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Resistance between red and black is close to 3k.  Between any of the others is either 1.5M or 3M.

I found this in my parts drawer.  Came out of a 90s-00s strat copy...can't remember the brand.  It looks like a dummy coil...metal slug with wound wire and 4 conductors.  If it is a dummy coil, why are there 4 conductors?  How would you go about wiring it up?

Use the buffer for the input and follow it with a small series cap and resistor and end with two volume pots. You won't have a buffered output (but you could use the other side of the opamp for that if that is what you want). You can switch only the wipers (influences taper and impedance) or wiper and terminal 3. In any case, pin 1 of both pots is always connected to ground, sucking up the DC build up.

the "small cap and resistor"...the cap to block DC and the resistor to act with the pot as a voltage divider?  or do they serve other functions?  With the cap and resistor in series I don't have to worry about the cap and potentiometer becoming a high pass filter correct?

yes, buffer and switchable attenuator.  I tried to talk him into one pot.  I was thinking variable resistor in parallel to fixed resistor in the negative feedback loop to set gain with the switch to add and remove the variable resistor.  He is set on 2 pots and unwavering.

I gave the caps a try with minimal effect if any. 

Taking a step back, is there a better approach to this?  Objective: a 2 pot pedal for controlling volume with a buffer to be used at the end of the effect chain.  Max volume is unity gain.  Sounds as though he wants to use it as a "boost" pedal with no coloration and no signal boost:). So essentially he wants a "signal cut" pedal:)

Would I be better off using 2 separate sides of a dual op amp and switch between them.  Use transistor instead?  Stick the pots at the end of the circuit with your typical "volume pot" setup?


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Thanks BuGG, I gave this a shot and it helped significantly.  There is still some noise when switching but I might just be hypercritical at this point.  I know mechanical switching is not silent switching.  Thanks very much for the suggestion!!

I have a friend that wants a simple pedal to set 2 different vol/gain levels and provide a buffer.  I thought a simple approach would be to use an op-amp and vary the feedback resistor.  I decided to lay it out as below in hopes to keep the impedance low on output.  He wants the max volume to be unity gain.  My problem is there is pop when I switch between pots.  I suspect DC build up.  I tried using "pull-down" resistors either side of the pots with no luck.  Do I need to use 2 separate sides of the op-amp and switch between op-amps?  Or can I utilize the current layout and deal with the DC?  Thanks for any help.

Reddesert, thank you for the in depth explanation.  I have a better understanding but will check the link and reread later tonight.
But what I understand, if I remove the op amp from the socket and probe on the "right side" of r5 I'd hear audio.  This also explains why it sounded like PIN6 was "grounding out" somewhere.


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Learnt me something new regardless.  Won't waste a bunch of time next trouble shoot trying hear the signal next time!


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Hmm.  Inquiring minds want to know!


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I built a basic op-amp overdrive last night and got very low output but everything sounded and functioned well otherwise.  I decided to use my audio probe to see where the output dropped and discovered there was no audio at PIN 6 (JRC4558) and very low output at PIN 7.  I decided it was probably the resistor in the negative feedback loop and found out I had some 1k resistors in my 22k bag.  Problem solved.
But now I'm confused as to why I don't get audio with my probe at the input (PIN 6) but I do at the output (PIN 7).  Can someone help me understand why I can't "hear" the signal at PIN6?
To keep it Madbean, here is a similar schematic:

http://www.ti.com/lit/ds/symlink/rc4558.pdf

Here's the spec sheet. If the link works.


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Link worked.  I'm missing something though.  Why can't I probe at pin 6 and hear what is being fed into the negative input pin?


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I built a basic op-amp overdrive last night and got very low output but everything sounded and functioned well otherwise.  I decided to use my audio probe to see where the output dropped and discovered there was no audio at PIN 6 (JRC4558) and very low output at PIN 7.  I decided it was probably the resistor in the negative feedback loop and found out I had some 1k resistors in my 22k bag.  Problem solved.
But now I'm confused as to why I don't get audio with my probe at the input (PIN 6) but I do at the output (PIN 7).  Can someone help me understand why I can't "hear" the signal at PIN6?
To keep it Madbean, here is a similar schematic:

I had no issues with mine.  I bought one off Amazon and one from Smallbear.  Both fit fine with a standard size jack


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I met the guy yesterday.  Real nice guy.  I popped the Morley AB pedal open in front of him and showed him the battery was only powering the LEDs and that the pedal was passive.  I suggested one battery would power those LEDs a very long time and that if it were mine I'd leave it as is.  He wants a D.C. Jack.  Who am I to argue?


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That etch is awesome


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