High Voltage OP amp

Trevor Wilson

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Sep 3, 2022, 12:34:51 AM9/3/22

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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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kayge

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Sep 3, 2022, 2:31:43 PM9/3/22

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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.

Phil Hobbs

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Sep 3, 2022, 3:06:31 PM9/3/22

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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

Trevor Wilson

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Sep 3, 2022, 6:44:13 PM9/3/22

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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.

Trevor Wilson

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Sep 3, 2022, 6:56:50 PM9/3/22

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**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.

Phil Allison

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Sep 3, 2022, 8:28:36 PM9/3/22

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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

Phil Hobbs

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Sep 4, 2022, 9:57:00 AM9/4/22

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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.

Trevor Wilson

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Sep 4, 2022, 4:10:09 PM9/4/22

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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.