I've been doing FM Tuner mods for about 25 years now. I can tell you with certainty there are still stations out there that broadcast high quality signals worthy of the effort. But you do need to make the effort - great tuner, outdoor antenna on rotor, etc. Many stations still have live broadcasts from the studio, or concert hall. They may not be available near you, but that does not mean they are not happening elsewhere
As mentioned already, the digital noise isolation, but also DSP processing precision can come into play to limit S/N ratio in car radio and portable chips. Better tuners can do 30 dB better S/N that all in one chips.
There is also the factor of station broadcast power, and receive antenna used.
You are much better off fully modding an existing great tuner for best sound versus trying to build one for yourself. There are areas for great improvement to older tuners that were made with very good RF and IF stages.
What is very doable - taking the detector output and building a "from scratch" post detector MPX / audio stage. You need to either pick a better MPX chip, or even more involved, design one yourself. Tim de Paravicini made one, for instance. There's a lot of mods listed at the tuner information center website. Co-founded that with 2 others back in 2001.
Bob
As mentioned already, the digital noise isolation, but also DSP processing precision can come into play to limit S/N ratio in car radio and portable chips. Better tuners can do 30 dB better S/N that all in one chips.
There is also the factor of station broadcast power, and receive antenna used.
You are much better off fully modding an existing great tuner for best sound versus trying to build one for yourself. There are areas for great improvement to older tuners that were made with very good RF and IF stages.
What is very doable - taking the detector output and building a "from scratch" post detector MPX / audio stage. You need to either pick a better MPX chip, or even more involved, design one yourself. Tim de Paravicini made one, for instance. There's a lot of mods listed at the tuner information center website. Co-founded that with 2 others back in 2001.
Bob
For FM, the ultimate signal-to-noise ratio (audio signal-to-noise ratio for very good reception) is usually determined by the phase noise of the frequency synthesizer, or the free-running local oscillator when you have an old radio that doesn't have a frequency synthesizer yet. In the case of the TEF668X, the analogue noise of the audio DAC also has some influence on the mono ultimate signal-to-noise ratio, it's negligible for stereo.
At RF levels that are reasonable but too low to reach the ultimate signal-to-noise ratio, it is usually mostly the atmospheric noise determining the audio noise floor. The front-end noise adds to the received atmospheric noise, but the front-end noise of any half-decent FM radio is below the typical atmospheric noise.
At low RF levels, modern car radios will normally outperform portable radios and old radios due to their weak-signal-processing features.
Ah - take the FM detector output of the best and coolest rf tuner and (after using it and a scope to minimize multipath) and connect that to a Paravicini post detector MPX / audio stage. With a complementary enclosure of course.
Bob, you were a founding member of fmtunerinfo?!
Paul
Bob, you were a founding member of fmtunerinfo?!
Paul
Paul;
Eric and I founded FM fmtunerinfo back in 2001, and shortly after we added Jim, who did all the "shootouts", then David who did "ricochets".
There are many other contributors, of course, making the tuner reviews a valuable resource.
Eric set up the web site, edits the reviews, and updates the tuner listings to this day.
That same year I started the Yahoo FMtuners chat group, which ran to 2016, when Yahoo shut down all groups. The database was transferred to groups.io FMtuners. where it continues today with the help of 4 moderators.
I started messing around with tuner IF filter swaps, cap and PS upgrades, then outboard post detector MPX/Audio/filter stages in 1999. At the time, very little was written about modding, aligning, and repairing tuners. Before that I mostly did DAC mods, one of which (DAC re-clocking) was writen up in The Audio Amateur back in '96 (Jitter RIP part II)
Most who do tuner mods agree the sound quality of many tuners with superb RF/IF stages can be improved with changes well known to those in the DIY Audio circles.
I personally have a rich local FM station environment broadcastug a diverse mix of content from 10 non-commercial stations, including 5 college stations, 2 full time classical, a roots/rock, and 2 mixed talk/variety stations.
There are 4 locally produced jazz shows every week, announcing who's playing at local clubs, and in the summer live classical music broadcasts from a local outdoor concert site.
So perhaps other can better understand my perspective on this source. Well worth the effort for me. I use a 9 element rotor mounted FM antenna, and can receive stations from over 80 miles away. I happen to love music, and also have a vast vinyl and CD collection, plus 4 streaming units throught the house. So FM isn't all I listen to...But yeah, I do listen all day long.
Bob
Eric and I founded FM fmtunerinfo back in 2001, and shortly after we added Jim, who did all the "shootouts", then David who did "ricochets".
There are many other contributors, of course, making the tuner reviews a valuable resource.
Eric set up the web site, edits the reviews, and updates the tuner listings to this day.
That same year I started the Yahoo FMtuners chat group, which ran to 2016, when Yahoo shut down all groups. The database was transferred to groups.io FMtuners. where it continues today with the help of 4 moderators.
I started messing around with tuner IF filter swaps, cap and PS upgrades, then outboard post detector MPX/Audio/filter stages in 1999. At the time, very little was written about modding, aligning, and repairing tuners. Before that I mostly did DAC mods, one of which (DAC re-clocking) was writen up in The Audio Amateur back in '96 (Jitter RIP part II)
Most who do tuner mods agree the sound quality of many tuners with superb RF/IF stages can be improved with changes well known to those in the DIY Audio circles.
I personally have a rich local FM station environment broadcastug a diverse mix of content from 10 non-commercial stations, including 5 college stations, 2 full time classical, a roots/rock, and 2 mixed talk/variety stations.
