100,000uf will not assure you will have good bass, you can obtain good bass with 20,000uf...with 100,000uf that much capacitance you will need a big transformer, heavy rectifiers and a soft-start. for a chip amp I find it "worthless" . Go discrete and then we are talking!!!
.
While I'm not here to cheer for the big bad capacitor (although it is cool), I can testify from first hand experience that increasing power supply capacitance will definately give better bass performance even with cheap chip amps. I pirated a no name chip amp from a "hi-fi" tabletop stereo "50+50 watts rms"
and put it in a small enclosure as a cheap and dirty power amp. It sounded thin. I added cheap Radio Shack 10,000 uF caps in parallel with the 2200 uF power supply caps and it sounded way better. It's pretty rockin for free. For many applications a properly designed circuit (careful attention to the poles) will circumvent the need for fancy pants capacitors. I know a lot of you guys get a woodie for expen$ive caps, but the truth is that in many applications they don't make a lick of difference.
Walter Jung did an excellent essay on choosing capacitors some years back. You can look it up if you're interested. He explains in detail what I only briefly mentioned, and a whole lot more.
Your answer is here
http://www.diyaudio.com/forums/solid-state/216409-power-supply-resevoir-size.html
What is your power supply voltage going to be? 4 or 8 ohm load?
You can experiment too. Try 4700, 10,000, and 20,000 uF and see if you can find the point of diminishing returns.
it says more about rejection ratio where the capacitors value doesnt make any sense. I do understand that but the equation between the ripple current and the capacitance is not understood. Example I need 10 amps continuous at the output considering Im having 3 LM3886 in parallel mode. So If I have a trafo at 24-0-24 ( 2 amps ) so its roughly 100VA then with bridge rectification it will give 34 volts so each chip can delver 3.79 amps of current at the output so how much capacitor to be used considering for each chip?
Taking the capacitor voltage is about 50volts
Ex: Nichicon KG 10000uf 50v ( rated ripple Arms is 4 amps )
so how can I choose the capacitor limit in psu?
Taking the capacitor voltage is about 50volts
Ex: Nichicon KG 10000uf 50v ( rated ripple Arms is 4 amps )
so how can I choose the capacitor limit in psu?
I found one thing for the Decoupling caps with the equations considering slew rate and change in the voltage when I is peak... for the LM3886 to be 220uf paralleled with 100 to 200nf film cap right at the input pins and according to the layout principles its better to connect the input wires right beside the input caps with 1uf series DC blocking cap. But regarding psu i need certain equations...
you did not get that from the datasheet!!!
each chip can only deliver 3.79Apk if there is a supply that deliver this current to the chip. If you have 3 chips then the supply would need to deliver 11.37Apk
try 4700uF as a start. Read advice in other websites. Read other Threads in this Forum. You will find advice ranging from 1000uF to 100000uF. All work to some extent. Some you may like, some you may not want to spend that much money on. This will become a big issue if you are planning 6 channels (3 for L & 3 for R).
you don't need equations to mount the local decoupling "right at the input pins".
I was going through that psu reservoir and I found these equations to calculate the psu capacitor value...
OK. Here is a nice webpage about unregulated power supply design, with just the bare basics:
Unregulated Power Supply Design
Their equation for the peak-to-peak amplitude of the ripple voltage is equivalent to the equation I gave for calculating capacitance based on Δi, Δt, and a desired Δv:
(1) Δv = i / (2fC)
where f is the supply frequency (60 Hz, in our case).
Solving for C, we get:
(2) C = i / (2fΔv)
which is equivalent to the equation I gave in post # 61:
(3) C ≥ (Δi Δt) / Δv
if we realize they are using 1 / 2f in place of Δt, because the rectified AC mains (and ripple) frequency is twice the mains supply frequency, f, and the time for one cycle at frequency f is 1/f, AND we realize that in (3), the Δi is usually PEAK current, not RMS, since it's usually applied for transients or short time periods.
