Capacitor FAQ

Frequently asked questions on capacitor types, ratings, brands, use and abuse.

Capacitor FAQ

Postby Tube2stomp » 19 Dec 2007, 12:33

Electrolytic output filter cap, what is it good for??

Greetings ppl :)

As a nick probably tells something about a poster, mine means that I know my way around tubes, but all this SSS (solid state stuff) is pretty foreign to me.
After I learned some basic SSS in order to do simple switching in an amp, I figured its time to start playing with pedals.

The two projects I want to start with, in order to get my legs (feet?) wet, will be cloning my Lovepedals E and COT50.
I read already about the E being a variation of the SoS (bufferless TS) and the COT being an LPB with clipping.
Not that it means that now I technicaly understand what every part inside does, but just to say "hey, I've done some readings" :D

So, with that said... how do you guys live with having huge electrolytics as audio path filter caps in some pedals???
With all the know how some of you have, can you suggest a way to eliminate that 10uF from the E?
I'm still waiting for my parts, but the idea of this electrocrap in the end really bugs me [smilie=wink.gif]


[smilie=a_help.gif]
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Postby John Lyons » 19 Dec 2007, 17:01

The large cap there at the end works in conjunction with the 500K level pot to reduce some of the high end, HPF. With a smaller cap or smaller pot the pedal is pretty bright/thin.
You could change the cap to a 1uf film/poly and add a 10K resistor after the 1uf cap and then a .002 cap to ground which will shave off some of the fizz. if you need more then add another 10k in series and another .002 to ground.
Or you can make the caps to ground .003...
The large electro slur the sound a bit adding a .01 in parallel would clear it up a bit and keep the layout relatively unchanged.
Sometimes the sluggish large caps can be a good thing though...

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Postby Tube2stomp » 19 Dec 2007, 19:06

I think you got some parts mixed up... or maybe in solid state land things work in a diferent way :?
HPF shaves the low end and lets all the highs thru from a certin freq knee.
How can it attanuate the high end?
Sure, if you use a smaller cap with the same resistance to ground, the knee goes up and you shunt higher freq to ground... giving the impression of too much high end.

The E has a vol pot of 500k with 10uF cap, that's wierd...
In another schem I see a 100k/22uF combo :shock:
The largest blocking/filtering cap I know of in tube amps is 100nF, and that's for bass amps :lol:

I'm confused.
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Postby analogguru » 19 Dec 2007, 19:27

You make a big mistake in believing that (every) "bootweaker" could have a technical knowledge.

The reality is different: "Bootweaking" is mainly fiddling around with existing circuits without thinking in a technical way.

Also a lot of so-called mojo is ceonnected with it (e.g. use of carbon-comp resistors etc.)

So if you try to understand "bootweaking" from a technical view you will get nuts.... There never ha been made a technical decision for the 10µF or 22µF electrolytic.... Look at the Zvex SHO: it is the same there..... and everybody is copying it without doubting the sense...

10µF would be necessary with a following (input) impedance of 2 kOhm only and 22µF if the following impedance is 1 kOhm.

So take a 1µF polyester-film-capacitor instead of it and be happy....

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Postby Tube2stomp » 19 Dec 2007, 21:00

I asked a technical question based on technical knowledge conflict I had here. how that turned into a believing and mojo issue? :roll:

I read all the E thread, some of you even built the pedal based on that info... with THAT cap size... yet over ten pages, talking even about how to improove parts of it, no one said a word about that electrocrap cap on the out put.

Well, looking around in more schematics here, I found one that you made (Fet Booster?), and guess what, it also has a 10uF on the output :wink:
Why?
Also one by Soulsonic, same thing, 10uF.
Yea and the ZVEX.
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Postby analogguru » 20 Dec 2007, 00:10

Well, looking around in more schematics here, I found one that you made (Fet Booster?), and guess what, it also has a 10uF on the output


Thats for economical reasons.... there is already a 10µF in use at the source, and there is this high value necessary.

As you may find, I don´t believe in mojo.... ou you know how many electrolytics wil have been passed before the signal will reach your ear ?

In every mixing-console are electrolytics used. In studio-applications the norm is that the output should be able to drive 600 Ohm loads, and that the input impedance of one unit is at least 10k. Now you have to choose the size of capacitors in a way that you don´t get any loss in frequency response > 1,5db @ 20 Hz. This determines the values. If you have enough money you can use 10µF polyester-caps for coupling.

Concerning my FET-booster, this one was designed I think in 1984, at a time where I designed a lot of studio-equipment, and for this reason i choose the coupling cap automatically to fulfill the requirements described above, Even when not needed. Not all of the effect pedals and/or amps have Zin >= 500k so I choose for the worst case.

If you don´t like it, use a film cap with the value of your choice depending on the input impedance of the following stage.

