Tantalum Capacitors in audio applications - Electronic Circuits Projects Diagrams Free

2camjohn · 22nd March 2008, 02:34 PM

I accquired a load of cheap tantalum caps.

I wanted to use them in decoupling the DC from an audio signal.

Some websites are very critical of tantalums in this application but I get the feeling the websites may be a little out of date.

Im just after opinions here?
Is it a good idea? If so what should I watch out for when using tantalum caps in audio decoupling?

audioguru · 22nd March 2008, 04:58 PM

Decoupling the DC from an audio signal???

DC is decoupled from a power supply. Then any capacitor type can be used.
Audio has coupling capacitors.

Metalized plastic film capacitors have the lowest distortion.
Tantalum and electrolytic coupling capacitors change value with voltage so the low frequencies will have even-harmonics distortion.
If the signal across a tantalum capacitor causes reversed polarity then the capacitor is a rectifier producing severe distortion.

whiz115 · 22nd March 2008, 05:09 PM

Quote:

Originally Posted by audioguru

Tantalum and electrolytic coupling capacitors change value with voltage so the low frequencies will have even-harmonics distortion

i don't understand that...
capacitance in an electrolytic varies according to voltage?!

also.. do you know if tantalums can be used for decoupling where
high ripple current exists? i'm confused about that because i have read
that they can more easily destroyed than electrolytics.

audioguru · 22nd March 2008, 05:41 PM

Go to Google and look at Distortion From Capacitors.
People at www.diyaudio.com say that distorting ceramic, electrolytic and tantalum capacitors have no business in an audio chain.

Tantalum capacitors are small so i think their ripple current rating is low.
I have had many tantalum capacitors blow up and disappear so I don't use them anymore.

2camjohn · 22nd March 2008, 05:53 PM

Quote:

Originally Posted by audioguru

Decoupling the DC from an audio signal???

DC is decoupled from a power supply. Then any capacitor type can be used.
Audio has coupling capacitors.

Metalized plastic film capacitors have the lowest distortion.
Tantalum and electrolytic coupling capacitors change value with voltage so the low frequencies will have even-harmonics distortion.
If the signal across a tantalum capacitor causes reversed polarity then the capacitor is a rectifier producing severe distortion.

Hi audioguru, thanks alot for the reply.

Sorry for my bad semantics. I did mean coupling.
(to remove the DC from an audio signal)

I did notice the difference between two circuits I made, (changing 3 ceramic 4.7uf for 1 22uF electrolytic made the sound seem very loose.. arg loose is a bad word.. I hope you get what I mean)

Would that make sense or did I just make the whole thing up?

I found metal film caps (polyester?) but they are such low values, Im using around 20uF right now to decouple audio signals (maximum 2v peak to peak)

Does that sound appropriate?
If so, are there metal film caps available in the size I require? I cant find any.

Cheers
John

audioguru · 22nd March 2008, 08:08 PM

I have some small 1uF 5% metalized plastic film capacitors. Larger size (really big) and higher value ones are used in good speakers' crossover networks.

If your audio circuit uses fairly high impedances then small metalized plastic film 0.33uf capacitors can be used as coupling capacitors. If the impedance is 120k ohms then a 0.33 coupling capacitor will have a flat response down to 20Hz.

Hero999 · 22nd March 2008, 08:12 PM

Surely the amount of distortion depends on the current flowing through the capacitor. A JFET amplifier with a 100nF ceramic input capacitor and an input impedance of 1M probably won't suffer from much distortion.

speakerguy79 · 22nd March 2008, 08:18 PM

Electrolytics as AC coupling capacitors are fine. Just make sure that the DC bias across them is enough. Using a tantalum as a coupling capacitor, that I have never tried - no real reason to when a cheap aluminum electrolytic does the job just fine @ audio frequencies. Keep the f3 well below 10hz - if you don't you'll wind up introducing distortion into the low frequencies. 10uF-100uF is plenty.

Do NOT ever allow the tantalum to see reverse bias in this application. An aluminum electrolytic would handle it OK,but a tantalum might go poof.

Honestly the best place to use these depending on voltage and size is as power supply decoupling capacitors and in voltage regulator circuits.

2camjohn · 23rd March 2008, 03:30 PM

Thanks again for all the information..

I will relegate my tantalums to power supply decoupling etc only.

