Working with Toshiba TA7117P/NTE1022 RM Decoder IC

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senorverde

Active Member
Joined
May 5, 2016
Messages
51
Hello folks.

I'm helping a friend build a cheap quad amp using Chinese DIY amp modules and the aforementioned Toshiba/NTE IC as a basic RM decoder/stereo enhance chip. Halfway through our design we thought it would not only be cool to accurately decode EV-4/DY albums, but also use dual ganged pots to vary the decoding coefficients on the fly (this IC lacks any phase shifting btw). The problem is, we're at a loss as how to come up with the required resistor values to match proper EV-4/DY decoding.

According to THIS ARTICLE found in the March 1973 edition of Wireless World, to calculate the resistor needed for frontal decoding all you would need to do is divide 7.3 by your frontal decoding coefficient and multiply 7.3 by your rear decoding coefficient to calculate the resistor value for that. In this case, the author chose a decoding coefficient of 0.414 for both frontal and rear decoding, and indeed 7.3/0.414 gives us 17.6329 or roughly the 18[Kohm] resistors used in the circuit.

Now, here's where we got a little confused. Regarding calculating the rear resistor values, we've found that 7.3*0.414 does not give us a number even close to 18. In fact, it gives us 3.022. Now, the only other resistor values that are somewhat close to that value on the included schematic are the two 2.7Kohm ones paralleled with the 18Ks. At this point we're unsure if these two values are suppose to correlate with each other. If they do, why didn't the author use a more common 3.3Kohm resistor? The NTE datasheet for the 1022, which is the modern drop-in equivalent, provides no help, and it gives the pins such cryptic names as, 'Bias' and 'Control Resistance'.

If anyone's worked with these ICs before in their own projects, or has seen them used in commercial applications (we were thinking either cheap stereos or car 8 track players), please feel free to share some information. Thank you!
 
I'm guessing that the text regarding blend resistor values (they are not determining decoding coefficients, simply proving variable amounts of crosstalk between the differential amplifiers) should perhaps read-

'The 18k resistors can be altered to a value of 7.3/ Crosstalk Ratio for the front speakers and the 2.7k resistors to a value of 7.3 X Crosstalk Ratio for the rear speakers'

Not sure it would be really worth all the effort to make the crosstalk infinitely variable though - this IC is little more than just away of implementing the Hafler speaker connection at line level (and can be done with a couple of any old op. amps if you want to).
 
I'm guessing that the text regarding blend resistor values (they are not determining decoding coefficients, simply proving variable amounts of crosstalk between the differential amplifiers) should perhaps read-

'The 18k resistors can be altered to a value of 7.3/ Crosstalk Ratio for the front speakers and the 2.7k resistors to a value of 7.3 X Crosstalk Ratio for the rear speakers'

Not sure it would be really worth all the effort to make the crosstalk infinitely variable though - this IC is little more than just away of implementing the Hafler speaker connection at line level (and can be done with a couple of any old op. amps if you want to).

Thank you for your reply! Although we could indeed use op amps, we wanted to have at least one vintage component in our amp. That, and the IC voltage requirements match those required by the two stereo amp modules and the phono preamp circuit.

As for having variable crosstalk, we thought it would be interesting to have the ability to change between a Hafler Circuit (i.e. no back center sound) and 'all around' stereo enhancement on the fly.
 
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