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  • High Voltage OP amp

    From Trevor Wilson@21:1/5 to All on Sat Sep 3 14:34:44 2022
    I am servicing a power amplifier which uses a dual, 8 pin DIP OP amp. Unfortunately, the rail Volts on the OP amp (LF353) is +/- 22 Volts. I
    am familiar with this particular amplifier and OP amp failure is quite a frequent thing. I need a suggested replacement. I am quite happy to use
    single OP amps, or SOICs, as I can employ a Brown Dog carrier to adapt
    to the existing layout. Ideally, a bit more performance over the LF353
    would be nice.

    And no, it is not possible to drop the rail Voltages. They must remain
    at +/-22 Volts.

    TIA


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  • From kayge@21:1/5 to Trevor Wilson on Sat Sep 3 18:31:38 2022
    On Sat, 03 Sep 2022 14:34:44 +1000, Trevor Wilson wrote:

    I am servicing a power amplifier which uses a dual, 8 pin DIP OP amp. Unfortunately, the rail Volts on the OP amp (LF353) is +/- 22 Volts. I
    am familiar with this particular amplifier and OP amp failure is quite a frequent thing. I need a suggested replacement. I am quite happy to use single OP amps, or SOICs, as I can employ a Brown Dog carrier to adapt
    to the existing layout. Ideally, a bit more performance over the LF353
    would be nice.

    And no, it is not possible to drop the rail Voltages. They must remain
    at +/-22 Volts.

    TIA

    Hello, TI's OPA552UA has up to +/-30V rails and a bit better slew rate (24V/uS)although it's a bit noisier. You may find a dual version of this
    at TI.

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  • From Phil Hobbs@21:1/5 to Trevor Wilson on Sat Sep 3 15:06:18 2022
    Trevor Wilson wrote:
    I am servicing a power amplifier which uses a dual, 8 pin DIP OP amp. Unfortunately, the rail Volts on the OP amp (LF353) is +/- 22 Volts. I
    am familiar with this particular amplifier and OP amp failure is quite a frequent thing. I need a suggested replacement. I am quite happy to use single OP amps, or SOICs, as I can employ a Brown Dog carrier to adapt
    to the existing layout. Ideally, a bit more performance over the LF353
    would be nice.

    And no, it is not possible to drop the rail Voltages. They must remain
    at +/-22 Volts.

    TIA

    What's the required output swing? A baby board with one or two zeners
    in the supply leads (plus a 100 nF-ish bypass between them) is pretty
    easy, at least if you get these things in a lot.

    Cheers

    Phil Hobbs

    --
    Dr Philip C D Hobbs
    Principal Consultant
    ElectroOptical Innovations LLC / Hobbs ElectroOptics
    Optics, Electro-optics, Photonics, Analog Electronics
    Briarcliff Manor NY 10510

    http://electrooptical.net
    http://hobbs-eo.com

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  • From Trevor Wilson@21:1/5 to Phil Hobbs on Sun Sep 4 08:44:09 2022
    On 4/09/2022 5:06 am, Phil Hobbs wrote:
    Trevor Wilson wrote:
    I am servicing a power amplifier which uses a dual, 8 pin DIP OP amp.
    Unfortunately, the rail Volts on the OP amp (LF353) is +/- 22 Volts. I
    am familiar with this particular amplifier and OP amp failure is quite
    a frequent thing. I need a suggested replacement. I am quite happy to
    use single OP amps, or SOICs, as I can employ a Brown Dog carrier to
    adapt to the existing layout. Ideally, a bit more performance over the
    LF353 would be nice.

    And no, it is not possible to drop the rail Voltages. They must remain
    at +/-22 Volts.

    TIA

    What's the required output swing?  A baby board with one or two zeners
    in the supply leads (plus a 100 nF-ish bypass between them) is pretty
    easy, at least if you get these things in a lot.

    Cheers

    Phil Hobbs


    **I need maximum output Voltage swing. Hence the designer (now deceased)
    chose a +/- 22 Volt supply. Hence the need for higher Voltage OP amps.


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  • From Trevor Wilson@21:1/5 to kayge on Sun Sep 4 08:56:46 2022
    On 4/09/2022 4:31 am, kayge wrote:
    On Sat, 03 Sep 2022 14:34:44 +1000, Trevor Wilson wrote:

    I am servicing a power amplifier which uses a dual, 8 pin DIP OP amp.
    Unfortunately, the rail Volts on the OP amp (LF353) is +/- 22 Volts. I
    am familiar with this particular amplifier and OP amp failure is quite a
    frequent thing. I need a suggested replacement. I am quite happy to use
    single OP amps, or SOICs, as I can employ a Brown Dog carrier to adapt
    to the existing layout. Ideally, a bit more performance over the LF353
    would be nice.

