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OP275 to drive low impedance network?
OP275 to drive low impedance network?
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Old 5th November 2017, 05:22 AM   #21
ammel68 is offline ammel68  United States
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OP275 to drive low impedance network?
Quote:
Originally Posted by Fast Eddie D View Post
I know. I've spent a lot of quality time browsing datasheets looking for something I can use. I avoid smd but did successfully design and build a circuit with a couple of smd parts - only because I couldn't find satisfactory legacy (through hole) parts.
Great...I'm so glad that "you know". Sorry that I wasted your and my time with my post #5 reply. Apparently you already know all about the 4556 from studying all those datasheets.
It's difficult to help someone who already thinks they know all about op-amp designs, though.

Good luck with your future builds Fast Eddie D and with your eyesight issues!
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Old 5th November 2017, 03:40 PM   #22
Fast Eddie D is offline Fast Eddie D  United States
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Join Date: May 2010
Location: Skokie Il
Quote:
It's difficult to help someone who already thinks they know all about op-amp designs, though.
If I knew all about op amp designs, I wouldn't ask the questions I ask, would I?

I know how to read a datasheet and what parameters are relevant to my designs. Sometimes I'm wrong. I try to learn. I learn a lot just reading here and if it's relevant to a design I'm working on I check it out for myself.

I'm just figuring things out that I was supposed to understand .35 years ago. That's because I spent 25 years working at the exchanges and didn't do hardly any electronics. I went after the money. It didn't turn out very well for me either in the long run, thanks to the events of 2007-2009.

So don't hesitate to point something out to me. I won't be insulted, and neither should you either.

Quote:
Good luck with your future builds Fast Eddie D and with your eyesight issues!
Thanks.
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Old 5th November 2017, 03:55 PM   #23
Fast Eddie D is offline Fast Eddie D  United States
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Location: Skokie Il
Quote:
Originally Posted by rayma View Post
Sorry. I do think that PRR could be right. Cataracts can be completely "cured" by replacing
the natural lens with a plastic lens. You should be checked out by an ophthalmologist soon.
I blew my eyes out with a massive corona right in my face. My sight fades in and out when exposed to bright light. Images become burned in my retina for minutes; sometimes even hours. My right eye has a damaged lens from shrapnel.

Quote:
Maybe your Skokie low vision group will have some suggestions. Medicaid might be an option for you.
I'm working six days a week (at a TERRIBLE job with no benefits, practically no pay, no days off EVER) and desperately want to find a better situation. I make too much money for medicaid or government assistance of any kind (not that I want it). All I want is an opportunity to make an honest living, using the skills I possess. It seems like too much to ask.

I recently came across an old pay stub from 1998 that I was using as a bookmarker. Take home pay for two weeks, $4200. Insurance deduction for two weeks, $17. Now my pay stub says take home pay for two weeks, $700. No insurance! Plus I have to hustle on the side, which just about doubles my income (yes I document and report it). Something went wrong, and I don't believe it was all my fault.
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Old 5th November 2017, 04:08 PM   #24
rayma is offline rayma  United States
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Quote:
Originally Posted by Fast Eddie D View Post
I blew my eyes out with a massive corona right in my face. My sight fades in and out when exposed
to bright light. Images become burned in my retina for minutes; sometimes even hours. My right eye
has a damaged lens from shrapnel.
Please see an ophthalmologist (not just an optometrist), even if you have in the past.
The damaged lens should be able to be replaced. I don't know about the light problem,
but you should see an expert. Your sight is priceless.
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Old 5th November 2017, 04:16 PM   #25
Fast Eddie D is offline Fast Eddie D  United States
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Quote:
Originally Posted by rayma View Post
Please see an ophthalmologist (not just an optometrist), even if you have in the past.
The damaged lens should be able to be replaced. I don't know about the light problem,
but you should see an expert. Your sight is priceless.
No $$$. I have to ride out a few more years until medicare. If I die first, it won't matter much because there won't be much to fight over (I still have a real nice house). All my loved ones are either dead or estranged from me (religion).

I played big and I lost bigger. Now I live a different life.

