|
Radio Road Which tuner to get and getting the most from it. Thank God, for the radio! |
|
|
|
Radio Road Which tuner to get and getting the most from it. Thank God, for the radio! |
|
In Reply to: I'll assume you already have a decent antenna! posted by Timbo in Oz on August 17, 2008 at 16:56:05:
Why NEW?valve tuners rebuilt OR
classic analogue SS
OR do UP the Yamaha!
here's TIC on the 1020
"Yamaha T-1020 (1986, $359, photo, closeup) search eBay
The T-1020 is a black digital tuner that was second in Yamaha's line behind the superb T-85. It has the electronic equivalent of 4 gangs. Although some of the T-1020's specs are similar to the T-85's, it lacks the T-85's four IF bandwidths and some other features. The T-1020 tunes in .1 MHz increments and fine-tunes in .01 MHz (10 kHz) increments, like the T-85 and other top Yamahas. It has the Computer Servo Lock (CSL) circuit that some hate, a 10-LED signal quality display, and 20 presets. Our contributor Jay reports, "There are signs of very high quality like loads of 1% resistors, a little copper fence protecting what is probably the IF stages, and copper screws used to ground the circuit boards to the chassis. The appearance is similar to the T-1000, but much better built, with a larger power transformer with some shielding around it. The T-1020 has two modes, DX and Local, which can be set manually or automatically. According to an advertising slick I bought off the Internet, this tuner also has RF servo gain control which automatically applies precise amounts of RF gain and an FM noise filter that is automatically activated to eliminate high-frequency noise." Yamaha claims that maximum RF gain is applied to weak or distant stations in the absence of adjacent interference signal for maximum sensitivity, but when a weak or distant station is near a stronger station, "an optimally determined amount of RF gain is applied to provide the highest sensitivity without saturating the RF stage."Our contributor Brian B. gave his T-1020 a thorough analysis and also offers some useful DIY tips: "The PCB has great markings, both for the functional sections and the adjustments. Even the mono and stereo distortion adjustments are labeled as such. The IF comes with two blue 250 kHz GDT filters (SFE10.7MX) and two 180s in narrow. Even after I aligned it the filter performance was not very good. Stations I can receive easily on my other tuners in narrow just weren't there. I wound up installing a 230 for one of the 250s and two 150s in narrow. For some reason I couldn't use two 230s without excessive distortion in wide (I use four in my Marantz 2265B receiver with no problem). The final (for now) filter setup yields about .05% THD in wide and mostly 0.1% in narrow, sometimes 0.2%. Distortion was unusually constant with input signal level, something I really appreciate. Neither of the two power supply pass transistors on the PCB had heatsinks. One was completely loose - its leads had come unsoldered. I wiggled it with the power on and was amazed that the tuner didn't go crazy. The other transistor was partially loose. Those were the first things I fixed once I got the board out. I put some small heatsinks made of metal PCB standoffs on each transistor. These transistors don't get nearly as hot as the ones in the Pioneer F-90, and small heatsinks help. The pass transistors in any T-1020 definitely should be checked for soldering. There is a wide green capacitor near the two micros. Looking closely, you can see the marking .047F, a twentieth of a Farad. Evidently this is the memory backup. The tuner has a tiny power transformer that gets rather hot, even though it is heat-sinked to the rear panel.
"You must remove the board to work on the T-1020. It is hardcabled to the front-panel boards, but enough of the other cabling is on connectors that you can partially remove the board and get to the solder side. I installed a trimmer cap in place of the fixed 45-pF (measured) cap to ground between the cascaded narrow filters. Adjusting this trimmer made a lot of difference in the narrow distortion. The source resistance for the first wide filter is adjustable to minimize stereo distortion. The CSL (computer servo lock) is pretty nifty. I don't know what it does exactly, but by probing with the scope and watching the dial, you can tell that it is sophisticated (which is not the same as effective, in general, but seems to be in this case). When autotuning, it will go past a station and come back. The search speed seems to vary. In the autobandwidth setting, it will try wide and then switch to narrow if it has to. You can force narrow or wide, which is great. If the signal is strong but really noisy for some reason and you've forced wide, the tuner will drop into mono. It seems to try hard to obtain a listenable signal. You can fine-tune in 10 kHz steps. I found this handy for some weak stations next to strong, but not as much as I had expected. AM will tune in 1 kHz steps, which is neat. I aligned the AM IF and it sounds good except that the audio is rolled off. The IF is wide enough for good-quality sound. There's probably a capacitor on the audio output that could be lowered to improve the AM response. I wish I had a circuit diagram so I could locate it. There is a spot in the AM section marked AMS, which I presume means AM stereo. No parts were installed there. The tuner does autotune on AM. In addition to the yellow IF ceramic filter, there is a little blue filter that I think is used as a discriminator on AM for autotuning.
