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Fluctuating high-pitch noise in op-amp circuit
Fluctuating high-pitch noise in op-amp circuit
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Old 20th November 2019, 11:23 PM   #21
Rolox is offline Rolox
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Join Date: Oct 2019
Quote:
Originally Posted by indianajo View Post
Put 33 pf disk caps parallel the op amp feedback resistors. Pins 1 & 2 and 7 & 6 usually.
I had to do that to my 33078 when I replaced the 4558 the mixer came with. In addition to a .1 uf between supply rails for every 2 packages.
When you replace a 6 v per microsec slew rate amp with a 20 v per microsec amp, make sure the high freq gain is killed by shorting it out with the feedback cap.
I couldn't hear the oscillation, but my cs800s amp fan was running on high at 1 w/ch. Had a working scope then for 2 weeks, saw ~ 1 mhz.
BTW the 5532 is a pretty quiet part. Just a bit of a hog on power supply current. There weren't any leaded DIP packages in stock the day I was buying "low noise op amp" from newark. Paid all of $.38 ea for ST33078. NJM2068 is another forgotten low noise low cost part. If you need low noise + high drive current for long lines or high capacitance filters, Peavey used NJM4580 in the 90's.
To be honest I am not sure it is oscillations - or if it is, something else in the circuit must be off/broken. Iíve seen OPA2132 behave in seemingly much worse situations...?...

But if it turns out it is oscillating and nothing else is faulty Iíll try with the 33pF caps, thanks for the tip
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Old 21st November 2019, 07:29 AM   #22
Rolox is offline Rolox
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Join Date: Oct 2019
Quote:
Originally Posted by voltwide View Post
Could you post a sound record file of your noise here?
Here it is. just turned it on and immediately it starts whistling like crazy.
Iphone microphone 2 inches from the horn tweeter - but sitting in the listening spot you hear it just as good.
can't wait to have you guys tell me what you think this might be... :-/

PS Edit: the file didn't upload. I need to convert it somehow. This is gonna be fun. Be right back...

Last edited by Rolox; 21st November 2019 at 07:34 AM.
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Old 21st November 2019, 07:41 AM   #23
Rolox is offline Rolox
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I guess it's here now?
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Old 21st November 2019, 07:42 AM   #24
Rolox is offline Rolox
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OKAY I had an .m4a file from iPhone, converted it in .mp3, still not uploading, if someone can tell me how to proceed... thanks in advance
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Old 21st November 2019, 07:42 AM   #25
Hicoco is offline Hicoco  France
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Location: Provence
Fluctuating high-pitch noise in op-amp circuit
Quote:
Originally Posted by Rolox View Post
Here it is. just turned it on and immediately it starts whistling like crazy.
Iphone microphone 2 inches from the horn tweeter - but sitting in the listening spot you hear it just as good.
can't wait to have you guys tell me what you think this might be... :-/

PS Edit: the file didn't upload. I need to convert it somehow. This is gonna be fun. Be right back...
Post it on YouTube..with the link here
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Old 21st November 2019, 08:01 AM   #26
Rolox is offline Rolox
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suspense..
Attached Files
File Type: mp4 Avenue de Tervueren.mp4 (556.9 KB, 32 views)
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Old 21st November 2019, 08:27 AM   #27
Rick PA Stadel is offline Rick PA Stadel  United States
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Join Date: Apr 2017
Location: greater Kansas City
Wow -- -- bet that is REALLY hard to put up with!

Sounds like something with a medium-performance microprocessor in it. There's too much structure to it for it to be something random like intermittent oscillation.

You wouldn't happen to have a mod-ed 1990's-era CD player nearby with its cover off ..? or plugged into the same outlet ..?

I sure feel your pain. That's awful.

Rick

Last edited by Rick PA Stadel; 21st November 2019 at 08:30 AM.
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Old 21st November 2019, 08:33 AM   #28
ubergeeknz is offline ubergeeknz  New Zealand
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Sounds like RFI from a microprocessor device to me as well. I guess the design makes it prone to this.
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Old 21st November 2019, 08:50 AM   #29
Rolox is offline Rolox
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Join Date: Oct 2019
Quote:
Originally Posted by Rick PA Stadel View Post
Wow -- -- bet that is REALLY hard to put up with!

Sounds like something with a medium-performance microprocessor in it. There's too much structure to it for it to be something random like intermittent oscillation.

You wouldn't happen to have a mod-ed 1990's-era CD player nearby with its cover off ..? or plugged into the same outlet ..?

I sure feel your pain. That's awful.

Rick
I have a 1987 Revox B226 used as drive and an SMSL SU-8 DAC. Maybe I can plug them in a different power strip from a different outlet and see if that helps?... :-(
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Old 21st November 2019, 09:03 AM   #30
Rolox is offline Rolox
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Join Date: Oct 2019
ok...
unplugged both CD drive and DAC won't change a thing.
Unplugged WiFi and TV box won't change a thing.
Unplugged monitor audio wireless transmitter (plugged on a tape out of my preamp, it sends bluetooth music to my bedroom where the receiver is) won't change a thing either :-(

what bugs me is if it's really interference somehow it would change even so slightly when I open or close the enclosure, except maybe if it comes from the mains.
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