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Postby Tube2stomp » 20 Dec 2007, 16:58

Thanks for the explanation mate.
Echonomics sucks but I can't argue with that :lol:

Anyway,I've done enough tube gear tweakings and retorings to know that there are things that are bad audio wise, and sticking electrolytics/ceramics in the audio path "just because", in my view is bad Audio Engineering.

On the subject of filter caps, why most (or a majority) of pedal schematics I looked at, have a filter cap on the input?
Is it a "just in case the source isn't blocked" thing, or is it something that works different in solid state then in tubes?

Thanks:)
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Postby analogguru » 20 Dec 2007, 17:43

Tube2stomp wrote:Thanks for the explanation mate.
Echonomics sucks but I can't argue with that :lol:

Anyway,I've done enough tube gear tweakings and retorings to know that there are things that are bad audio wise, and sticking electrolytics/ceramics in the audio path "just because", in my view is bad Audio Engineering.

That´s a weak argument. There is nothing wrong with electrolytics if you use them properly, what means no reverse polarity...

If you connect two 100µF electrolytics in series - minus tied to minus and from there a resistor 47k to ground you have a bipolar electrolytic at the two plus connections possible for use in a split supply. Now connect a 1µF polyester-film-capacitor in parallel and nobody will listen "the bad sound of an electrolytic".... You can do that with 2x 10µF and a 100n film cap too...

On the subject of filter caps, why most (or a majority) of pedal schematics I looked at, have a filter cap on the input?


I assume that you mean the coupling caps on the input...

Is it a "just in case the source isn't blocked" thing, or is it something that works different in solid state then in tubes?


Yes, mostly.....
If it is a transistor/Fet-stage non blocking would lead to a shift of the DC-bias causing a misbias resulting in a non-working stage.

Did you ever connect the anode of a tube-based amplifiying stage to the grid of the next amplyfing stage without blocking ?

And someties the input-cap is also used as a high-pass filter of some sort.

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Postby Tube2stomp » 21 Dec 2007, 12:29

analogguru wrote:That´s a weak argument. There is nothing wrong with electrolytics if you use them properly, what means no reverse polarity...


There is a big gap between doing the same job electricaly wise and sound wise.
Is there something wrong with transistor/opamp based amps?
Of course not, but do they sound the same as tubes?
Hell no :wink:
(I have many friends in the local audiophile scene so over the years had many hours of critical listenings to solid state systems costing like small houses lol)


I assume that you mean the coupling caps on the input...


Yes.

Yes, mostly.....
If it is a transistor/Fet-stage non blocking would lead to a shift of the DC-bias causing a misbias resulting in a non-working stage.


Do you mean even if the source end has a blocking cap?
By saying "transistor/Fet" do you mean the whole solid state variants as in JFET/OpAmp/MOSFET/Bi-Polar?
FET is JFET or is there one called just FET :oops: :lol:


Did you ever connect the anode of a tube-based amplifiying stage to the grid of the next amplyfing stage without blocking ?


Sure.
Open any Marshall amp (and many others) from the last 35 years and you'll see direct coupling between the cathode follower that drives the tone stack and the common cathode stage sourcing it.
You could also do direct coupling when going into a balanced/defferential pair like a Schmitt splitter.
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Postby analogguru » 21 Dec 2007, 13:50

(I have many friends in the local audiophile scene so over the years had many hours of critical listenings to solid state systems costing like small houses lol)


Next time take a solid-state-amp connect a resistor the same value as the impedance of the speaker (to reduce the damping factor) and then do the comparision..... Maybe you have to add a LPF at 10khz....

Do you mean even if the source end has a blocking cap?


Yes..... because on the input of a transistor stage you have a bias divider. If there is any pull-down resistor after the blocking cap it will falsify the bias without an input coupling cap.

By saying "transistor/Fet" do you mean the whole solid state variants as in JFET/OpAmp/MOSFET/Bi-Polar?
FET is JFET or is there one called just FET :oops: :lol:


I only mentioned FET´s to make a difference to bipolsar transistors cause they are differently biased....

Did you ever connect the anode of a tube-based amplifiying stage to the grid of the next amplyfing stage without blocking ?


Sure.
Open any Marshall amp (and many others) from the last 35 years and you'll see direct coupling between the cathode follower that drives the tone stack and the common cathode stage sourcing it.
You could also do direct coupling when going into a balanced/defferential pair like a Schmitt splitter.

[/quote]

Boaah.... such a bullshit.... can you read ?

when you look exactly I wrote :
....to the grid of the next amplyfing stage.....


As a tube expert: can you tell me by which factor a cathode follower "amplifies" the signal ? If it is only 1 or below, then it doesn´t amplify und thus cannot be called an amplifying stage....

It appears to me that you only want to argue .... sorry that I don´t have enough time for this... I think your question should be already answered enough.