First we can note that the "3300 uF per Amp" rule would give, using equation (1), with C = 3300uF x 3.54A rms = 11682uF, a p-p ripple amplitude of Δv = 2.52 Volts. (Or was that rule for Amps PEAK? That would be 16500 uF, and 1.79 Volts p-p ripple.)
But the ripple voltage is not the only rail disturbance. And the ripple calculation in (1) only took into account a constant load current. Our load will pull current from the caps that will not be constant. It will be sinusoidal, probably a half-cycle sine at a time, in the simplest case of one pure tone. It might be worse than that but that means that the capacitance requirement for that can be a lower bound, i.e. a minimum.
So I started out thinking that the lowest frequency would need the longest current draw and would be the worst case. I looked at 15 Hz as an example. The period for one cycle of 15 Hz can be found using
(4) T (sec) = 1 / f (Hz)
as 1 / 15 = .0667 sec.
So we know that just to supply the current for the rising half of the positive part of a 15 Hz sine wave, we would have to go from 0 Amps to 5 Amps Peak (worst case) in one-fourth of a cycle, or 0.0167 sec.
Using equation (4), we can get C in terms of the Δv we decide we can tolerate: C = (5A)(0.0167 sec) / Δv, or C = .083500 / Δv , for 15 Hz, which can also be rearranged to give Δv = .083500 / C for 15 Hz.
BUT THEN I realized that since the charging pulses are faster than 15 Hz, and would actually re-charge the caps up to four times during a half-cycle of 15 Hz, that the equations in the previous paragraph were not valid because of that, and that 60 Hz would probably be a better "worst case".
60 Hz is 0.00417 sec per 1/4th cycle. So, C ≥ (5A)(0.004170 sec) / Δv, or
(5) C ≥ 0.020850 / Δv , for 60 Hz (note that it's 20850 uF for 1V Δv), and
(6) Δv = 0.020850 / C , for 60 Hz.
Note that the Δv in (5) and (6) is in addition to the mains ripple.
If we used the 11682 uF given by the "3300 uF pr Amp" rule, that would give Δv = 1.78 Volt of ADDITIONAL rail-voltage disturbance, which is 71% more (1/√2 more) than what we thought the 3300 uF rule would give us. (Or if that rule was supposed to be for PEAK amps, it would have given 16500 uF and 1.79 V p-p 120 Hz ripple, which would give an additional 1.26 Volts of rail disturbance due to the positive half of our 60 Hz tone, or 42% more.)
That might be especially inconvenient if we were also using a linear regulator, since the current humps pulled by the load would cause voltage sags that would essentially pull the troughs of the ripple voltage downward farther than planned, by up to 71% of its originally-calculated amplitude, which might be likely to cause the regulator's input minus output voltage difference to become less than it's dropout voltage spec, during parts of the troughs, which would get really ugly.
It would only possibly be 71% [or 42%, if the rule was for peak amps] worse when we were driving the amp all the way to the rail. But the bottom of the ripple waveform would come down lower than we thought, by some percentage, at every volume setting.
If we were happy with the mains ripple that the "3300 uF per Amp" rule was going to give us, then it looks like we should ADD 71% (or 42% if the rule used peak current instead of RMS) to the capacitance value it gave us, AND to the rule, in order to keep the worst-case rail disturbance the same.
