OP amp equivalents - Page 1
Forum section: electronics / projects

author: cowasaki
author_rank: Frequent Contributor
timestamp: October 17, 2019, 07:28:40 pm
content: Is there an op amp equivalent database?I'm repairing random amplifiers there are certain op amps that turn up regularly but also some that I just haven't seen for a while. Even if I only use the equivalent to test and diagnose problems before ordering the right ones

author: DaJMasta
author_rank: Super Contributor
timestamp: October 17, 2019, 07:58:23 pm
content: Are they from a specific series or something? A lot of models are still around, but something like RCA's SK series replacement parts usually are listed in reverse - they were marketed as replacements for a variety of amps, so you'd be better off looking up the part and finding what they would replace.Otherwise, if you have a datasheet for the original, you can probably get a close match for gain bandwidth product, input bias current, voltage range, slew rate, etc. and get something pretty close or better specified than the original. Maybe what they're used for is a better place to start? A lot of opamp uses don't really demand any particular replacement, but higher bandwidth, high sensitivity frontends, low distortion requirements, etc. could push you towards a good general replacement for the application.

author: mzzj
author_rank: Super Contributor
timestamp: October 17, 2019, 08:01:53 pm
content: Google for op amp cross reference” and you get quite many hits

author: cowasaki
author_rank: Frequent Contributor
timestamp: October 17, 2019, 08:05:09 pm
content: Quote from: mzzj on October 17, 2019, 08:01:53 pmThanks! I tried several google searches but hadn't typed just that. That has brought up a few thanks.

author: Zero999
author_rank: Super Contributor
timestamp: October 17, 2019, 09:03:05 pm
content: It's much better to learn about the different types of op-amps and why a certain part can be used as a substitute.Start by reading about the basic op-amp parameters:Gain bandwidth product.Slew rate.Equivalent input noise voltage.Bias current.Input offset voltage.Common mode range.Supply voltage range.Maximum output current.Then there are the different types of input stages with J-FET, MOSFET and BJT being the most common.I appreciate this can be daunting. My advice would be to ask a question here about substituting a specific op-amp for another.If you know why, then you won't need a list of substitutions. You'll be able to find a suitable alternative by using the parametric search feature provided by many component distributors such as Mouser and Digikey. In fact even without really understanding why, the parametric search can help, but it's always better to understand what you're doing, rather than working blind.

author: schmitt trigger
author_rank: Super Contributor
timestamp: October 17, 2019, 09:16:44 pm
content: To Zero's comprehensive list, I would add to check for package type.It is disappointing to find an otherwise "excellent" opamp substitute, only to find that it is no longer available in DIP-8 or DIP-14.Having said this, that is the reason for the SMT to DIP adapter boards.

author: Audioguru again
author_rank: Regular Contributor
timestamp: October 18, 2019, 03:10:35 pm
content: Opamps that fail regularly are usually fake or defective ones from China. They have the same part number as good ones so a list of "equivalents" is useless. Buy good opamps locally instead.

author: dom0
author_rank: Super Contributor
timestamp: October 18, 2019, 05:21:42 pm
content: Quote from: cowasaki on October 17, 2019, 07:28:40 pmAudio op amps aren't particularly critical. Most standard BJT types are largely interchangeable, since their specs are generally very similar. You want to make sure that you don't replace a slow op amp with an op amp that has a much higher GBWP, but beyond that the specs generally don't matter much. NE5532 is for example a drop-in replacement for most Japanese (JRC/Rohm) dual BJTs.Replacing these kind of op amps with more modern, much faster devices (ala LM4562/LME49720 etc.) is generally unwise, and may actually change the "colourisation of the sound" by introducing some RF oscillations that are demodulated and thus mixed with the audio in later stages :-)Loads of people will tell you that audio op amsp areextremely criticaldevices that need to be very carefully selected and any change in part number, let alone manufacturer, will change the colourisation of the sound drastically. I'll leave it to you what to make of such claims.

author: cowasaki
author_rank: Frequent Contributor
timestamp: October 18, 2019, 05:59:21 pm
content: Quote from: dom0 on October 18, 2019, 05:21:42 pmMany thanks. It was just for those times when I want to check the operation of one before purchasing the correct one if the original was at fault.A few days ago I picked up a Peavey TKO-65 for £10 which someone's "friend" had tried to repair! I felt it was worth buying for the transformer and 15" speaker if nothing else. Anyway I attached my signal generator with a 2v 600Hz sine wave and looked at the output which was an amplified version of the input but with random additional sine waves all over it. I checked the output of the first op amp and the output was a nice clean amplified sine wave whilst the output of the second op amp was the randomly overlaids sine waves...... Hence my questionBUTI then decided to check further into the circuit and whilst checking the transistor Q9 I managed to slip and short the emitter to groundIt was for maybe a tenth of a second. I moved my hand away and as I did the fuse blew. I replaced it and the replacement blew. I then removed the transistor and checked it out of circuit. It was still working so I replaced it and I checked the current across the fuse which was 3.2 amps when the fuse in 1.6 amps.So now I have to fix the problem I caused firstI've managed to fix the last 10 amps I bought and this is the first potential failure.

author: mzzj
author_rank: Super Contributor
timestamp: October 20, 2019, 03:47:51 pm
content: Hard short circuits are at least easy to fix compared to something that just misbehaves occasionally.

author: cowasaki
author_rank: Frequent Contributor
timestamp: October 20, 2019, 03:59:02 pm
content: Quote from: mzzj on October 20, 2019, 03:47:51 pmYes. Looking forward to using my new workshop. Just waiting for my son in law and son to arrive to collect the last bit of furniture and then I can put everything away and look at the board. I’m collecting a load of variacs tomorrow hopefully that should avoid some possible issues with further repairs.

author: dom0
author_rank: Super Contributor
timestamp: October 20, 2019, 05:13:37 pm
content: If you shorted a driver in the output stage then it is quite probable that both (but very likely at least one) halves of the output stage are dead.

author: cowasaki
author_rank: Frequent Contributor
timestamp: October 20, 2019, 05:59:31 pm
content: Quote from: dom0 on October 20, 2019, 05:13:37 pmI will be having a look tomorrow. These were the transistors prior to the final output stage transistors (Q9) as per attached schedule. I ran out of time but my workshop is now free for me to have a proper look.