    And no, it is not possible to drop the rail Voltages. They must remain
    at +/-22 Volts.

    TIA

    Hello, TI's OPA552UA has up to +/-30V rails and a bit better slew rate (24V/uS)although it's a bit noisier. You may find a dual version of this
    at TI.

    **Thanks for that. I can probably live with a higher noise level. I like
    the idea of a higher speed OP amp.

    I found a couple available locally, though there is a long lead time for
    more. I can live with that.

    Thanks for the tip.



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  • From Phil Allison@21:1/5 to Trevor Wilson on Sat Sep 3 17:28:34 2022
    Trevor Wilson wrote:
    =================
    I am servicing a power amplifier which uses a dual, 8 pin DIP OP amp. Unfortunately, the rail Volts on the OP amp (LF353) is +/- 22 Volts.

    ** That is a mistake, all versions of the Sumo 9 used nominal +/-20V rails fed from series regs with 20V zeners.

    I need a suggested replacement.

    ** Which MUST be a FET input op-amp.


    And no, it is not possible to drop the rail Voltages.

    **Course it is, they are meant to be 19.5V each anyway.

    They must remain at +/-22 Volts.

    ** Humbug.

    ..... Phil

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  • From Phil Hobbs@21:1/5 to Trevor Wilson on Sun Sep 4 09:56:50 2022
    Trevor Wilson wrote:
    On 4/09/2022 5:06 am, Phil Hobbs wrote:
    Trevor Wilson wrote:
    I am servicing a power amplifier which uses a dual, 8 pin DIP OP amp.
    Unfortunately, the rail Volts on the OP amp (LF353) is +/- 22 Volts.
    I am familiar with this particular amplifier and OP amp failure is
    quite a frequent thing. I need a suggested replacement. I am quite
    happy to use single OP amps, or SOICs, as I can employ a Brown Dog
    carrier to adapt to the existing layout. Ideally, a bit more
    performance over the LF353 would be nice.

    And no, it is not possible to drop the rail Voltages. They must
    remain at +/-22 Volts.

    TIA

    What's the required output swing?  A baby board with one or two zeners
    in the supply leads (plus a 100 nF-ish bypass between them) is pretty
    easy, at least if you get these things in a lot.


    **I need maximum output Voltage swing. Hence the designer (now deceased) chose a +/- 22 Volt supply. Hence the need for higher Voltage OP amps.

    Sure, but typically not everything in a circuit needs to swing the full
    supply range. You're losing at least a couple of V_BEs on each end
    now--in fact the LF353 datasheet minimum output swing is +-3 V from the
    rails (+-12 on +-15 supplies) even at light loads.

    There are nice things in the 40V range such as the MC34072, which
    typically swings +14 to -14.7 off +-15 if fairly lightly loaded. It's
    also a lot quieter than the LF353, not that you probably care much in a
    power amp.

    Cheers

    Phil Hobbs

    --
    Dr Philip C D Hobbs
    Principal Consultant
    ElectroOptical Innovations LLC / Hobbs ElectroOptics
    Optics, Electro-optics, Photonics, Analog Electronics
    Briarcliff Manor NY 10510

    http://electrooptical.net
    http://hobbs-eo.com

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  • From Trevor Wilson@21:1/5 to Phil Allison on Mon Sep 5 06:10:03 2022
    On 4/09/2022 10:28 am, Phil Allison wrote:
    Trevor Wilson wrote:
    =================
    I am servicing a power amplifier which uses a dual, 8 pin DIP OP amp.
    Unfortunately, the rail Volts on the OP amp (LF353) is +/- 22 Volts.

    ** That is a mistake, all versions of the Sumo 9 used nominal +/-20V rails fed from series regs with 20V zeners.

    **Oops. You are correct. The negative rail is fed from a 20 Volt zener
    and the positive rail is fed from a series transistor, with the base
    tied to a 20 Volt zener, in series with a forward biased diode.


    I need a suggested replacement.

    ** Which MUST be a FET input op-amp.

    **Yes. There is that.



    And no, it is not possible to drop the rail Voltages.

    **Course it is, they are meant to be 19.5V each anyway.

    They must remain at +/-22 Volts.

    ** Humbug.

    **True enough. I had neglected to examine the schematic before I posted. According to the schem, it is +/- 20 Volts.



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