In any case, we might as well come up with a general equation that will take into account BOTH the worst-case mains ripple AND the transient voltage sags that our signals might induce. There might be some "overlap" between those causes and effects but this should give a safe minimum capacitance:
For the transient component, from (3) we can substitute 1/4f for Δt, assuming that 1/4 cycle at the AC Mains frequency is the worst case, and get
(7) C = ipeak / (4fΔv)
and in order to take into account both the DC and transient components of Δv we can combine (7) with (2) to get the total C needed:
(8) C = [ iRMS / (2fΔv) ] + [ ipeak / (4fΔv) ]
Then we can solve for Δv:
(9) Δv = [ iRMS / (2fC) ] + [ ipeak / (4fC) ]
If we convert iRMS to ipeak, pull out the common denominator factor, then clean up the remaining fractions, we get:
(10) Δv = (0.6036)(ipeak)/fC
or
(11) C = (0.6036)(ipeak) / (f Δv)
where
f is the AC Mains frequency,
ipeak is the power supply's peak (rail) voltage (not RMS), i.e. ipeak = Vrail/Rload, and
Δv is your choice of an acceptable worst-case voltage-rail variation.
(So it looks like the new rule should be "≥ 5600 uF per Amp (peak)".)
So, assuming that the "3300 uF per amp" rule meant PEAK amps, and without considering whether or not the 1.79 Volts worst-case peak-to-peak ripple amplitude that it gave is "good enough", the minimum total reservoir capacitance needed in order to REALLY get a worst-case of less than or equal to 1.79 Volts Δv should be, using (11):
C = [(0.6036)(5)] / [(60)(1.79)] = 28100 uF
We might also want to add 15% or more to that, to account for variations in mains voltage and transformer regulation.
So maybe 33000 uF would be a better number.
(I hope that someone will check my math and logic.)
-----------------------------------------------------------
but what actually makes as 3300uf as 1 amp?
what is Ipeak? is it current in the speaker load?
OK. Here is a nice webpage about unregulated power supply design, with just the bare basics:
Unregulated Power Supply Design
Their equation for the peak-to-peak amplitude of the ripple voltage is equivalent to the equation I gave for calculating capacitance based on Δi, Δt, and a desired Δv:
(1) Δv = i / (2fC)
where f is the supply frequency (60 Hz, in our case).
Solving for C, we get:
(2) C = i / (2fΔv)
which is equivalent to the equation I gave in post # 61:
(3) C ≥ (Δi Δt) / Δv
if we realize they are using 1 / 2f in place of Δt, because the rectified AC mains (and ripple) frequency is twice the mains supply frequency, f, and the time for one cycle at frequency f is 1/f, AND we realize that in (3), the Δi is usually PEAK current, not RMS, since it's usually applied for transients or short time periods.
First we can note that the "3300 uF per Amp" rule would give, using equation (1), with C = 3300uF x 3.54A rms = 11682uF, a p-p ripple amplitude of Δv = 2.52 Volts. (Or was that rule for Amps PEAK? That would be 16500 uF, and 1.79 Volts p-p ripple.)
But the ripple voltage is not the only rail disturbance. And the ripple calculation in (1) only took into account a constant load current. Our load will pull current from the caps that will not be constant. It will be sinusoidal, probably a half-cycle sine at a time, in the simplest case of one pure tone. It might be worse than that but that means that the capacitance requirement for that can be a lower bound, i.e. a minimum.
So I started out thinking that the lowest frequency would need the longest current draw and would be the worst case. I looked at 15 Hz as an example. The period for one cycle of 15 Hz can be found using
(4) T (sec) = 1 / f (Hz)
as 1 / 15 = .0667 sec.
So we know that just to supply the current for the rising half of the positive part of a 15 Hz sine wave, we would have to go from 0 Amps to 5 Amps Peak (worst case) in one-fourth of a cycle, or 0.0167 sec.
Using equation (4), we can get C in terms of the Δv we decide we can tolerate: C = (5A)(0.0167 sec) / Δv, or C = .083500 / Δv , for 15 Hz, which can also be rearranged to give Δv = .083500 / C for 15 Hz.
BUT THEN I realized that since the charging pulses are faster than 15 Hz, and would actually re-charge the caps up to four times during a half-cycle of 15 Hz, that the equations in the previous paragraph were not valid because of that, and that 60 Hz would probably be a better "worst case".
