[Early B.]

Can someone either provide a link or explain in layman's terms how by-pass caps work? I've searched the 'net, but only run across very technical explanations. Thanks.

[G Georgopoulos]

Can someone either provide a link or explain in layman's terms how by-pass caps work? I've searched the 'net, but only run across very technical explanations. Thanks.

These are placed in parallel with an impendance,and as the frequency varies their impendance also varies,for example if the frequancy rises the capacitor impendance will decrease thus bypassing the rise in frequancy

[Rclark]

I believe what's going on is the bypass cap allows the main capacitor to discharge its contents more fully and handle the next incoming signal as cleanly as it can. Filters out electrical noise this way. All my gear has these little bypass caps in them. Well, everything but my latest amps, which are pretty much technologically beyond any hobbyist cap-tinkering kind of stuff.

[ptmconsulting]

But how do you know what value to use as a bypass?
Well the general rule of thumb is 1/100th of the large cap. So a 10uF cap should have a bypass of .1uF.

What does a bypass do for the signal if it is used in the signal path?
The theory, as I understand it, is a smaller value cap will affect the signal higher in frequency. So a .01uF cap will allow less signal through it than a 1uF cap and give you more of the "air" in the extreme upper end.

How do bypasses affect power supply caps?
I think that was answered above, allowing them to react more quickly to a power requirement, thereby "speeding up" the piece of equipment.

What about a bypass cap across a battery power supply?
Batteries are clean suppliers of power, but they are not quick suppliers of power. A cap is far quicker than a battery at releasing its charge, so a bypass across a bettery power supply should also speed up the delivery of power to the component. However, you need a sufficiently sized cap, so no .1uF caps here. Try a 100-1500uF film cap instead so it has sufficient juice for the job.

[cheap-Jack]

Hi.

But how do you know what value to use as a bypass?
Well the general rule of thumb is 1/100th of the large cap. So a 10uF cap should have a bypass of .1uF.

(1) What does a bypass do for the signal if it is used in the signal path?
The theory, as I understand it, is a smaller value cap will affect the signal higher in frequency. So a .01uF cap will allow less signal through it than a 1uF cap and give you more of the "air" in the extreme upper end.

(2) How do bypasses affect power supply caps?
I think that was answered above, allowing them to react more quickly to a power requirement, thereby "speeding up" the piece of equipment.

(3) What about a bypass cap across a battery power supply?
Batteries are clean suppliers of power, but they are not quick suppliers of power. A cap is far quicker than a battery at releasing its charge, so a bypass across a battery power supply should also speed up the delivery of power to the component. However, you need a sufficiently sized cap, so no .1uF caps here. Try a 100-1500uF poly cap instead so it has sufficient juice for the job.

(1) Yes, a film cap is commonly installed parallel to the final filter cap, which is always a large capacitance 'lytic cap, to allow HF audio signal to pass thru with less loss.

(2) As said in (1)

(3) Yes, a very very large 'lytic cap, over 1 farad to 20 farads,, is always recommended to install across a battery used to power high O/P amps, such as 12V power boosters for car audio which consume multi amperes high currents whenever we crank up the car audio volume. Such large cap acts like a current reservoir once fully charged by the car dynamo will help the battery to provide constant currents consumed by the car audio power amps.

Where you can get 1,00-1,500uF poly cap?? I assume poly cap you mean PP or PE type "poly" film caps, correct? I want to buy some such hugh size "poly" film caps!!!!!!!

That said, for home audio, such high hugh current 'reservoirs' are NO need! Bypass caps of much smaller capacitance of metallized PP or PE film will do a good job to bypass HF audio signal.

This is particularly imperial for Class A amps where the music signal passed thru the last filter cap to complete the signal return circuit.

c-J

[underdawg]

The best literature I found on bycass caps was from welborne labs catalog when ron explained the effects of bypass capacitors in the power supply and in the circuits based on his testing.

[Early B.]

The best literature I found on bycass caps was from welborne labs catalog when ron explained the effects of bypass capacitors in the power supply and in the circuits based on his testing.

Do you have a link?

[Davey]

Actually, the type of "bypassing" you fellas are referring to here is more correctly called shunting.

Some of the older fellas who've worked on old radio/TV gear will know that a bypass capacitor was employed (in many instances) in amplifier stages to bypass a resistor.  Generally for the purpose of increasing AC gain in the circuit without affected cathode bias.

Only in recent years has silly audiophile jargon redefined the term to something with a different meaning. 

Anyways, the concept is simple.  There's an ESR associated with all capacitors and shunting smaller capacitors (which generally have lower ESR) values across bigger ones will result in 'composite' capacitor with lower ESR than the larger one would otherwise.

Cheers,

Dave.

