Comments on: LM358 Op-Amp Issues https://blog.nearfuturelaboratory.com/2011/07/28/lm358-op-amp-issues/ Clarify Today, Design Tomorrow Fri, 18 Aug 2017 17:58:48 +0000 hourly 1 https://wordpress.org/?v=5.5.1 By: julian https://blog.nearfuturelaboratory.com/2011/07/28/lm358-op-amp-issues/#comment-646 Tue, 16 Aug 2011 05:26:00 +0000 http://www.nearfuturelaboratory.com/?p=5342#comment-646 In reply to LPM.

Yep, definitely. I’ve sourced some. I’m also finicky about the “feel” of the potentiometers. The ones I have now have detents..that feels rather digital to me, so I’m looking around for log taper ones that turn with a bit of resistance.

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By: LPM https://blog.nearfuturelaboratory.com/2011/07/28/lm358-op-amp-issues/#comment-645 Tue, 16 Aug 2011 01:25:26 +0000 http://www.nearfuturelaboratory.com/?p=5342#comment-645 Consider using log-taper pots if you are concerned. Human hearing is not linear so a linear pot doesn’t ‘feel’ right. Its because the log response of the human ear makes them seem to put too much adjustment range in some areas and not enough in others. Most volume knobs in commercial electronics are log-taper for this reason.

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By: julian https://blog.nearfuturelaboratory.com/2011/07/28/lm358-op-amp-issues/#comment-644 Wed, 10 Aug 2011 17:43:30 +0000 http://www.nearfuturelaboratory.com/?p=5342#comment-644 In reply to palimdrones.

I think I’m close — not that I’m trying to make cold fusion in a mayonaise jar or anything..this should be easy, but then there’s also the fact that I’ve never messed much with sound circuits. I’ve actually been obsessing a bit too much on the potentiometers and their “action” — how well then turn and stuff, which is a bit over the top. I want to combine a mixer that can handle a variety of sources — stereo as well as mono — and line levels and such. At a minimum, it should handle my music player as a stereo source, an additional stereo source and two mono sources. The mono sources should be able to be panned either left or right. I’d like to learn about spatialization of sound in hardware — I think some phase delay might work. For this I’d like it if I could have an “effects send” aspect to this so I can send a source though an “auxiliary processing module” and then have it come back into the mixer…whew..

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By: palimdrones https://blog.nearfuturelaboratory.com/2011/07/28/lm358-op-amp-issues/#comment-643 Tue, 09 Aug 2011 16:08:18 +0000 http://www.nearfuturelaboratory.com/?p=5342#comment-643 nothing helpful to add but i’ll be keeping an eye on this! i’ve wanted a small portable mixer to combine old mp3 players, minidiscs, etc, anything that makes sound and is portable and is probably obselete- music from a few buttons!

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By: julian https://blog.nearfuturelaboratory.com/2011/07/28/lm358-op-amp-issues/#comment-642 Mon, 01 Aug 2011 17:35:30 +0000 http://www.nearfuturelaboratory.com/?p=5342#comment-642 In reply to LPM.

@LMP @foo You both are right! I hadn’t paid attention to the fact that my audio signal was swinging below my ground! Knot head, I am.. I just glanced at the Pk-Pk and just sort of mentally *shrugged. Thanks! I connected my -V to the negative (-5v) side of my supply and it worked out.

And here, I just attached the V- to the -5V fixed output of my little power supply, and the V+ to the variable output and set it to +5V.

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By: LPM https://blog.nearfuturelaboratory.com/2011/07/28/lm358-op-amp-issues/#comment-641 Thu, 28 Jul 2011 23:26:02 +0000 http://www.nearfuturelaboratory.com/?p=5342#comment-641 One thing not made explicit in your schematic is how you are powering the op-amps. Do you have a split supply or a single supply? (For instance, do you have gnd and +5V or do you have -5V, gnd and +5V rails?) From your scope screenshots it appears to me that you are using a single supply. When you use the function generator to drive the input to your op amp below the supply you are forward biasing a parasitic diode in the device, and a large current is clamping the input to gnd. I suggest putting a 1/2Vcc dc offset on your function generator and reducing the amplitude of the input signal to remain within the supply rails of the op amp at all points and see if there is any improvement.

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By: foo https://blog.nearfuturelaboratory.com/2011/07/28/lm358-op-amp-issues/#comment-640 Thu, 28 Jul 2011 17:07:47 +0000 http://www.nearfuturelaboratory.com/?p=5342#comment-640 You feeding a AC signal to a circuit that works in the ground – V+ range. Replace the polarized caps with unpolarized ones, and replace the op-amps with duel supply ones(+-9 volts should work for what you are doing).

If you want to keep your op-amps, you still need to repalce the polarized caps, but a 100k resistor between ground and pin 2, and pin2 and V+. This gives a DC offset to the signal. The output caps remove it again.

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