60 Hz is 0.00417 sec per 1/4th cycle. So, C ≥ (5A)(0.004170 sec) / Δv, or
(5) C ≥ 0.020850 / Δv , for 60 Hz (note that it's 20850 uF for 1V Δv), and
(6) Δv = 0.020850 / C , for 60 Hz.
Note that the Δv in (5) and (6) is in addition to the mains ripple.
If we used the 11682 uF given by the "3300 uF pr Amp" rule, that would give Δv = 1.78 Volt of ADDITIONAL rail-voltage disturbance, which is 71% more (1/√2 more) than what we thought the 3300 uF rule would give us. (Or if that rule was supposed to be for PEAK amps, it would have given 16500 uF and 1.79 V p-p 120 Hz ripple, which would give an additional 1.26 Volts of rail disturbance due to the positive half of our 60 Hz tone, or 42% more.)
That might be especially inconvenient if we were also using a linear regulator, since the current humps pulled by the load would cause voltage sags that would essentially pull the troughs of the ripple voltage downward farther than planned, by up to 71% of its originally-calculated amplitude, which might be likely to cause the regulator's input minus output voltage difference to become less than it's dropout voltage spec, during parts of the troughs, which would get really ugly.
It would only possibly be 71% [or 42%, if the rule was for peak amps] worse when we were driving the amp all the way to the rail. But the bottom of the ripple waveform would come down lower than we thought, by some percentage, at every volume setting.
If we were happy with the mains ripple that the "3300 uF per Amp" rule was going to give us, then it looks like we should ADD 71% (or 42% if the rule used peak current instead of RMS) to the capacitance value it gave us, AND to the rule, in order to keep the worst-case rail disturbance the same.
In any case, we might as well come up with a general equation that will take into account BOTH the worst-case mains ripple AND the transient voltage sags that our signals might induce. There might be some "overlap" between those causes and effects but this should give a safe minimum capacitance:
For the transient component, from (3) we can substitute 1/4f for Δt, assuming that 1/4 cycle at the AC Mains frequency is the worst case, and get
(7) C = ipeak / (4fΔv)
and in order to take into account both the DC and transient components of Δv we can combine (7) with (2) to get the total C needed:
(8) C = [ iRMS / (2fΔv) ] + [ ipeak / (4fΔv) ]
Then we can solve for Δv:
(9) Δv = [ iRMS / (2fC) ] + [ ipeak / (4fC) ]
If we convert iRMS to ipeak, pull out the common denominator factor, then clean up the remaining fractions, we get:
(10) Δv = (0.6036)(ipeak)/fC
or
(11) C = (0.6036)(ipeak) / (f Δv)
where
f is the AC Mains frequency,
ipeak is the power supply's peak (rail) voltage (not RMS), i.e. ipeak = Vrail/Rload, and
Δv is your choice of an acceptable worst-case voltage-rail variation.
(So it looks like the new rule should be "≥ 5600 uF per Amp (peak)".)
So, assuming that the "3300 uF per amp" rule meant PEAK amps, and without considering whether or not the 1.79 Volts worst-case peak-to-peak ripple amplitude that it gave is "good enough", the minimum total reservoir capacitance needed in order to REALLY get a worst-case of less than or equal to 1.79 Volts Δv should be, using (11):
C = [(0.6036)(5)] / [(60)(1.79)] = 28100 uF
We might also want to add 15% or more to that, to account for variations in mains voltage and transformer regulation.
So maybe 33000 uF would be a better number.
(I hope that someone will check my math and logic.)
-----------------------------------------------------------
but what actually makes as 3300uf as 1 amp?
what is Ipeak? is it current in the speaker load?
Lets consider that if im getting 10 amps as I peak then its 60000uf. Once I remembered a mail response from Jeff Rowland stating that if an amplifier is capable of delivering 15 amps of continuous current in the speaker load then its a serious pa speaker or a big subwoofer you can drive any driver in 12 inch range. Hence using 3 or 6 chips in Bridge-parallel can drive any speaker i think...
