Fairfield circuitry unpleasant surprise - help?!

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tome.talevski
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Post by tome.talevski »

Hello everyone!

I’ve attempted to assembled the Fairfield circuitry - unpleasant surprise Vero layout thats on the guitar FX layouts webpage (link below)… with limited success! I’ve owned this pedal and am quite familiar with how it sounds and operates. The best way to describe how my attempt sounds is very gated.... like its being starved of power. The pedal actually operates and functions as it should… all the switches and knobs change the signal as they should however its very very gated and almost filtered… the onset pot needs to be all the way CW to get any signal through… I also have to dig into the guitar to push the signal through. Im fairly confident ive populated the board correctly and very carefully… ive tripled checked for solder bridges etc.. Im using a circuit testing pedal that definitely works fine.. Ive used all the correct components.. although for the IC I used a TL072CP… not sure the CP makes any difference? I didn’t think it would.

I’ve listed all the values below… hopefully there is something obvious that stands out…! In some areas you’ll notice two different values.. the changes are in response to the gate switch.




Q1 J201s

D: 6.9
S: .12
G: 0

Q2 J201s

D: 2.6 // 3.7
S: .11. // .11
G: 0 // 0

Q3 2N3904

E: 3.15
B: 3.6
C: 8.9

D1 1N4148

Positive: 1.7 // 4
Neg: 1.6 // 3.8

D2 5v1 zener - 1n4733

Positive: 0
Neg: 5.25

D3 1N4148

Positive: 4 // 1.7
Neg: 3.24 // 8.4

D4 1n5817

Positive: 9.1
Neg: 8.9

IC - TL072CP

1: 1.6 // 4
2: 1.7 // 3.8
3: 1.8 // 3.8
4: 0 // 0
5: 3.7 // 3.7
6: 1.7 // 4
7: 8.4 // 3.3
8: 8.9 // 8.9



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tome.talevski
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Post by tome.talevski »

UPDATE

Ok, so here’s where im at. I’ve done my best to take notes and provide as much info as I can… hope someone can help me figure this out! :)

I changed the Q1 drain from 16k to 33k which brought it down to 4.80 from 6.9.

I changed the Q2 drain from 33k to 27k which brought it up to 4.65 // 3.45 from 2.6 // 3.7.

Overall, its made a 70% difference from what it was although still doesn’t sound like it should. It still sounds overly spluttery and gated like its not receiving enough power? Or something else. I’ve updated the numbers below which have changed a bit since swapping the resistors. Where there are two numbers, the first number refers to the gate switch prongs 1 and 2, the second number is gate switch 2 and 3.

Also, when the gate switch 1 prongs 1 and 2 are engaged along with the crush switch 2 and 3, there is no sound at all. I wonder whether theres a clue here with regards to the issue…. All other switch configurations produce sound.

When gate SW 1and2 along with Crush SW 1and 2 are engaged and the onset is fully CW… its producing ongoing buzzing. Goes away when its turned CCW a little.

When gate SW 2and3 along with Crush 2and3 is just a very gated fuzz… with the onset turn CCW 50% theres no sound.

Again, thanks for your help dudes!


QQ1 J201s

D: 4.8
S: .12
G: 0

Q2 J201s

D: 4.65 // 3.45
S: .11. // .11
G: 0 // 0

Q3 2N3904

E: 3.15
B: 3.6
C: 8.9

D1 1N4148

Positive: 1.7 // 4
Neg: 1.6 // 3.8

D2 5v1 zener - 1n4733

Positive: 0
Neg: 5.25

D3 1N4148

Positive: 1.76 // 4
Neg: 8.4 // 3.2

D4 1n5817

Positive: 9.1
Neg: 8.9

IC - TL072CP

1: 1.76 // 4
2: 1.61 // 3.8
3: 1.8 // 3.8
4: 0 // 0
5: 4.64 // 3.7
6: 1.7 // 4
7: 8.4 // 3.3
8: 8.9 // 8.9

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plush
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Post by plush »

You are building unverified stripboar layout.

Have your tried building it on a breadboard first?

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tome.talevski
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Post by tome.talevski »

Hey, yes its unverified although there was someone who did breadboard it and gave it the all clear on the guitarFXlayouts page. I was hoping the figures above would show an obvious error that I couldn't possibly pick up.

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Post by andy-h-h »

I just skimmed through that layout (which is not mine by the way ;-) ) and I couldn't see any errors.

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tome.talevski
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Post by tome.talevski »

Thanks Andy.. how do the figures I posted look? I’ve also posted this issue up on the original thread and where the Q3 base voltage was pointed out as too low..? As well as the Q2 drain not being stable..

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Post by tome.talevski »

This issue was resolved.. a layout error (which is now rectified) resolved most of the issues. There was some oscillation that was overcome by biasing the Q2 drain to .4v as opposed to .5 which made the difference!

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