FM-Stereo-Tuner: Currently vs Vintage Version - e.g. Accuphase T-1200 (DDS) vs. Sequerra Model No. 1

The multipath blend is the key.
I added that to my pioneer sx780 and the specs are within a hair of this unit.
After after redesigning the power supply for low noise and crosstalk thd will be lower.
*original pioneer figures
82db and 76db stereo 0.08 thd mono
Stereo is worse thd at 0.3 at 6khz.
Not sure if the blend lowers stereo thd however the sound is great.
 
Yeah, I might have to do that with this T-1000 on a couple of high-SQ but low-power college stations about 20 miles away. It doesn't dx that well. I have 2 Amazon 4-element FM antennas in the attic pointed that way now, and another 2 on the way - I would like 3 dB more signal with the 4, but you know, loss. Then I'll rig a switch with a resistor and blend L&R until it has as much hiss as maybe a cassette. (With dolby!)
 
it seems there's now a reasonably priced directional antenna available again in the usa; you might want to check it out:
https://www.nesselectronics.com/pro...sb80-fm-antenna-omni-directional-41-boom-copy

and there's a low loss balun you can fab; i really need to build mine, as i'm in a difficult reception area, towards the bottom of a ~1200' ridge w/all my stations ~45 miles away on the other side. "Properly constructed, it will typically have a loss of 0.3 dB at the center of the FM band." (interestingly enough, there's a low power college station - 950w - that i receive quite well, as it's 20 miles west of the back end of my winegard hd6065. it must be picking up the reflection off the ridge my antenna is pointing at.)
https://web.archive.org/web/20110831104218/http://homepage.mac.com/kenwetzel/Low_Loss_Balun.htm

and i use one of these, that i have found to be extremely effective at reducing noise, with no apparent sonic penalty. plugged into a tape loop or processor loop, you can have it in the signal pat when needed, and out, the rest of the time. carver tx1-11
https://web.archive.org/web/20110831104218/http://homepage.mac.com/kenwetzel/Low_Loss_Balun.htm

doug s.
 
The big difference between Accuphase high end tuners and the car radio chips are the 3 key specs - dynamic range, stereo separation, and distortion.
For example, look at how poorly the RDA5807FP does here - these specs are surpassed by most low end analog tuners you can buy on Ebay for $30
These specs - 35 dB separation, 0.2% distortion, 53-55 dB signal to noise ratio are OK for cars and little portables, but not close to any top tuners made since ~1970 or so...

Also, fyi these is a DIY subgroup focused on FM tuner stuff with some designs and schematics for HD/IBOC filters, MPX filters, etc.
DIY subgroup - FMtuners.groups.io
 

Attachments

  • RDA5807FP.PNG
    RDA5807FP.PNG
    55.3 KB · Views: 14
For example, a minimum FM input IP3 of 80 dBuV would be some 35 dB too low for a car radio chip, even for dirt cheap car radios. On the other hand, the supply current of a car radio chip can be much larger than the 20 mA that this chip draws; anything that doesn't overheat the chip is OK.
 
Last edited:
TEF6687 is an example of a real car radio chip with digital IF processing. Its full datasheet is confidential, but could be downloaded from the internet anyway a couple of weeks ago. It is a chip meant for dirt cheap car radios with only one aerial input. SAF775X is a series of car radio chips for fancier car radios.
 
Doug,

You might just be pioneering Ridge-Bounce FM! If you have a huge reflection, then just get the reflection. The legendary Winegard CA-6065. I had 4 up north. I left them in the attic when we moved down here - - too big to rotate in the attic we have now!

The Blue Sky SBFM9 in the link is inspired by the Channel Master Stereo Probe 9, hands-down the baddest FM antenna name ever.
In a sentence: "Even though I've put a Channel Master Stereo Probe 9 on my Cornell Dublier CD-44, that girl still seems bored."

Paul
 
bravi, very doubtful. i bought a japan-spec t109, and it needed a special part to be swapped out, in order for it to be north american spec. the part was only ~$75, but it took over a year for one of his buddies who worked at accuphase to sneak it out in a large parts shipment headed to the usa. i'm sure the same would apply to euro-spec.

doug s.
 
From the digital IF radio ICs I know, TEF6686 (available from Mouser), or TEF6687 if you can buy them somewhere without needing to buy a full reel. All digital IF radio ICs need a good RF PCB design, but the TEF668X is not as critical as most digital IF radio ICs, especially not when you switch off any digital interfaces you don't need. Besides, the TEF6687 full datasheet (as opposed to its useless short-form datasheet) can be found when you look around on the internet, it also covers the other TEF668Xs.

Although I never tried, its HVQFN32 package might still be hand-solderable if you find a way to solder its exposed die pad. It has an exposed die pad for good RF grounding as well as for heat sinking, it has to be connected to a ground plane via many vias. If hand-soldering does not work, you need hot air or a reflow oven.

The output coupling capacitors of the audio DAC can, of course, better be film capacitors or NP0/C0G capacitors than the X7R capacitors mentioned in the datasheet. Unfortunately, film capacitors and large NP0 capacitors are too expensive for cheap car radios.
 
  • Thank You
Reactions: jenimitso
You can buy TEF6688 at digikey for $8.62, 1400 in stock. TEF6688 Digikey

We were discussing the little Qodosen DX286 portable at groups.io FMtuners recently, which uses the similar TEF6686
You can buy those for $79 / $89 without/with battery, and it can use an external antenna and has a stereo headphone output.

It has exceptional reception, but it won't sound quite as good as a 70's Pioneer TX-9100 though, according to someone who did the comparison.
DX-286
 
  • Like
Reactions: jenimitso
It must either be a big battery or go empty quite quickly, if they use an NXP TEF6686... Car radio ICs can easily draw ten times as much power as portable radio ICs.

Edit: I see in the thread you linked to that they use Li-ion cells of about 3 Ah. Makes sense.
 
Last edited:
  • Like
Reactions: jenimitso