Prompted by what you guys said, I set up a blind test with some decent headphones and I can definately tell the difference between two circuits I have here. (identical design, but one has bipolar electrolytics and one has multilayer ceramics).

In comparison to the circuit with ceramic, the electrolytic one sounds a bit like its been recorded in a seashell.

I think ive already decided metal film caps are too expensive in the values I need (the price for each component would cost pounds rather than pennies)

But Im really curious if going to metalised film would give a similar step up in quality over the ceramics. If thats even possible.

Hero999 · 23rd March 2008, 03:39 PM

Could you pleas post the test circuit.

Have you tried oversizing the electrolytic capacitor?

The chances are, if it's just a simple push-pull (on-sided not bridged) class A-B output stage then an electrolytic will do since there's no chance of it becomming reversed biased.

2camjohn · 23rd March 2008, 04:01 PM

Quote:

Originally Posted by Hero999

Could you pleas post the test circuit.

Have you tried oversizing the electrolytic capacitor?

The chances are, if it's just a simple push-pull (on-sided not bridged) class A-B output stage then an electrolytic will do since there's no chance of it becomming reversed biased.

From what people have posted above, it seems like Im oversizing my components already. Im using 47uF where 2uF would suffice.

Also, since I used bipolar capacitors for the electrolytics, reverse biased wont be an issue here? Or am I missing something?

Ill draw up the schematic for the test circuit and post it up as soon as I can.

John

Hero999 · 23rd March 2008, 07:17 PM

Quote:

Originally Posted by 2camjohn

The audio source is just my PC sound card right now.
It claims to be some kind of high fidelity one.

Have you looked at the circuit board?

My sound card has electrolytic capacitors on it and I wouldn't be surprised if yours does. I'm reasonably sure that there will be some electrolytic capacitors somewhere in the audio chain, even if it was before the sound was converted to a digital format.

SSman · 19th August 2008, 06:18 PM

I'm all over this issue 2camjohn.
I have been selling tantalum capacitor passive filters for high end audiophile use (at a discount). First, don't believe all that crap. Its mostly bad judgement propted up by big business that can't change. Jargon doesn't help. You can use tantalums where you use bipolar electrolytic. Actually a non-polar electrolytic can have higher reverse voltage than forward voltage which is why they started the jargon -nonpolar or bipolar. It is misleading. It only means this condition has been designed out by making the cathode larger instead of tiny so that if the liquid electrolyte does break over (normally it binds its ions tightly) there is no damage. First lets back up. All capacitors are polar. All have reverse currents called leakage. This reverse current must be present to reset the device to begin its next cycle of operation. To decouple the DC - a GREAT IDEA I may ad, you just use a large capacitor because it cannot pass the class A DC bias than is common on power amps and some op amps operate in class A mode. To couple with a capacitor in audio usually means just using a low value like 4.7uf because at somewhere between 3000 and 5000 hertz it will have an 8 ohm capacitive reactance and since that matches the speaker it will optimize power transfer. It also helps cover the high end of the spectrum. and NO YOU ARE NOT PICKING HIGH VALUES for your filter in the 30 to 90 uf range. The very small value use a very large inductor, (hi filter) and are trying to duplicate a Bessel filter. Really bessels are powered devices but the Butterworth have been called 'slow' due to the larger value capacitors.
Its easier to get a fast rise in the capacitive reactance and inductance combined called impedance when you use that method. But keep working on it and be VERY careful about talking to anyone who is not active full time in circuit design of filters and component selection. I have had no problems with tantalums at all. There may be a justified fear of DC, but you seem to already realize how to solve that problem. Block it. One side is enough. And to put to bed some other nonsense that is online all over the place - Tantalums store just as long as electrolytics. No, you can't put two tantalums back to back and make the bipolar. It is just jargon for the way the electrodes sizes are constructed. Yes they have much lower leakage currents. All capacitors act like rectifiers, it just means its a better capacitor, about 2-1/2 time more capacitance per surface area than electrolytic, thats why. Also the low ESR makes the coil Q higher, but that is not good if the Q causes reverberation past the time of the next cycle of the capacitor. Thats where the absurd idea that tantalum capacitors cause distortion when used in audio circuts came from originally I think, and now everybody with a theory is jumping on the bandwagon to claim a new piece of escoterica. Since my stereo splitter boxes get kinda ugly to use huge coils like a speaker crossover, I don't sweat this problem at all but sure, if you need to get more volume out because your pre-amp is a weener and your power amp cant budge out more than say 35 or 40 watts per channel, by all means, use 150 micro henries or more and pay some stupid price. I'll settle for turning up the amplifiers to max and not having it really loud, but just real solid backed sound. Some people should just listen to themselves. They'ld be emailing Kennedy Audio and asking more questions - like that ever happens..

