Radio Road: REVIEW: Proton AT-670 Tuner by FRG7SWL

Model:	AT-670
Category:	Tuner
Suggested Retail Price:	$150 used
Description:	90s-era F.M. tuner combining superb sound with dx-ability
Manufacturer URL:	Proton

Review by FRG7SWL on February 05, 2013 at 12:17:44
IP Address: 75.48.8.207 Add Your Review
for the AT-670

Acquired Proton's 90s-era AT-670 tuner last summer via curiosity from a Radio Road inquiry. OP requested info on several locally available tuners, one of which was a 670. Told OP of experience with a Proton in-dash car radio back in 80s. F.M. was king in those daze. It was amazing to have a car radio which could snag any signal from Chico, Davis, Nevada City, San Fran, Stockton, & Woodland which entered Sactown like a hot-shot home tuner. With Larry Schotz Noise Reduction engaged, distant stations were nearly as quiet as locals. Parked upon Oroville Dam (no longer permitted since 9/11) Bay Area signals boomed in from nearly 200 miles away. Fidelity tended towards warm side of neutral. Low life jacked hooptie, though, smashing Proton radio in process. Could not find Proton replacement, thus it was Pioneer Super Tuners for successive Crown Vics. So it was nice to be re-acquainted with classique robust Proton tonality after nearly a quarter century. Unfortunately, today's F.M. dial is plagued by digital radio frequency interference. If you're a lower-end-of-dial denizen, there's more co-channel interference from station proliferation too. With a little elbow grease, Proton's AT-670 can combat those demons quite nicely. Thanks to F.M. dx-wizard Greg Gortman's recommendations, replace stock wide intermediate frequency filters CF-101 and CF-104 with MuRata 180 Khz ceramic filters. In narrow mode, replace stock CF-102 with MuRata 150 Khz ceramic filter, & MuRata 110 Khz ceramic filter in CF-103 slot. Stock capacitor C511, 330 uf @ 35 volts, was precariously close to a regulator heat fin. A 470 uf @ 35 volt replacement not only provided better clearance, it improved sound quality & helped Schotz Noise Reduction's efficiency. Although Proton car unit was analog & 670 digital, both shared Proton's warmly neutral house sound. Car unit, though, could be fine tuned for less noise whilst retaining stereo signal. A luxury also available from F.M. section of Sangean's ATS-909 shortwave portable, a contemporary sibling (N.A.D., Proton, & Sangean gear was manufactured in Sangean's Taiwan facilities). 670 only receives stereo signal on station's precise dial location, though. Tune .5 Mhz on either side, & signal reverts to mono. As for A.M., it has terrible front-end overload across dial with long wire antenna from local high power stations. Which is quite a disappointment, since fidelity and signal-snagging prowess are decent. Too bad A.M. section from Proton car unit wasn't implemented instead. One other minor caveat, if you have Samsung's DTB-H260 Digital HDTV receiver. Remote will turn AT-670 on-n-off whilst channel surfing. Which can be quite disturbing on occasion. As an F.M. dx machine, Proton's AT-670 is just as capable as Carver's TX-11. Both, however, are just a smidge behind Sony's now legendary XDR-F1HD in that category. Legendary reviewer Leonard Feldman summarized Proton's AT-670 in Audio magazine's March '92 issue thusly : "This combination of visual (Reinhold Weiss) and electronic (Larry Schotz) design talents, aided and abetted by Proton's production facilities, has produced a tuner that any FM radio lover or connisseur of elegantly styled audio components would be proud to own. The AT-670 lets you program 18 FM stations and 9 AM frequencies. The FM tuner section is equipped with the refined Schotz Noise Reduction system, which can be turned on and off as required. Generally, it can be left on since, for strong signals, it does not impair reception quality in any way. The only negative comment I have concerning this tuner's performance has to do with its AM section. Frankly, I can't believe that Schotz had anything to do with the design of the AM circuitry; it must have been left over from a much earlier model. In any event, most of us don't buy tuners of this category to listen to AM. These days, all too few FM stations put out the kind of clean, wide-range signal that can benefit from being received by a tuner such as the AT-670. If you are fortunate enough to live in an area where some FM stations are worth listening to, the Proton AT-670 is certainly a tuner worth owning and enjoying. After all, digital audio broadcasting, from the looks of things, is still many years away. Meanwhile, the AT-670 is a worthwhile alternative". 73s para Sactown!!!

Product Weakness:	Reverts from stereo to mono when de-tuned .5 Mhz up or down from received station's primary frequency; Disappointing A.M. section; Will power on-n-off via interference from Samsung DTB-H260F remote when channel surfing
Product Strengths:	Warmly neutral-sounding F.M. tuner capable of exemplary DX-ability; Simple Mods help combat today's digital radio frequency interference-plagued airwaves

Associated Equipment for this Review:

Amplifier: Carver MXR-130
Preamplifier (or None if Integrated): Mitsubishi DA-C20
Sources (CDP/Turntable): Denon DCM-450; Yamaha P-07
Speakers: Mesa/Celestion MC-90s, with Dynaudio D28AF tweets
Cables/Interconnects: Calrad
Music Used (Genre/Selections): Bop To Pop To Hip-Hop and Beyond
Time Period/Length of Audition: 6 months plus
Other (Power Conditioner etc.): Belkin
Type of Audition/Review: Product Owner

Amplifier:	Carver MXR-130
Preamplifier (or None if Integrated):	Mitsubishi DA-C20
Sources (CDP/Turntable):	Denon DCM-450; Yamaha P-07
Speakers:	Mesa/Celestion MC-90s, with Dynaudio D28AF tweets
Cables/Interconnects:	Calrad
Music Used (Genre/Selections):	Bop To Pop To Hip-Hop and Beyond
Time Period/Length of Audition:	6 months plus
Other (Power Conditioner etc.):	Belkin
Type of Audition/Review:	Product Owner