My understanding has been that electrolytic caps HAVE to go one direction but I'm seeing in more than one application that isn't true. So, for instance, in the case of the tube bender side of a hoof reaper (schematic included) how does the "backwards" cap c2 affect the sound?
(https://i.postimg.cc/xccTScqK/Screenshot-2023-03-03-13-19-18-71-f541918c7893c52dbd1ee5d319333948.jpg) (https://postimg.cc/xccTScqK)
IMHO, it has nothing to do with "sound"..
C2 positive leg looks to about 1/10 of power supply where negative leg looks to GND (via R1 pull-down resistor)..
^ That is the correct way for the input cap. There was a time when I didn't know any better and I thought the + end should always face the input and the - end the output because I had seen schematics where the coupling caps were all that way and then wondered why the volume control on my guitar crackled when turned. Wrong of course, the - end always faces closest to ground which a passive guitar having no DC voltage surely is.
look at C6 - is it forwards or backwards?
Quote from: duck_arse on March 04, 2023, 08:00:12 AM
look at C6 - is it forwards or backwards?
I thought that was the problem cap (C6)
C6 orientation could be reversed with no issue..
For circuit iddling (no signal), Q2 is in cut-off region (no Base voltage) so cap negative leg is "floating"..
In case of D1 was a resistor (or a Ge diode) and considering Q2 leakage current significant, C6 polarity should be reversed..
For C6 I agree with antonis.
It's not a good idea applying a recipe to determine cap polarity. You really have to know what the actual voltages are at each end of the cap. Inter-stage caps are the most likely place where errors occur.
The only recipe you can eyeball reliably for an amplifiers is:
If you look at a circuit and one end of the cap has a resistor to ground then the voltage at that point is zero.
The other end of the cap is either zero (due to another resistor to ground), or a positive voltage due to some voltage in the circuit (assuming a negative ground circuit).
In your circuit this rule would apply to: C2, C5, C6, C10 and even C4, C7.
The only tricky one is C6 but even then one side has a path to ground.
When you have diodes and switching power supply circuits that rule can be wrong because you can generate negative voltages.
C6 and C2 is 1uF, you could use non-polar cap for peace of mind.
Quote from: anotherjim on March 04, 2023, 05:15:34 AM
There was a time when I didn't know any better and I thought the + end should always face the input and the - end the output
That's where I'm at then. Thanks everyone for helping me level up.
Look at C12 in these two Foxx circuits.
(Tone pot)
Comments ?
(https://i.postimg.cc/mc6208fG/foxxschematic.gif) (https://postimg.cc/mc6208fG)
(https://i.postimg.cc/Kk6cYj8q/ggg-ftm-sc.png) (https://postimg.cc/Kk6cYj8q)
JD's version is correct, but the cap surely doesn't need to be that large, therefore not polarized.
Quote from: Phend on March 05, 2023, 08:30:11 AM
Look ar C12 in these two Foxx circuits.
(Tone pot)
Comments ?
(https://i.postimg.cc/mc6208fG/foxxschematic.gif) (https://postimg.cc/mc6208fG)
(https://i.postimg.cc/Kk6cYj8q/ggg-ftm-sc.png) (https://postimg.cc/Kk6cYj8q)
C12 will have less/more resistance to ground depending on where the tone controls is set. Does going through the c11 cap make a difference? I feel like you would tie negative to r22 so there is a consistent ground path. Is that right?
Voltage difference between C12 legs is about 500mV (Q4 Base bias - 1 Ge diode drop..)
Taking into account that most electros can withstand more than 1V reverse voltage, both orientations should be considered OK..
P.S.
FWIW, "safe" reverse voltage value coincides with that of exceeding the maximum rated working one.. :icon_wink:
FWIW - This information about ratings is from an electrolytic capacitor manufacturer:
(https://i.postimg.cc/dDwLWSHz/capacitor-rating-detail.png) (https://postimg.cc/dDwLWSHz)
Quote from: Phend on March 05, 2023, 08:30:11 AM
Look at C12 in these two Foxx circuits.
(Tone pot)
Comments ?
(https://i.postimg.cc/mc6208fG/foxxschematic.gif) (https://postimg.cc/mc6208fG)
Phend, 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 .....
If in doubt, stick in a temporary ceramic and measure the voltage to ground either side!
FTM scheme is a perfect example of every cap + facing the input although it could be a drawing error. The DC polarity in circuit rule seems simple and obvious but I don't think it was ever spelt out in any of the DIY electronics mags and primer books I read in my youth.
Sometimes, they can't make up their minds although the polarity in those cases probably doesn't matter 'cause no DC difference or very little such as in the Roland 808...
