European audio press, but received little recognition in the U.S. Its front end consists of 5 varactors (equivalent to 5 gangs) for FM, in a sealed module that isn't represented in detail on the schematic, and 2 for AM. The FT-5500 MKII has a wide/narrow selector that changes the bandwidth for both FM and AM. The IF section in Wide mode has 2 ceramic filters around a group delay circuit and 2 gain stages. In Narrow mode, the group delay circuit is bypassed by 2 more ceramic filters, for a total of 4 filters in Narrow. The FT-5500 MKII's "FCCS" (Field Condition Computer System) appears to be similar to Onkyo's "APR" system. When the FCCS push-button is selected, the tuner auto-scans 2.5 MHz up and down the band from the tuned frequency to assess the potential interference and signal strength, and then selects the optimum RF and IF settings. These can be manually overridden, but the computer seems to always get it right. Stations' FCCS settings can also be stored in each of the 16 memory preset settings. One (not-uncommon) shortcoming is that the muting switch and stereo/mono are on the same button, which prevents one from choosing to listen in stereo to stations with signal strength below the muting threshold. The digital signal-strength indicator has exceptional range, 10 to 80 dB microvolt, which equates to 21 to 91 dBf (add eleven to the display). The FT-5500 MKII also has an auto quieting control (a blend circuit) and recording calibration tone button. Ray found that his sample, in a side-by-side comparison to a stock Kenwood KT-7550, was better at quieting weak signals and sounded much better. The FT-5500 MKII also outperformed the KT-7550 on AM. Ray says that he has had several other tuners, including a Pioneer TX-9800, and prefers the Hitachi overall. Ray did some mods to his FT-5500 MKII as can be seen here. He changed where the the de-emphasis is done. Stock, it was in the feedback loop of the op-amp (built into the MPX chip). He added a new op-amp output stage, and added the RC components to implement the de-emphasis in a passive filter. See the Modified Tuner Report for Jim's reviews of Ray's two mod attempts, and see Ray's report on a shootout between his modded FT-5500 MKII and a stock Hitachi FT-007 in the above writeup for the latter tuner.
Our panelist Eric found that Ray's FT-5500 MKII had excellent selectivity in Narrow mode, with good quieting on weak stations adjacent to stronger locals. Our contributors Tim and Ann chime in: "We've been putting our recently acquired FT-5500 MKII through its paces and Ray is on to something, IOHO. It's a damn fine tuner. It's closer to having that McIntosh 'house' sound than any non-McIntosh tuner we've listened to here. It does not have as much 3-D depth as some tuners we've listened to, but it does have a very, very good midrange, the bass is phenomenal, and the highs are good as well. And the built-in digital signal strength meter calibrated in dBs is just as accurate, we've found, as using a scope to help aim our antenna, and it's a whole lot better than trying to use a standard signal strength meter like so many tuners use." The FT-5500 MKII usually sells for $85-140 on eBay. The more common FT-5500 (1981, $350, photo, usually $20-50 on eBay but $102 in 7/05) is believed to be somewhat similar. Ray says, "The FT-5500 was the ground-breaker with the initial release of the FCCS technology. The MKII has different pilot tone cancellation to reduce HF audio garbage. Also, the MKII's memory presets include the FCCS RF and IF settings, and the front end was revised to include use of GaAs FETs. The MKII has improved pilot filtering and is more resistant to out-of-band RF noise." [EF][RFM] |
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发表于 2006-8-25 17:05
