Been working on this in the background - another fuzz

[fuzzbuzzfuzz]

Excellent and unexpected

I'm fortunate to own a couple of the originals, so it will be interesting to hear this new take.

[laurie]

Excellent and unexpected

I'm fortunate to own a couple of the originals, so it will be interesting to hear this new take.

Its close. A bit more "open" because of the modern components, but the essence is there.

[Pepe]

Maybe swapping some capacitors for tantalums could be helpful to approach the vintage sound?

Today we can only speculate how the fuzzes from back in the day might have sounded when they came fresh out of the factory.

[laurie]

Maybe swapping some capacitors for tantalums could be helpful to approach the vintage sound?

Today we can only speculate how the fuzzes from back in the day might have sounded when they came fresh out of the factory.

That's the absolute right question, what did they sound like back in the day? And through what amp?

Mine will-be-what-it-will-be. It is a good fuzz - it doesn't need to be a perfect replica.

[fuzzbuzzfuzz]

Looking froward to hearing it Laurie

[laurie]

Build is progressing slowly.

The heart of the pedal is this two transistor arrangement (Q3 and Q4) - it acts as a frequency doubler to give the octave fuzz effect.
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Octave doubler1.jpg (111.63 KiB) Viewed 1639 times

[laurie]

The design uses a BJT phase splitter (Q2) to create two out-of-phase signals. These signals are then fed into a paired "push-push" differential stage (Q3 and Q4). When properly balanced, the fundamental frequency is canceled out in Q3/Q4, leaving an accurate, full-wave rectified frequency double.

For the octave effect to be the most effective, Q3 and Q4 must have *exactly* the same hFE and Vf. If Q3 has a hFE of 124, then Q4 must also have a hFE of 124.

This is difficult to guarantee. So I bought a very expensive transistor tester. My cheap Amazon one doesn't cut it, and it is in now in the recycling (https://www.amazon.ca/dp/B08YNB7K8G). The Amazon one just wasn't accurate.

And.

Transistors are very heat sensitive when measuring to this level of accuracy. Touching them increases the gain by as much as 5% to 10%. From (say) 121 to (say) 127. So they are finnicky to measure.

I built a test rig with a cooling fan. Insert the transistor. Wait 30 seconds and then take a series of readings until the hFE settles down to a fixed amount.

I need 25 matched pairs for the first little build run. It has taken over 3 hours sorting through the bag of devices so far.

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Transistor tester.jpg (376.05 KiB) Viewed 1638 times

[laurie]

Additionally, R13 and R18 must be matched, and R14 and R17 must be matched to keep the bias point exactly the same in both Q3 and Q4.

R9 and R10 also need to be matched. With a nuance... R10 passes a fraction more current than R9 (IE = IC + IB)

IC is 120 times the size of IB. It is close enough if R9 = R10.

I think I've spent nearly 10 hours matching components so far!

[Pepe]

Octave Fuzz?! Count me in!

[fuzzbuzzfuzz]

Intense and precise Laurie, we expect nothing else

Looking forward to the final build.

Have you thought much about the switching arrangmenets etc?