SSman · 19th August 2008, 11:59 PM

Well I'll skip the whole coupling thing as the output of a filter and the input of the power amp are two different things, but my point was that a filter can be used directly connecting speakers to its output, even though they probably are not intended to be used as a speaker crossover.
As for even harmonics, first there are only a few devices thought to pass the odd harmonics, you can read about that on my web page as I've had articles from experts on it for years. So why say that about tantalum capacitors?
Secondly about changing value - there are charts you can google that show that this is certainly not true at all of surface mount tantalums. If you really are stuck in the 1950's or 1060's and can't affor the ten dollars for a lot of 2000 surface mounts on a reel or want to keep a stiff upper lip and pay 50 cents each for small quantities of what are really almost obsolete axial tantalums, go right ahead and be my guest and keep up the guru work.
Where's your ashram, india?

speakerguy79 · 20th August 2008, 12:23 AM

Will two tants back-to-back form a 'bipolar' device (large signal AC safe?) If not, will one tant and one aluminum electrolytic do so? Which will create the most even order distortion of these two configurations?

audioguru · 20th August 2008, 12:57 AM

I am a Canadian, not an Indian.
I was called an audioguru by a salesman at a job i had.

Odd harmonics are caused by symmetrical compression or clipping.
Even harmonics are caused when something causes one polarity of an AC waveform to be amplified or attenuated more than the other polarity of the AC waveform, LIKE A TANTALUM COUPLING CAPACITOR.

Tantalum capacitors are horrible. They short and blow up. They change their value with applied voltage. They cause bad distortion in audio circuits.

Metalized plastic film capacitors are perfect in audio circuits. They have no distortion.
All high quality speakers use them in passive crossover networks. Cheap speakers use non-polar electrolytics. I don't think any speaker is made with tantalum capacitors in the crossover network.

SSman · 20th August 2008, 03:30 AM

Sorry but design science does not make such claims based on what is used in expensive overpriced products versus ones desiged to wise engineering constraints and cost tradeoffs. You must be saying such nonsense to voice some marketing priciple or mission. Just show us one graph or oscilliscope trace from any industry standatd ASTM methid. That's why thy have to have ASTM _ SOME PEOPLE JUST DON'T GET IT RIGHT. Yes I will cocede that tanralums are less tolerant of poor designs, especially when used in series. You might consider that pricey products have to anticipate that probem and so are trying to design around it when they use metal film capacitors and can afford 9 times the volume they take up cimpared to tantalums because the pricy black box is a clumsy ugly thing anyway.

kchriste · 20th August 2008, 04:30 AM

Quote:

Originally Posted by SSman

To decouple the DC - a GREAT IDEA I may ad, you just use a large capacitor because it cannot pass the class A DC bias than is common on power amps and some op amps operate in class A mode. To couple with a capacitor in audio usually means just using a low value like 4.7uf because at somewhere between 3000 and 5000 hertz it will have an 8 ohm capacitive reactance and since that matches the speaker it will optimize power transfer.

Um what do you mean here? Coupling the output of an amplifier to an 8Ω speaker with a 4.7µF capacitor will sound horrible and tinny. You seem to be talking about amplifier output coupling capacitors and crossover networks all in one sentence.
If I remember tomorrow, I'll try some Mylar, Electrolytic, and Tantalum caps on the distortion analyzer (At the 3db down point on an RC network) and report back. I remember trying some ceramic ones in the past and they definitely added distortion but not as much as I thought they would.

audioguru · 20th August 2008, 02:29 PM

You don't need to measure the distortion of capacitors. It has already beedn done and documented:
1) Douglas Self designed an audio power amplifier that has distortion of only 0.0005% at low and mid frequencies. He wrote a tutorial about reducing distortion. He has a graph of the sharp rise in distortion caused by an electrolytic coupling capacitor.

2)AVX tested an "ordinary" tantalum coupling capacitor which has high distortion and tested their best tantalum capacitor that has the same amount of distortion as an electrolytic one. They do not show the zero distortion of a film capacitor.

