Fuzzy Fox - capacitors

[taxfree]

A long search on the forums did not allow me to understand why the 10u electrolytic capacitors that connect to the bases of Q3 and Q4 have different polarities in schemes and layouts (Pedalpcb, Fuzzcentral, GuitarFXLayouts, Sabrotone, GGG, etc.). Madbean uses 1uf film and it confuses me even more. Does polarity and value have an influence or not?

 

[jwin615]

Here's a good Google result

What determines the orientation of a coupling/blocking capacitor in an amplifier circuit?

"In analog circuits, a coupling capacitor is used to connect two circuits such that only the AC signal from the first circuit can pass through to the next while DC is blocked. This technique helps to

electronics.stackexchange.com

A few things going on here.
1) a hpf is formed but all result in a filter point of 1-10hz, so no audible effect.
2) DC block, there's no reason to use a electrolytic for DC block unless you need a higher value(1uf+) that you can't get in a film cap because it forms a high pass filter, as previously stated.
3) as stated in the link above, the + side of the electrolytic should be oriented toward the side of greater voltage potential. Not much worry here but I would avoid a 10v rated cap. You also need low esr caps in this case
4) I see no reason for electrolytics, a 1uf film is fine. Otherwise, a non-polarised electrolytic could be used, again low esr. I prefer not using electrolytics in areas where the entire audi path passes through them.
Tantalum or silver mica are also options here.

I just woke up, so if there are areas that aren't 100% correct or misleading, apologies.
Hope this helps

 

[spi]

I went through the same questioning.

Many people have built it successfully both ways, so it probably doesn't matter. The only thing I found near an explanation was that the voltages weren't high enough to matter in this circuit, and that Electrolytic caps could tolerate a small amount of reverse voltage for a short time, but it didn't sound definitive to me.

In the end I just chose to use non-polarized caps for the two that are reversed.

 

[Feral Feline]

I read somewhere the + side of the electrolytic should always point at the nearest transistor.
That may or may not be a good rule of thumb, but there are always exceptions to any rule.


People seem to be hung up on a mythical limit to 1µ for box-film, and anything bigger will have to be electrolytic. NOT TRUE.


Because I play bass, I like to use 2µ2 Box Film caps often where only 1µ might be required for guitar.
There are box film from Wima that go up to 4µ7 and available from Tayda.

Kinda handy for builds like Rats, where the cap after the op-amp is a 4µ7 and that 1µ at the end I've replaced with a 2µ2 while experimenting. Can't remember the final value I put in my build.

Also good for some Muff versions that have 10µ couplers, you can run two of those 4µ7 in parallel to get 9µ4, close enough to 10µ.
Great for the "white can" Ram.

Some would argue that you can't hear a difference between electrolytic and box-film... Find out for yourself, make your own decision on that
— just make sure the difference isn't the difference in value of the caps. Compare a true measured matching value to each, these things have bigger tolerance drift than metal-resistors after all and depending on brand, batch and whatever can be out by up to 20% — even the big Wima is 10%. So that Wima could be as big as 5µ17 while the electrolytic being compared might be on the low side of 10% at 4µ23.
Comparing 5µ2 vs 4µ2, depending on their function in the circuit, you'll likely hear a big difference!

Let's say they sound the same, my argument would be still for that big box film, or tantalum, as from what Ive read electrolytics don't last as long. Just make sure the electrolytics and tantalums are oriented correctly +/- or the magic (&smelly) smoke will be released.

 

[Robert]

I followed the schematic I had at the time and it works as it should, but if I had it to do over again (and I likely will at some point) I would reverse C6 and C11.

 

[BuddytheReow]

I followed the schematic I had at the time and it works as it should, but if I had it to do over again (and I likely will at some point) I would reverse C6 and C11.

To the OP's question. Why reverse them?

 

[Feral Feline]

To the OP's question. Why reverse them?

That rule of thumb comes in to play.


The cool thing is, we can reverse C6 and C11 without a redo of the board and schematic.

 

[Robert]

The right side of C6 will always be more positive than the left.

C5 blocks any DC from reaching the sustain pot, the other side of C6 is directly connected to the base of Q3 which has a positive DC bias.

Similar situation with C11, C8 blocks any DC from entering the tone control circuit. The other side is connected to the base of Q4 which also has a positive DC bias.

 

[taxfree]

I read somewhere the + side of the electrolytic should always point at the nearest transistor.
That may or may not be a good rule of thumb, but there are always exceptions to any rule.


People seem to be hung up on a mythical limit to 1µ for box-film, and anything bigger will have to be electrolytic. NOT TRUE.


Because I play bass, I like to use 2µ2 Box Film caps often where only 1µ might be required for guitar.
There are box film from Wima that go up to 4µ7 and available from Tayda.

Kinda handy for builds like Rats, where the cap after the op-amp is a 4µ7 and that 1µ at the end I've replaced with a 2µ2 while experimenting. Can't remember the final value I put in my build.

Also good for some Muff versions that have 10µ couplers, you can run two of those 4µ7 in parallel to get 9µ4, close enough to 10µ.
Great for the "white can" Ram.

Some would argue that you can't hear a difference between electrolytic and box-film... Find out for yourself, make your own decision on that
— just make sure the difference isn't the difference in value of the caps. Compare a true measured matching value to each, these things have bigger tolerance drift than metal-resistors after all and depending on brand, batch and whatever can be out by up to 20% — even the big Wima is 10%. So that Wima could be as big as 5µ17 while the electrolytic being compared might be on the low side of 10% at 4µ23.
Comparing 5µ2 vs 4µ2, depending on their function in the circuit, you'll likely hear a big difference!

Let's say they sound the same, my argument would be still for that big box film, or tantalum, as from what Ive read electrolytics don't last as long. Just make sure the electrolytics and tantalums are oriented correctly +/- or the magic (&smelly) smoke will be released.




View attachment 61887

View attachment 61888

That's a great point about tolerances!