And I am not alone either. Most of my colleagues blew out way worse than me in the Big Purge of 2007-2009. Trillions of dollars were destroyed thanks to several big banks folding. Bankruptcy courts made the remaining behemoths as whole as they could (taxpayers picked up the rest of the tab) and gave all other plaintiffs $0. Remember? It was all in the papers.

I'm the only one that didn't lose their house. High rollers, all of us.

Last edited by Fast Eddie D; 5th November 2017 at 04:22 PM.
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Old 5th November 2017, 04:44 PM   #26
rayma is offline rayma  United States
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Quote:
Originally Posted by Fast Eddie D View Post
No $$$. I have to ride out a few more years until medicare. If I die first, it won't matter much
because there won't be much to fight over (I still have a real nice house).
Maybe it's time to downsize, sell the house, and get the eye care that you need.
The cost of care would be only a small fraction of your house's value.
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Old 5th November 2017, 04:53 PM   #27
Fast Eddie D is offline Fast Eddie D  United States
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Location: Skokie Il
Thought about that. Rent is way higher than my mortgage. I would net about $250K is I sold today. That's not very much money. I have to think about how I'm going to survive if I live another 25 years (which is very likely).

At some point I'll probably try to find someone to move in with me. But I absolutely hate living with people. (Cats are OK.) I love visitors, and I love it when they leave too.

At this point I haven't given up on finding gainful employment, and I'm trying to be realistic about the obstacles. Sadly my biggest obstacle is my experience; people always say "you're overqualified" which is code for "you're a nasty old fartbutt and besides we can never pay you what you're used to."
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Old 5th November 2017, 05:02 PM   #28
rayma is offline rayma  United States
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Quote:
Originally Posted by Fast Eddie D View Post
At this point I haven't given up on finding gainful employment, and I'm trying to be realistic
about the obstacles. Sadly my biggest obstacle is my experience.
In a large urban area with public transportation, there's still a good chance of finding a better job.
Keep looking, and maybe downgrade your experience in some cases, if it might help.
If you have a PhD, only say that you have a BS, etc.

How about borrowing for your medical expenses, with the house as collateral?
Also, take a look at this. Financial Aid for Eye Care | National Eye Institute

Last edited by rayma; 5th November 2017 at 05:18 PM.
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Old 8th November 2017, 04:16 PM   #29
Fast Eddie D is offline Fast Eddie D  United States
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Thanks Ray, that's the plan. And I don't get out much because I work and then go home.

I talk to a lot of people that say they might call me "some day." And I still believe they might.

Back on topic, I'm building an inverting buffer board. The panel mount board will have the network and a relay. It's more complicated than I wanted it to be, but I've been trying to conjure up a decent variable "loudness" control for a while.

And also on closer analysis of the network, the passband impedance actually varies from 2.5K (control counterclockwise) to 1.2K (control clockwise). If you powered up the circuit with the control clockwise, it was stable. Then if you turned the control clockwise, it would start to oscillate when it was turned almost all the way up. You had to turn it all the way down to get it to stop oscillating.
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Old 1st March 2018, 06:39 AM   #30
Fast Eddie D is offline Fast Eddie D  United States
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Well I am ready to revisit this topic again, hopefully once and for all.

I did build a satisfactory board using OP275 as the buffer. While I am still going to tweak the network ( and most likely build a final board) I did get over the instability hump. I've been building a couple other circuits and I had another problem with a board that I've been using for a year that employs an OPA2134 as a buffer and x2 voltage amplifier. This circuit worked great for a year, listened every day. But I added a bass compensation circuit (separate board) and there was oscillation that I traced to this 2134 that buffers the volume control. I popped a 275 in there and it's rock solid now and definitely passes the listening test.

The moral of the story is that the OPA2134 has an Achilles's heel and it's the output stage. A complex reactive load will introduce that fatal pole that introduces instability. I'm sure there's a way around it and I hope to find out. But I don't think it's a universal chip for op amp rolling. I've read comments that the 2134 sounds "veiled" and now I wonder if it was popped into an old circuit that was far from optimized. I still have two 2134s in the signal chain in my preamp (including right at the input) and it certainly doesn't sound "veiled" at all.
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