Op amp input +/-

[WGTP]

After reading R.G.s explainations of op amp operation in the IM thread I started wondering if there is an audible difference in using the - input like a Muff Fuzz vs. the + like most other op amp based distortions with diodes in the feedback loop.   :shock:

I really encourage everyone to try a Muff Fuzz variant with mixed with a single or mis-matched diodes in the loop.  

[Johan]

If I didnt missunderstod when i learned about op-amps long time ago, the +input is a voltagedetecting input and the -input is currentdetecting input. if that is correct (R.G ? ) it allmost has to make a difference, depending on what you drive the input with, series resistance and probably a few more factors..try and see...

Johan

[spongebob]

You mean an inverting opamp gain stage? Don't think it would distort different, except that the output signal is inverted.

[Mark Hammer]

As always, there is an article on the guitar-related pros and cons of using op-amps in inverting vs noninverting mode in one of the issues of DEVICE I have posted on my site at:  http://hammer.ampage.org

[WGTP]

Thanks Mark, semi educational (which means I probably understood 1/2 of it.    

It looks like my beloved Muff Fuzz is in the small number of distortions that use the inverting input.  Your designs and most distortions use the non-inverting input.  I guess that should tell me something.   :shock:

If 2 gain stages weren't being used in the Muff Fuzz, it would be impossible to get input impedance high enough to retain the tone of the guitar and get lots of gain with little noise.  Looks like I shouldn't use carbon resistors, I need quiet op amps and I need to match the resistor to ground with the size of the input resistor.  Is that it?  :?

I was just wondering if anyone thought there were sonic differences?  

[puretube]

technically absolutely no sonic differencies in the opamp`s inputs themselves -
except for those, depending on different circuit topology
concerning different impedances/resulting frequency responses....

(of course, some mojo in there, though   )

[WGTP]

In looking at the gain calculations, I'm using a 1k between stages and a 1meg in the feedback loop of the second stage so the gain is 1000 :shock:

With a 470k resistor in the first stage loop and a 100k input resistor, the first stage is at a gain of 5 :roll:

If I use a smaller input cap, it doesn't load the pickup and starts getting mid-rangy/Rockman sounding, like Gary's Mockman.   :lol:

I'm not finding the distinct difference between diodes in the feedback loop and diodes to ground that you would expect, and all that gain might explain it.  There is so much distortion going on, it's hard to hear the differences.  

Last night I had 1 LED in the loop and 2 to ground at the end and it sounded pretty Hot and Bothered.    

I like to turn ou the lights and watch them blink, it gives me an idea of how much clipping is going on.