I found the value for 4 amps of Ipeak in load with 1.7volts of ripple voltage we need to have ~24000uf of capacitance with 15% of regulation of voltage at mains it can go max of 30000uf of cap to get the required current output. So if we require 10 amps its just double that value so it can be 60000uf. When we have 6 chips in BPA config then I believe for each chip the Ipeak is 3 amps so roughly 18000uf per chip for the input voltage of 28volts and for total 6 chips then it will 1,08,000uf which is what I though in the beginning but expecting the 18amp of sudden current is too high for any voice coil....
I agree. Don't waste your time with audio grade bulk capacitors. Hell, don't waste your time with audio grade anything. It's bullsh*t. Just because it's in a sleek gold and black package doesn't make it any better than regular caps. Those are 85 degrees C caps. Crap. Do yourself a favor. Get some good quality Japanese caps. Panasonic, Nichicon, Nippon/United Chemicon, or Rubycon. Get 105 degrees C. Save yourself some money and then lastly, don't fool yourself into thinking that a bulk capacitor changed the sound of your amp. You have to be mad.
I really like the DIY audio world, but holy hell, take a breath once in a while. Yes, certain parts do sound better for audio. But please, there's no need to spend $50 on a film capacitor! Wimas are expensive enough! Hell a $0.25 Panasonic would probably sound EXACTLY the same. But no one dare say that...
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you know, it ain't that hard to make Your verry own capacitor.
Actualy its not hard to obtain copper or aluminium foil.
And allso not hard to find thin paper rolls.
And yess, you got it right, just sandwitch them and roll it like a joint.
Then mesure what You got.
Copper is from a point of view a better choice.
Since it is a better cnductor, and easy to solder the leads.
There are formulas to calculate the final result, but beware, it assumes You manage to get the plates to be absolute paralell.
If You want some intresting tests, then roll Your self a cap, and use it vs a high priced one.
For a verry simplistic test just use ordinary aluminium foil , that can be purchased at any store.
Your mother/wife will probably have it at home in the kitchen.
You need to cut the whole roll, to be less a bit then a roll of TOILET paper.
Use the most inexpensive one, its thinner.
You will manage to have 2 rolls of aluminium foil.
(know this from experience)
I did not use it as a powersupply cap, i just made one for fun used as input capacitor for an amplifier.
The hard part is to align the 2 rolls of aluminium foil and he 2 rolls of toilet paper, so when You roll it You get a quite big capacitor.
Actualy later i found it is way less problematic if You lay down the layers unrolled on the floor, and use the aluminium foil's original paper pipe as a former to wind up Your capacitor.
Result is dependant on how well You roll it.
Now, if something, than that is a one high grade capacitor.
The next level of avolution is to soak the paper into non conductive oil prior rolling it.
If You ask me nothing beats homebrew
Actualy its not hard to obtain copper or aluminium foil.
And allso not hard to find thin paper rolls.
And yess, you got it right, just sandwitch them and roll it like a joint.
Then mesure what You got.
Copper is from a point of view a better choice.
Since it is a better cnductor, and easy to solder the leads.
There are formulas to calculate the final result, but beware, it assumes You manage to get the plates to be absolute paralell.
If You want some intresting tests, then roll Your self a cap, and use it vs a high priced one.
For a verry simplistic test just use ordinary aluminium foil , that can be purchased at any store.
Your mother/wife will probably have it at home in the kitchen.
You need to cut the whole roll, to be less a bit then a roll of TOILET paper.
Use the most inexpensive one, its thinner.
You will manage to have 2 rolls of aluminium foil.
(know this from experience)
I did not use it as a powersupply cap, i just made one for fun used as input capacitor for an amplifier.
The hard part is to align the 2 rolls of aluminium foil and he 2 rolls of toilet paper, so when You roll it You get a quite big capacitor.
