# how do I wind a 660 mH coilfor a guitar pedal?

#### GopherT

Joined Nov 23, 2012
8,012

#### nitko12

Joined Oct 14, 2015
13
Inductance that high might be worth buying one instead. About $25. What saturation current & DC resistance is needed? I dont know, but i dont think it needs too much current #### GopherT Joined Nov 23, 2012 8,012 I dont know, but i dont think it needs too much current No, but the DC resistance is important because it biases one of the 2N3904 transistors. That is one reason why most of the DIY attempts to duplicate this pedal seem to fail. #### Dr.killjoy Joined Apr 28, 2013 1,196 GopherT is right just buy the right coil cause if you don't have the right tools to build and test the coil to make sure it's within spec then your just wasting time and guessing.. Last edited: #### Papabravo Joined Feb 24, 2006 14,885 First you have to find a suitable core material. Then you have to read the datasheet carefully and figure out how many turns you need. Then you have to test it to make sure your design calculations were correct. Then you have to try it out in your circuit. If it works -- great; but if it doesn't then you'll either have to redesign the circuit for figure out what went wrong. #### GopherT Joined Nov 23, 2012 8,012 I dont know, but i dont think it needs too much current It will look something like this when you are done if you have an automated winding machine. If you don't have an automated winding machine, it will look like a spool of kite string after you reel the kite back in. Without perfectly placed wire, the inductance will not match the calculated values (if you have a calculator that can handle multiple layers of windings). Something like this has too many air gaps between the "wires" and you will end up with more layers than planned which results in lower and lower inductance so you have to add more and more wraps which are increasingly distant from the core and add less and less inductance. Last edited: #### AnalogKid Joined Aug 1, 2013 8,833 On the Dunlop website is a video about their successor to the original CryBaby. At 4:25 is an image of the inductor, obviously a custom-made part from a volume manufacturer. http://www.jimdunlop.com/product/535q-cry-baby-multi-wah Digi-Key has over 125,000 inductor types. If you sort for in stock and 500-700 mH, you get three: http://www.digikey.com/product-search/en/inductors-coils-chokes/fixed-inductors/196627?k=&FV=fff40003,fff80013,4c02c7,4c0466,4c0475,4c0476&mnonly=0&newproducts=0&ColumnSort=0&page=1&stock=1&quantity=0&ptm=0&fid=0&pageSize=500$2.62 plus shipping

None of these are low profile radial-mount torroids, but it's a place to start.

ak

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#### Alec_t

Joined Sep 17, 2013
11,817
i dont think it needs too much current
Less than 1uA rms according to LTspice. And the inductance value isn't critical. 500mH gives much the same frequency response as 660mH.
Here's the sim file if anyone wants to play.

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#### AnalogKid

Joined Aug 1, 2013
8,833
According to the guys who developed the replacement/expanded device, they changed from 500mH to 535 mH because "it just sounded better".

ak

#### GopherT

Joined Nov 23, 2012
8,012
According to the guys who developed the replacement/expanded device, they changed from 500mH to 535 mH because "it just sounded better".

ak
I'd like to know what exactly sounded better. The audio output or the fact that one of the guys stumbled upon a 535 mH part at a lower price - so the profit sounded better.

#### AnalogKid

Joined Aug 1, 2013
8,833
In the same way my sister cannot see the physics of the world around her the way I do, I can't hear music the way she does - and she's only semi-pro. A small open-frame torroid with that high an inductance value is a full-custom or modified-standard part, not a catalog item. Can a 5% change in inductance value affect the Q enough to affect the notch enough affect the sound enough to be perceived and evaluated by a trained pro - absolutely.

Guitar people are nutzoid about their effects boxes. They buy salvaged 301's from Russia because they think those decades-old chips sound better than new ones, and they want that sound in their fuzz box. For a friend, I took his box, removed the chip, and replaced it with a DIP socket so we could go back and forth between a 301 and 741. Turns out that I *can* hear the difference. Also turned out that I didn't care, but he did.

ak

#### tracecom

Joined Apr 16, 2010
3,944
I can *taste* the difference between an egg laid by one of my Black Copper Marans hens and a white egg from the grocery store, but of course I want to be able to.

#### GopherT

Joined Nov 23, 2012
8,012
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#### ian field

Joined Oct 27, 2012
6,539
First you have to find a suitable core material. Then you have to read the datasheet carefully and figure out how many turns you need. Then you have to test it to make sure your design calculations were correct. Then you have to try it out in your circuit. If it works -- great; but if it doesn't then you'll either have to redesign the circuit for figure out what went wrong.
Someone told me Wah-wah pedals use a ferrite pot core for the inductor - easy to get high inductance, but prone to core saturation. That could even be part of the distortion effect.

The inductance value probably isn't critical, some designs show 500mH. Its basically a sliding notch filter - there's other components that can be altered to compensate for shifted inductance value.

#### GopherT

Joined Nov 23, 2012
8,012
Someone told me Wah-wah pedals use a ferrite pot core for the inductor - easy to get high inductance, but prone to core saturation. That could even be part of the distortion effect.

The inductance value probably isn't critical, some designs show 500mH. Its basically a sliding notch filter - there's other components that can be altered to compensate for shifted inductance value.
Agreed. This particular design requires some interaction with the user - tipping the foot pedal forward/back to sweep the filter (or it can be left stationary). For any specific inductor value and desired notch frequency, the user just changes the foot pedal position slightly. I can't see that a 5% changes to the inductor is going to impact anything that cannot be adjusted with the foot pedal.

#### AnalogKid

Joined Aug 1, 2013
8,833
Someone told me Wah-wah pedals use a ferrite pot core for the inductor - easy to get high inductance, but prone to core saturation. That could even be part of the distortion effect. The inductance value probably isn't critical, some designs show 500mH. Its basically a sliding notch filter - there's other components that can be altered to compensate for shifted inductance value.
Actually, it is a sliding, moderately high Q, resonant bandpass filter. Beyond the intentional frequency response alteration, distortion is avoided, and left ot other effects boxes such as fuzz and overdrive.

For any particular inductance value and pedal setting, the circuit has a resonant frequency, impedance, gain, and Q. While changing the pedal position can shift the resonant frequency to compensate for a change in inductance, both the bandwidth and gain also will change. Turning a production variance into a feature, the newer pedal has an adjustable Q. Again, I'm not saying any of these things are significant to most people, but the purists are just like guys who can tell the difference between two almost identical brands of tires, or strains of barley in home-brew, or the over 500 different shades of black in fabrics, or the voicing of a piano, or bell diameter in crash cymbals, or or or...

ak

#### ian field

Joined Oct 27, 2012
6,539
Actually, it is a sliding, moderately high Q, resonant bandpass filter. Beyond the intentional frequency response alteration, distortion is avoided, and left ot other effects boxes such as fuzz and overdrive

ak
That's the by the book description, but AFAIK: its a sliding notch filter in the nfb loop of the amplifier.

#### #12

Joined Nov 30, 2010
18,216
They buy salvaged 301's from Russia
OMG! I have a dozen (virgin) LM301's from 1973. How much are they going for?

#### ian field

Joined Oct 27, 2012
6,539
OMG! I have a dozen (virgin) LM301's from 1973. How much are they going for?
They're worth what someone will give you for them - and finding that person will probably cost you more than that.