My metalized poly film capacitors are not large and are not expensive. The EPCOS brand of a 330nF/5%/63V one costs less than 15 cents US at Newark and is about 6mm wide (5mm leads spacing), 5mm high and 2mm thick.

kchriste · Yesterday, 02:23 AM

Quote:

Originally Posted by audioguru

You don't need to measure the distortion of capacitors. It has already been done and documented

Well, I did it anyway, just for fun:
I used a HP8903B audio analyzer and connected a single pole passive RC highpass filter on the output of the audio generator running at 5Vrms @ 160Hz. R was 600Ω, C was 1µF and the distortion analyzer was connected across the resistor. The results are below:

Direct connection with 600Ω load resistor only (No capacitor) = 0.002%

Distortion with no DC bias on the capacitor under test:

Metal film = 0.002%
Electrolytic = 0.016%
Dip Tantalum = 0.425%
Ancient axial Tantalum = 0.028%
SMD Ceramic = 0.420%

Distortion with 9V DC bias on the capacitor under test:

Metal film = 0.0035%
Electrolytic = 0.029%
Tantalum Dip = 0.190%
Ancient axial Tantalum = 0.022%
SMD Ceramic = 0.609%

The only result that puzzled me was the Ancient axial Tantalum until I googled it and saw that it was still listed on the NASA site.

audioguru · Yesterday, 02:40 AM

NASA use tantalum capacitors because they don't freeze like electrolytic capacitors do.

SSman · Today, 09:49 PM

Thanks. That data is definitely helpful. But it only confirms that putting filtered DC through capacitors, espeically tantalums, is not a good idea even though maybe 1 or 2 percent of the amplifiers might do that.
The reason if I am understanding where this is going, that tantalums distort more readily if DC biased is that they have electrons crowding one electrode as part of the design - so that the magnetic field created reinforces the flow of capacitive current instead of working against it as the eddy current of any other capacitor would. Have you considered the improvement in lower distortion due to lower resistance and improved response time that tantalums offer. Remember the point of my last post was all about tantalums in series. I was trying to avoid a discussion here of coupling capacitors as it is off topic, but as you said a filter like I specified would sound very tinny all by itself. But without it you can't design a two pass only filter that covers those frequencies that you are calling tinny. Well enough about that as it gets into different types of filters - lets just assume we mean constant current circuits here and very simple and basic textbook stuff. Thats not now what I'm into as a study to improve my passive filters but you never know, you learn something every day. Anyway, if distortion was such a hugh bid deal, whey are not all amplifiers made with MOSFETs. They only have half the distortion of any other type amp. Then there is the whole tube thing that is still popular in spite of my web page rant and rave about that particular shortcoming as well as high end or headroom losses and the limitiing of innovation that they introduce.
I'll keep this short and just say putting 9 volts DC into a tantalum cap and claiming it has higher distortion does not even begin to convince me that electrolytics - even so called audio or np or bipolar ones, are even close to tantalums for superior design and innovation opportunities in audio.
And to speaker guy - yes you can put an electrolytic after a tantalum, but first the electrolytics must always have its neg electrode toward the negative side - you can get away with ignoring that on tantalums must of the time, but in series, I would also orient it as marked, assuming mark is positive. You can't always tell the polarity by using diode mode on a DV meter just so you know. You can do it by picking up the magnetic field as the inner electrode always gets shielding, but unless you've got old vintage stuff the datasheet or tech support should get you straight. It is espeically important to adjust for the time constant by using a tuning resistor on both the capacitors across the + to - side and they must be different values. Unless your trying to do a bit of wave shaping (I may have to kill you but I do this in my new filter design) it may not be worth the trouble or cost unless you already have sunk costs in the components. But sure, you can block AC that way but since 2 in series have less capacitance than the lowest of the pair you may not want to. Any capacitor blocks AC really and DC mostly unless we are talking very small or large cap values where filtered DC currents for power supply can happen or powered circuits where almost anything is possible; unlikely but possible. As far as passive blocking - AC does not get through any audio frequency capacitor. It just caused electrons collected on the plate to jump off or recollect. No current ever flows directly. The leaking is related to oriented domains in the material, as noted above, an intended condition to improve effiency. So, sure the curve for reverse current is steaper than electrolytics that claim to be non-polarized. I could call it non-engineered if I wanted to get a reputation as nasty.

