Questionable component in this circuit

[Electrojosh86]

1550E in what looks to be a resistor? Is it a typo? Correct value?

 

[Audioguru]

I wish they would say "Ohms" instead of "E". It is 1550 Ohms.
But you do not want two of these extremely simple "Multiple Feedback Bandpass Filters" in series as the difference subcarrier sidebands filter in a stereo encoder because this simple filter has a peak at about 38kHz with much less level above and below. The filter should have a flat bandpass from 23kHz to 53khz and drop sharply above and below.

The circuit is missing 15kHz lowpass filters at the left and right channel inputs so that high audio frequencies do not beat with the 19kHz pilot tone.

 

[Electrojosh86]

Do eliminate a set of band pass filtered?

 

[Audioguru]

Look in Google for Stereo Encoder Theory to learn about what is necessary in the circuit:
1) The subcarrier sidebands MUST have a filter that is flat from 23kHz to 53kHz and have sharp cutoffs above and below.
2) The left and right channel inputs MUST have brick-wall lowpass filters at 15kHz.

 

[schmitt trigger]

I don't know whether the LM555 has sufficient stability to be used as your clock source.

But if you do use it, make sure that you use temperature-stable resistors and capacitors on its timing components.

 

[Electrojosh86]

Thanks for the replies. I already have a low pass filter for each input channel. I don't know if I was going to try this circuit as I already have an NJM2035 but have a very ugly tone coming from it (sound like the 19khz pilot) built per data sheet but if built that way tone goes away but no stereo reception. Don't know. Just a learning thing for me.

 

[Audioguru]

An FM stereo radio is supposed to have brick wall filters to attenuate the 19kHz stereo pilot tone but pass audio frequencies up to 15kHz.