Tantalum and Non Polar - why?

[saxtim]

What's the purpose of tantalums and non polars?

Firstly, Take the tube screamer for example - it uses 2 .22uf tants. Now at my local store, tants and films are reasonably comparable in price - so I don't think thats the issue.  I had a thought that maybe there is some sort of advantage to using a polarised cap here, and I've never seen an aluminium elec smaller the 1uf - so maybe thats why?  I do know that some people though like subbing in films for these, which are non polar anyway.  So is there any reason why there is a polarised cap here?

Secondly, Non polar - take the tube screamer again, 2 1uf NPs - any reason to have these instead of using normally elecs?  I can see that these would be cheaper than using a 1uf film cap (and save space I imagine).  Maybe that's the reason?  But would polarised caps not work here?

Anyone care to explain?
tim

[Boofhead]

In the early days of effects tantalums were much smaller than electrolytics (and for that matter films) that's why you see them in effects.  Note it's only recently (say the last decade) that very small electro's have become readily  available.  Tants tend to last longer than electro's but I don't believe that was a concious choice at that time.  In some ckts tant have their own sound - I doubt that was a concious factor the early days either.

take the tube screamer again, 2 1uf NPs

In circuits where the DC voltage on either side of the cap is about the same the voltage across the cap is near zero voltags and  NP electro caps and films are a better choice than Electro's - basically there's no DC bias across the cap which is a undesirable way to operate an electro.  So for properly engineered effects you will see NP  electro's  in some positions - NP electro's are fairly easy to get these days (and they are much smaller and cheaper than films when you get to the larger values).

[Dai H.]

volumetric efficiency

[LP Hovercraft]

Could one of you explain the tonal differences between tantalum and electrolytic?  According to a few capacitor audiophiles, tantalum has a bad name.  I made an Ampeg Scrambler clone once with pure tantalum on the polarized end and I liked the results.  They last longer, but what specifically are the drawbacks?

[Boofhead]

Tantalums produce distortion, that's why the audiophile don't use them.  Only you can decide whether you like the distortion produced by tantalums - how much distortion depends on the specific circuit and position in the circuit, no easy answers....

[gez]

Electronics World produced a rather dry (but useful) series of articles last year covering capacitor 'sound'.  Largish Tantalums weren't even considered as they distorted 10X more than the cheapest electrolytic.  If I recal, distortion is mainly 3rd harmonic and the same applies to electrolytics in general.  

NPs used as coupling caps came out of it well, but all that stuff is for audiophiles.  You can use distortion (in FX units) to colour sound to your liking.

[Dai H.]

Use what you want. Use your ear to decide.  There might be some practical considerations, like the failure mode (like tants in the power supply), or space, price, availability, etc., but use what sounds good. There might be a diff. or maybe there won't, but it's subjective anyhow. Some people say, there is none no matter what you use, so...  That could be how it is for you or not. Try it and see.