19th August 2008, 11:47 PM	(permalink)
audioguru	Modern speakers rely on the extremely low output impedance of a modern solid-state amplifier to damp their resonances. Modern amplifiers certainly don't have an 8 ohm output impedance. Many have an output inpedance of only 0.02 ohms for a damping factor of 400. Tantalum capacitors change their value when their DC voltage changes. So they "modulate" the signal with even harmonics when used as audio coupling capacitors. Electrolytic capacitors modulate a small amount and plastic film capacitors are perfect. __________________ Uncle $crooge

22nd March 2008, 02:34 PM	(permalink)
2camjohn	Tantalum Capacitors in audio applications I accquired a load of cheap tantalum caps. I wanted to use them in decoupling the DC from an audio signal. Some websites are very critical of tantalums in this application but I get the feeling the websites may be a little out of date. Im just after opinions here? Is it a good idea? If so what should I watch out for when using tantalum caps in audio decoupling? __________________ The first rule of mstechca club is do not talk about mstechca club. http://www.electro-tech-online.com/s...induser&u=1245

22nd March 2008, 04:58 PM	(permalink)
audioguru	Decoupling the DC from an audio signal??? DC is decoupled from a power supply. Then any capacitor type can be used. Audio has coupling capacitors. Metalized plastic film capacitors have the lowest distortion. Tantalum and electrolytic coupling capacitors change value with voltage so the low frequencies will have even-harmonics distortion. If the signal across a tantalum capacitor causes reversed polarity then the capacitor is a rectifier producing severe distortion. __________________ Uncle $crooge

22nd March 2008, 05:41 PM	(permalink)
audioguru	Go to Google and look at Distortion From Capacitors. People at www.diyaudio.com say that distorting ceramic, electrolytic and tantalum capacitors have no business in an audio chain. Tantalum capacitors are small so i think their ripple current rating is low. I have had many tantalum capacitors blow up and disappear so I don't use them anymore. __________________ Uncle $crooge

22nd March 2008, 08:08 PM	(permalink)
audioguru	I have some small 1uF 5% metalized plastic film capacitors. Larger size (really big) and higher value ones are used in good speakers' crossover networks. If your audio circuit uses fairly high impedances then small metalized plastic film 0.33uf capacitors can be used as coupling capacitors. If the impedance is 120k ohms then a 0.33 coupling capacitor will have a flat response down to 20Hz. __________________ Uncle $crooge

22nd March 2008, 08:12 PM	(permalink)
Hero999	Surely the amount of distortion depends on the current flowing through the capacitor. A JFET amplifier with a 100nF ceramic input capacitor and an input impedance of 1M probably won't suffer from much distortion. __________________ I also post at the following sites: http://www.stop-microsoft.org http://www.heated-debates.com Screen name: Aloone_Jonez

22nd March 2008, 08:18 PM	(permalink)
speakerguy79	Electrolytics as AC coupling capacitors are fine. Just make sure that the DC bias across them is enough. Using a tantalum as a coupling capacitor, that I have never tried - no real reason to when a cheap aluminum electrolytic does the job just fine @ audio frequencies. Keep the f3 well below 10hz - if you don't you'll wind up introducing distortion into the low frequencies. 10uF-100uF is plenty. Do NOT ever allow the tantalum to see reverse bias in this application. An aluminum electrolytic would handle it OK,but a tantalum might go poof. Honestly the best place to use these depending on voltage and size is as power supply decoupling capacitors and in voltage regulator circuits.

23rd March 2008, 03:30 PM	(permalink)
2camjohn	Thanks again for all the information.. I will relegate my tantalums to power supply decoupling etc only. Prompted by what you guys said, I set up a blind test with some decent headphones and I can definately tell the difference between two circuits I have here. (identical design, but one has bipolar electrolytics and one has multilayer ceramics). In comparison to the circuit with ceramic, the electrolytic one sounds a bit like its been recorded in a seashell. I think ive already decided metal film caps are too expensive in the values I need (the price for each component would cost pounds rather than pennies) But Im really curious if going to metalised film would give a similar step up in quality over the ceramics. If thats even possible. __________________ The first rule of mstechca club is do not talk about mstechca club. http://www.electro-tech-online.com/s...induser&u=1245

23rd March 2008, 03:39 PM	(permalink)
Hero999	Could you pleas post the test circuit. Have you tried oversizing the electrolytic capacitor? The chances are, if it's just a simple push-pull (on-sided not bridged) class A-B output stage then an electrolytic will do since there's no chance of it becomming reversed biased. __________________ I also post at the following sites: http://www.stop-microsoft.org http://www.heated-debates.com Screen name: Aloone_Jonez