(https://i.postimg.cc/259qQvHt/Roland-808-snippet.png)
... look at amps 16 & 19. Even spec 6.3v caps on a +/-15v powered circuit since the feedback caps should never see much difference in voltage across them.
i'm being too lame to read the whole thread, but basically, in the end with any electro or marked cap, you want the negative side always <or outer wraps of the cap> to go to GROUND potential to help nuke noise as well as protect the cap. the outer wrap helps shield the cap from noise and hash.
positive side needs to go toward the voltage potential... remember, ground is often just the neutral point between positive and negative potentials, so in some cases, like pnp fuzzes, you DO need to reverse the cap polarities with the electros... sorry if oversimplifying, trying to make it dude speak so newbs can understand it <of which i still am one all these years later, so...>
basically what i do if i have a schematic, is look to see which side is gonna have a positive voltage flowing to it, and that gets the +
usually its either power supply filtering or coupling cap in a lot of circuits, so doing it this way is fairly safe in most circumstances.
or use your meter if you have no schematic, and see what the voltages are where the cap needs to go, or, with stuff off, read the resistance to ground from one or the other nodes if unknown... one side will show significantly less resistance to ground than the other most of the time, and that would get the negative lead.
so far, this has worked for me when i need to sub something in cuz i'm out of something or need a specific value or voltage or whatever.
also remember, you can always fake a np cap by tieing the cathodes of two electros together, and just using the anodes.
in 9v circuits you can usually get away with just the caps themselves... say ya wanted 1u, np... you don't have, so you can use two 2.2's negative to negative and get an approximate value of 1.1uf, which is within a 10% tolerance and should work fine.
higher voltages, you may wanna parallel each cap with a resistor too, maybe 22k or so probably would do, but i'd have to look it up to be sure or mess with it. its just to even out the voltages so one cap doesn't go over voltage and smoke itself.
sorry for the book.
final thought... don't always trust the schematics, cuz often there may be a mistake in orientation on the schem, the layout, even the pcb.
check it out first before building, and it becomes pretty clear USUALLY which orientation is gonna be right, but remember, it will vary depending on function... power supply filtering may be different from coupling caps.
peace
QuoteI don't think it was ever spelt out in any of the DIY electronics mags and primer books I read in my youth.
I like the cap symbol with the + marking more than any of the old symbols. Some of the older cap symbols were ambiguous unless that was the only symbol you knew - I'm pretty sure a few articles and commercial schematics flipped the meaning on occasion (I would look at the power supply cap direction first).
QuoteSometimes, they can't make up their minds although the polarity in those cases probably doesn't matter 'cause no DC difference or very little such as in the Roland 808...
If you want to be pedantic some of the bipolar opamps have DC input bias current and that causes a real DC voltage in the opamp circuit so you can split hairs that way. For things like the NE5534 the input bias is quite high; some audio circuits are end up with 1V DC offset and you end up getting close to the recommended limit FSFX posted (voltages over about 1V de-plate the electrolytic capacitor).
For input and output caps with 0V DC you could argue the device is more likely to be connected to a positive voltage so the cap + should go toward the external connections. Even I don't always follow that rule, probably brainwashed from the old transistor circuits.
+1 what FiveSeven said:
Who needs a coupling cap that large anyway?!? Thus far, I've always been able to design out any need to go over 470n or so. Even 18K impedance gets the rolloff down to 20Hz, so it's generally not hard. Just "Avoid electrolytics in the signal path" is a simple and workable strategy!
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.. :icon_wink:
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.
(https://kicad-info.s3.dualstack.us-west-2.amazonaws.com/original/3X/e/b/ebc1b4cca3e6870504ae28e5c667571f6db00367.png)
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,
(https://image.slidesharecdn.com/petersheerin-symbolicconfusion-100610204332-phpapp02/95/symbolic-confusion-8-728.jpg?cb=1276203225)
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. :icon_rolleyes:
(https://i.postimg.cc/QFstqydb/5-AC018-CD-9-A69-4-EBB-BA5-A-B9-E3025193-CF.gif) (https://postimg.cc/QFstqydb)
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.
(https://i.postimg.cc/bSwLGL1z/106727865-10163773749140246-830833351453912744-n.jpg) (https://postimg.cc/bSwLGL1z)
(https://i.postimg.cc/HVK3xwng/107094697-10163773749135246-4019433839426903965-n.jpg) (https://postimg.cc/HVK3xwng)
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.
(https://i.postimg.cc/XGgKMgrp/cute-black-and-white-cat.webp) (https://postimg.cc/XGgKMgrp)
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..?? :icon_biggrin:
Quote from: Phend on March 08, 2023, 07:54:29 AM
Any comments on those two caps ..... ?
Chong 10uF 16Vdunno if that counts as comments.
Apparently