alum. electrolytics vs tantalum caps

[jvegas]

i'm putting a together an overdrive pedal and i was looking too use tananlum caps for the electrolytic stage of the pedal i'm just wondering what  would be the best type of tananlum to use. here is a list of what i have in mind<molded axial tantalum><high-temp wet tantalum><radial-dipped tantalum><resin- dipped solid tantalum> or should i use aluminum type instead? i just want it to make the pedal quiet as much as possible. i'll be using metal-flim resistor to and for the other caps some sliver mica and metal flim too.this should keep it some what quieter? i hope!! if anyone has any thoughts on this subject please fell free to share them with me.

j.

[KORGULL]

Click on the "search" link at the top of this page and type in tantalum vs electrolytic in the "search for" field.
You will find alot of stuff to read on this subject.

You might want to check out this article too:http://www.diyguitarist.com/Misc/CapacitorFieldGuide.htm

[Paul Marossy]

Get whichever tantalum cap fits your layout. There's not going to be huge differences in sound between an axial or a radial tantalum cap. 

[soggybag]

There was some infromation on Jack Ormans site Muzique.com about caps. I think he was saying tantalum were no good for audio, and electrolytics were good if they are of the low ESR type. But don't quote me on this it's been a while since I read it.

[KORGULL]

http://www.muzique.com/cap_faq.htm
http://www.muzique.com/editor.htm

[Paul Marossy]

Tantalum capacitors produce at least 10 times more distortion than even a cheap electrolytic

Yeah, but who could really hear 0.020% distortion in a tantalum cap vs. 0.001% in a low ESR electrolytic cap - or at least be truly bothered by it?! I can actually hear some very subtle differences between a tantalum and an electro cap, but not enough to convince me to never use tantalums. Anyhow, maybe that accounts for the certain "graininess" people associate with tantalum caps?

[soggybag]

Tantalums are sized just perfect for stompbox useages. They're cheap too. Lately I have been really liking the Metalized film caps in the boxes. These are also very small and fit well into small boxes and tight layouts.

[Stevo]

I havent seen a scheme with a tant. except the RED LLAMA...Wonder why way huge picked a tant if they are undesirable?

[Paul Marossy]

I havent seen a scheme with a tant. except the RED LLAMA...Wonder why way huge picked a tant if they are undesirable?

Paraphrased from the "Capacitor Field Guide" at my website:


"A tantalum cap has a dielectric capable of giving very high capacitance in a very small space. It also has a very high capacitance value per unit volume. They have reasonably low self inductance and very low ESR as well. Leakage current is usually very low, much better than electrolytics. They should be avoided in audio coupling (bipolar) circuits." These are usually dry type caps, so they theoritically can nver go bad. Now read about the electrolytic type cap.


"Electrolytic caps are named for the chemicals that cause the dielectric to exist. Electrolytic caps have plates wound from a long, thin strip of aluminum foil. The dielectric is a thin (several atoms thick) coating of aluminum oxide (an excellent insulator). The aluminum oxide is formed by a chemical reaction between the electrolyte and the aluminum, in the presence of an electric field. This formed dielectric gives the capacitors some unique advantages and disadvantages. Electrolytic caps have very large capacitances per unit space, since the dielectric is so thin. The dielectric can tailored to allow voltages up to about 450 VDC, the upper limit for electrolytic caps. The disadvantages of the electrolytic come from the electrolyte itself, and how the dielectric is formed. The electrolyte will dry up in time, causing the capacitors to gradually decrease in capacitance. Pushing the capacitor beyond its ratings (either voltage, polarity, or ripple current) will increase the pressure in the cap until it either vents (and loses electrolyte) or explodes. The other problem is that if the electrolytic cap is not used for a long time, the dielectric becomes thinner, decreasing the voltage it can withstand. The dielectric needs an electric field (charge) in order to maintain its strength.

Electrolytics that have been unused (either in storage or in unused equipment) can have their dielectric layers restored by slowly applying increasing levels of DC voltage. The procedure can take days. Electrolytics suffer from accelerated aging at elevated temperatures. A rule of thumb is that their life is cut in half for each 10 degree Celsius rise above ambient (25C). For all these reasons, electrolytics have a limited life and the user may expect to replace them at some time in the future. Excess hum on a power supply, unstable rolling picture on a monitor are often signs of an electrolytic nearing the end of its useful life. Electrolytic capacitors have a substantial amount of leakage and Dielectric Absorption. This can be a problem in timing circuits, and often limits their use. Some designs (like the 555 timer) minimize these faults by operating the capacitor at voltages where this is less of a problem. The temperature stability of electrolytics is poor and seldom specified."


Maybe that is why the are in the Red Llama? The Ibanez Tube Screamer has one or two.

[jvegas]

thank all of you, very much for all your input on this subject ,i now have some very valueable information on this matter which will help me in making the right choice of cap too use.

j.

[Vsat]

I've seen tantalum caps used in the AUDIO PATH of lots of collectible/desirable/sought after old 70's vintage gear. Same for disk ceramics. That's not a reason to recommend them though, but perhaps worth considering if large capcitance/small size and good reliability is important. They must be properly applied however, or they will be failure-prone, instead of reliable. This means designing the circuit so the tantalums never see even a small reverse bias under any conditions. Very large ceramic caps (100 uF, 6.3V, fairly small size, Murata) are now available. These may be a longer-life alternative to aluminum electrolytics, but the ceramic used in these will create even more distortion than the tantalums. But perhaps they would sound just fine for a particular application. If the circuit is designed to create distortion in the first place, the small amount of distortion created by the capacitors probably won't even be noticeable.
Cheers, Mike

[Paul Marossy]

This means designing the circuit so the tantalums never see even a small reverse bias under any conditions

Yep, that's the downside of tantalum caps. It's really easy to kill 'em.