There are 4 locally produced jazz shows every week, announcing who's playing at local clubs, and in the summer live classical music broadcasts from a local outdoor concert site.
So perhaps other can better understand my perspective on this source. Well worth the effort for me. I use a 9 element rotor mounted FM antenna, and can receive stations from over 80 miles away. I happen to love music, and also have a vast vinyl and CD collection, plus 4 streaming units throught the house. So FM isn't all I listen to...But yeah, I do listen all day long.
Bob
Here's a link to an Analog Devices article that speaks about data word size DSP processing issues and the effect on dynamic range (towards the end).
AD article on dynamic range and word size
Designers of FM radio chips that use DSP processing have to make these choices - A/D bits, and word processing length, to keep first keep everything real-time. And fit the cost and power requirements for the target market. I don't know the numbers for A/D bits used in these radio chips, or DSP math precision, but my gut feeling is that both limit the ultimate dynamic range they specify in the ~55 dB range. OK for cars and portables, but not comparable to specs found on better high end FM tuners. I spent half my career in applications with real-time high speed (GS/s) A/D processing, where this issue is always a factor. As an example, the Accuphase T-109 has a signal to noise ratio of 90dB ! Accuphase T-109 Specs
from the AD article -
"A 16-bit DSP may suffice for low cost audio applications where processing is not complex and SNR requirements are around 75 dB. However, 16-bit DSPs using single precision computations will not be adequate for precise processing 16-bit signals. When using 16-bit A-D and D-A Converters in an audio system that will process `CD-quality' signals having a dynamic range of 90 - 96 dB, a 16-bit data path may not be adequate as a result of truncation and rounding errors accumulating during execution of the DSP algorithm."
AD article on dynamic range and word size
Designers of FM radio chips that use DSP processing have to make these choices - A/D bits, and word processing length, to keep first keep everything real-time. And fit the cost and power requirements for the target market. I don't know the numbers for A/D bits used in these radio chips, or DSP math precision, but my gut feeling is that both limit the ultimate dynamic range they specify in the ~55 dB range. OK for cars and portables, but not comparable to specs found on better high end FM tuners. I spent half my career in applications with real-time high speed (GS/s) A/D processing, where this issue is always a factor. As an example, the Accuphase T-109 has a signal to noise ratio of 90dB ! Accuphase T-109 Specs
from the AD article -
"A 16-bit DSP may suffice for low cost audio applications where processing is not complex and SNR requirements are around 75 dB. However, 16-bit DSPs using single precision computations will not be adequate for precise processing 16-bit signals. When using 16-bit A-D and D-A Converters in an audio system that will process `CD-quality' signals having a dynamic range of 90 - 96 dB, a 16-bit data path may not be adequate as a result of truncation and rounding errors accumulating during execution of the DSP algorithm."
You keep suggesting portable and car radios are of comparable performance, but in my experience, the requirements on car radios are much tougher than those on portable radios, except for power dissipation. I know, as I was in the design teams of both car radio chips and portable radio chips, both with analogue and with digital IF processing.
Regarding word lengths, the ADCs are usually sigma-delta ADCs as these can work with very simple anti-alias filters. I don't know what word lengths are used in the decimation chains, digital mixers and digital baseband processing and if I did, I would not be allowed to tell you, but I do know that no system designer would spend most of the noise budget or most of the dynamic selectivity budget on digital quantization noise. Adding a bit to reduce digital noise by 6.02 dB is much cheaper than quadrupling analogue current and/or area to gain 6.02 dB on the analogue side.
Regarding the Accuphase tuner, you have to subtract 9.64 dB from the ultimate stereo signal-to-noise ratio and 10.46 dB from the ultimate mono signal-to-noise ratio when comparing them to NXP numbers, because Accuphase specifies the audio signal-to-noise ratios relative to maximum deviation and NXP to a nominal frequency deviation of 22.5 kHz. I haven't checked whether Accuphase uses 75 us or 50 us de-emphasis, NXP always uses the worst case: 50 us. Even then, the Accuphase numbers are pretty good, so they must have a pretty good frequency synthesizer. Of course you only reach the ultimate signal-to-noise ratio under ideal reception conditions.
Regarding word lengths, the ADCs are usually sigma-delta ADCs as these can work with very simple anti-alias filters. I don't know what word lengths are used in the decimation chains, digital mixers and digital baseband processing and if I did, I would not be allowed to tell you, but I do know that no system designer would spend most of the noise budget or most of the dynamic selectivity budget on digital quantization noise. Adding a bit to reduce digital noise by 6.02 dB is much cheaper than quadrupling analogue current and/or area to gain 6.02 dB on the analogue side.
Regarding the Accuphase tuner, you have to subtract 9.64 dB from the ultimate stereo signal-to-noise ratio and 10.46 dB from the ultimate mono signal-to-noise ratio when comparing them to NXP numbers, because Accuphase specifies the audio signal-to-noise ratios relative to maximum deviation and NXP to a nominal frequency deviation of 22.5 kHz. I haven't checked whether Accuphase uses 75 us or 50 us de-emphasis, NXP always uses the worst case: 50 us. Even then, the Accuphase numbers are pretty good, so they must have a pretty good frequency synthesizer. Of course you only reach the ultimate signal-to-noise ratio under ideal reception conditions.
Hi doug s,
I recently bought an Accuphase T1000 tuner which is working perfectly so far (it sounds better than the T-108 I had before); in the thread from 2024-08-07 you offered the possibility to send the service manual to interested guys.
May I ask you sending me this manual to my email dieter.zahradnik@gmail.com?
Thanks in advance for your help!
Dieter