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substitute 4558 op amp for guitar compressor?

scorp

Nov 29, 2013
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It's there a replacement for it? I'm uploading the schematic.

Thanks
 

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davenn

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the 4558 is readily available, why do you want to sub it ?

Dave
 

scorp

Nov 29, 2013
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Also, would the pots be audio taper or linear taper?

Thanks

Found the answer to this..
Thanks
 
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davenn

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see if radio shack have 1458 its the same chip different manufacturer

DAve
 

scorp

Nov 29, 2013
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The best kid I've built are ones that explain how the circuit worked. Since this circuit is not in kit form, can someone please explain how it works?

Thanks for your time
Jeff
 

duke37

Jan 9, 2011
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Starting at the op-amp, this has a gain of 23. The output is rectified and smoothed to give a positive feedback voltage.

The feed back voltage is fed to the second fet which is turned on when the gate is less negative. This shorts the signal to ground. So, the larger the signal, the more the attenuation. giving a more constant output.

The first fet is there to adjust the effectiveness of fet2
 

scorp

Nov 29, 2013
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Starting at the op-amp, this has a gain of 23. The output is rectified and smoothed to give a positive feedback voltage.

The feed back voltage is fed to the second fet which is turned on when the gate is less negative. This shorts the signal to ground. So, the larger the signal, the more the attenuation. giving a more constant output.

The first fet is there to adjust the effectiveness of fet2

Thank you
 

KrisBlueNZ

Sadly passed away in 2015
Nov 28, 2011
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see if radio shack have 1458 its the same chip different manufacturer
They're not the same. The main difference is the GBP (gain-bandwidth product) but this varies significantly between manufacturers. A clear example is STMicroelectronics, who manufacture both types. Their 4558 has a GBP three times higher than their 1458.

I think, from memory, that the 1458 is a dual 741. The 4558 is a newer design. It's also newer than the LM358, I think, which is probably the commonest pin-compatible device, but also has the lowest GBP.

In this circuit you might not notice the difference, since the gain is only 23.
 

davenn

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yeah i was kinda hoping it would do OK :)

gosh I have dozens of 4558's here, use them in several commercial products I produce

he must be able to find someone in his country that sells them in small numbers

Dave
 
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