Stuff you wanted to know but were afraid to ask

[JTEX]

How in the hell do you calculate the gain on this output section on the Informant/DRV? Normally on a noninverting gain stage like this you'd take R14 and divide it by R13 then add one. Not only is R13 way bigger than R14, it's going to ground with no capacitor instead of vref.
View attachment 83430

This is basically a unity gain buffer. R13, C10 and R14 could all be eliminated and replaced with a simple short between pins 6 and 7 and the circuit would work almost exactly the same. I have no idea why they're there. Maybe as placeholders in case you want to mod it?

 

[cdwillis]

That's what I thought at first, but then I thought maybe I'm just not clever enough to understand it. I was making a Rat style pcb recently and used a TL071 for the buffer instead of the jfet then I added the option of making it a gain stage for more output volume.

I built an Informant then I ended up trading it. I can't remember how the volume compared to my Rat.

 

[lowpitch]

I got a bunch of 10uF MLCCs. Can I use these instead of electrolytics in power decoupling situations without problems?

 

[JTEX]

I got a bunch of 10uF MLCCs. Can I use these instead of electrolytics in power decoupling situations without problems?

Normally yes. In fact that's probably their best use case. Just be aware that their capacitance decreases significantly as the DC voltage across them approaches their rated voltage.

 

[lowpitch]

Normally yes. In fact that's probably their best use case. Just be aware that their capacitance decreases significantly as the DC voltage across them approaches their rated voltage.

These are rated at 25VDC. So fine for 9V operation, iffy for 18V?

 

[JTEX]

These are rated at 25VDC. So fine for 9V operation, iffy for 18V?

They might be down to around 50% of nominal capacitance at that voltage. That could very well still be fine in many decoupling situations, where cap values are not that critical.

You might want to look up Voltage Coefficient of Capacitance.

 

[lowpitch]

They might be down to around 50% of nominal capacitance at that voltage. That could very well still be fine in many decoupling situations, where cap values are not that critical.

You might want to look up Voltage Coefficient of Capacitance.

Thank you! I'll look that up.

 

[CheapSuitG]

Here is mine thing I am afraid to ask.

What does the stand alone Klon buffer do?

 

[lowpitch]

Here is mine thing I am afraid to ask.

What does the stand alone Klon buffer do?

Prevents the circuit after it from loading down your guitar pickups or whatever circuit preceeds it which can negatively impact tone, just like any other buffer really but it's the Klon buffer. So there's that More info on buffers: https://forum.pedalpcb.com/threads/whats-a-buffer-how-do-they-work-and-why-would-we-want-one.15244/

 

[jcpst]

Here's the portion of the klon circuit

 

[CheapSuitG]

Great answers, thank you.

Another question - Washer order for footswitch, jacks etc. I have an idea but what is standard practice?

 

[lowpitch]

Great answers, thank you.

Another question - Washer order for footswitch, jacks etc. I have an idea but what is standard practice?

Height adjustment nut if applicable, lock washer (toothed thingie), enclosure panel, flat washer, nut

 

[giovanni]

Height adjustment nut if applicable, lock washer (toothed thingie), enclosure panel, flat washer, nut

I learned this the hard way. Being mocked indirectly by folks on this forum.

 

[andrewsrea]

My question is: Why is the musician's equation = (current number + 1)?

For example: How many pedals do you really need? A: current number + 1.

Happy Friday, everyone!

 

[tegendemuur]

The first lie they teach you at school is that there are no stupid questions.

That being said, I find impedance - "resistance to current" - to be such a vague concept. Anyone here who can sort of paint a picture for my mind to grab onto? Perhaps via the liquid representations that are so very common to explain electronics? My mind just doesn't do abstractness well. Math has been a hell all my life; give me the concreteness of physics any time of the day!

 

[mybud]

The first lie they teach you at school is that there are no stupid questions.

That being said, I find impedance - "resistance to current" - to be such a vague concept. Anyone here who can sort of paint a picture for my mind to grab onto? Perhaps via the liquid representations that are so very common to explain electronics? My mind just doesn't do abstractness well. Math has been a hell all my life; give me the concreteness physics any time of the day!

https://www.techtarget.com/whatis/definition/impedance may be helpful.

 

[jcpst]

Oh I got one- I know this information is scattered around and I’ve seen some of it before.

Regarding Capacitors: In what scenarios can you substitute different types? I get that you have to consider polarity if you go from non-polarized to polarized. But what’s good for audio path, not good for audio path, etc. I’ve got ceramic, film, electrolytic, tantalum, mlcc…

 

[JTEX]

[...]But what’s good for audio path, not good for audio path, etc. I’ve got ceramic, film, electrolytic, tantalum, mlcc…

Best for audio path:

up to about 47nF: C0G ceramic, or film (film caps tend to be larger, pricier and easier to damage while soldering).
from 47nF to maybe 4.7uF: film
above that: electrolytic

I wouldn't use tantalum for audio (or anything, really). When they go bad, they tend to burn a hole in your PCB like a mini-thermite.

MLCCs using X5R or X7R dielectric can be ok for non-critical audio path use (such as guitar effects), if you know what you're doing. Their capacitance can vary a lot with the DC bias across, and also with temperature. Best used for DC filtering, switching power supplies and the like. If you do have to use them with audio (I do), make sure the voltage across them (DC or AC) is much lower than their rated voltage, to avoid distortion and loss of capacitance. They can also be microphonic, so be careful in high gain circuits or you might get squealing/oscillations.

MLCCs using Z5U and Y5V dielectrics: just say no! They're terrible.

 

[Aentons]

The first lie they teach you at school is that there are no stupid questions.

That being said, I find impedance - "resistance to current" - to be such a vague concept. Anyone here who can sort of paint a picture for my mind to grab onto? Perhaps via the liquid representations that are so very common to explain electronics? My mind just doesn't do abstractness well. Math has been a hell all my life; give me the concreteness physics any time of the day!

Resistance is like a head on collision. Impedance is how fast you have to zig and zag to get thru

 

[tegendemuur]

Resistance is like a head on collision. Impedance is how fast you have to zig and zag to get thru

Ah, I like that one!