Quote from: ElectricDruid on March 06, 2023, 03:43:12 PM
I've always been able to design out any need to go over 470n or so.

As far as there is no involvement with grounded Emitter CE amps..

For overdrive/distortion circuit where the amplifiers clip you have to be careful about changing the cap values.   When a stage clips the input impedance drops considerably and there's a lot of interaction with the coupling caps.   In the case of this thread I suspect going from 1uF to 470n wouldn't be an issue but in general you should listen to what it sounds like *at all settings* before changing caps.

QuoteAs far as there is no involvement with grounded Emitter CE amps.

There's plenty of places where you can't just "put in" smaller caps.

For low noise designs you want to keep the impedances low as possible and that pushes the size of the coupling caps up.  In some cases you might have to trade some noise to get the cap size down, or put two caps in parallel.

What you will see in a lot of professional equipment is opamp designs with hardly any coupling caps.    Simple transistor stages often force you to use coupling caps, especially when the sound of the amp/preamp/pedal comes into it.

Back in the days before Wima/block cap the non-polar caps were enormous for anything over about 100n, and not that cheap.  Most people used electro's even if it wasn't desirable.   When the NP electro caps became available people stated using those - that's why you see people like Boss using NP electro caps.   The smaller Wima/block caps allows you to replace a lot of those parts - hence the mods you see in those pedals with Wima/block caps.  Nowadays with SMD you want to keep the caps small for size reasons - also, a lot of 1uF and over parts aren't that great anyway.

Got it, look at em (the electro symbol) in the schematic like fish or other swimming up stream towards the input.

The worst ones are column 1 rows 2 and 3, especially with all the artistic variations thrown in.

Thank god most of those don't turn up very often!

I'd say there's less than ten of those I've actually seen used on a schematic.

QuoteThank god most of those don't turn up very often!

I'd say there's less than ten of those I've actually seen used on a schematic.

Indeed, when you have too many symbols *nobody* knows what they mean!

There's symbols for a lot of funky resistors too.  There are funky parts that do exist, so I'm OK with that.

but ...

IEC (yep, IEC) have gone too far with their switch symbols,


IEC safety symbols and symbols on medical equipment have suffered similar fates.  As a manufacturer you just look up the table and use the right one - you are forced to bow to the rules but I doubt many users know what they mean.

This schematic for the super fuzz from 1968 must have puzzled the folks who had to populate the circuit boards! No polarity indicated.  In fact, I should check my superfuzz build - may have some incorrectly oriented 10uF caps. 

QuoteNo polarity indicated

Left as an exercise for the student.

Elephant in the room?

My understanding is that electrolytic caps REQUIRE polarising voltage to establish the thin dielectric. 

What is the actual capacitance of those 1uF and 2.2uF caps that we see at the input of older circuits?

1%, 5%, 20%, 50% of their rated capacitance?
What effect might it have on tone that some of the input signal is increasing and decreasing the capacitance of the capacitor?
🤷
Time for the learned folk to help out, please.
🙏

QuoteMy understanding is that electrolytic caps REQUIRE polarising voltage to establish the thin dielectric.

It's true that a small positive voltage will help capacitor stay in spec.  If you look at FSFX's quoted text, which is very common across manufacturers, you can go as much as -1V for "short periods".   Short periods in some of the older standards (IEC have standards for caps) was something like 125hrs *but* it requires a positive voltage applied for some time to come back into spec.   At the end of 125hrs the cap leakage would no doubt increase.   The main thing that changes is the leakage. 

The fuzzy zone has always been zero bias.   Electrolytic caps left on the shelf are sometimes only guaranteed to be in spec for 500hrs [Edit: these low values are at full temp], others might go out to 1 year (~8000hs).   Whatever the period it's the usually the leakage spec that is out, and after that if you then to place a high voltage across the cap you could get a high current (There is a process called reforming, search archives for my old post).  Some examples show caps blowing up others simply come back to life.

With audio circuits operating the caps at zero bias, no-one is going to come along and put a high voltage across it.  The circuit is sitting there with the cap at zero bias.   The cap leakage will go up according to the spec but in circuit the leakage at 0V bias is still small and most circuits don't care if a small amount of leakage is present.  So that's why we don't see any problems.   If there was -1V applied for long periods we might expect to see some issue and because there is a voltage across the cap any leakage will eventually have some effect on circuit.

In all this we are talking DC voltage applied to the cap.

QuoteWhat is the actual capacitance of those 1uF and 2.2uF caps that we see at the input of older circuits?
1%, 5%, 20%, 50% of their rated capacitance?

The very old caps had tolerances like -10%/+50% or -20%/+50% which means it wasn't uncommon to find higher capacitances.   I'd say around late 70s early 80s's the tolerances weren't that bad.    Also it wasn't uncommon at that time to find -20%/+20% caps.   You will see audio circuit which cared about the capacitance value pretty much always use -20%/+20% caps. [EDIT: the wide tolerance in the older caps was one reason you see Tantalums used, not the only reason though.]

QuoteWhat effect might it have on tone that some of the input signal is increasing and decreasing the capacitance of the capacitor?

While you get some distortion from a capacitor it's not enormous - there's plenty of capacitor distortion articles around   The thing about plating and de-plating is they are slow processes and you won't see any significant effects at instantaneous points on an AC signal.   The DC bias effects are applied for long periods.

Another factor is how much current is passing through the caps.

Quote from: brett on March 06, 2023, 07:56:59 PM
My understanding is that electrolytic caps REQUIRE polarising voltage to establish the thin dielectric. 

You're showing your age there grandad! Zero bias is fine with modern caps

Even amps get into symbols.

QuoteEven amps get into symbols.

40 or so non-standard symbols can't help users.  It's like software these days the icons only make sense to the people that created them - totally meaningless to normal humans.

Quote from: Rob Strand on March 07, 2023, 04:50:04 PM
40 or so non-standard symbols can't help users.  It's like software these days the icons only make sense to the people that created them - totally meaningless to normal humans.

QuotePhend, Phend, Phend - what abot the Sustain cap, no mention? any time you see a cap plus pointing towards a cap minus without some DC source in between, youse needs to ask yourself .....

I see that on the fuzzcentral circuit. Those two connected to the Sustain pot. The GGG circuit is not like that.
Any comments on those two caps like ducks answer ? 

Are you some kind of gossipy stringer or what, Phend..?? 

Quote from: Phend on March 08, 2023, 07:54:29 AM
Any comments on those two caps ..... ?

Chong 10uF 16V

dunno if that counts as comments.

Apparently