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Which opamps to change in P990 Cd player

Sam Mcdonald
Intellectual 330 points
Other Parts Discussed in Thread: OPA1642, OPA1612, LME49860

Hello

I am not sure which opamps to change in my Technics SL-P990 cd player. Thomas helped me with choosing a suitable opamp, thanks again the OPA1642.

A  japanese website M5238pf Mitsubishi made in I / V conversion" .

from the service manual

IC805,806,807, 808 are IC Buffer AMP M5238FP

IC 809, 810 are IC Amplifer NJM5532 ( near adjustment screws)

IC 811,812 are IC Filter NJM5532

IC 813, 814 are IC Amplifer M5238FP

I thought IC809 ,810 and IC81, IC814 as in the manual they are IC amplifer? which opamps do i need to change. Thanks in Advance

Regards

Sam

photo of opamp arrangement

  • 0
    Intellectual 330 points
    I plan to use OPA1642, i would think that 813 and 814 would be best to change? if i am unsure of which to change - least in the circuit they are the output opamp. thanks Sam
  • 0 in reply to Sam Mcdonald
    TI__Guru* 93105 points

    Hi Sam,

    It is difficult to know where in this system its greatest performance limitations exist. Likely, the designers took each stage's design into careful consideration and attempted to optimize them for best performance. Therefore, possibly the only benefits from changing op amps might be reduced noise and/or distortion. As a rule an analog signal chain benefits most from placing the highest performance, low noise, low distortion amplifiers at the beginning of the chain where the signal levels are at their lowest levels. U13 and U14 are out the end of the chain and are connected as unity-gain buffers. Those stages may benefit somewhat if the OPA1642 has lower distortion than the original amplifiers, but is something that would have to be determined by measurement. It probably couldn't be detected by ear.

    Regards, Thomas

    PA - linear Applications Engineering

  • 0 in reply to Thomas Kuehl
    Intellectual 330 points
    Hi Thomas,
    Thank you for the reply and help.
    The beginning of the chain is : IC805,806,807, 808 are IC Buffer AMP M5238FP just after the DAC. There may not be any sonic benefits? just lower noise and distortion figures look much better on the newer OPA1642.

    Regards
    Sam

    pdf.datasheetcatalog.com/.../mXrxqrq.pdf
  • 0 in reply to Sam Mcdonald
    TI__Guru* 93105 points

    Hi Sam,

    Indeed the sonic benefits would be those gained from the lower distortion and noise of the OPA1642. However, it then comes down to the ability of the listener's ability to detect the improvements.

    Regards, Thomas

    PA - Linear Applications Engineering

  • 0 in reply to Thomas Kuehl
    Intellectual 330 points
    Hi Thomas,
    The distortion is much lower, though noise appears better on the old though the readings are different. The OPA1612 and OPA1642, distortion is much better. Replacing the lesser quality opamps in another Technics player with the OPA1642, the improvements were noticed right away, even was better to my ears over the other identical Technics player with upgraded LME49860.

    Old P990 opamp
    FEATURES
    • Low noise, input-referred noise Vp,ti= 1.9pVrms(typ.)(Rs=100k0 BW10Hz-30kHz FLAT)S/N=73dB(typ.)
    (Shorted input, RIAA, IHF-A network, PHONO 2.5mVrms)
    • High input impedance due to J-FET input
    Ri 1000M O (typ.)
    • High slew rate SR= 20V/ s(tYP.)
    • High gain, low distortion
    Gvo=100dB(typ.), THD=0.002% (Gv=35.6dB, RIAA, Vo=5Vrms)

    The OPA1642 and OPA612 are much better in distortion and noise
    I'll put them at the begging of the chain after the opamp and at the end of the chain - the other opamps in the middle have all the adjustments etc of the player, so best left, as you said the benefits is mostly at the beginning of the chain.

    Thanks again
    Regards
    Sam