Is there an alternative to electrolytic caps ?

[gainreduction]

I'm not a tech so be easy on me if this is a stupid question.

I'm about to re-cap my console and wondering if there are other kinds of caps that can be used instead of electrolytics which have a limited lifespan and a bad reputation.

Or is quality electrolytics (been recommended Panasonic and rubycon) the only way to go ?

thanx.

[matta]

If the caps are polarized, as is the case of most lytics (I say most since you do get non polarized caps) it is best to stick with them. Lytics are much smaller in footprint then say polyesters etc in the same value and so to find a poly in the same value it would have a footprint at least a couple times the size.

Lytics are not that bad and these days you get much better quality ones like Panasonics, Rubycons Nichicons etc. I'd suggest going for a low ESR type, high voltage (105 degree temps) and if you get a reputable brand you should get at least 15-20 years out of them, if not longer. And caps do have a sound, esp. if they are in the signal path so don't skimp with cheap no names!

Also remember that polarized means that they have a + and – so make SURE you put the caps in the correct way around, also make sure you get at least the min voltage of the caps you are replacing or if in doubt go a big higher, so if you pull a 25V, don't worry about putting in a 35V in it's place. Also in a pinch it is better to go up in value never down... so if you pull a 80uF cap and can only get some 100uF's, fear not, just don't stick in say a 22uF! (I have to add the disclaimer that these are always guestimates without seeing the actual circuit and its interaction)

Just remember that heat is a cap killer so the cooler you keep the piece of gear the longer they will last you.

Hope that helps you, and there is no such thing as a stupid question! I love it when engineers are interested in how there gear works/operates and there are many folks here who are always willing to jump in and help.


Cheers

Matt

[gainreduction]

Thanks Matt. thumbsup

[JohnRoberts]

Originally Posted by gainreduction

I'm not a tech so be easy on me if this is a stupid question.

I'm about to re-cap my console and wondering if there are other kinds of caps that can be used instead of electrolytics which have a limited lifespan and a bad reputation.

Or is quality electrolytics (been recommended Panasonic and rubycon) the only way to go ?

thanx.

As has already been noted, the size of equivalent film capacitors is prohibitive, especially in the context of consoles that are often pretty tight pcb layouts.

IMO the bad reputation of elctrolytics is underserved when properly used. In consoles they are typically used for DC blocking so as long as the LF pole is set arbitrarily low and they are working into relatively high impedances they will be pretty accurate.

You may want to pay attention to ESR/ESL in circuits where they are called on to do more work, like in the gain leg of a mic preamp where the working impedance at high gains may be relatively low to keep preamp noise down.

Another characteristic you might want to pay attention to is in the mic preamp front ends where they are often called on to block phantom voltage. The leakage characteristic of some of the newer minaturized electrolytics may cause audible noise (this is difficult to parse out from cap data sheets since it's not the amount but character of the leakage that matters. You might want to try a few samples first or listen to specific advice from others who have experience with a given cap series in that application).

The main place where their bad reputation is deserved is in cheap speaker crossovers where they are operating at higher currents and can have significant, varying terminal voltages in the heart of the audio band where we are more likely to hear any non-ideal artifacts generated.

Have fun and do no harm.

JR

[Wavebourn]

TOA-RX216 console that I used as a mechanical foundation for my console contained lot of bipolar electrolytics in signal path. Just for experiment, I replaced some of them with metal film capacitors. There were mostly 10 mkF caps, but most significan improvement was obtained by replacing input cap 1 mkF with metal film one: significantly quieter hiss and less distortions. Also, I shifted all OpAmps in class A, an overall result was like good tube console (however, mostly because of A class amps).

http://wavebourn.net/images/audio/toa_pre_1.gif

http://wavebourn.net/images/audio/toa_pre_2.gif

However, when I replaced opamps in mic preamps by tubes and made discrete summing and line driver amps I got most significant improvement.

But anyway, replacing electrolytics by metal film caps (if they fit) gives audible improvements.

[Minion]

Also I hear that Bypassing the Lytics that are in the signal path with a good quality 0.1uF Metal Film or poly cap helps reduce the High frequency distortions that Lytics are known to cause.....

[Wavebourn]

Originally Posted by Minion

Also I hear that Bypassing the Lytics that are in the signal path with a good quality 0.1uF Metal Film or poly cap helps reduce the High frequency distortions that Lytics are known to cause.....

Yes, in case of big capacitance when poly caps of such capacitance would be too big in size smaller caps may be soldered in parallel.

[JohnRoberts]

Originally Posted by Minion

Also I hear that Bypassing the Lytics that are in the signal path with a good quality 0.1uF Metal Film or poly cap helps reduce the High frequency distortions that Lytics are known to cause.....

Back in the '70s I did some experiments with paralleling electrolytics with film caps to improve their performance in a difficult application (mostly to improve DF, ESL, and ESR). I found the optimal size for a parallel film cap was no smaller than 10% of the total capacitance to get significant performance improvements. In my experiments more than 10% was wasted and less than 10% was ineffective. The capacitor in question was setting a LF pole in a phono preamp gain stage. By adding the appropriate film capacitor in parallel the circuit's phase response at 20kHz improved tens of degrees (probably due to lower ESL).

For many applications a film cap of even 1/10th the nominal capitance will still be rather large and if the original cap isn't working that hard in the first place there won't be much deviation from ideal to improve. So yes this works but I would use it selectively.

Good Luck,

JR