Actualy later i found it is way less problematic if You lay down the layers unrolled on the floor, and use the aluminium foil's original paper pipe as a former to wind up Your capacitor.
Result is dependant on how well You roll it.
Now, if something, than that is a one high grade capacitor.
The next level of avolution is to soak the paper into non conductive oil prior rolling it.
If You ask me nothing beats homebrew
Wow! In the past few days there seems to be many posts on several threads where people are flaming the reports and posts of others. I don't think that is fair or necessary. Please indulge me while I use a non-audio, non-technical scenario to explain.
We have a room where one wall has an oil painting hung between two windows with old fashion pull down shades. The opposite wall - there is a door and a small blue statue atop a pedestal. Two members of the same family are placed in the middle of the room - back to back - and asked to describe the room. The only condition is that neither is allowed to move their gaze from straight forward. You can see where this is going. When asked if there is a door in the room two honest but completely different answers are given. What color are the window shades? ..produces - "white" and "there are no windows in this room." How tall is the statue? .................
Now I would ask that this concept be applied to component selection, use and review in the family of diy electronics. Posting reports based on one’s actual experience need not necessarily be considered an invitation for challenge, criticism and dispute. In the above example, all responses are truthful, accurate and completely valid. One should also note there are two other walls in that room that haven't been seen (experienced) by either family member - a myriad of additional possibilities. So also may be the case in the selection and use of components in the world (room) of diy audio.
Personally, I am neither wealthy nor dumb enough to blindly buy or endorse any component based on its price or packaging. Other than the sheer fun of doing projects, the main reason I joined the forum is to get the best bang for my audio dollars - read: save money. In the past couple years I have found myself paying 10 to 20 times more than "normal" for two or three caps, resistors and transformers. I parted from my hard earned cash on those occasions for only one reason.
I began learning and performing music (trombone) as a child in 1958. I was fortunate enough to have participated in high school, university and a smidgen of professional groups, the experience of which has been one of my greatest treasures. If I have to pay extra for a do-dad or two that makes what comes out of the circuits I build sound more like what I hear from that trumpet dude over there, I'll do it. If not, the cash stays in my pocket. Nothing more - nothing less.
I have always been blown away by the amount of advanced technical knowledge posted on the forum by people who really know their stuff. Their willingness to share and jump in to solve difficulties is something not found easily elsewhere. I would contend combining that advantage with the reports - as well as questions - from novices like myself, prove to be the life blood of this entire forum - regardless of the topic being discussed.
Why then I ask, is there a need for the flaming (ego based) posts that seem to be so prevalent. It seems to introduce so much dis-service to the nature, value and beauty at the core.
I can't count the number of times I have been frustrated by not being able to find one particular emoticon in the smilies list. "PEACE". Maybe the forum admins might think to add it - making its position first and its size the largest.
We have a room where one wall has an oil painting hung between two windows with old fashion pull down shades. The opposite wall - there is a door and a small blue statue atop a pedestal. Two members of the same family are placed in the middle of the room - back to back - and asked to describe the room. The only condition is that neither is allowed to move their gaze from straight forward. You can see where this is going. When asked if there is a door in the room two honest but completely different answers are given. What color are the window shades? ..produces - "white" and "there are no windows in this room." How tall is the statue? .................
Now I would ask that this concept be applied to component selection, use and review in the family of diy electronics. Posting reports based on one’s actual experience need not necessarily be considered an invitation for challenge, criticism and dispute. In the above example, all responses are truthful, accurate and completely valid. One should also note there are two other walls in that room that haven't been seen (experienced) by either family member - a myriad of additional possibilities. So also may be the case in the selection and use of components in the world (room) of diy audio.
Personally, I am neither wealthy nor dumb enough to blindly buy or endorse any component based on its price or packaging. Other than the sheer fun of doing projects, the main reason I joined the forum is to get the best bang for my audio dollars - read: save money. In the past couple years I have found myself paying 10 to 20 times more than "normal" for two or three caps, resistors and transformers. I parted from my hard earned cash on those occasions for only one reason.