[underdawg]

i am sorry i have not found or heard from ron in years, not sure if he is still in business. I will look at my catalog selection and find a catalog but it is lengthy, maybe some one has one of welborne labs catalogs saved  they can email to you.

[Ethan Winer]

Can someone either provide a link or explain in layman's terms how by-pass caps work?

The most common bypass cap is a disk ceramic. Electrolytic power supply caps have a large amount of series inductance, which renders them less effective at high frequencies. Disk ceramic caps are built differently, so using both types in parallel offers high capacitance to handle the 60 Hz mains frequency, but a low impedance at very high frequencies to prevent circuits from oscillating. The text and drawing below are from my Audio Expert book. The strip at the top of the drawing shows a large-value cap before it's rolled up to save space.

--Ethan

Disk ceramic capacitors are also made from many parallel sections, with ceramic between the plates for insulation. Ceramic caps are inexpensive, but they can differ as much as 10 or even 20 percent from their stated value. Their capacitance also varies with temperature, and they have relatively high distortion and piezoelectric properties. But being made from parallel plates rather than rolled-up strips, they have very low series inductance. Ceramic capacitors are common in high-frequency circuits, and they’re often used in power supplies and audio circuits in parallel with electrolytic caps to assure a low impedance at high frequencies. If you need ceramic capacitors having some minimum capacitance, simply buy them 20 percent larger to account for their poor tolerance. With power supply capacitors, having more capacitance never hurts.

[cheap-Jack]

Hi.

(1) On old radio/TV gear.. a bypass capacitor was employed (in many instances) in amplifier stages to bypass a resistor.  Generally for the purpose of increasing AC gain in the circuit without affected cathode bias.

(2) Only in recent years has silly audiophile jargon redefined the term to something with a different meaning. 

(3) There's an ESR associated with all capacitors and shunting smaller capacitors (which generally have lower ESR) values across bigger ones will result in 'composite' capacitor with lower ESR than the larger one would otherwise.

Cheers,

Dave.

(1) In old radio designs, where there was only one single stage with limited voltage gain to drive the O/P power stage, a bypass cap was always used across the cathode bias resistor to prevent current NFB across the cathode resistor, so as to maintain the limited gain available to drive the O/P power stage.
Not for "increasing AC gain in the circuit".

(2) The HD audios we have todate, many decades later than our grandpa's Lo-Fi radio era, can deliver high definition reproduction that we hear the sonic difference among different makes of bypass cap. Total different ballgame to play audio today, my friend.

(3) Sorry, small caps get higher ESR vs larger caps get lower ESR. Take the very common bypass cap, which is electrolytic, a 22uF aluminum canned 'lytic cap gets 0.1 - 3R ESR vs a 100uF same type cap gets 0.05- 0.5R ESR.

Ceramic disc caps are for sure NOT the "most common" bypass caps used in audios.

c-J

[cheap-Jack]

Hi.

The most common bypass cap is a disk ceramic. --

Ceramic disc caps are mainly used for VHF use, not common at all for audios.

I only use ceramic disc caps for RFI/EMI bypassing at one-point star grounding point for each audio channel. For audio bypassing as used for cathode bias resistors & last filter caps, thanks but no thanks.

In the ESR schematic of a ceramic disc you posted, I found it over simplified as there is no insulation resistance & dielectric loss resistance which should be included.

c-J

[Davey]

It would "increase" gain relative to if it were not there.  In fact most of those circuits would work just fine with the bypass capacitor removed....just with lower signal gain.

Regarding ESR of smaller caps...if you'll re-read again, I said "generally."

Ceramic disc caps ARE the most common bypass caps used in audio equipment.  Open up just about any electronic device and you'll see many local bypass caps used near the active stages......most probably ceramic.
Ceramic caps would not be the most common caps used in shunting operations in speaker crossovers, etc, etc.

Cheers,

Dave.

[cheap-Jack]

Hi.

(1) It would "increase" gain relative to if it were not there.  In fact most of those circuits would work just fine with the bypass capacitor removed....just with lower signal gain.

(2) Regarding ESR of smaller caps...if you'll re-read again, I said "generally."

(3) disc caps ARE the most common bypass caps used in audio equipment.  Open up just about any electronic device and you'll see many local bypass caps used near the active stages......most probably ceramic.
Ceramic caps would not be the most common caps used in shunting operations in speaker crossovers, etc, etc.

(1) So for the sake of the readers who is not so electronically knowledgeable, please state precisely!

(2) What "general"? It is a reverse fact, my friend.

(3) Show me any audio amp schematic that use ceramic discs as audio bypass, to save your argument. It is important for our readers who want to learn the right thing.

c-J

[Davey]

Sorry, you've got the wrong fellow if your objective is some silly back/forth on this topic.  Conclude from that whatever you want.

Ethan (much smarter than me) made the initial statement regarding disc bypass caps, so if you need a silly argument maybe you can engage him? 

