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Hashtag Octothorpe
Joined: Jun 11, 2017 Posts: 57 Location: Grand Rapids MI
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Grumble
Joined: Nov 23, 2015 Posts: 1294 Location: Netherlands
Audio files: 30
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Posted: Sun Jan 27, 2019 3:40 pm Post subject:
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did i wrote instrument amplifier? it is actualy instrumentation amplifier, inamp for short.
here is the diagram if you want to make one with opamps:
you see that the inputs are very high impedance which you can change by having a resistor to gnd (1Mohm or something in that order) the way you use the opamp gives an input resistance of 100k on the - input and 1100k on the + input so that could be responsible for some of the noise.
also: are you sure it is noise and not oscillation?
i didn’t match my transistors for my first build, but i did for my second one, but i didn’t notice any difference. Last edited by Grumble on Sun Jan 27, 2019 3:47 pm; edited 1 time in total |
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Hashtag Octothorpe
Joined: Jun 11, 2017 Posts: 57 Location: Grand Rapids MI
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Posted: Sun Jan 27, 2019 3:43 pm Post subject:
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nope, you wrote "instrumentation amplifier" my mistake. I know what they are now, but I had never heard of such a thing! And they're not TOO expensive -- less than $1 each from Aliexpress... but I am spoiled by $0.07 NE5532s or TL074s. |
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Grumble
Joined: Nov 23, 2015 Posts: 1294 Location: Netherlands
Audio files: 30
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Posted: Sun Jan 27, 2019 3:50 pm Post subject:
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i am more spoiled: i make use of the sample program from analog devices, so i get them for free 😀🤙🏻 _________________ my synth |
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Hashtag Octothorpe
Joined: Jun 11, 2017 Posts: 57 Location: Grand Rapids MI
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Posted: Sun Jan 27, 2019 3:55 pm Post subject:
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LOL right? People with their VST and DAW "throw a compressor on these twenty tracks" while I brag about having TWO compressors. |
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VA1
Joined: Aug 20, 2018 Posts: 98 Location: Nederland
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Posted: Wed Apr 10, 2019 7:19 am Post subject:
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Maybe you can post some audio ? |
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VA1
Joined: Aug 20, 2018 Posts: 98 Location: Nederland
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Posted: Tue Apr 23, 2019 7:07 am Post subject:
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Still no audio from that noise ?
I made various filters with opamps like you try, they all still are noisey.
You are using a dual supply schematic for a single supply thing.
How i made it : both sides go into inverting amplifier :
4K7 input resistor and 10K feedback resistor, half volt in the non-inverting input.
Then both go to comparator with 10K input resistors and 330K feedback resistor, no half volt needed.
You can use the fourth opamp to generate half volt. |
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ixtern
Joined: Jun 25, 2018 Posts: 145 Location: Poland
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Posted: Tue Apr 23, 2019 11:55 pm Post subject:
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It is hard to say what is making noise. There are some possibilities:
- resistors. Resistors, especially big resistances (100kOhm and more) and low quality (usually carbon types) may make substantial noise.
- transistors. Some transistors are more noisy than others. Lately I've been making noise generator. To test different noise sources I've mounted socket to change transistors and the winner was... BF423 (biggest noise). Try to use low-noise types, like BC109, BC239, BC549, BC550, etc.
- OpAmps. TL074 is not the low-noise one. Low-noise OpAmps are usually bipolar, not JFETs. E.g. typical noise at 1kHz for TL072 is 18nV/HZ, for NE5532 5nV/Hz. For lower frequencies is even worse for JFETS: at 10 Hz TL072 has 45 nV/Hz, NE5532 has 10 nV/Hz.
Notice that bipolar OpAmps like NE5532 have usually much larger input bias currents so some offset voltage may occur if resistors on + an - inputs are not equal.
- power supply quality. Use not only electrolytic caps, but ceramic ones in parallel also to filter high-frequency noise. |
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VA1
Joined: Aug 20, 2018 Posts: 98 Location: Nederland
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Posted: Thu Apr 25, 2019 7:59 am Post subject:
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Transistors may also differ between eachother from the same type for noise generator, you always need to select one, or use a trimmer lateron.
You might make a noise generator that clips with a luck transistor.
About the noise, ( if the TS ever read this : you still need to post audio )
I like the noisey filter, i even use high eq to boost the noise, why :
because laptop/mobile phone producers dont have that.
Ofcourse some people who dont know analog complain. |
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elektrouwe
Joined: May 27, 2012 Posts: 143 Location: Germany
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Posted: Thu Apr 25, 2019 1:46 pm Post subject:
Re: Noisy TB-303 clone, how to fix? |
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"... It's made worse if there's Arduinos driving LEDs.."
+5V rails is suspicious then. Is it filtered like +12Vis ?
try a 47uF || R24. |
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VA1
Joined: Aug 20, 2018 Posts: 98 Location: Nederland
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Posted: Fri May 10, 2019 7:46 am Post subject:
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About the noise generator ( my favourite subject )
Some brands have stable noise over all transistors.
If you buy the same BC547B from another brand, the noise can differ per transistor.
There are no noise generator specefications in the datasheet so it dont matters. |
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