Can someone help me understand the Capacitor values on these pcbs?

[drgonzo1969]

So I recently went down the rabbit hole of having pcbs fabricated by jlcpcb. I had some random stuff fabricated I found on pcbway and osh park shared projects. However, one of the pcb makers uses different capacitor numbers than I am used too. Can someone help me understand these values? I will post a photo of the pcbs and a link to the schematic. thanks in advance!

Mid-Fi - Demo Tape fuzz - Share Project - PCBWay

Mid-Fi - Demo Tape fuzz

www.pcbway.com

 

[Robert]

https://www.jameco.com/Jameco/workshop/CircuitNotes/cn-capacitors.html

 

[drgonzo1969]

https://www.jameco.com/Jameco/workshop/CircuitNotes/cn-capacitors.html

Sweet! Thanks for the quick response.

 

[KR Sound]

The 472 is 4n7 and 473 is 47n

That’s the way you’ll find them written in the caps themselves usually- the third number denotes the number of zeroes that follow

472 = 4,700pF = 4.7nF
473 = 47,000pF = 47nF

 

[drgonzo1969]

Ya that's what I thought was going on but it wasn't clicking in my brain and I wanted to check with you guys before I soldered it all together. Thanks for sorting this out for me.

 

[JTEX]

View attachment 70913

Sorry about the derailing. but I am curious how this circuit can make any sound, seeing how the input goes straight into Vb and then through a 47uF cap to ground...

 

[Robert]

Sorry about the derailing. but I am curious how this circuit can make any sound, seeing how the input goes straight into Vb and then through a 47uF cap to ground...

That 47uF doesn't belong on VB, it should just be the 100K voltage divider biasing the opamp with no filter cap to ground.

 

[JTEX]

I'd much rather keep the cap and just add an input inpedance-setting resistor between pin 3 and Vb instead. And why even have both Vb and Vc? One is enough for both opamps. Weird circuit... I could keep going.

 

[drgonzo1969]

Is the pcb faulty? Should I bother assembling?

 

[Robert]

You just need to determine which one of those 47uF electrolytic caps connect to pin 3 of the first opamp and omit it.

 

[drgonzo1969]

Haha ok. I guess that’s what I get for straying away from PPCB products.

 

[JTEX]

As a treasure hunt, try to find a copper pour (copper island) on this PCB that actually connects to anything.

 

[drgonzo1969]

As a treasure hunt, try to find a copper pour (copper island) on this PCB that actually connects to anything.

Here is both sides of pcb.

 

[KR Sound]

Ya, all the grounds are just connected together, which is fine. Keeping the rest of the copper doesn’t do anything really other than it going down the drain in the production process and making more work for the designer.

 

[JTEX]

They do actually recover the copper from solution and reuse it for copper deposition on other boards. Unconnected (isolated) copper islands on a PCB are not normally ok. They can make nice little antennas for picking up interference, and would not pass DRC in a PCB design tool.

 

[KR Sound]

They do actually recover the copper from solution and reuse it for copper deposition on other boards

That’s cool. I just assumed it all went to waste.

 

[JTEX]

Here is both sides of pcb.

All of the islands that I oh-so-prettily colorized should be connected together and to ground. Left floating, they make the circuit perform worse than if they weren't there at all. Parasitic coupling between sections, noise pickup etc. On the other hand, if grounded as they should be, they might make the circuit immune enough to outside noise that you can get away with using it in an unshielded plastic enclosure.

 

[szukalski]

If they had thinner traces then there would probably be a continuous plane!

 

[KR Sound]

If they used the ground plane, there’d be fewer traces too.

 

[JTEX]

So many little puzzling things in this design... Why, for instance, did they use two TL071s and not a single 072 instead?