I got mine off ebay for £60.
Has worked fine for numerous years now.
You can always sell it on after you have finsihed with it for a similar price.
My first reaction is, "get a scope or get a different hobby!"
That said, you can do a lot with a little if you're very clever. Most radio hobbyists in the past didn't have scopes, either because they couldn't afford them, or because the scopes of the day didn't cover the frequencies needed. It was common to make an RF probe for a common voltmeter using a germanium diode and small capacitor. One could make basically the same thing to look for oscillation- any reading is cause for concern. I've also looked for high frequency oscillations and diode switching noise with an old transistor radio tuned between stations. The problem with these ideas is that if you know enough to use them, you probably know enough not to have made the original opamp mistakes to begin with.
BTW, excellent post!
That said, you can do a lot with a little if you're very clever. Most radio hobbyists in the past didn't have scopes, either because they couldn't afford them, or because the scopes of the day didn't cover the frequencies needed. It was common to make an RF probe for a common voltmeter using a germanium diode and small capacitor. One could make basically the same thing to look for oscillation- any reading is cause for concern. I've also looked for high frequency oscillations and diode switching noise with an old transistor radio tuned between stations. The problem with these ideas is that if you know enough to use them, you probably know enough not to have made the original opamp mistakes to begin with.
BTW, excellent post!
I suppose it depends on what you do, but my scope is probably the most useful piece of kit I've got. If the only thing you're going to get up to is little more then opamp rolling, then I'm sure you'll think that a scope is a waste of money - Mooly's thread would naturally disagree and I know this will perhaps irritate some of the opamp rollers, but if you haven't got the ability to measure if a new substitution is stable, then don't even bother doing it. There are of course lots of substitutions one can make without causing oscillations, the trouble here is that the more stable opamps don't tend to be a part of the crowd that's supposed to sound 'better'.
Mooly, nice thread!
I've seen many threads on internet where DIY hobbyists replace op-amps on their tastes. At first I thought there would be possibility of stability issues but as nobody talked about it, eventually I accepted the idea it wasn't a deal. Now I discovered swapping op-amps it's not that simple.
I was about to replace the stock op-amps of my MiniMax DAC, but because of your warning I will rethink it as I don't have a scope.
Thank you very much indeed!
I've seen many threads on internet where DIY hobbyists replace op-amps on their tastes. At first I thought there would be possibility of stability issues but as nobody talked about it, eventually I accepted the idea it wasn't a deal. Now I discovered swapping op-amps it's not that simple.
I was about to replace the stock op-amps of my MiniMax DAC, but because of your warning I will rethink it as I don't have a scope.
Thank you very much indeed!
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Great thread but that first post is just plain scary!! 
Disclaimer. I own an O'scope. Bought used on eBay.
Disclaimer. I own an O'scope. Bought used on eBay.
Great thread but that first post is just plain scary!!
Disclaimer. I own an O'scope. Bought used on eBay.
Thanks Pano... and Mooly with a scope is indeed a scary site 😱
I wish I had a scope but a second hand one costs about $300 here. It's too much investment for a hobby. It's not cost-effective at all.
If you are swapping op-amps in your equipment for upgrade purposes, I have put up a 10 point check list up on my website.
http://hifisonix.com/wordpress/wp-content/uploads/2010/10/Opamp-in-Audio-10-Point-Guide.pdf
http://hifisonix.com/wordpress/wp-content/uploads/2010/10/Opamp-in-Audio-10-Point-Guide.pdf
That great Audio Maniac. Good luck with your designs!
Let me also thank Mooly here for originally posting some waveforms up that triggered the discussion!
Let me also thank Mooly here for originally posting some waveforms up that triggered the discussion!
fantastic Mooly!!, i admit to once being one of those opamp rollers, in fact its one of the things that got me started in diy. but in the years since, I've spent most of my time in those opamp threads warning and arguing with people about dropping opamps (mostly wideband) into circuits blind (cranky chips exactly like and most notably ad797, or arguing about the audible difference between ad797arz and brz, seriously).
one of my personal favourites is people performing specific modifications to put chips like buf634 and lme49600/10 into wideband mode for headphone amps.
I haven't yet got a scope, but its the next piece of kit for purchase along with a variac, already have bench voltmeter, 5 dmms and a few Jerry rigged add ons for testing gM etc
one of my personal favourites is people performing specific modifications to put chips like buf634 and lme49600/10 into wideband mode for headphone amps.
I haven't yet got a scope, but its the next piece of kit for purchase along with a variac, already have bench voltmeter, 5 dmms and a few Jerry rigged add ons for testing gM etc