capacitor question (p3a)

[elizard]

I've a question about the input capacitor for elliot's p3a. It's supposed to be a 4.7uF capacitor. Now, in a guide somewhere i read its supposed to be a di-electric (preferably) polypropylene/polystyrene

On digikey (where i'm getting the rest of my parts) the ony thing that come up w/ dielectric are ceramic caps. Also polypropylene/polystyrene only go up to 2.2uF i believe (and their physical size is quite large, so 2 wouldn't fit on the board ..).

Anyway, any comments as to which i should use (preferably the digikey part number).

Thanks.

would this one work (part number: 495-1131-ND)?
It does say in the data sheet its a dielectric.

http://ca.digikey.com/scripts/DkSear...110246&Site=CA

[Freddie]

The capacitor you suggested will work just fine

[Magura]

4.7 uF polypropylene is quite common...a search would do the trick.

If im not mistaken Farnell got some.

Magura

[Cradle22]

Hi!

The digikey item you've selected would work for you. It is a MKT cap, which is considered inferior to types like MKP.

But MKP (preferred) or FKP are bigger than MKT/MKS caps.

For me, preferred order would be:
Polarized elko, bipolar elko, ceramics, MKS, MKT, MKP, FKP, Mica (and maybe paper-in-oil caps)
But FKP and Mica should be out of question (not in production in the needed value range, or way too expensive and too big).

You could even omit the input cap, if you've got no DC-offset from your pre-amp / source (but always check, otherwise you could destroy your speakers).

Oh, and the size does not really matter. I am using pretty big Mundorf caps, mounted "outside" of the PCB (you can always try using caps intended for loudspeaker XO designs, since they often have lower voltage ratings, and therefore are smaller).

Or get polarized BlackGate elkos, like a lot of people do for their GainClones...

Hope this helped,

Arndt

[john curl]

We have been through this for decades! If you want the 'best' then only teflon will do, next is polystyrene, then polypropylene, then polycarbonate, then down the road, is mylar. Significant DA is the most important difference.

[elizard]

Originally posted by Cradle22
Hi!

The digikey item you've selected would work for you. It is a MKT cap, which is considered inferior to types like MKP.

But MKP (preferred) or FKP are bigger than MKT/MKS caps.

For me, preferred order would be:
Polarized elko, bipolar elko, ceramics, MKS, MKT, MKP, FKP, Mica (and maybe paper-in-oil caps)
But FKP and Mica should be out of question (not in production in the needed value range, or way too expensive and too big).

You could even omit the input cap, if you've got no DC-offset from your pre-amp / source (but always check, otherwise you could destroy your speakers).

Oh, and the size does not really matter. I am using pretty big Mundorf caps, mounted "outside" of the PCB (you can always try using caps intended for loudspeaker XO designs, since they often have lower voltage ratings, and therefore are smaller).

Or get polarized BlackGate elkos, like a lot of people do for their GainClones...

Hope this helped,

Arndt

that was the answer i was looking for, thank you

btw, in my gc i'm using a BG cap ..

Magura: That's why I specified digikey .. i know i can get it from other places, but when you have to pay $10+ for shipping from each source, you want to have as few sources as possible (it'll turn out to be 1 in my case .. just digikey, which is only $8 in shipping charges)
I don't want to order from newark just for one cap if i don't have to ..

[mhb]

Elizard,

The cap you identified has 15mm lead spacing, you need a box cap with 5mm lead spacing.

The Epcos 50v 3.3uF will work and fit fine. That'll give you an F3 of 2hz, so you shouldn't lose any LF performance

Cheers,

M

[elizard]

Originally posted by mhb
Elizard,

The cap you identified has 15mm lead spacing, you need a box cap with 5mm lead spacing.

The Epcos 50v 3.3uF will work and fit fine. That'll give you an F3 of 2hz, so you shouldn't lose any LF performance

Cheers,

M

an even better response, thank you!

[elizard]

Ok, another question. For the cap/resistor connected in the mains in the following image, is it a connection that's between live/neutral? As well, does the resistor have to be any significant wattage, or just a simple 1/4watt?

http://sound.westhost.com/p3a-f2.gif

Also, is there a benefic to actually using the resistor/cap across the live/neutral? What is it?

oh yeah, and how "risky" would it be to use 35V capacitors in the power supply (i've some 33000uF lying around)? The rails should be around 30-32V (my transformer is 22v secondaries)?

[cabbagerat]

oh yeah, and how "risky" would it be to use 35V capacitors in the power supply (i've some 33000uF lying around)? The rails should be around 30-32V (my transformer is 22v secondaries)?

I honestly can't recommend 35V types for this Power Supply. They are rated to 35V DC with no ripple. With the ripple coming out of the bridge (full wave rectified AC) the cap will be operating outside it's rating and will probably suffer overheating problems, leakage and even failure.