I began learning and performing music (trombone) as a child in 1958. I was fortunate enough to have participated in high school, university and a smidgen of professional groups, the experience of which has been one of my greatest treasures. If I have to pay extra for a do-dad or two that makes what comes out of the circuits I build sound more like what I hear from that trumpet dude over there, I'll do it. If not, the cash stays in my pocket. Nothing more - nothing less.
I have always been blown away by the amount of advanced technical knowledge posted on the forum by people who really know their stuff. Their willingness to share and jump in to solve difficulties is something not found easily elsewhere. I would contend combining that advantage with the reports - as well as questions - from novices like myself, prove to be the life blood of this entire forum - regardless of the topic being discussed.
Why then I ask, is there a need for the flaming (ego based) posts that seem to be so prevalent. It seems to introduce so much dis-service to the nature, value and beauty at the core.
I can't count the number of times I have been frustrated by not being able to find one particular emoticon in the smilies list. "PEACE". Maybe the forum admins might think to add it - making its position first and its size the largest.
which oil to use? I think its better to get a dedicated guy to pay a month salary and build the required caps instead of paying huge like 300 USD for some decent caps. But why are they so expensive? when somebody can do it at home with less hassle...
ex: what is silver/gold/oil in mundorf?
what is cast cap from Duelund ?
ex: what is silver/gold/oil in mundorf?
what is cast cap from Duelund ?
Hey Arty,
What you propose is interesting and looks like a fun way to spend some time experimenting. My question though is (and I'm not trying to be a smart a..) how would one miniaturize all that for practical use in an amp. I'm feeling a slight tug on my left leg right now, but I'm game. Got any links to share?
What you propose is interesting and looks like a fun way to spend some time experimenting. My question though is (and I'm not trying to be a smart a..) how would one miniaturize all that for practical use in an amp. I'm feeling a slight tug on my left leg right now, but I'm game. Got any links to share?
A properly designed circuit will for the most part not require fancy pants boutique capacitors. If you place the poles far enough out of the frequency range (example put a -3dB bass rolloff between 1 and 5 Hz) then the operation of the capacitor is negligible within the intended range. Any effects of the capacitor will be "swamped" out by the impedance of the input or the feedback resistor.
Another good practice is to place the poles as far apart as possible. For example, I might have the input rolloff at 5 Hz and the feedback rolloff at 0.5 Hz.
Capacitors have inductance too, and there is a frequency at which the capacitor will stop behaving like a capacitor and start behaving like an inductor. This is one reason why we sometimes bypass electrolytics with small capacitors that are designed for higher frequency circuits. And you don't need expensive capacitors to obtain good results either.
In circuits where the impedance of the capacitor is significant, like tone controls and RIAA circuits, then choosing the right capacitor is much more crucial to circuit performance. As an example, a Mitsubishi reciever had a poorly designed and poorly implemented bass control. It used a 0.5 uF electrolytic in the tone shaping circuit! I replaced them with some capacitors from Radio Shack (mylar I guess) that weren't cheap, but they weren't $30 a piece either. It certainly improved the sound, if for no better reason than one of the electrolytics was dodgy and introducing an occasional crackle. I also replaced some other electrolytics too, which I selected from a large and inexpensive assortment kit I bought somewhere. I switched some poles around, but with such an antiquated and comprimised design I'm not convinced it made any difference.
I'm not promoting or refuting anything here, but a question does come to mind. If supposed "higher grade" capacitors are so unnecessary and marginally effective, why haven't simple market forces caused companies to stop making them. Though I agree there is a lot of hype and a lot of people fall for it, it's hard for me to believe so many companies could fool so many people for so many years successfully. How does one determine where to draw the line between fancy boutique, and well worth a few extra bucks.?
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