Diode wattage

I’m building a Face Melter, but I’m sure this pertains to any build.

Docs call for 1N5239A diodes. 1/2w, 9.1v. I have 1 watt, 9.1v, diodes. (1n4739 & ECG 139A)

I know they will work, but will it sound different? I’m still learning schematics, but it looks like they are clipping diodes?
 
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Certainly not like any clipping configuration I've ever seen...

But I could be wrong. Seems like a feedback loop that regulates the gate voltage? Little beyond my knowledge level...

But...wattage shouldn't be an issue as long as the Vf is similar between the two...though I don't know if we're selecting for that here...

I'll say you're probably fine with the 1 watters, but I'll defer to the more knowledgeable members...
 
That's a protection diode for the MOSFET. There shouldn't be an issue with the power rating. The important part is the voltage.
I mean, that was my first thought too, but the bs170 has an absolute maximum rating of 60vdc.

Plus...9.1v zener voltage, typically it'll see something less than 4.5v reverse with VREF being half of input at 9v.

I'm used to seeing zeners used as protection diodes when their anode is tied directly to ground. I'm super curious as to exactly what this thing is doing in this circuit.
 
Right. MOSFETs are also very sensitive to ESD. Transients, static discharge, excessive ripple (maybe not that one in the case here), can all destroy the device. It's easier to put in the diode and not have to worry about it.
 
Thanks everyone. I’ve been building pedals for about a year and a half, but am just starting to learn exactly what goes on in the circuit. Plus being kind of noob in reading schematics. I learn so much everyday. I’m a welder by trade, but after 30 years, I think I should of became an electrician.
 
Thanks everyone. I’ve been building pedals for about a year and a half, but am just starting to learn exactly what goes on in the circuit. Plus being kind of noob in reading schematics. I learn so much everyday. I’m a welder by trade, but after 30 years, I think I should of became an electrician.
Let me tell you a story...

I was on a jobsite with an electrician one day. We were both up in the ceiling, I was working on fixing a limit switch on a fire smoke damper, he was fucking around in a junction box.

We get to chatting. Turns out he's fully bought into some conspiracy nonsense, so I talk with him because I'm facinated by this particular flaw in human reasoning.

He starts explaining to me how there's two parts to everything in the galaxy. Black and white. Good and evil. Protons and Neutrons. Life and dea....

"Hold up" I said, incredulous, "Back up, that bit about protons and neutrons"

"Yeah?" he responded, dull glaze in his eyes

"Aren't you forgetting something there?"

A more flummoxed expression, I have never seen. He eventually conjured the will to utter a single syllable: "Huh?"

"Electrons," I said, exasperated. "Protons, Neutrons, and electrons"

.......
............
.....................

"What's an electron?" the *electrician* eventually replied.

True story. Hell, at least as a welder you're working with DC on a regular basis. I'm an HVAC service tech, so my background is all alternating current, inductive loads, and relay logic. We're all learning here.

So...alright, static discharge. I can wrap my head around that. Zeners are cheap, warranties are expensive.

...that'd have to be one hell of a shock. I can appreciate a mindset that leans heavily on the "overbuild it" side of things though.
 
Getting back to the original question...

The diode on Q1 is for ESD protection as Benny_Profane says. We should protect Q1 because its gate connects to the input jack. Any wattage zener will provide the necessary protection. 7.5V - 15V are all acceptable voltage ratings. The 60V rating on a BD170 is for Vds. We're not protecting the drain, we're protecting the gate. Vgs,max is ±20V, so we need something below 20V and something larger than the +3V max gate threshold. Higher wattage zeners have higher capacitance. Will you hear the diff between 1/4W and 1W? Probably not. You will hear the diff between a 1W a 50W zener. Why is there a protection diode on Q2? No good reason. My guess is the designer did not understand ESD protection and just copied stuff from someone else's schematic.
 
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