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Postby JHS » 21 Dec 2007, 15:57

The 10uF cap blocks DC-coltage at the output and in combination with the 500k you'll have a low pass filter, killing some highs.

The sound will be different if you use a 10uF audio cap or cheap rough foil electrolytic. If you decide to use the 10uF choose an audio type with plain foil.

Furthermore 10uF was chosen to prevent big frequency losses on the low and high end, generated by smaller electrolytic caps.
Due to those losses electrolytics always perform like a bandpass filter.

You can use a metalfilm or poly 1uF cap and a 50-100k pot, maybe the sound is a bit clearer due to the better cap.

Furthermore instead of the 1uF cap you can use 2x 470nF metalfilm caps and a poly 100pF cap, all wired parallel (often seen in highend Hifi stuff). Technical, this is a 1uF cap with nearly linear frequency response.

Maybe the highs are to much upfront in the sound with a good cap yielding in a somewhat sterile tone, that's the drawback.

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Postby Greg » 21 Dec 2007, 23:59

JHS

Thank you for a clear and informative post !!

No arguments, no sarcasm, no "matching wits" - just the facts - it's appreciated..


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Postby analogguru » 22 Dec 2007, 00:08

Greg_G wrote:JHS

Thank you for a clear and informative post !!

No arguments, no sarcasm, no "matching wits" - just the facts - it's appreciated..


:thumbsup


If you appreciate BS then you should be happy with this "informative post" ....

The 10uF cap blocks DC-coltage at the output and in combination with the 500k you'll have a low pass filter, killing some highs.


BS, a capacitor followed by a resistor to ground never can be a LPF only a HPF. Above 1 MHz the inductivity of a capacitor may play a role and for m a LPF... but this never wiull be true in the audible range....

And the rest is also only untechnical mojo-diction without any proof...

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Postby JHS » 22 Dec 2007, 16:17

Sorry Analogguru, my fault. Highpass filter is correct, LP was a typo.

The rest is no mojo. The trick with the parallel wired caps is commen in the Hifi-tuner scene. Also used in a lot of highend studio stuff.

Rough foil electrolytics are total crap for audio use. They are compact and very cheap but produce a lot of distortion and kill headroom, that's the reason that nobody use them in Hifi stuff. I wouln't hesitate to use rough foil electrolytics Cs in non-audio-circuits, like dimmer ect..

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Postby bajaman » 22 Dec 2007, 22:04

They are compact and very cheap but produce a lot of distortion and kill headroom

but this may be of some advantage in a distortion design :lol: :lol:
I agree though, if you must use electros for couplers, use bipolars or at least connect twice the required value back to back and parallel this combination with a good film cap of 10% of the value to allow the clarity in the high end.
very common practice in high end audio - sometimes an even smaller polystyrene or silver mica is also paralled :wink:
cheers
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? mf, uf, and mfd et... Newbie question

Postby platinum321 » 30 Dec 2007, 20:23

Am I correct that mf, uf, and mfd all represent the same measurement called microfarad?

What is the R for as in resistor 390R ?

I would like to buy some stuff at Small Bear and on schematics that call for Capacitors uf or for resistors R I am unsure how to translate into parts from Small Bear. They all read mf not uf and don't know what the R is for regarding resistors.

Here are a couple of examples

R1 390R
C1 47uf


Thanks in advance for any help.
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Re: ? mf, uf, and mfd et... Newbie question

Postby super velcroboy » 30 Dec 2007, 20:32

platinum321 wrote:Am I correct that mf, uf, and mfd all represent the same measurement called microfarad?

What is the R for as in resistor 390R ?

I would like to buy some stuff at Small Bear and on schematics that call for Capacitors uf or for resistors R I am unsure how to translate into parts from Small Bear. They all read mf not uf and don't know what the R is for regarding resistors.

Here are a couple of examples

R1 390R
C1 47uf


Thanks in advance for any help.


i would not used mf. You can easily confuse that with milli farad (10^-3) versus micro farad (uf = 10^-6).

390R is 390 ohms
47uF is 47 microfarad, or 0.047 millifarad or 47000 nF (nanofarad) or 47000000 pf (picofarad)
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Postby platinum321 » 31 Dec 2007, 03:37

Thank you so much Velcro I appreciate the help in the matter. I can see clearly now the rain is gone. . .
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Postby modman » 09 Jan 2008, 09:09

Rule of thumb:

1000 pico Farad pF = 1 nano Farad nF
1000 nana Farad nF = 1 micro Farad uF
1000 micro Farad uF = 1 milli Farad mF

:wink:
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Are these capacitors any good?

Postby supro » 18 Jan 2008, 16:11

Im salvaging components on this recorder, I want to know if the standing caps are electrolytics or can I reuse them...they seem to be metal film.
Oh and how do I rescue these BC 140 Ge transistors wothout burning them out?...I have a 25 watt soldering gun.
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