19th August 2008, 06:18 PM	(permalink)
SSman	Im on it I'm all over this issue 2camjohn. I have been selling tantalum capacitor passive filters for high end audiophile use (at a discount). First, don't believe all that crap. Its mostly bad judgement propted up by big business that can't change. Jargon doesn't help. You can use tantalums where you use bipolar electrolytic. Actually a non-polar electrolytic can have higher reverse voltage than forward voltage which is why they started the jargon -nonpolar or bipolar. It is misleading. It only means this condition has been designed out by making the cathode larger instead of tiny so that if the liquid electrolyte does break over (normally it binds its ions tightly) there is no damage. First lets back up. All capacitors are polar. All have reverse currents called leakage. This reverse current must be present to reset the device to begin its next cycle of operation. To decouple the DC - a GREAT IDEA I may ad, you just use a large capacitor because it cannot pass the class A DC bias than is common on power amps and some op amps operate in class A mode. To couple with a capacitor in audio usually means just using a low value like 4.7uf because at somewhere between 3000 and 5000 hertz it will have an 8 ohm capacitive reactance and since that matches the speaker it will optimize power transfer. It also helps cover the high end of the spectrum. and NO YOU ARE NOT PICKING HIGH VALUES for your filter in the 30 to 90 uf range. The very small value use a very large inductor, (hi filter) and are trying to duplicate a Bessel filter. Really bessels are powered devices but the Butterworth have been called 'slow' due to the larger value capacitors. Its easier to get a fast rise in the capacitive reactance and inductance combined called impedance when you use that method. But keep working on it and be VERY careful about talking to anyone who is not active full time in circuit design of filters and component selection. I have had no problems with tantalums at all. There may be a justified fear of DC, but you seem to already realize how to solve that problem. Block it. One side is enough. And to put to bed some other nonsense that is online all over the place - Tantalums store just as long as electrolytics. No, you can't put two tantalums back to back and make the bipolar. It is just jargon for the way the electrodes sizes are constructed. Yes they have much lower leakage currents. All capacitors act like rectifiers, it just means its a better capacitor, about 2-1/2 time more capacitance per surface area than electrolytic, thats why. Also the low ESR makes the coil Q higher, but that is not good if the Q causes reverberation past the time of the next cycle of the capacitor. Thats where the absurd idea that tantalum capacitors cause distortion when used in audio circuts came from originally I think, and now everybody with a theory is jumping on the bandwagon to claim a new piece of escoterica. Since my stereo splitter boxes get kinda ugly to use huge coils like a speaker crossover, I don't sweat this problem at all but sure, if you need to get more volume out because your pre-amp is a weener and your power amp cant budge out more than say 35 or 40 watts per channel, by all means, use 150 micro henries or more and pay some stupid price. I'll settle for turning up the amplifiers to max and not having it really loud, but just real solid backed sound. Some people should just listen to themselves.

19th August 2008, 11:59 PM	(permalink)
SSman	Not exactly Well I'll skip the whole coupling thing as the output of a filter and the input of the power amp are two different things, but my point was that a filter can be used directly connecting speakers to its output, even though they probably are not intended to be used as a speaker crossover. As for even harmonics, first there are only a few devices thought to pass the odd harmonics, you can read about that on my web page as I've had articles from experts on it for years. So why say that about tantalum capacitors? Secondly about changing value - there are charts you can google that show that this is certainly not true at all of surface mount tantalums. If you really are stuck in the 1950's or 1060's and can't affor the ten dollars for a lot of 2000 surface mounts on a reel or want to keep a stiff upper lip and pay 50 cents each for small quantities of what are really almost obsolete axial tantalums, go right ahead and be my guest and keep up the guru work.

20th August 2008, 12:23 AM	(permalink)
speakerguy79	Will two tants back-to-back form a 'bipolar' device (large signal AC safe?) If not, will one tant and one aluminum electrolytic do so? Which will create the most even order distortion of these two configurations? Last edited by speakerguy79; 20th August 2008 at 12:23 AM.

