FM/AM Tuner

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#121
I want to replace sony tuner with CXA1238 single chip.

Hi All,

I have a sony mini hi-fi system and its radio tuner is not working. So I want to replace the tuner with CXA1238 single IC as its a high quality tuner.
Can it be replaced with CXA1238 single IC chip?
Please help me to do this.

Thanks.
Nuwan Mahesh.
 
#124
FYI --- I have a Magnum DynaLab MD102 analog FM only tuner. As I do not live in or near a city, the broadcasts are almost out of range for this tuner. Even an amplified antenna doesnt help a lot. the few good stations i get are just 'good' quality sound. Finally, unhappy with this situation, I began the search for a better tuner.
Then I learned that the Yamaha T-2 was one of the better tuners of yester-year and I picked one up for a very good price - like new (1/10th the price of a MD102). This T-2 tuner is fantastic! Not only do I get the stations loud and clear now, the sound quality is quit transparent and better than I have heard from an FM tuner in years. The T2 has lived up to its reputation. So, I'll go thru it and replace the obvious with upgraded parts (electro caps etc) and use it as my 'new' tuner.

Thx-RNMarsh
 
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#127
RNMarsh said:
This T-2 tuner is fantastic! Not only do I get the stations loud and clear now, the sound quality is quit transparent and better than I have heard from an FM tuner in years. The T2 has lived up to its reputation. So, I'll go thru it and replace the obvious with upgraded parts (electro caps etc) and use it as my 'new' tuner.

Thx-RNMarsh
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This is a top Tuner. Front end design is exemplar (even for later tuners with varicap tuning elements) Good design overall. Congratulations for the choise.

There is no coupling electrolytic cap across the RF/IF/AF signal path except only at Post Amp PCB AF out (C427,C431/C428,C452 3.3/16 BP and these are already bypassed).
IMO there is not much for capacitors tweaking. PSU is descent too.

Better PS decoupling at the B+ input of Front End PCB and Filtering/decoupling B+ input of Digital PCB may worth a try.

In case you have missed it, schematic is available here: http://www.fmtunerinfo.com/T-2schematic.jpg (* 🙂 )




Dude111 said:
I find that the BEST radios now a days are CAR RADIOS!!! (They have some of the BEST FRONT ENDS i have seen in 30 years!! -- ESPECIALLY FOR AM RECEPTION (FM REJECTION IS QUITE GOOD ALSO))
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I haven’t looked into modern car radios but the aged ones owed part of their good performance to the variable inductor tuning (in contrast to variable capacitor for home units)

George

(*) Look in your e-mail box
 
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#129
Pulse counting detector. Thank you Alain.
What a coincidence. Yesterday afternoon I was reading about Pulse Counting TX/RX principle on my 1947 volume Radio Engineering Frederick E. Terman (*)

Kenwood used such detectors in some of it’s renowned FM home tuners. 600T, KT-80, KT-615, KT-815, KT-917, KT-1000, KT-1100, L-07TII but not for later models.
(Kenwood had a long history in RF world under the brand name Trio )

George

(*) The 1937 edition is in the Internet Archives. http://ia700204.us.archive.org/21/items/RadioEngineering/Terman-RadioEngineering.pdf
 
#131
Very well.
This says at least three things:

1.Pulse detector may not be the best detector .
2.Any type of detector –even theoretically inferior- can be made to perform properly, depending on implementation details.
3.The output signal quality of the tuner does not depend only on the detector’s quality.

Three yes from me.

George
 
#134

Yes davidsrsb. There are many variables. Reading only Chapter XIII of the dated version of Terman I linked before, one can get an idea of how many details in each functional block play a role.


True. (*)
These effects are not easy to identify if not probing the loops, even in the case of properly aligned units.

Good reception conditions and having my diy tuner constantly powered, allow me to have these two feedback loops disabled.

George

(*) Especially on tube tuners due to tube aging.
 
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#137
I don't see why having a THD <0.01% from the discriminator is futile. There are FM transmitters/exciters in production that are capable of <0.01% THD with residual noise in excess of <-90dB unweighted. Bench FM stereo generators have this level of capability, I don't see any technical reasons why broadcast FM stereo transmitter can't have better performance.

davidsrsb said:
There is also the issue of "Good Enough ie the engineers rule of 10x is enough" - Over-engineering for a detector with <0.01% harmonic distortion is futile given the performance of the transmitter modulator
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#138
0.01% Tx plus 0.01% Rx discriminator do not necessarily provide 0.01% (or thereabouts) audio. Two issues stop this:
1. multipath propagation - always present to some extent, although hopefully low
2. IF filters in the receiver - always a trade-off between selectivity and FM distortion

In my view there is little point in aiming for better than about 0.1% on peaks. An ordinary decent FM receiver might only manage 0.5% or so. In many cases the stereo decoder will degrade things a little further.
 
#139
hitachi_nut said:
I don't see why having a THD <0.01% from the discriminator is futile. There are FM transmitters/exciters in production that are capable of <0.01% THD with residual noise in excess of <-90dB unweighted. Bench FM stereo generators have this level of capability, I don't see any technical reasons why broadcast FM stereo transmitter can't have better performance.
Click to expand...
Real transmitters have big cavity flters on their outputs to meet adjacent channel spectrum purity regulations. These cause distortion.
The distortion in FM radio is low order and goes down with amplitude, so it's not objectionable

I'm sorry I don't remember my old Sansui tuner model, I sold it 20 years ago
 
#140
All speculation, can you give actual experience, numbers or a paper that was scrutinized by peers that support what you are saying?

Multipath can be reduced and IF filters comes in different flavors some with very low group delay and decent badwidth. With analog broadcast, the medium is not perfect but there are ways to reduce "coloring" the information passing through it. I find it hard to comprehend what you are proposing not to utilize available technologies, i.e. low THD discriminators :scratch:

Tx THD of 0.01% + Rx THD of 0.01% = 0.01% audio, where did you get this idea from, certainly not from me?

Before we delve more into this topic, have you aligned FM tuners with THD <0.02% in stereo w/ 75kHz deviation, S/N in excess of 90dB (unweighted) and aligned LC filters with BW <200kHz and achieve over 70dB separation @1kHz and listened to the unit and compare it another less spec'd unit and here the difference between them? Well I did.

DF96 said:
0.01% Tx plus 0.01% Rx discriminator do not necessarily provide 0.01% (or thereabouts) audio. Two issues stop this:
1. multipath propagation - always present to some extent, although hopefully low
2. IF filters in the receiver - always a trade-off between selectivity and FM distortion

In my view there is little point in aiming for better than about 0.1% on peaks. An ordinary decent FM receiver might only manage 0.5% or so. In many cases the stereo decoder will degrade things a little further.
Click to expand...
 
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