Capacitor Etiquette???

Loud & Clear

"Welcome To The Machine"
Do To An Illness, It Has Been Several Years Since I Have Been Actively Involved Here In the Forum...

But I Have Noticed A Phenomenon... I Have Seen, And Read Several Threads, Where "Polarized" Electrolytic Capacitors, Of A Certain Value, Are Being Replaced By "Film" Caps Of A Much Smaller Value... I Am Talking Primarily In "Audio Coupling"...

I Have Studied The Site, And Cannot Seem To Find A Explanation For This, Be It Math Related Or Some Type Of Ratio... I Do Know I Like The Idea, I Have Several Coupling Caps That Could Desperately Stand That Upgrade... I Was Going To Replace Said Capacitors With Nichy Muse ES, Then Bypass That With A .01uf PolyProp Film & Foil, But I Would Rather Just Install A Nice Polypropylene Film & Foil, Or Metalized Polyprop In Its Place, That Is Not Comparative In Size, To A 55 Gallon Drum...

Can Someone Please Direct Me To A Thread With An Explanation, Or Enlighten Me On This Subject??? Many Thanks In Advance... :)
 
Last edited:


In the above figure, the capacitor and resistor form a high pass filter. To maintain a flat response down to a given frequency, a capacitor size is chosen to obtain a -3dB cut-off that is 2 octaves below the desired frequency, i.e., for 20Hz, the F3 cut-off would be 5Hz. If the capacitor used is an electrolytic type, the capacitor size used is typically increased 10-fold to minimize the distortion within the pass-band (that results from the use of an electrolytic capacitor).
 
Electrolytic capacitors (in the signal path) are a compromise between getting the desired value in a minimum physical size, but also with minimum degradation of signal passing through them. Other types of capacitor are much better at this, but hitherto have not been available in the (smaller) values (and smaller physical size) normally associated with electrolytics. So it is now perfectly possible to replace (for example) a 50V, 1µF electrolytic capacitor with a film capacitor of the same value/voltage/size.

There you have it. (although modern film cap values up to 4.7µF @63V can be used in place of modern electrolytics, their use limited only by size, and cost).

Additionally the beauty of film caps is that they can be used to replace polarised AND non-polarised electrolytics. :yes:
 
Last edited:
I Appreciate The Comebacks Hyperion, And Leestereo... I Understood The Size Issue, But Didn't Realize What Leestereo Explained, Was A Feasible Situation... That Is Just Something I Did Not Know... Hard To Believe There Is Something Out There, I Did Not Know!!! ;)

I Don't Want To Get A Big Thing Started, But WIMA Caps Seem To Be The Magic Bullet... Though Most Things, Just Aren't What They Seem... Therefore, I Just Cannot Bring Myself To Trust Those "Red" Magic Pills... :scratch2:
 
I did rebuilds with and without Wima's. To be honest, I haven't - yet - noticed a sonic difference.

Wima's in higher capacitor values are rather more expensive than let's say Nichicon ES Muse (bipolar) and FG Fine Gold (regular) that I use for rebuilds.

Still, I also need to say I never did a 1 to 1 comparison; one amp rebuilt with regular electrolytics and one with as much film caps as possible. It is in the back of my head to do it one day, but I need a couple of months before I will have the opportunity to do it. Meanwhile I could think about which amp to use for it, perhaps a Marantz 1060 would be a nice one, I think I still have two in storage. These are also suitable to replace all diodes and transistors too, so that this will not have an influence on the final result.
 
I Appreciate The Comebacks Hyperion, And Leestereo... I Understood The Size Issue, But Didn't Realize What Leestereo Explained, Was A Feasible Situation... That Is Just Something I Did Not Know... Hard To Believe There Is Something Out There, I Did Not Know!!! ;)

I Don't Want To Get A Big Thing Started, But WIMA Caps Seem To Be The Magic Bullet... Though Most Things, Just Aren't What They Seem... Therefore, I Just Cannot Bring Myself To Trust Those "Red" Magic Pills... :scratch2:

One more thing, they last forever compared to standard electrolytics.
 