"My favorite adjustment is labeled IF offset. This is a trimpot that the microprocessor reads on power-up. The micro adjusts the offset in 10 kHz steps based on what it finds on this pot. The stock filters had orange dots (25 or 30 kHz higher than 10.7 MHz) but with this trimpot you can use any set of filters you happen to have laying around. I set the offset not for minimum distortion but for symmetrical filter shoulders in narrow mode. This maximizes adjacent-channel rejection (or rather it equalizes it on both sides of center). It is really fun to watch the control signals when you autotune. I found a place where I could see the raw discriminator DC output as fed to the intelligence. Wild waveforms appear here as the CSL operates. It does not at all do a simple search.
"The front end is not OEMed. Yamaha put it on a separate board with a shield around the mixer and oscillator. The RF tracking was way off, the first time I've ever seen that. I installed an F-connector in place of the funny Euro thing. (This time when I drilled out the hole I didn't go too far and obliterate the RF coil as I did in a Technics ST-8044.) The RF input circuit uses a center-tapped antenna coil to provide both 75- and 300-Ohm inputs. There is no balun, no balun loss, and no need to make a tradeoff between higher sensitivity by removing the balun and the convenience of leaving it in place. I had aligned the T-1020 using its 300-Ohm inputs and had to retweak the input stage a bit when I went to 75 Ohms. It looks as if it may have a balanced mixer, but I'm not sure because I don't have the circuit diagram. I saw no evidence of RF overload here in my RF-rich environment where many tuners stumble. The audio output level is fixed and is noticeably lower than that of my other tuners, which is only a problem when A/B testing. The display is a pleasing all-red, except for the green signal-strength meter. There are ten steps illuminated in pairs - in other words, it's a simple five-level meter gussied up to appear as ten. I don't care for this sort of thing. The tuner has nice ergonomics and is very easy to use. Unlike some tuners, everything is stored in memory for a station, including any fine-tuning offset. This is very convenient."
Brian later added: "Last week I added a low-pass filter between the FM detector and stereo decoder in my T-1020 to reduce noise in wide-IF mode due to adjacent-channel stations and IBOC (HD Radio) sidebands. The filter was very effective, but the tuner's automatic reception system didn't realize that the tuner now performed better than stock. It kept switching to the narrow filter or to mono on stations that I wanted to receive with the wide filter in stereo. With my antenna pointed at L.A. where I get lots of adjacent-channel signals, nearly every station was downshifted to narrow mode. I could force wide, but this was inconvenient, and in a couple of cases the tuner switched to mono, from which there was no escape. All but a couple of the signals were quite listenable in wide. The tuner consistently switched to narrow for one IBOC station even though the residual noise level was now so low it seemed to be dominated by vinyl surface noise, not reception artifacts. I removed the tuner PCB and looked at the traces underneath. The op-amp that fed the stereo decoder, where I had spliced in the filter, also fed two other circuits. They were labeled something like DC Detect and FM Squelch. The latter surely generated the signals that the microprocessor used for its signal-quality decision. I cut a trace and fed the output of the postdetection filter to the two circuits as well as to the stereo decoder. Since the filter passes DC and has unity gain, the net effect should be to present the correct supersonic noise levels to the decision circuits.
"The trick worked and now the tuner behaves as if it knows what it's doing. It is much more convenient to use now that automatic bandwidth selection works properly. The tuner promptly switches over to narrow mode for stations that really do need it. The only remaining anomaly I've noticed is that the tuner does not mute when there's no signal. But it still autotunes properly, even on weak signals with no antenna connected. Apparently the tuner uses different criteria for muting and for signal detection when auto-tuning. This is a problem only when a memorized station has faded out. With the addition of the postdetection filter, I think the T-1020 is an excellent tuner. It is more resistant to RF overload than any I have tested. The automatic tuning is also the best I've come across. The 10-kHz fine tuning comes in handy. But without the postdetection filter, it has too much adjacent-channel noise, much more than other tuners. I would have dumped it." The T-1020 usually sells for $50-80 on eBay, with recent highs of $105-115 between 7/05 and 1/06, and a recent low of $34 in 3/06."
WarmestTimbo in Oz
The Skyptical Mensurer and Audio ScroungerAnd gladly would he learn and gladly teach - Chaucer. ;-)!
'Still not saluting.'
http://www.theanalogdept.com/tim_bailey.htm
This post is made possible by the generous support of people like you and our sponsors:
Follow Ups
- The tuner? depends if there are stations worth it, butttttt - Timbo in Oz 08/17/0819:10:11 08/17/08 (0)
Top of Page ]
[ Contact Us ]
[ Support/Wish List ]
[ Copyright © 2025, Audio Asylum, all rights reserved ]
