# 'sizzle' sound from fuzz pedal



## estimated_eyes (Jun 16, 2020)

Hey all,

Recently built a silicon Sunflower Fuzz and it sounds great!

I have noticed that when turning the fuzz knob from about 90-100% I am getting a 'sizzle' sound sustaining off each note played.

Here's a clip with 1. clean guitar 2. the pedal on with fuzz about 3 o'clock 3. fuzz all the way up with 'sizzle' sound (very prominent toward the end of the clip with low E)

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		https://soundcloud.com/dogsongs%2Fsunflower-fuzz-build-sizzle-noise

Listening back to this clip, its less prominent than in person.

I noticed touching Q2 while this is happening has an effect on the prominence of the noise.

Anyone have an idea what is causing this? Normal? Sheilding? Product of using transistor sockets?


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## benny_profane (Jun 16, 2020)

Try putting a small cap (start with 47pF or whatever you have that’s close) between the base and collector of Q2. That should shave off the hiss without drastically altering the high frequency output.


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## estimated_eyes (Jun 16, 2020)

benny_profane said:


> Try putting a small cap (start with 47pF or whatever you have that’s close) between the base and collector of Q2. That should shave off the hiss without drastically altering the high frequency output.



Thanks!

I've been playing around with different transistors and noticed it changes each time (some more noticeable than others) (bc108b, bc108c, 2n2222)

The way I have the pedal set up currently I am not using the fuzz pot dimed (or past 3 o'clock), so its taking that hiss and sizzle out.

In light of learning I was curious what was causing the sound or if its related to transistors, normal for the circuit, etc. ?


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## benny_profane (Jun 16, 2020)

The base-collector cap is a pretty common fix here—either on Q1 or Q2. Without getting into too much detail about impedance / reactance (which I’m not really in a place to explain anyway), the transistor is going into RF oscillation and you’re hearing that in the audio band. The cap is in the feedback path and reducing the the gain of the transistor and forming a LPF.

The transistor stages are common emitter amplifiers. The input goes to the base and the output goes through the collector. The emitter is _common_ to both (usually tied to GND or another reference). The output is anti-phase (inverted) to the input. So, the collector-base feedback path reduces the frequency range of the input signal. If you increase the capacitor value, you start reducing more of the frequency range and begin to decrease the overall gain of the transistor.

There are other factors in play here, but it’s an artifact of the gain stage scheme and with the transistors themselves. Like you found while swapping devices: other transistors with different electrical characteristics will exhibit different performance.


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## estimated_eyes (Jun 23, 2020)

benny_profane said:


> The base-collector cap is a pretty common fix here—either on Q1 or Q2. Without getting into too much detail about impedance / reactance (which I’m not really in a place to explain anyway), the transistor is going into RF oscillation and you’re hearing that in the audio band. The cap is in the feedback path and reducing the the gain of the transistor and forming a LPF.
> 
> The transistor stages are common emitter amplifiers. The input goes to the base and the output goes through the collector. The emitter is _common_ to both (usually tied to GND or another reference). The output is anti-phase (inverted) to the input. So, the collector-base feedback path reduces the frequency range of the input signal. If you increase the capacitor value, you start reducing more of the frequency range and begin to decrease the overall gain of the transistor.
> 
> There are other factors in play here, but it’s an artifact of the gain stage scheme and with the transistors themselves. Like you found while swapping devices: other transistors with different electrical characteristics will exhibit different performance.



Thanks @benny_profane !


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## benny_profane (Jun 23, 2020)

Let us know how things go for you!


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## estimated_eyes (Jul 10, 2020)

@benny_profane 

I ended up swapping a few of the resistors in and out, and positions, to find the best combination. Found a pair that sounds great!


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## benny_profane (Jul 10, 2020)

estimated_eyes said:


> @benny_profane
> 
> I ended up swapping a few of the resistors in and out, and positions, to find the best combination. Found a pair that sounds great!


So you ended up changing the bias and didn’t need to add a capacitor? Which resistors did you alter? In any case, glad you got it working to your liking!


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## estimated_eyes (Jul 14, 2020)

@benny_profane 

Sorry I completely misspoke on my last comment.

I swapped a couple different BC108 transistors I had to see which combination had the best results. I found a set that sound good where I have the pedal set.

I may end up adding that cap down the road, but since I'm not maxing the fuzz pot its not really necessary.


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## Chuck D. Bones (Jul 14, 2020)

You couldn't dial-out the sizzle with the SUNDIAL or either of the trimpots?  

I agree with Benny's suggestion of adding a cap to Q2.  Lotta FF circuits have a cap there to control the HF gain.

IMO, the FUZZ pot should be C1K.  It's very touchy at the CW end of rotation and C-taper makes it a little less touchy.

BTW, your link to the sound clip is broken.


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