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My old stereo amp got coffee spilled on it. I replaced it with the latest model from the same manufacturer.

I am an old-world person, and prefer simple approaches - i.e., radio buttons to select from multiple RCA inputs. My whole system is built around that. The problem is the new amp doesn't have 3 RCA inputs: it has two RCA line-ins, plus a phono input. The phono is, of course, low level and equalized to offset the treble-heavy output of the phono cartridge.

I would like to use the phono input for another of line-in since it, too, has an unbalanced RCA jack input.

Most of my experience is with professional audio where 0 dBm is fixed as the nominal level; the line is balanced; and there is no odd EQ at work. In that case, matching the high-level source to the low-level input could be cleaned up with an H-pad of resistors alone.

I can hack something out, but does anyone know of a stylized/standard approach to using the low-level and equalized RCA phono input so it can (for example) be used as an input for unbalanced line-level sources? This looks to me like it would be a T-pad with a capacitor or two to get the equalization right in addition to reducing the input level?

eSurfsnake
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    Does this help: https://www.epanorama.net/circuits/phono.html? – Edin Fifić Apr 16 '20 at 18:26
  • Products that convert line level to phono level exist. You could also modify the amplifier to bypass the RIAA circuitry, some amps even have jumpers or switch inside to make the selection whether the phono input is line level or phono level. – Justme Apr 16 '20 at 19:41
  • that epanorama link got flagged by malwarebytes as a phishing site. Beware. – hacktastical Apr 16 '20 at 23:21
  • Trying to go the other way: from line level output from CD player to using the turntable/phono input. So it is attenuation and frequency modification. – eSurfsnake Apr 17 '20 at 00:48

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The standard RIAA preamp compensation is (closely) modeled as a 50Hertz low pass filter, with a 2-octave wide plateau from 500 to 2,000 Hertz..

So you want the opposite of that: a 50Hrtz High pass filter, with plateau.

And of course a 60dB attenuation before the High pass.

analogsystemsrf
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