Dumble Overdrive Special #124 build video series

[pompeiisneaks]

So I'd say that it's not in the imagination, I think some people (not me) have very sensitive ears and it is a fact that different components of those devices have different properties of the materials involved (ceramic vs mica). So there is some 'audible' difference that some can hear that others' can't. That doesn't mean that the math you're showing isn't also 100% correct. This was why I wasn't massively worried initially about the 300 vs 270pF difference, but realize that both have potentially different 'sweep zones'. If they happened to 'drift' towards one another, then you get identical tonality from the two stages, but if they happened to drift away, they may sound different enough to be audible by those with more sensitive ears.

Does it change the overall character of the amp? Not sure. I don't think so but I know I have hearing damage from being in the Army in Iraq, and being in loud rock bands . I do think that paying for a few extra bucks on some caps that seem really easy to swap in/out, makes sense to me.

OTOH, often I get busy with life and the next build to forget that kind of thing

~Phil

[Charlie Wilson]

OK Phil you were a bit more diplomatic about your response than I am going to be. All of what I stated has been said many times before on this forum. I will say this, it is Dumble 101 that you measure all components before you put them in the amp. I know to the pico farad the value of my ceramic discs. In my opinion, the difference between a functioning amplifier and one that sounds great is all the stuff the graph guys say are in your imagination.
CW

[pompeiisneaks]

OK Phil you were a bit more diplomatic about your response than I am going to be. All of what I stated has been said many times before on this forum. I will say this, it is Dumble 101 that you measure all components before you put them in the amp. I know to the pico farad the value of my ceramic discs. In my opinion, the difference between a functioning amplifier and one that sounds great is all the stuff the graph guys say are in your imagination.
CW

This begs a question for me, none of the DMM's I have, have a useful measurement range for pF. I looked and even the higher end Fluke 87 V goes lower than 0.01 nF so it can't accurately measure pF.

How do you measure pF in caps accurately? I hear it's nightmarishly hard, due to things like capacitance in leads, etc. Is it a requirement to have a dedicated capacitance meter, and if so, what ones are accurate enough to trust?

~Phil

[Charlie Wilson]

Phil, yes I get that the multimeters are a little challenged when it comes to measuring capacitance. I use a separate capacitance meter. Not a real fancy one but it serves my purpose. It is not quite as important that I have a laboratory accurate reading of a capacitor, just a fairly accurate relative measurement. To me, measuring means nothing without listening and what I hear is way more important to me than what I measure. Example, I like in the Classic tone stack to have the treble cap right at 330pf. A little lower and the clean side can sound a little harsh(with a Fender) and the OD doesn't have quite the upper mid push. Go higher and I start to loose the chime on the upper end. My ears, and I repeat, my ears like 330pf as measured by my cheap capacitace meter purchased from CE Dist.
CW

[erwin_ve]

I think Modman confuses bypass caps with snubber caps. His graphs are high pass filter, the snubber is low pass filter.
And I agree with Charlie, 20-30pF is very noticable with snubbers.
Choosing between ceramic and silver mica is not that hard. The ceramic has several standard series which have specs that can be delivered by different manufactors.
Look for the X5F series. The are very stable with the heat (up to 185F with 15% tolerance) from the tubes.

[pompeiisneaks]

Thanks guys!

~Phil

[modman]

I think Modman confuses bypass caps with snubber caps. His graphs are high pass filter, the snubber is low pass filter.

"A snubber is a device used to suppress ("snub") a phenomenon such as voltage transients in electrical systems, pressure transients in fluid systems or excess force or rapid movement in mechanical systems."
it's to prevent pops when switching... nothing to do with the audio path even. I showed a filter to demonstrate even there you will not be able to hear the difference.
https://www.wikiwand.com/en/Snubber

And I agree with Charlie, 20-30pF is very noticable with snubbers.

In what build and could you link to a schematic?

Choosing between ceramic and silver mica is not that hard. The ceramic has several standard series which have specs that can be delivered by different manufactors.
Look for the X5F series. The are very stable with the heat (up to 185F with 15% tolerance) from the tubes.

15% on 250pF = +/- 37.5pF

[modman]

Screenshot from 2018-03-14 23-33-10.png

Found it: I think it's a cap and then a resistor to ground, hence a high pass filter:

Screenshot from 2018-03-14 23-35-49.png

Screenshot from 2018-03-14 23-39-09.png

What am i missing?

