EHX - Signal Pad  [schematic]

All about modern commercial stompbox circuits from Electro Harmonix over MXR, Boss and Ibanez into the nineties.
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jupagblkxten
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Post by jupagblkxten »

Seems like there's some interest around this pedal so here's the lowdown:

1 meg (log) pot wired as a volume control. 220p (ceramic) cap to ground off the input.

Simple. No battery required.

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weirdbeard
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Post by weirdbeard »

hi, i'm new at building effects and have been interested in this pedal. could you post a wiring diagram of this? thanks

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fergus_nz
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Post by fergus_nz »

are you sure the cap goes to ground? :hmmm:
would've thought it'd be a treble bypass something like this: http://seymourduncan.ru/new/s/treble-bleed_mod.jpg

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xmugmugmugx
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Post by xmugmugmugx »

I know it's a fairly simple design but i'm having trouble figuring out how to put it together. Anyone have any tips.

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kdmay
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Post by kdmay »

xmugmugmugx wrote:I know it's a fairly simple design but i'm having trouble figuring out how to put it together. Anyone have any tips.
+1 please!! Probably a simple voltage divider network, but I've heard about the use of inductors to retain high end so unsure of the internals. Or if there are any other designs that achieve the same thing I would be interested in ideas

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okgb
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Post by okgb »

I don't think you would see inductors in a passive design
unless it was a cut circuit otherwise you'd need some make up gain

Is it more than your average gtr volume control ?

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kdmay
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Post by kdmay »

fergus_nz wrote:are you sure the cap goes to ground? :hmmm:
would've thought it'd be a treble bypass something like this: http://seymourduncan.ru/new/s/treble-bleed_mod.jpg
Thanks - I might just build this into a pedal!
lolbou wrote:Topics merged. Use the search function :wink: ...
Apologies - need to touch up on my search skills, didn't even see this.

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nickeroo
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Post by nickeroo »

I am a pedal "n00b". How would one make the above description:

"1 meg (log) pot wired as a volume control. 220p (ceramic) cap to ground off the input." foot switch-able?

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Hides-His-Eyes
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Post by Hides-His-Eyes »

nickeroo wrote:I am a pedal "n00b". How would one make the above description:

"1 meg (log) pot wired as a volume control. 220p (ceramic) cap to ground off the input." foot switch-able?
treat it like an effect, and look at the standard effects wrappers on Beavis Audio or Geofex.

http://www.beavisaudio.com/techpages/StompboxWiring/
Testing, testing, won too fwee

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nickeroo
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Post by nickeroo »

Thank you, but I have a question (sorry!)

What would I do with the V+ pad on the board? Just wire the + of the LED right to the power jack?

Input and output pads would be the lugs on the volume pot?

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Hides-His-Eyes
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Post by Hides-His-Eyes »

What would I do with the V+ pad on the board? Just wire the + of the LED right to the power jack?
Yup.
Input and output pads would be the lugs on the volume pot?
Yup.
Testing, testing, won too fwee

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nickeroo
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Post by nickeroo »

Well, I wired it up but it is VERY noisy on or off.

When I turn the effect on and turn the vol pot it turns to very loud humming quickly (no guitar).

When I put the effect in the metal box, the effect stops working.

I reckon I have a grounding problem??

I wired the Sleeve of stereo jack onto the vol pot. Also sleeve of the mono jack to vol pot.

I wired the vol pot like a guitar, input from effect to first lug, middle lug is output, centre lug to vol pot casing.

I do not think it should be this hard!

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Hides-His-Eyes
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Post by Hides-His-Eyes »

Try connecting the ground lug to the grounds of the in and output jacks, instead of to itself. :)
Testing, testing, won too fwee

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Post by Dirk_Hendrik »

Since I got one for free with a decent designed eq of another brand;

http://www.dirk-hendrik.com/temp/EHX_signal_pad.pdf

Not worth the wear of my screwdriver... :roll: So far for innovation.
Sorry. Plain out of planes.

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marshmellow
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Post by marshmellow »

Wooo. And nice output impedance when it's actually in use.
"Treble pad" might be a better name...

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bobo
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Post by bobo »

When turn down pot the tone also changed. Anyone can advise how to mod it. Thank you

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Post by mysticwhiskey »

bobo wrote:When turn down pot the tone also changed. Anyone can advise how to mod it. Thank you
If you mean you lose treble when you turn down the level pot, then you could probably add a so-called 'treble bleed' cap and resistor in parallel across pins 2 and 3 of the pot, like what is done for guitar wiring. Typical values are say R=150K and C=1nF.

Image

Try it out with some test leads with alligator clips first, see if it makes an acceptable difference.

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bobo
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Post by bobo »

mysticwhiskey wrote:
bobo wrote:When turn down pot the tone also changed. Anyone can advise how to mod it. Thank you
If you mean you lose treble when you turn down the level pot, then you could probably add a so-called 'treble bleed' cap and resistor in parallel across pins 2 and 3 of the pot, like what is done for guitar wiring. Typical values are say R=150K and C=1nF.

Image

Try it out with some test leads with alligator clips first, see if it makes an acceptable difference.

Yes, it will lose treble when turn down the level pot. I will try per your information. Thank you

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Kenal
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Post by Kenal »

And does this scheme work like a RC-filter, doesn't it? What about to remove C2 wiring to the ground to avoid the tone changing?

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marshmellow
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Post by marshmellow »

:slap:
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