Thanks Again Folks... Here Is My Thoughts (as I have Not tried this before) I Have A JBL X-over, I Have An Input Op Amp (tl072, which I plan on leaving, specs on that chip are fine, besides, the circuit was designed around that chip) The Inverting & Non Inverting Are Coupled By 4.7uf Polarized Electrolytics, And Also, The Output From That Chip Uses The Same 4.7uf Axial Lead Cap. (which is a bonus for me, as axial caps leave me with enough room, to install axial films) To Couple It To The Next Stage... Now If I Am Reading This Right, I Could Replace Those 4.7uf Electrolytics With .47uf Film & Foil Units??? There Is Two Stages. The Last Stage Is 2 x TL074's... Now On The Input Coupling, There Are 25uf. Electolytics. And For The Actual Outputs, We Have 100uf. Electrolytic Coupling Caps, That Stand Between The Op Amp, And Your Amplifier... I'll Get To That, Then I Get To That... I Just Have To Wrap My Mind Around This Replacing "Electrolytics With Films"... If The Above Mentioned 10x Smaller Ratio Holds Out, Well That Would Be Great... Anyone & Everyone Are Invited To Jump In Here, Take Me By The Ear, And Lead Me Down The "St8 & Narrow" Path Brother... ;) I Appreciate, And Highly Value You Opinions "Hyperion & jeromach...
 
...I Have A JBL X-over, I Have An Input Op Amp (tl072, which I plan on leaving, specs on that chip are fine, besides, the circuit was designed around that chip) The Inverting & Non Inverting Are Coupled By 4.7uf Polarized Electrolytics, And Also, The Output From That Chip Uses The Same 4.7uf Axial Lead Cap. (which is a bonus for me, as axial caps leave me with enough room, to install axial films) To Couple It To The Next Stage... Now If I Am Reading This Right, I Could Replace Those 4.7uf Electrolytics With .47uf Film & Foil Units???...

That the original design used electrolytic capacitors that are 10X larger than required by the high-pass filter F3 cut-off calculation is not a given. Before replacing an electrolytic capacitor with a smaller film-type capacitor, one should do the relevant math. In this case, if the input to the TL072 is direct (i.e., no other resistor shunting to ground at the input), then the input impedance is 10¹² ohms (as per the spec. sheet) and hence, a 4.7µF capacitor, or even a 0.47µF, would be massively over-sized. Do you have a schematic of the JBL x-over?
 
Oh There Is Resistors In Series, And One That Parallels To Ground... I Haven't Looked At The Schematic For A While, I'm Just Righting This Off The Top Of My Head... I Appreciate Your Help Leestereo, And I Will See If I Can Find The Diagram In My Computer, And Get It Posted ASAP...
 
Here Is A Copy Of The Schematic... Very Hard To See... Thanks...
 

Attachments

  • JBL 5234 Schematic.jpg
    JBL 5234 Schematic.jpg
    73.1 KB · Views: 32
The effective input impedance is 47kohm (R3), and with the stock 4.7µF capacitor (C1), the input high pass filter F3 is ~0.7Hz; the replacement film type can be as small as 1.0µF (F3=3.4Hz). A 1.0µF would also be appropriate as the TL072 output capacitor (C3).
 
The effective input impedance is 47kohm (R3), and with the stock 4.7µF capacitor (C1), the input high pass filter F3 is ~0.7Hz; the replacement film type can be as small as 1.0µF (F3=3.4Hz). A 1.0µF would also be appropriate as the TL072 output capacitor (C3).
Ok, Thank You... Do You Have An Equation For This? Also, Looking At The Schematic, There Is The R1 Resistor Which = 47K As Well, And If I Was Going By The High Pass Filter You Have Drawn Out Above. Wouldn't That Put Those Resistors In Series, Making It One Resistor Of 94K ?

Just Making Darn Good & Sure I Understand This... I Want It In My Knowledge Base...

Many Thanks...

EDIT: I've Been Putting Some Study In On This... It's Been A "Long" Time Since I Graduated Electronics... ;) http://www.electronics-tutorials.ws/filter/filter_3.html
 
Last edited:
The equation is: F3=1/(2*pi*R*C)

R1 and R3 form an L-pad, attenuates the signal level.

The impedance of the filter is R3 in parallel with the TL072 input impedance (since the op amp impedance is so large, R# is the effective resistance).
 
The equation is: F3=1/(2*pi*R*C)

R1 and R3 form an L-pad, attenuates the signal level.

The impedance of the filter is R3 in parallel with the TL072 input impedance (since the op amp impedance is so large, R# is the effective resistance).
Ok, Now I'm Seeing It, Much Like Tapping An L-pad (potentiometer set at exactly 1/2) - Voltage Divider Situation... I'll Run That Equation A Few Times, See If I Can Stir Up The Grey Matter A Little...

Thanks...
 
Last edited:
F3=1/(2*pi*R*C) - 6.28 x 47000 x .0000047 = 1.387 Therefore 1/1.39 = .72... F3 = .7 And That Says It All... I Appreciate The Help Leestereo...
 
Back
Top Bottom