Author Topic: Cupcake 2020- noise  (Read 349 times)

bschobs

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Cupcake 2020- noise
« on: August 03, 2020, 02:06:48 PM »
So I boxed up this cupcake last night and she has a couple of issues:

1 - When I measure the trim pot gate, the closest I can get to the suggested 1.5v is 1.0v, and that is with the trim pot dialed all the way counter clockwise.

2 - If I play even moderately loudly on my guitar, I get a crackling sound coming from the effect. This does not occur in bypass.

I can provide more details if needed but my assumption is maybe an incorrect value somewhere? Can anyone point me towards some good starting points?

She’s not the prettiest on the inside...





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midwayfair

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Re: Cupcake 2020- noise
« Reply #1 on: August 05, 2020, 07:14:31 PM »
Please take voltages on everything.

Did it work out of the box? Generally we ask that people not box a circuit until they have confirmed it's working.

What kind of pickups are in your guitar?
Did you make any substitutes for the FETs, and where did you get them?

In addition, measure the following:

1. Measure the voltage on the cathode of your germanium diode with no input and with the guitar input.
2. Measure the drain--source resistance of Q1 with and without guitar input.
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Matmosphere

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Re: Cupcake 2020- noise
« Reply #2 on: August 05, 2020, 11:15:27 PM »
Maybe reflow the solder joints for the grounds, and check the 9v connection to the foot switch, that looks like it might not be making a great connection.

But yeah, what midwayfair said, measuring the voltages is the way to go here.

bschobs

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Re: Cupcake 2020- noise
« Reply #3 on: August 11, 2020, 10:25:00 PM »
Hey guys, I'm sure you've lost plenty of sleep wondering whether or not I got this thing working correctly lol.

Alright so I took voltages and reflowed the power and grounds and maybe a couple of others that could have been questionable, then took readings again.  Also re-tested and still will get this kind of trashy sounding noise that isn't at all musical coming into the signal and the trimpot is still basically ineffective.

Germanium diode voltage is the same with guitar plugged in or not.  Zero.  (0.1 if on the 200|m setting)

The rest are as follows.  The first number is in the build doc as it should be, the second is my actual reading:

IC 1
1 - 5.04 - 5.00
2 - 5.04 - 5.00
3 - 4.92 - 4.12
4 - 0 - 0
5 - 0 - 0
6 - 9.16 - 8.52
7 - 9.16 - 8.52
8 - 9.18 - 9.12

Q1
D - 2.12 - 1.04
S - 2.14 - 1.46
G - 1.32 - -.02

Q2
D - 9.2 - 9.12
S - 2.92 - 2.19
G - 2.14 - 1.46


midwayfair

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Re: Cupcake 2020- noise
« Reply #4 on: August 12, 2020, 08:48:56 AM »
Germanium diode voltage is the same with guitar plugged in or not.  Zero.  (0.1 if on the 200|m setting)

Not just "plugged in" -- you need an actual input signal.

The diode rectifies (half-wave rectifies) the AC signal coming out of the chip. You need an audio going into to the pedal for there to be an AC signal there for it to rectify.

Play a chord on your guitar while measuring the voltage on the diode. It should jump negative.
Myself's music & things I make: http://jonpattonmusic.com. My band: http://midwayfair.org. PCBs of my designs from: http://www.1776Effects.com (Bearhug Comp & Cardinal Harmonic Trem); http://www.jmkpcbs.com (Hamlet+ delay & Blue Warbler envelope vibe); Snow Day OD/Flabulanche: www.madbeanpedals.com