[martin manning]

It's effectively just a cap to ground.

What's up with replacing almost all of your previous posts with latin gibberish?

[pompeiisneaks]

I hadn't seen that, got a link?

Here's the latest video and I'm livestreaming tonight at 7pm PST, 10pm EST, check the channel for the details:




~Phil

[Finom1]

Phil,
Thank you for all your hard work and sharing your wisdom with us!!!

[pompeiisneaks]

No problemo Fino

~Phil

[erwin_ve]

Screenshot from 2018-03-14 23-33-10.png

Found it: I think it's a cap and then a resistor to ground, hence a high pass filter:
Screenshot from 2018-03-14 23-35-49.png
Screenshot from 2018-03-14 23-39-09.png

What am i missing?

NO it's a low pass filter.
We are trying to give user experiences to Pompeii. He's got the balls to show every move he makes on YouTube, which I think is a modern kind of heroism. So let's not pollute this topic with misunderstandings.

[pompeiisneaks]

Screenshot from 2018-03-14 23-33-10.png

Found it: I think it's a cap and then a resistor to ground, hence a high pass filter:
Screenshot from 2018-03-14 23-35-49.png
Screenshot from 2018-03-14 23-39-09.png

What am i missing?

NO it's a low pass filter.
We are trying to give user experiences to Pompeii. He's got the balls to show every move he makes on YouTube, which I think is a modern kind of heroism. So let's not pollute this topic with misunderstandings.

Thanks, I basically figure that everyone can learn from my mistakes and successes

I appreciate everyone's help here. I also was very happy that Charlie Wilson made it to the last livestream and was a great contributor to the discussion. I would be happy if any of you other geniuses would come along and forward the discussion and catch my SNAFU's

~Phil

[modman]

Screenshot from 2018-03-14 23-33-10.png

Found it: I think it's a cap and then a resistor to ground, hence a high pass filter:
Screenshot from 2018-03-14 23-35-49.png
Screenshot from 2018-03-14 23-39-09.png

What am i missing?

NO it's a low pass filter.
We are trying to give user experiences to Pompeii. He's got the balls to show every move he makes on YouTube, which I think is a modern kind of heroism. So let's not pollute this topic with misunderstandings.

I am not an electronics engineer. I just learned this stuff off the interwebz. I am not ashamed to say that, schools are dead, I learned to repair my toaster, pave my patio, and a lot more too. So I'm also begging to be corrected.

If the signal goes through a capacitor and then through a resistor, it will create a high pass filter. It will cut out part of the signal on the bass side of the spectrum. Check the wiki link for the formula to calculate which frequencies will be affected. Instead of messing with that formula you can just plug your values in this calculator:
http://www.trance-cat.com/electrical-ci ... ulator.php

The graphs accompanying it shows that all with a 250pF and 1k5 it cuts anything below 424Hz. With 270pF, anything below 392Hz.
If you know your guitar low E string is 82Hz, it's clear we are affecting the guitar signal. As this part of the circuit is the distortion, this matters even more to the 'sound' of the distortion.
Putting a 500pF in there will make a substantial difference. Then we are doubling the value... But really saying 20pF more or less will make a difference... in distortion circuit maybe yes, but as I said, you need to have high precision capacitors and be able to measure them accurately. It's hard measuring, I think Phil wondered about this in one of his videos, because the capacitance of the leads need to be taken into account to measure values that low really accurately.
This is also a non-inverting feedback loop... it feeds signal back through the cathode. But I might be wrong...

I appreciate everyone's help here. I also was very happy that Charlie Wilson made it to the last livestream and was a great contributor to the discussion. I would be happy if any of you other geniuses would come along and forward the discussion and catch my SNAFU's

Phil, don't mean to hijack the thread, discussion is still on topic of the relevance of that cap beyond mere hearsay. I do think your a hero for what you are doing with your build, because despite a lot of mp3 demoes, there is in my perhaps too critical mind, too much doubt about the documentation on the Dumbles to start a build myself. I think anybody on this forum would be dying to see anybody just do an iPhone video display of the amp they've built. Inside and out. Run over the problems they've encountered and how they solved it. The biggest plug for this forum is still Fuchs mentioning it in his interview... that's the only reason I came here. That made me believe there is info here, but it really seems to be scattered.

what's a snufa?