[sdiy] Faster LM358 replacement

sleepy_dog at gmx.de sleepy_dog at gmx.de
Mon Feb 26 00:47:31 CET 2018


Tom Wiltshire wrote:
> Could you change the filter design instead?
>
> A MFB filter will give you better performance higher up in the stop band than a Sallen-Key for example. You might be able to design around the op-amp limitations.
Well, for a filter with higher order than those indeed sallen key based 
couple of boards I have here, I already made it MFB for I was advised 
that component tolerance becomes prohibitive in higher order sallen-key.
I'd still like to not just throw away the boards I have, so if I can get 
a cheap-ish replacement, it would still be nice.

> Some discussion here:
>
> http://www.ti.com/lit/an/slyt306/slyt306.pdf
Thanks!

- Steve



>
> The other big difference is that one is inverting and the other isn’t, but you might be able to fix that by flipping the DAC data upside down.
>
> Tom
>
> ==================
>         Electric Druid
> Synth & Stompbox DIY
> ==================
>
>> On 25 Feb 2018, at 21:30, sleepy_dog at gmx.de wrote:
>>
>> Hey,
>>
>> say, what opamp could I use as a faster replacement for the LM358?
>> Should be able to work with GND as negative supply and get the output (almost) there like the LM358.
>> Would be nice to have one that also can run up to +15V, but for my scenario at hand, 5V supply is enough.
>> And it would be nice to know one that's also not very expensive. It's probably hard to beat lm358 price... but let's not exaggerate ;)
>>
>> The application is an active filter to treat the DAC output for CV. Turns out the LM358 doesn't do such a good job there even at just a few kHz, i.e. the response curve starts to become less steep at the higher end quickly. (which even LTspice predicts, but I didn't bother to try the circuit with a LM358 model until now)
>>
>>
>> - Steve
>>
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