20th August 2008, 12:57 AM	(permalink)
audioguru	I am a Canadian, not an Indian. I = was called an audioguru by a salesman at a job i had. Odd = harmonics are caused by symmetrical compression or clipping. Even harmonics are caused when something causes one polarity of an AC waveform to be amplified or attenuated more than the other polarity of the AC waveform, LIKE A TANTALUM COUPLING CAPACITOR. Tantalum capacitors are horrible. They short and blow up. They change their value with applied voltage. They cause bad distortion in audio circuits. Metalized plastic film capacitors are perfect in audio circuits. They have no distortion. All high quality speakers use them in passive crossover networks. Cheap speakers use non-polar electrolytics. I don't think any speaker is made with tantalum capacitors in the crossover network. __________________ Uncle $crooge

20th August 2008, 03:30 AM	(permalink)
SSman	Design science Sorry but design science does not make such claims based on what is used in expensive overpriced products versus ones desiged to wise engineering constraints and cost tradeoffs. You must be saying such nonsense to voice some marketing priciple or mission. Just show us one graph or oscilliscope trace from any industry standatd ASTM methid. That's why thy have to have ASTM _ sOME PEOPLE JUST DON'T GET IT RIGHT. Yes I will cocede that tanralums are less tolerant of poor designs, especially when used in series. You might consider that pricey products have to anticipate that probem and so are trying to design around it when they use metal film capacitors and can afford 9 times the volume they take up compared to tantalums because the pricy black box is a clumsy ugly thing anyway.

Yesterday, 02:40 AM	(permalink)
audioguru	NASA use tantalum capacitors because they don't freeze like electrolytic capacitors do. __________________ Uncle $crooge

Today, 09:49 PM	(permalink)
SSman	Very interesting Thanks. That data is definitely helpful. But it only confirms that putting filtered DC through capacitors, espeically tantalums, is not a good idea even though maybe 1 or 2 percent of the amplifiers might do that. The reason if I am understanding where this is going, that tantalums distort more readily if DC biased is that they have electrons crowding one electrode as part of the design - so that the magnetic field created reinforces the flow of capacitive current instead of working against it as the eddy current of any other capacitor would. Have you considered the improvement in lower distortion due to lower resistance and improved response time that tantalums offer. Remember the point of my last post was all about tantalums in series. I was trying to avoid a discussion here of coupling capacitors as it is off topic, but as you said a filter like I specified would sound very tinny all by itself. But without it you can't design a two pass only filter that covers those frequencies that you are calling tinny. Well enough about that as it gets into different types of filters - lets just assume we mean constant current circuits here and very simple and basic textbook stuff. Thats not now what I'm into as a study to improve my passive filters but you never know, you learn something every day. Anyway, if distortion was such a hugh bid deal, whey are not all amplifiers made with MOSFETs. They only have half the distortion of any other type amp. Then there is the whole tube thing that is still popular in spite of my web page rant and rave about that particular shortcoming as well as high end or headroom losses and the limitiing of innovation that they introduce. I'll keep this short and just say putting 9 volts DC into a tantalum cap and claiming it has higher distortion does not even begin to convince me that electrolytics - even so called audio or np or bipolar ones, are even close to tantalums for superior design and innovation opportunities in audio. And to speaker guy - yes you can put an electrolytic after a tantalum, but first the electrolytics must always have its neg electrode toward the negative side - you can get away with ignoring that on tantalums must of the time, but in series, I would also orient it as marked, assuming mark is positive. You can't always tell the polarity by using diode mode on a DV meter just so you know. You can do it by picking up the magnetic field as the inner electrode always gets shielding, but unless you've got old vintage stuff the datasheet or tech support should get you straight. It is espeically important to adjust for the time constant by using a tuning resistor on both the capacitors across the + to - side and they must be different values. Unless your trying to do a bit of wave shaping (I may have to kill you but I do this in my new filter design) it may not be worth the trouble or cost unless you already have sunk costs in the components. But sure, you can block AC that way but since 2 in series have less capacitance than the lowest of the pair you may not want to. Any capacitor blocks AC really and DC mostly unless we are talking very small or large cap values where filtered DC currents for power supply can happen or powered circuits where almost anything is possible; unlikely but possible. As far as passive blocking - AC does not get through any audio frequency capacitor. It just caused electrons collected on the plate to jump off or recollect. No current ever flows directly. The leaking is related to oriented domains in the material, as noted above, an intended condition to improve effiency. So, sure the curve for reverse current is steaper than electrolytics that claim to be non-polarized. I could call it non-engineered if I wanted to get a reputation as nasty. Last edited by SSman; Today at 10:09 PM.