Which caps to use??

[Stabist]

Hi!

My idea about building A3 converted into idea of building A5 - the heatsinks that I've got can easily disipate that 50 more Watts ...
The transformer still wasn't bought so there are no limits around the voltage available; I have 16 matched IRFP240 - that's more than enough; and I have a big box of second hand capacitors by Sprague - the computer grade ones 36D ... - with diferent voltages ...

Nevertheless - I'm facing a litle problem now - I have 4 pcs of 50V/69.000uF available - it's truth that they are 13 years old but are still OK!

- but because of my design demands - each hetasink on each side as my respect to original Aleph design which is still the best one ever for me! - I'm facing a litle problem:

- if I'm building a dual mono design - all 4 caps must be included - but there is not enough space - and also the total capacity is 276.000uF - which is acordingly to some posts here way too much and without inductors the riple will increase ... Is the way to handle with it only with using polyester-tvpe capacitors in parallel or the inductors are necesarry??

- if I use only two - the capacity is OK; OK, that means there is no dual mono design - and for 2 of them there is more then enough place inside the amp and all is OK ...

- the third option - here in Slovenia JAMICON capacitors are quite user-friendly regarding the price - and I can buy 12pcs 10.000uF/50V of them for very reasonable sum - the equivalent Philips ("the blue ones") are around 3 times more expencive ... - and so I san built a dual mono design without problems, the space will not be a problem, ... BUT - I don't know - I think the Spragues as a real quality caps and nevertheless they are used and old can still be much much better ... Or is that just a dream in my imagination???

So for which one would you decide??

The other thing is - I can still make some more space so that all 4 Spragues and dual mono design can be used and all - it will just take a lot more of hardware work from me to be done around the chassis design ... So if that's the best solution - that's the way it will be ...

Thanks for the patience to read all that and for your hepl!!

Regards from Slovenia

[Mad_K]

I would build dual monos with 2*69000uF per channel. Try to get a transformer with dual secondaries, and use one secondary for each channel.
This way you can substitute the caps for better parts later (if not satisfied/when they are really old/you can afford them). It is always good to have some extra space. Remember that good quality caps are usually larger than equvivalent spec'ed cheap ones. Having 140000uF per channel is just perfect. Put a film cap in paralell, and you're good to go!

Good luck!

[Stabist]

Hi!

The transformer type will not be a problem - because it will be done specially for the A5 - and any combination of rails and voltage can be ordered - the only limit is max. power - 2kVA - so I intend to order 2x(2x24V) 750VA one ... I thing it will be more than enough ..

Dual mono is something that was allready planed - I shall build it up with the help of Kirc who is building his own example - PCB will be the same; heatsinks and design of the chassis completely different - the only problem was with the space - but as said - I shall re-design the chassis a bit to get some extra cm and all 4 caps can be included ...

Thanks for the reply!

[Tomasz Rodak]

Originally posted by Mad_K
I would build dual monos with 2*69000uF per channel. Try to get a transformer with dual secondaries, and use one secondary for each channel.
This way you can substitute the caps for better parts later (if not satisfied/when they are really old/you can afford them). It is always good to have some extra space. Remember that good quality caps are usually larger than equvivalent spec'ed cheap ones. Having 140000uF per channel is just perfect. Put a film cap in paralell, and you're good to go!

Good luck!

What should be the nominal capacitance of the film caps ?

[Christer]

It is sometimes recommended to format old electrolytics before
using them. I haven't tried it myself yet, but I have some old
caps that I might try it on. The procedure is to slowly
increase the voltage over the cap from zero up to its rated
voltage and then slowly decrease it to zero again. This is
claimed to improve the performance and increase the lifetime
of the caps. Actually, one of the sources I have for this might
even be interpreted as recommending the procedure also for
brand new lytics.

[peranders]

Christer, you don't have to be so cautious.

My trick has been DC source plus a series resistor. In my case 230 AC, half wave rectified, 47 kohm 4 W. Let the caps be connected for a week or so.

Discharge the caps via a resistor and then measure the leakage. Be carefull when increasing voltage if you use a regular A-meter. Trick: Charge with 10 A range then decrease the range.

The caps can be much better but on the other hand they will be "formated" anyway only by usage! Leakage is also no problem when you use them as smoothing caps. Maybe you can see the condition of the caps if you test the leakage.

[UrSv]

Actually RIFA used to recommend formatting so I am with you on that one Christer. I always do for new ones as well and I donät think it will hurt...

/UrSv

[Mad_K]

Originally posted by Tomasz Rodak


What should be the nominal capacitance of the film caps ?

Whatever you have laying around. 0,1-10uF is a nice range. I am rebuilding my Balanced Zen Linestage right now, and i bought 0,47uF Evox Rifa, type MMK (metalized polyester) to bypass all the electrolytic ones with.

here's a link that might be of interest:

http://tnt-audio.com/clinica/ssps1_e.html