Obsolete opamp replacement

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bill981
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Obsolete opamp replacement

Post by bill981 » Thu Nov 10, 2016 2:17 pm

My PR&E Airwave 20 analog console took a lightning hit and it looks like either the OP275 driver/buffer amps are bad, or (worse) the OP176s have gone fubar. The OP275s are still available, but the OP176 ones seem to be unobtanium. I haven't been able to find a replacement yet, and am turning to those who might know where some are hiding.

Lee_Wheeler
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Re: Obsolete opamp replacement

Post by Lee_Wheeler » Thu Nov 10, 2016 3:13 pm

TLO81 is a plug and play replacement if you can find them.

I think you can find NTE857M through most outlets and they will work as well.

It will ignite a slew rate war by the op amp snobs but one of the DEs I had years ago built up a preamp with 30 741 op amps stacked back to back and had a set of Stax headphones. On the "preamp" was a straight wire bypass switch and he challenged all of the golden ears in the room to tell the difference in a blind test. It was a fairly small group with a dozen or so engineers and not a single person, my self included, could reliably tell the difference with statistical significance.

...Lee

ChuckG
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Re: Obsolete opamp replacement

Post by ChuckG » Thu Nov 10, 2016 6:50 pm

Lee_Wheeler wrote: It will ignite a slew rate war by the op amp snobs
You can compensate by using that gold-plated, oxygen free AC line cord. Oh, and an audiophile-approved outlet:
http://www.wattgate.com/products/381/

Pricing you ask? About $150. We are all in the wrong business. :lol:
<><><><><><><><><>
Chuck Gennaro
Central Wisconsin

BigRed
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Re: Obsolete opamp replacement

Post by BigRed » Thu Nov 10, 2016 11:18 pm

ChuckG wrote:
Lee_Wheeler wrote: It will ignite a slew rate war by the op amp snobs
You can compensate by using that gold-plated, oxygen free AC line cord. Oh, and an audiophile-approved outlet:
http://www.wattgate.com/products/381/

Pricing you ask? About $150. We are all in the wrong business. :lol:
Ah, that's not worth wasting your time with. What you need to be doing is digging out those old 833A's buried under the junk in the back of the transmitter room and dusting them off . . . :)

http://www.stereophile.com/tubepoweramp ... zaEOBup.97

BigRed
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Re: Obsolete opamp replacement

Post by BigRed » Thu Nov 10, 2016 11:49 pm

Lee_Wheeler wrote:TLO81 is a plug and play replacement if you can find them.

I think you can find NTE857M through most outlets and they will work as well.

It will ignite a slew rate war by the op amp snobs but one of the DEs I had years ago built up a preamp with 30 741 op amps stacked back to back and had a set of Stax headphones. On the "preamp" was a straight wire bypass switch and he challenged all of the golden ears in the room to tell the difference in a blind test. It was a fairly small group with a dozen or so engineers and not a single person, my self included, could reliably tell the difference with statistical significance.

...Lee
How do you measure the slew rate of a 741? With a stop watch. :)

The slew rate is relatively meaningless without other information like the stage gain, the amplifier bandwidth, etc. I remember a certain Rupert Neve console that used 741's in the microphone input audio path. Sounded just fine.

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Dale H. Cook
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Re: Obsolete opamp replacement

Post by Dale H. Cook » Fri Nov 11, 2016 7:18 am

BigRed wrote:How do you measure the slew rate of a 741? With a stop watch. :)
IMHO the best early treatment of slewing induced distortion in op amps was by Walter Jung (author of "Op Amp Cookbook" and other works), "Slewing Induced Distortion" (The Audio Amateur, 8 (1977):1:4-9, 20; 2:22-39; 3:21-28, 57; 4:22-28). In it he discussed the causes and effects of slewing induced distortion, techniques for measuring it, a circuit for listening tests, and objective and subjective conclusions.
BigRed wrote:The slew rate is relatively meaningless without other information like the stage gain, the amplifier bandwidth, etc.
A principal conclusion of Jung's series is that the minimum satisfactory slew rate for an op amp is determined by circuit conditions, and he reached that conclusion forty years ago
Dale H. Cook, Contract Engineer, Roanoke/Lynchburg, VA
http://plymouthcolony.net/starcityeng/index.html

Lee_Wheeler
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Re: Obsolete opamp replacement

Post by Lee_Wheeler » Fri Nov 11, 2016 7:49 am

BigRed wrote:
How do you measure the slew rate of a 741? With a stop watch. :)
I think it was in furlongs per fortnight.

...Lee

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Deep Thought
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Re: Obsolete opamp replacement

Post by Deep Thought » Fri Nov 11, 2016 10:24 am

Lee_Wheeler wrote:It will ignite a slew rate war by the op amp snobs
I remember more than one such snob sniffing at the time that the tight peak limiting achieved by the original Optimod 8000 was solely due to slew-rate limiting in the 741s it used.

Back to the topic at hand...any of the TL0*1s should work in an audio amplifier circuit.
Mark Mueller • Mueller Broadcast Design • La Grange, IL • http://www.muellerbroadcastdesign.com

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Deep Thought
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Re: Obsolete opamp replacement

Post by Deep Thought » Fri Nov 11, 2016 10:26 am

ChuckG wrote:You can compensate by using that gold-plated, oxygen free AC line cord. Oh, and an audiophile-approved outlet:
http://www.wattgate.com/products/381/

Pricing you ask? About $150. We are all in the wrong business. :lol:
That won't do you any good...unless you also install the matching Wattgate AC outlet.
Mark Mueller • Mueller Broadcast Design • La Grange, IL • http://www.muellerbroadcastdesign.com

bill981
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Re: Obsolete opamp replacement

Post by bill981 » Fri Nov 11, 2016 11:06 am

Lee & Deep,

Thanks for the help. The consoles are in great shape otherwise, and I'd hate to have to replace them.

COMMENG
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Re: Obsolete opamp replacement

Post by COMMENG » Fri Nov 11, 2016 11:52 am

Dale H. Cook wrote:
BigRed wrote:How do you measure the slew rate of a 741? With a stop watch. :)
IMHO the best early treatment of slewing induced distortion in op amps was by Walter Jung (author of "Op Amp Cookbook" and other works), "Slewing Induced Distortion" (The Audio Amateur, 8 (1977):1:4-9, 20; 2:22-39; 3:21-28, 57; 4:22-28). In it he discussed the causes and effects of slewing induced distortion, techniques for measuring it, a circuit for listening tests, and objective and subjective conclusions.
BigRed wrote:The slew rate is relatively meaningless without other information like the stage gain, the amplifier bandwidth, etc.
A principal conclusion of Jung's series is that the minimum satisfactory slew rate for an op amp is determined by circuit conditions, and he reached that conclusion forty years ago

Another good source is Chapter 5 of: Sergio Franco's, Design with Operational Amplifiers and Analog Integrated Circuits. In this chapter he discusses the limitations of opamps and slew-rate limiting is one of those.

COMMENG

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