Cheers,

Dave.

[cheap-Jack]

Hi.

Sorry, you've got the wrong fellow if your objective is some silly back/forth on this topic.  Conclude from that whatever you want.

Ethan (much smarter than me) made the initial statement regarding disc bypass caps, so if you need a silly argument maybe you can engage him? 

Cheers,

Dave.

What "silly back/forth" ? Whatever we posted in any public technical forum, please make it is correct as it would be read by millions of readers worldwide. I simply want to make it correct for those readers who want to learn. Nothing personal, my friend.

Simply admit what you posted was incorrect & back off gracefully. No hard feeling.

c-J

[Ethan Winer]

Ceramic disc caps ARE the most common bypass caps used in audio equipment.  Open up just about any electronic device and you'll see many local bypass caps used near the active stages......most probably ceramic.

Exactly. It's not like they're in the signal path.

--Ethan

[Steve]

 
Ceramic disc caps ARE the most common bypass caps used in audio equipment.  Open up just about any electronic device and you'll see many local bypass caps used near the active stages......most probably ceramic.

Ceramics are used because their very high frequency resonating properties, in the multi mega hertz range (mhz), depending upon
the value. For example, a typical .001uf and similiar value 1kv disc ceramic has a self resonance from 10mhz to over 50 mhz.
(also depends upon the lead length.) This made disc ceramics useful for removing RFI/EMI from circuits in the AC line,
where real garbage can infiltrate.

However, disc ceramic capacitors also possess the piezo effect, as well as problems with DA and DF,
so bypassing with them in a high quality signal path (say decoupling capacitor/last power supply
filter capacitor) is obviously degrading to the signal. They are usually so small it probably would not help anyway.
They also exhibit voltage stress points which can break down, thus higher voltage rated caps are
usually used. Even well designed plastic coupling caps will have some inductance and esr and sometimes
can benefit from bypass caps.

Large electrolyics have internal inductance problems, self resonance is as low as 2khz, but even medium
size don't often make 15khz. Above that point inductive properties take over. Bypassing with smaller caps
(hopefully not disc) allows the impedance to continue to drop at higher frequencies on many caps.

Ceramincs are used in auto rigs because of RFI and EMI issues presented by the auto's electrical system.
That is probably what you saw.

In home stereo use, they are used in the AC arena, where RF or other EMI problems commonly enter (although there
are other areas to enter depending upon the other components which might emit RF). Even Micas are
basically better than ceramics. Tantalums are about the only worse caps.

Of course back in oldie days, wax/paper and oil caps, both physically large and easily becoming leaky
were used extensively; they did not last. I have seen some tiny ceramics used in tone circuits where
high impedances and small values of capacitances were needed, but you can obtain better now a days for cheap.

A perfect capacitor would present a perfect short at all audio frequencies, while being perfectly open to DC voltages.

Cheers.

[cheap-Jack]

Hi.

(1) Ceramincs are used in auto rigs because of RFI and EMI issues presented by the auto's electrical system.
That is probably what you saw.

(2) In home stereo use, they are used in the AC arena, where RF or other EMI problems commonly enter (although there are other areas to enter depending upon the other components which might emit RF).

(3)  Even Micas are basically better than ceramics.

(4) Of course back in oldie days, wax/paper and oil caps, ..

A perfect capacitor would present a perfect short at all audio frequencies, while being perfectly open to DC voltages.

(1) Yes, ceramic caps are mainly for killing RFI/EMI areas, like auto amps

(2) That't exactly how I always use for draining off RFI/EMI noises - at the central grounding point of ALL the phono-preamps & power amps I built, located just adjacent to the signal I/P jacks - being most effective.
     For audio signal bypass, there are tons of much better selection of caps than ceramics.

(3) Yes, the 'hysteresis' curve of mica caps is more linear than any ceramics. IMO, ceramic caps get the worse non-linear curve among most if not all types of caps.

(4) Paper-in-oil caps get the most linear 'hysteresis' curve among all types of caps & would sound the best.

As per Steve Bench's caps test report, ceramic caps exhibit the most non-linear curve, lower voltage rating is even worse. That's why I only use 2KV rated ceramic caps for the RFI/EMI draining devices in ALL the audio amps I built. For audio signal path bypass, thanks but NO thanks.

Even worse, ceramic caps' linearity changes with frequency.

I always use PP or PE caps for coupling & bypass in audio signal paths, including last filter caps bypass.

c-J

[Early B.]

I believe what's going on is the bypass cap allows the main capacitor to discharge its contents more fully and handle the next incoming signal as cleanly as it can. Filters out electrical noise this way.

Can you elaborate on this? It appears that the circuit transmits the sonic qualities of the by-pass cap, not the main capacitor. How does that occur?